1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
use crate::store::{StoreData, StoreOpaque, Stored};
use crate::{
    AsContext, AsContextMut, CallHook, Engine, Extern, FuncType, Instance, StoreContext,
    StoreContextMut, Trap, Val, ValRaw, ValType,
};
use anyhow::{bail, Context as _, Result};
use std::future::Future;
use std::mem;
use std::panic::{self, AssertUnwindSafe};
use std::pin::Pin;
use std::ptr::NonNull;
use std::sync::Arc;
use wasmtime_runtime::{
    raise_user_trap, ExportFunction, InstanceHandle, VMCallerCheckedAnyfunc, VMContext,
    VMFunctionBody, VMFunctionImport, VMHostFuncContext, VMOpaqueContext, VMSharedSignatureIndex,
    VMTrampoline,
};

/// A WebAssembly function which can be called.
///
/// This type can represent either an exported function from a WebAssembly
/// module or a host-defined function which can be used to satisfy an import of
/// a module. [`Func`] and can be used to both instantiate an [`Instance`] as
/// well as be extracted from an [`Instance`].
///
/// [`Instance`]: crate::Instance
///
/// A [`Func`] "belongs" to the store that it was originally created within.
/// Operations on a [`Func`] only work with the store it belongs to, and if
/// another store is passed in by accident then methods will panic.
///
/// # `Func` and `async`
///
/// Functions from the perspective of WebAssembly are always synchronous. You
/// might have an `async` function in Rust, however, which you'd like to make
/// available from WebAssembly. Wasmtime supports asynchronously calling
/// WebAssembly through native stack switching. You can get some more
/// information about [asynchronous configs](crate::Config::async_support), but
/// from the perspective of `Func` it's important to know that whether or not
/// your [`Store`](crate::Store) is asynchronous will dictate whether you call
/// functions through [`Func::call`] or [`Func::call_async`] (or the typed
/// wrappers such as [`TypedFunc::call`] vs [`TypedFunc::call_async`]).
///
/// # To `Func::call` or to `Func::typed().call()`
///
/// There's a 2x2 matrix of methods to call [`Func`]. Invocations can either be
/// asynchronous or synchronous. They can also be statically typed or not.
/// Whether or not an invocation is asynchronous is indicated via the method
/// being `async` and [`call_async`](Func::call_async) being the entry point.
/// Otherwise for statically typed or not your options are:
///
/// * Dynamically typed - if you don't statically know the signature of the
///   function that you're calling you'll be using [`Func::call`] or
///   [`Func::call_async`]. These functions take a variable-length slice of
///   "boxed" arguments in their [`Val`] representation. Additionally the
///   results are returned as an owned slice of [`Val`]. These methods are not
///   optimized due to the dynamic type checks that must occur, in addition to
///   some dynamic allocations for where to put all the arguments. While this
///   allows you to call all possible wasm function signatures, if you're
///   looking for a speedier alternative you can also use...
///
/// * Statically typed - if you statically know the type signature of the wasm
///   function you're calling, then you'll want to use the [`Func::typed`]
///   method to acquire an instance of [`TypedFunc`]. This structure is static proof
///   that the underlying wasm function has the ascripted type, and type
///   validation is only done once up-front. The [`TypedFunc::call`] and
///   [`TypedFunc::call_async`] methods are much more efficient than [`Func::call`]
///   and [`Func::call_async`] because the type signature is statically known.
///   This eschews runtime checks as much as possible to get into wasm as fast
///   as possible.
///
/// # Examples
///
/// One way to get a `Func` is from an [`Instance`] after you've instantiated
/// it:
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let engine = Engine::default();
/// let module = Module::new(&engine, r#"(module (func (export "foo")))"#)?;
/// let mut store = Store::new(&engine, ());
/// let instance = Instance::new(&mut store, &module, &[])?;
/// let foo = instance.get_func(&mut store, "foo").expect("export wasn't a function");
///
/// // Work with `foo` as a `Func` at this point, such as calling it
/// // dynamically...
/// match foo.call(&mut store, &[], &mut []) {
///     Ok(()) => { /* ... */ }
///     Err(trap) => {
///         panic!("execution of `foo` resulted in a wasm trap: {}", trap);
///     }
/// }
/// foo.call(&mut store, &[], &mut [])?;
///
/// // ... or we can make a static assertion about its signature and call it.
/// // Our first call here can fail if the signatures don't match, and then the
/// // second call can fail if the function traps (like the `match` above).
/// let foo = foo.typed::<(), (), _>(&store)?;
/// foo.call(&mut store, ())?;
/// # Ok(())
/// # }
/// ```
///
/// You can also use the [`wrap` function](Func::wrap) to create a
/// `Func`
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let mut store = Store::<()>::default();
///
/// // Create a custom `Func` which can execute arbitrary code inside of the
/// // closure.
/// let add = Func::wrap(&mut store, |a: i32, b: i32| -> i32 { a + b });
///
/// // Next we can hook that up to a wasm module which uses it.
/// let module = Module::new(
///     store.engine(),
///     r#"
///         (module
///             (import "" "" (func $add (param i32 i32) (result i32)))
///             (func (export "call_add_twice") (result i32)
///                 i32.const 1
///                 i32.const 2
///                 call $add
///                 i32.const 3
///                 i32.const 4
///                 call $add
///                 i32.add))
///     "#,
/// )?;
/// let instance = Instance::new(&mut store, &module, &[add.into()])?;
/// let call_add_twice = instance.get_typed_func::<(), i32, _>(&mut store, "call_add_twice")?;
///
/// assert_eq!(call_add_twice.call(&mut store, ())?, 10);
/// # Ok(())
/// # }
/// ```
///
/// Or you could also create an entirely dynamic `Func`!
///
/// ```
/// # use wasmtime::*;
/// # fn main() -> anyhow::Result<()> {
/// let mut store = Store::<()>::default();
///
/// // Here we need to define the type signature of our `Double` function and
/// // then wrap it up in a `Func`
/// let double_type = wasmtime::FuncType::new(
///     [wasmtime::ValType::I32].iter().cloned(),
///     [wasmtime::ValType::I32].iter().cloned(),
/// );
/// let double = Func::new(&mut store, double_type, |_, params, results| {
///     let mut value = params[0].unwrap_i32();
///     value *= 2;
///     results[0] = value.into();
///     Ok(())
/// });
///
/// let module = Module::new(
///     store.engine(),
///     r#"
///         (module
///             (import "" "" (func $double (param i32) (result i32)))
///             (func $start
///                 i32.const 1
///                 call $double
///                 drop)
///             (start $start))
///     "#,
/// )?;
/// let instance = Instance::new(&mut store, &module, &[double.into()])?;
/// // .. work with `instance` if necessary
/// # Ok(())
/// # }
/// ```
#[derive(Copy, Clone, Debug)]
#[repr(transparent)] // here for the C API
pub struct Func(Stored<FuncData>);

pub(crate) struct FuncData {
    kind: FuncKind,

    // This is somewhat expensive to load from the `Engine` and in most
    // optimized use cases (e.g. `TypedFunc`) it's not actually needed or it's
    // only needed rarely. To handle that this is an optionally-contained field
    // which is lazily loaded into as part of `Func::call`.
    //
    // Also note that this is intentionally placed behind a pointer to keep it
    // small as `FuncData` instances are often inserted into a `Store`.
    ty: Option<Box<FuncType>>,
}

/// The three ways that a function can be created and referenced from within a
/// store.
enum FuncKind {
    /// A function already owned by the store via some other means. This is
    /// used, for example, when creating a `Func` from an instance's exported
    /// function. The instance's `InstanceHandle` is already owned by the store
    /// and we just have some pointers into that which represent how to call the
    /// function.
    StoreOwned {
        trampoline: VMTrampoline,
        export: ExportFunction,
    },

    /// A function is shared across possibly other stores, hence the `Arc`. This
    /// variant happens when a `Linker`-defined function is instantiated within
    /// a `Store` (e.g. via `Linker::get` or similar APIs). The `Arc` here
    /// indicates that there's some number of other stores holding this function
    /// too, so dropping this may not deallocate the underlying
    /// `InstanceHandle`.
    SharedHost(Arc<HostFunc>),

    /// A uniquely-owned host function within a `Store`. This comes about with
    /// `Func::new` or similar APIs. The `HostFunc` internally owns the
    /// `InstanceHandle` and that will get dropped when this `HostFunc` itself
    /// is dropped.
    ///
    /// Note that this is intentionally placed behind a `Box` to minimize the
    /// size of this enum since the most common variant for high-peformance
    /// situations is `SharedHost` and `StoreOwned`, so this ideally isn't
    /// larger than those two.
    Host(Box<HostFunc>),

    /// A reference to a `HostFunc`, but one that's "rooted" in the `Store`
    /// itself.
    ///
    /// This variant is created when an `InstancePre<T>` is instantiated in to a
    /// `Store<T>`. In that situation the `InstancePre<T>` already has a list of
    /// host functions that are packaged up in an `Arc`, so the `Arc<[T]>` is
    /// cloned once into the `Store` to avoid each individual function requiring
    /// an `Arc::clone`.
    ///
    /// The lifetime management of this type is `unsafe` because
    /// `RootedHostFunc` is a small wrapper around `NonNull<HostFunc>`. To be
    /// safe this is required that the memory of the host function is pinned
    /// elsewhere (e.g. the `Arc` in the `Store`).
    RootedHost(RootedHostFunc),
}

macro_rules! for_each_function_signature {
    ($mac:ident) => {
        $mac!(0);
        $mac!(1 A1);
        $mac!(2 A1 A2);
        $mac!(3 A1 A2 A3);
        $mac!(4 A1 A2 A3 A4);
        $mac!(5 A1 A2 A3 A4 A5);
        $mac!(6 A1 A2 A3 A4 A5 A6);
        $mac!(7 A1 A2 A3 A4 A5 A6 A7);
        $mac!(8 A1 A2 A3 A4 A5 A6 A7 A8);
        $mac!(9 A1 A2 A3 A4 A5 A6 A7 A8 A9);
        $mac!(10 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10);
        $mac!(11 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11);
        $mac!(12 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12);
        $mac!(13 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13);
        $mac!(14 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14);
        $mac!(15 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15);
        $mac!(16 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15 A16);
    };
}

mod typed;
pub use typed::*;

macro_rules! generate_wrap_async_func {
    ($num:tt $($args:ident)*) => (paste::paste!{
        /// Same as [`Func::wrap`], except the closure asynchronously produces
        /// its result. For more information see the [`Func`] documentation.
        ///
        /// # Panics
        ///
        /// This function will panic if called with a non-asynchronous store.
        #[allow(non_snake_case)]
        #[cfg(feature = "async")]
        #[cfg_attr(nightlydoc, doc(cfg(feature = "async")))]
        pub fn [<wrap $num _async>]<T, $($args,)* R>(
            store: impl AsContextMut<Data = T>,
            func: impl for<'a> Fn(Caller<'a, T>, $($args),*) -> Box<dyn Future<Output = R> + Send + 'a> + Send + Sync + 'static,
        ) -> Func
        where
            $($args: WasmTy,)*
            R: WasmRet,
        {
            assert!(store.as_context().async_support(), concat!("cannot use `wrap", $num, "_async` without enabling async support on the config"));
            Func::wrap(store, move |mut caller: Caller<'_, T>, $($args: $args),*| {
                let async_cx = caller.store.as_context_mut().0.async_cx().expect("Attempt to start async function on dying fiber");
                let mut future = Pin::from(func(caller, $($args),*));

                match unsafe { async_cx.block_on(future.as_mut()) } {
                    Ok(ret) => ret.into_fallible(),
                    Err(e) => R::fallible_from_trap(e),
                }
            })
        }
    })
}

impl Func {
    /// Creates a new `Func` with the given arguments, typically to create a
    /// host-defined function to pass as an import to a module.
    ///
    /// * `store` - the store in which to create this [`Func`], which will own
    ///   the return value.
    ///
    /// * `ty` - the signature of this function, used to indicate what the
    ///   inputs and outputs are.
    ///
    /// * `func` - the native code invoked whenever this `Func` will be called.
    ///   This closure is provided a [`Caller`] as its first argument to learn
    ///   information about the caller, and then it's passed a list of
    ///   parameters as a slice along with a mutable slice of where to write
    ///   results.
    ///
    /// Note that the implementation of `func` must adhere to the `ty` signature
    /// given, error or traps may occur if it does not respect the `ty`
    /// signature. For example if the function type declares that it returns one
    /// i32 but the `func` closures does not write anything into the results
    /// slice then a trap may be generated.
    ///
    /// Additionally note that this is quite a dynamic function since signatures
    /// are not statically known. For a more performant and ergonomic `Func`
    /// it's recommended to use [`Func::wrap`] if you can because with
    /// statically known signatures Wasmtime can optimize the implementation
    /// much more.
    ///
    /// For more information about `Send + Sync + 'static` requirements on the
    /// `func`, see [`Func::wrap`](#why-send--sync--static).
    #[cfg(compiler)]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "cranelift")))] // see build.rs
    pub fn new<T>(
        store: impl AsContextMut<Data = T>,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, &[Val], &mut [Val]) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let ty_clone = ty.clone();
        unsafe {
            Func::new_unchecked(store, ty, move |caller, values| {
                Func::invoke(caller, &ty_clone, values, &func)
            })
        }
    }

    /// Creates a new [`Func`] with the given arguments, although has fewer
    /// runtime checks than [`Func::new`].
    ///
    /// This function takes a callback of a different signature than
    /// [`Func::new`], instead receiving a raw pointer with a list of [`ValRaw`]
    /// structures. These values have no type information associated with them
    /// so it's up to the caller to provide a function that will correctly
    /// interpret the list of values as those coming from the `ty` specified.
    ///
    /// If you're calling this from Rust it's recommended to either instead use
    /// [`Func::new`] or [`Func::wrap`]. The [`Func::wrap`] API, in particular,
    /// is both safer and faster than this API.
    ///
    /// # Unsafety
    ///
    /// This function is not safe because it's not known at compile time that
    /// the `func` provided correctly interprets the argument types provided to
    /// it, or that the results it produces will be of the correct type.
    #[cfg(compiler)]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "cranelift")))] // see build.rs
    pub unsafe fn new_unchecked<T>(
        mut store: impl AsContextMut<Data = T>,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, &mut [ValRaw]) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let store = store.as_context_mut().0;
        let host = HostFunc::new_unchecked(store.engine(), ty, func);
        host.into_func(store)
    }

    /// Creates a new host-defined WebAssembly function which, when called,
    /// will run the asynchronous computation defined by `func` to completion
    /// and then return the result to WebAssembly.
    ///
    /// This function is the asynchronous analogue of [`Func::new`] and much of
    /// that documentation applies to this as well. The key difference is that
    /// `func` returns a future instead of simply a `Result`. Note that the
    /// returned future can close over any of the arguments, but it cannot close
    /// over the state of the closure itself. It's recommended to store any
    /// necessary async state in the `T` of the [`Store<T>`](crate::Store) which
    /// can be accessed through [`Caller::data`] or [`Caller::data_mut`].
    ///
    /// For more information on `Send + Sync + 'static`, see
    /// [`Func::wrap`](#why-send--sync--static).
    ///
    /// # Panics
    ///
    /// This function will panic if `store` is not associated with an [async
    /// config](crate::Config::async_support).
    ///
    /// # Examples
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// // Simulate some application-specific state as well as asynchronous
    /// // functions to query that state.
    /// struct MyDatabase {
    ///     // ...
    /// }
    ///
    /// impl MyDatabase {
    ///     async fn get_row_count(&self) -> u32 {
    ///         // ...
    /// #       100
    ///     }
    /// }
    ///
    /// let my_database = MyDatabase {
    ///     // ...
    /// };
    ///
    /// // Using `new_async` we can hook up into calling our async
    /// // `get_row_count` function.
    /// let engine = Engine::new(Config::new().async_support(true))?;
    /// let mut store = Store::new(&engine, MyDatabase {
    ///     // ...
    /// });
    /// let get_row_count_type = wasmtime::FuncType::new(
    ///     None,
    ///     Some(wasmtime::ValType::I32),
    /// );
    /// let get = Func::new_async(&mut store, get_row_count_type, |caller, _params, results| {
    ///     Box::new(async move {
    ///         let count = caller.data().get_row_count().await;
    ///         results[0] = Val::I32(count as i32);
    ///         Ok(())
    ///     })
    /// });
    /// // ...
    /// # Ok(())
    /// # }
    /// ```
    #[cfg(all(feature = "async", feature = "cranelift"))]
    #[cfg_attr(nightlydoc, doc(cfg(all(feature = "async", feature = "cranelift"))))]
    pub fn new_async<T, F>(store: impl AsContextMut<Data = T>, ty: FuncType, func: F) -> Func
    where
        F: for<'a> Fn(
                Caller<'a, T>,
                &'a [Val],
                &'a mut [Val],
            ) -> Box<dyn Future<Output = Result<(), Trap>> + Send + 'a>
            + Send
            + Sync
            + 'static,
    {
        assert!(
            store.as_context().async_support(),
            "cannot use `new_async` without enabling async support in the config"
        );
        Func::new(store, ty, move |mut caller, params, results| {
            let async_cx = caller
                .store
                .as_context_mut()
                .0
                .async_cx()
                .expect("Attempt to spawn new action on dying fiber");
            let mut future = Pin::from(func(caller, params, results));
            match unsafe { async_cx.block_on(future.as_mut()) } {
                Ok(Ok(())) => Ok(()),
                Ok(Err(trap)) | Err(trap) => Err(trap),
            }
        })
    }

    pub(crate) unsafe fn from_caller_checked_anyfunc(
        store: &mut StoreOpaque,
        raw: *mut VMCallerCheckedAnyfunc,
    ) -> Option<Func> {
        let anyfunc = NonNull::new(raw)?;
        debug_assert!(anyfunc.as_ref().type_index != VMSharedSignatureIndex::default());
        let export = ExportFunction { anyfunc };
        Some(Func::from_wasmtime_function(export, store))
    }

    /// Creates a new `Func` from the given Rust closure.
    ///
    /// This function will create a new `Func` which, when called, will
    /// execute the given Rust closure. Unlike [`Func::new`] the target
    /// function being called is known statically so the type signature can
    /// be inferred. Rust types will map to WebAssembly types as follows:
    ///
    /// | Rust Argument Type  | WebAssembly Type |
    /// |---------------------|------------------|
    /// | `i32`               | `i32`            |
    /// | `u32`               | `i32`            |
    /// | `i64`               | `i64`            |
    /// | `u64`               | `i64`            |
    /// | `f32`               | `f32`            |
    /// | `f64`               | `f64`            |
    /// | (not supported)     | `v128`           |
    /// | `Option<Func>`      | `funcref`        |
    /// | `Option<ExternRef>` | `externref`      |
    ///
    /// Any of the Rust types can be returned from the closure as well, in
    /// addition to some extra types
    ///
    /// | Rust Return Type  | WebAssembly Return Type | Meaning               |
    /// |-------------------|-------------------------|-----------------------|
    /// | `()`              | nothing                 | no return value       |
    /// | `T`               | `T`                     | a single return value |
    /// | `(T1, T2, ...)`   | `T1 T2 ...`             | multiple returns      |
    ///
    /// Note that all return types can also be wrapped in `Result<_, Trap>` to
    /// indicate that the host function can generate a trap as well as possibly
    /// returning a value.
    ///
    /// Finally you can also optionally take [`Caller`] as the first argument of
    /// your closure. If inserted then you're able to inspect the caller's
    /// state, for example the [`Memory`](crate::Memory) it has exported so you
    /// can read what pointers point to.
    ///
    /// Note that when using this API, the intention is to create as thin of a
    /// layer as possible for when WebAssembly calls the function provided. With
    /// sufficient inlining and optimization the WebAssembly will call straight
    /// into `func` provided, with no extra fluff entailed.
    ///
    /// # Why `Send + Sync + 'static`?
    ///
    /// All host functions defined in a [`Store`](crate::Store) (including
    /// those from [`Func::new`] and other constructors) require that the
    /// `func` provided is `Send + Sync + 'static`. Additionally host functions
    /// always are `Fn` as opposed to `FnMut` or `FnOnce`. This can at-a-glance
    /// feel restrictive since the closure cannot close over as many types as
    /// before. The reason for this, though, is to ensure that
    /// [`Store<T>`](crate::Store) can implement both the `Send` and `Sync`
    /// traits.
    ///
    /// Fear not, however, because this isn't as restrictive as it seems! Host
    /// functions are provided a [`Caller<'_, T>`](crate::Caller) argument which
    /// allows access to the host-defined data within the
    /// [`Store`](crate::Store). The `T` type is not required to be any of
    /// `Send`, `Sync`, or `'static`! This means that you can store whatever
    /// you'd like in `T` and have it accessible by all host functions.
    /// Additionally mutable access to `T` is allowed through
    /// [`Caller::data_mut`].
    ///
    /// Most host-defined [`Func`] values provide closures that end up not
    /// actually closing over any values. These zero-sized types will use the
    /// context from [`Caller`] for host-defined information.
    ///
    /// # Examples
    ///
    /// First up we can see how simple wasm imports can be implemented, such
    /// as a function that adds its two arguments and returns the result.
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::<()>::default();
    /// let add = Func::wrap(&mut store, |a: i32, b: i32| a + b);
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $add (param i32 i32) (result i32)))
    ///             (func (export "foo") (param i32 i32) (result i32)
    ///                 local.get 0
    ///                 local.get 1
    ///                 call $add))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[add.into()])?;
    /// let foo = instance.get_typed_func::<(i32, i32), i32, _>(&mut store, "foo")?;
    /// assert_eq!(foo.call(&mut store, (1, 2))?, 3);
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// We can also do the same thing, but generate a trap if the addition
    /// overflows:
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::<()>::default();
    /// let add = Func::wrap(&mut store, |a: i32, b: i32| {
    ///     match a.checked_add(b) {
    ///         Some(i) => Ok(i),
    ///         None => Err(Trap::new("overflow")),
    ///     }
    /// });
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $add (param i32 i32) (result i32)))
    ///             (func (export "foo") (param i32 i32) (result i32)
    ///                 local.get 0
    ///                 local.get 1
    ///                 call $add))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[add.into()])?;
    /// let foo = instance.get_typed_func::<(i32, i32), i32, _>(&mut store, "foo")?;
    /// assert_eq!(foo.call(&mut store, (1, 2))?, 3);
    /// assert!(foo.call(&mut store, (i32::max_value(), 1)).is_err());
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// And don't forget all the wasm types are supported!
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::<()>::default();
    /// let debug = Func::wrap(&mut store, |a: i32, b: u32, c: f32, d: i64, e: u64, f: f64| {
    ///
    ///     println!("a={}", a);
    ///     println!("b={}", b);
    ///     println!("c={}", c);
    ///     println!("d={}", d);
    ///     println!("e={}", e);
    ///     println!("f={}", f);
    /// });
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $debug (param i32 i32 f32 i64 i64 f64)))
    ///             (func (export "foo")
    ///                 i32.const -1
    ///                 i32.const 1
    ///                 f32.const 2
    ///                 i64.const -3
    ///                 i64.const 3
    ///                 f64.const 4
    ///                 call $debug))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[debug.into()])?;
    /// let foo = instance.get_typed_func::<(), (), _>(&mut store, "foo")?;
    /// foo.call(&mut store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Finally if you want to get really fancy you can also implement
    /// imports that read/write wasm module's memory
    ///
    /// ```
    /// use std::str;
    ///
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// # let mut store = Store::default();
    /// let log_str = Func::wrap(&mut store, |mut caller: Caller<'_, ()>, ptr: i32, len: i32| {
    ///     let mem = match caller.get_export("memory") {
    ///         Some(Extern::Memory(mem)) => mem,
    ///         _ => return Err(Trap::new("failed to find host memory")),
    ///     };
    ///     let data = mem.data(&caller)
    ///         .get(ptr as u32 as usize..)
    ///         .and_then(|arr| arr.get(..len as u32 as usize));
    ///     let string = match data {
    ///         Some(data) => match str::from_utf8(data) {
    ///             Ok(s) => s,
    ///             Err(_) => return Err(Trap::new("invalid utf-8")),
    ///         },
    ///         None => return Err(Trap::new("pointer/length out of bounds")),
    ///     };
    ///     assert_eq!(string, "Hello, world!");
    ///     println!("{}", string);
    ///     Ok(())
    /// });
    /// let module = Module::new(
    ///     store.engine(),
    ///     r#"
    ///         (module
    ///             (import "" "" (func $log_str (param i32 i32)))
    ///             (func (export "foo")
    ///                 i32.const 4   ;; ptr
    ///                 i32.const 13  ;; len
    ///                 call $log_str)
    ///             (memory (export "memory") 1)
    ///             (data (i32.const 4) "Hello, world!"))
    ///     "#,
    /// )?;
    /// let instance = Instance::new(&mut store, &module, &[log_str.into()])?;
    /// let foo = instance.get_typed_func::<(), (), _>(&mut store, "foo")?;
    /// foo.call(&mut store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn wrap<T, Params, Results>(
        mut store: impl AsContextMut<Data = T>,
        func: impl IntoFunc<T, Params, Results>,
    ) -> Func {
        let store = store.as_context_mut().0;
        // part of this unsafety is about matching the `T` to a `Store<T>`,
        // which is done through the `AsContextMut` bound above.
        unsafe {
            let host = HostFunc::wrap(store.engine(), func);
            host.into_func(store)
        }
    }

    for_each_function_signature!(generate_wrap_async_func);

    /// Returns the underlying wasm type that this `Func` has.
    ///
    /// # Panics
    ///
    /// Panics if `store` does not own this function.
    pub fn ty(&self, store: impl AsContext) -> FuncType {
        self.load_ty(&store.as_context().0)
    }

    /// Forcibly loads the type of this function from the `Engine`.
    ///
    /// Note that this is a somewhat expensive method since it requires taking a
    /// lock as well as cloning a type.
    fn load_ty(&self, store: &StoreOpaque) -> FuncType {
        FuncType::from_wasm_func_type(
            store
                .engine()
                .signatures()
                .lookup_type(self.sig_index(store.store_data()))
                .expect("signature should be registered"),
        )
    }

    /// Gets a reference to the `FuncType` for this function.
    ///
    /// Note that this returns both a reference to the type of this function as
    /// well as a reference back to the store itself. This enables using the
    /// `StoreOpaque` while the `FuncType` is also being used (from the
    /// perspective of the borrow-checker) because otherwise the signature would
    /// consider `StoreOpaque` borrowed mutable while `FuncType` is in use.
    fn ty_ref<'a>(&self, store: &'a mut StoreOpaque) -> (&'a FuncType, &'a StoreOpaque) {
        // If we haven't loaded our type into the store yet then do so lazily at
        // this time.
        if store.store_data()[self.0].ty.is_none() {
            let ty = self.load_ty(store);
            store.store_data_mut()[self.0].ty = Some(Box::new(ty));
        }

        (store.store_data()[self.0].ty.as_ref().unwrap(), store)
    }

    pub(crate) fn sig_index(&self, data: &StoreData) -> VMSharedSignatureIndex {
        data[self.0].sig_index()
    }

    /// Invokes this function with the `params` given and writes returned values
    /// to `results`.
    ///
    /// The `params` here must match the type signature of this `Func`, or a
    /// trap will occur. If a trap occurs while executing this function, then a
    /// trap will also be returned. Additionally `results` must have the same
    /// length as the number of results for this function.
    ///
    /// # Panics
    ///
    /// This function will panic if called on a function belonging to an async
    /// store. Asynchronous stores must always use `call_async`.
    /// initiates a panic. Also panics if `store` does not own this function.
    pub fn call(
        &self,
        mut store: impl AsContextMut,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        assert!(
            !store.as_context().async_support(),
            "must use `call_async` when async support is enabled on the config",
        );
        self.call_impl(&mut store.as_context_mut(), params, results)
    }

    /// Invokes this function in an "unchecked" fashion, reading parameters and
    /// writing results to `params_and_returns`.
    ///
    /// This function is the same as [`Func::call`] except that the arguments
    /// and results both use a different representation. If possible it's
    /// recommended to use [`Func::call`] if safety isn't necessary or to use
    /// [`Func::typed`] in conjunction with [`TypedFunc::call`] since that's
    /// both safer and faster than this method of invoking a function.
    ///
    /// Note that if this function takes `externref` arguments then it will
    /// **not** automatically GC unlike the [`Func::call`] and
    /// [`TypedFunc::call`] functions. This means that if this function is
    /// invoked many times with new `ExternRef` values and no other GC happens
    /// via any other means then no values will get collected.
    ///
    /// # Unsafety
    ///
    /// This function is unsafe because the `params_and_returns` argument is not
    /// validated at all. It must uphold invariants such as:
    ///
    /// * It's a valid pointer to an array
    /// * It has enough space to store all parameters
    /// * It has enough space to store all results (not at the same time as
    ///   parameters)
    /// * Parameters are initially written to the array and have the correct
    ///   types and such.
    /// * Reference types like `externref` and `funcref` are valid at the
    ///   time of this call and for the `store` specified.
    ///
    /// These invariants are all upheld for you with [`Func::call`] and
    /// [`TypedFunc::call`].
    pub unsafe fn call_unchecked(
        &self,
        mut store: impl AsContextMut,
        params_and_returns: *mut ValRaw,
    ) -> Result<(), Trap> {
        let mut store = store.as_context_mut();
        let data = &store.0.store_data()[self.0];
        let anyfunc = data.export().anyfunc;
        let trampoline = data.trampoline();
        Self::call_unchecked_raw(&mut store, anyfunc, trampoline, params_and_returns)
    }

    pub(crate) unsafe fn call_unchecked_raw<T>(
        store: &mut StoreContextMut<'_, T>,
        anyfunc: NonNull<VMCallerCheckedAnyfunc>,
        trampoline: VMTrampoline,
        params_and_returns: *mut ValRaw,
    ) -> Result<(), Trap> {
        invoke_wasm_and_catch_traps(store, |caller| {
            let trampoline = wasmtime_runtime::prepare_host_to_wasm_trampoline(caller, trampoline);
            trampoline(
                anyfunc.as_ref().vmctx,
                caller,
                anyfunc.as_ref().func_ptr.as_ptr(),
                params_and_returns,
            )
        })
    }

    /// Converts the raw representation of a `funcref` into an `Option<Func>`
    ///
    /// This is intended to be used in conjunction with [`Func::new_unchecked`],
    /// [`Func::call_unchecked`], and [`ValRaw`] with its `funcref` field.
    ///
    /// # Unsafety
    ///
    /// This function is not safe because `raw` is not validated at all. The
    /// caller must guarantee that `raw` is owned by the `store` provided and is
    /// valid within the `store`.
    pub unsafe fn from_raw(mut store: impl AsContextMut, raw: usize) -> Option<Func> {
        Func::from_caller_checked_anyfunc(store.as_context_mut().0, raw as *mut _)
    }

    /// Extracts the raw value of this `Func`, which is owned by `store`.
    ///
    /// This function returns a value that's suitable for writing into the
    /// `funcref` field of the [`ValRaw`] structure.
    ///
    /// # Unsafety
    ///
    /// The returned value is only valid for as long as the store is alive and
    /// this function is properly rooted within it. Additionally this function
    /// should not be liberally used since it's a very low-level knob.
    pub unsafe fn to_raw(&self, store: impl AsContext) -> usize {
        self.caller_checked_anyfunc(store.as_context().0).as_ptr() as usize
    }

    /// Invokes this function with the `params` given, returning the results
    /// asynchronously.
    ///
    /// This function is the same as [`Func::call`] except that it is
    /// asynchronous. This is only compatible with stores associated with an
    /// [asynchronous config](crate::Config::async_support).
    ///
    /// It's important to note that the execution of WebAssembly will happen
    /// synchronously in the `poll` method of the future returned from this
    /// function. Wasmtime does not manage its own thread pool or similar to
    /// execute WebAssembly in. Future `poll` methods are generally expected to
    /// resolve quickly, so it's recommended that you run or poll this future
    /// in a "blocking context".
    ///
    /// For more information see the documentation on [asynchronous
    /// configs](crate::Config::async_support).
    ///
    /// # Panics
    ///
    /// Panics if this is called on a function in a synchronous store. This
    /// only works with functions defined within an asynchronous store. Also
    /// panics if `store` does not own this function.
    #[cfg(feature = "async")]
    #[cfg_attr(nightlydoc, doc(cfg(feature = "async")))]
    pub async fn call_async<T>(
        &self,
        mut store: impl AsContextMut<Data = T>,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()>
    where
        T: Send,
    {
        let mut store = store.as_context_mut();
        assert!(
            store.0.async_support(),
            "cannot use `call_async` without enabling async support in the config",
        );
        let result = store
            .on_fiber(|store| self.call_impl(store, params, results))
            .await??;
        Ok(result)
    }

    fn call_impl<T>(
        &self,
        store: &mut StoreContextMut<'_, T>,
        params: &[Val],
        results: &mut [Val],
    ) -> Result<()> {
        // We need to perform a dynamic check that the arguments given to us
        // match the signature of this function and are appropriate to pass to
        // this function. This involves checking to make sure we have the right
        // number and types of arguments as well as making sure everything is
        // from the same `Store`.
        let (ty, opaque) = self.ty_ref(store.0);
        if ty.params().len() != params.len() {
            bail!(
                "expected {} arguments, got {}",
                ty.params().len(),
                params.len()
            );
        }
        if ty.results().len() != results.len() {
            bail!(
                "expected {} results, got {}",
                ty.results().len(),
                results.len()
            );
        }
        for (ty, arg) in ty.params().zip(params) {
            if arg.ty() != ty {
                bail!(
                    "argument type mismatch: found {} but expected {}",
                    arg.ty(),
                    ty
                );
            }
            if !arg.comes_from_same_store(opaque) {
                bail!("cross-`Store` values are not currently supported");
            }
        }

        let values_vec_size = params.len().max(ty.results().len());

        // Whenever we pass `externref`s from host code to Wasm code, they
        // go into the `VMExternRefActivationsTable`. But the table might be
        // at capacity already, so check for that. If it is at capacity
        // (unlikely) then do a GC to free up space. This is necessary
        // because otherwise we would either keep filling up the bump chunk
        // and making it larger and larger or we would always take the slow
        // path when inserting references into the table.
        if ty.as_wasm_func_type().externref_params_count()
            > store
                .0
                .externref_activations_table()
                .bump_capacity_remaining()
        {
            store.gc();
        }

        // Store the argument values into `values_vec`.
        let mut values_vec = store.0.take_wasm_val_raw_storage();
        debug_assert!(values_vec.is_empty());
        values_vec.resize_with(values_vec_size, || ValRaw::i32(0));
        for (arg, slot) in params.iter().cloned().zip(&mut values_vec) {
            unsafe {
                *slot = arg.to_raw(&mut *store);
            }
        }

        unsafe {
            self.call_unchecked(&mut *store, values_vec.as_mut_ptr())?;
        }

        for ((i, slot), val) in results.iter_mut().enumerate().zip(&values_vec) {
            let ty = self.ty_ref(store.0).0.results().nth(i).unwrap();
            *slot = unsafe { Val::from_raw(&mut *store, *val, ty) };
        }
        values_vec.truncate(0);
        store.0.save_wasm_val_raw_storage(values_vec);
        Ok(())
    }

    #[inline]
    pub(crate) fn caller_checked_anyfunc(
        &self,
        store: &StoreOpaque,
    ) -> NonNull<VMCallerCheckedAnyfunc> {
        store.store_data()[self.0].export().anyfunc
    }

    pub(crate) unsafe fn from_wasmtime_function(
        export: ExportFunction,
        store: &mut StoreOpaque,
    ) -> Self {
        let anyfunc = export.anyfunc.as_ref();
        let trampoline = store.lookup_trampoline(&*anyfunc);
        Func::from_func_kind(FuncKind::StoreOwned { trampoline, export }, store)
    }

    fn from_func_kind(kind: FuncKind, store: &mut StoreOpaque) -> Self {
        Func(store.store_data_mut().insert(FuncData { kind, ty: None }))
    }

    pub(crate) fn vmimport(&self, store: &mut StoreOpaque) -> VMFunctionImport {
        unsafe {
            let f = self.caller_checked_anyfunc(store);
            VMFunctionImport {
                body: f.as_ref().func_ptr,
                vmctx: f.as_ref().vmctx,
            }
        }
    }

    pub(crate) fn comes_from_same_store(&self, store: &StoreOpaque) -> bool {
        store.store_data().contains(self.0)
    }

    fn invoke<T>(
        mut caller: Caller<'_, T>,
        ty: &FuncType,
        values_vec: &mut [ValRaw],
        func: &dyn Fn(Caller<'_, T>, &[Val], &mut [Val]) -> Result<(), Trap>,
    ) -> Result<(), Trap> {
        // Translate the raw JIT arguments in `values_vec` into a `Val` which
        // we'll be passing as a slice. The storage for our slice-of-`Val` we'll
        // be taking from the `Store`. We preserve our slice back into the
        // `Store` after the hostcall, ideally amortizing the cost of allocating
        // the storage across wasm->host calls.
        //
        // Note that we have a dynamic guarantee that `values_vec` is the
        // appropriate length to both read all arguments from as well as store
        // all results into.
        let mut val_vec = caller.store.0.take_hostcall_val_storage();
        debug_assert!(val_vec.is_empty());
        let nparams = ty.params().len();
        val_vec.reserve(nparams + ty.results().len());
        for (i, ty) in ty.params().enumerate() {
            val_vec.push(unsafe { Val::from_raw(&mut caller.store, values_vec[i], ty) })
        }

        val_vec.extend((0..ty.results().len()).map(|_| Val::null()));
        let (params, results) = val_vec.split_at_mut(nparams);
        func(caller.sub_caller(), params, results)?;

        // See the comment in `Func::call_impl`'s `write_params` function.
        if ty.as_wasm_func_type().externref_returns_count()
            > caller
                .store
                .0
                .externref_activations_table()
                .bump_capacity_remaining()
        {
            caller.store.gc();
        }

        // Unlike our arguments we need to dynamically check that the return
        // values produced are correct. There could be a bug in `func` that
        // produces the wrong number, wrong types, or wrong stores of
        // values, and we need to catch that here.
        for (i, (ret, ty)) in results.iter().zip(ty.results()).enumerate() {
            if ret.ty() != ty {
                return Err(Trap::new(
                    "function attempted to return an incompatible value",
                ));
            }
            if !ret.comes_from_same_store(caller.store.0) {
                return Err(Trap::new(
                    "cross-`Store` values are not currently supported",
                ));
            }
            unsafe {
                values_vec[i] = ret.to_raw(&mut caller.store);
            }
        }

        // Restore our `val_vec` back into the store so it's usable for the next
        // hostcall to reuse our own storage.
        val_vec.truncate(0);
        caller.store.0.save_hostcall_val_storage(val_vec);
        Ok(())
    }

    /// Attempts to extract a typed object from this `Func` through which the
    /// function can be called.
    ///
    /// This function serves as an alternative to [`Func::call`] and
    /// [`Func::call_async`]. This method performs a static type check (using
    /// the `Params` and `Results` type parameters on the underlying wasm
    /// function. If the type check passes then a `TypedFunc` object is returned,
    /// otherwise an error is returned describing the typecheck failure.
    ///
    /// The purpose of this relative to [`Func::call`] is that it's much more
    /// efficient when used to invoke WebAssembly functions. With the types
    /// statically known far less setup/teardown is required when invoking
    /// WebAssembly. If speed is desired then this function is recommended to be
    /// used instead of [`Func::call`] (which is more general, hence its
    /// slowdown).
    ///
    /// The `Params` type parameter is used to describe the parameters of the
    /// WebAssembly function. This can either be a single type (like `i32`), or
    /// a tuple of types representing the list of parameters (like `(i32, f32,
    /// f64)`). Additionally you can use `()` to represent that the function has
    /// no parameters.
    ///
    /// The `Results` type parameter is used to describe the results of the
    /// function. This behaves the same way as `Params`, but just for the
    /// results of the function.
    ///
    /// The `S` type parameter represents the method of passing in the store
    /// context, and can typically be specified as simply `_` when calling this
    /// function.
    ///
    /// Translation between Rust types and WebAssembly types looks like:
    ///
    /// | WebAssembly | Rust                |
    /// |-------------|---------------------|
    /// | `i32`       | `i32` or `u32`      |
    /// | `i64`       | `i64` or `u64`      |
    /// | `f32`       | `f32`               |
    /// | `f64`       | `f64`               |
    /// | `externref` | `Option<ExternRef>` |
    /// | `funcref`   | `Option<Func>`      |
    /// | `v128`      | not supported       |
    ///
    /// (note that this mapping is the same as that of [`Func::wrap`]).
    ///
    /// Note that once the [`TypedFunc`] return value is acquired you'll use either
    /// [`TypedFunc::call`] or [`TypedFunc::call_async`] as necessary to actually invoke
    /// the function. This method does not invoke any WebAssembly code, it
    /// simply performs a typecheck before returning the [`TypedFunc`] value.
    ///
    /// This method also has a convenience wrapper as
    /// [`Instance::get_typed_func`](crate::Instance::get_typed_func) to
    /// directly get a typed function value from an
    /// [`Instance`](crate::Instance).
    ///
    /// # Errors
    ///
    /// This function will return an error if `Params` or `Results` does not
    /// match the native type of this WebAssembly function.
    ///
    /// # Panics
    ///
    /// This method will panic if `store` does not own this function.
    ///
    /// # Examples
    ///
    /// An end-to-end example of calling a function which takes no parameters
    /// and has no results:
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn main() -> anyhow::Result<()> {
    /// let engine = Engine::default();
    /// let mut store = Store::new(&engine, ());
    /// let module = Module::new(&engine, r#"(module (func (export "foo")))"#)?;
    /// let instance = Instance::new(&mut store, &module, &[])?;
    /// let foo = instance.get_func(&mut store, "foo").expect("export wasn't a function");
    ///
    /// // Note that this call can fail due to the typecheck not passing, but
    /// // in our case we statically know the module so we know this should
    /// // pass.
    /// let typed = foo.typed::<(), (), _>(&store)?;
    ///
    /// // Note that this can fail if the wasm traps at runtime.
    /// typed.call(&mut store, ())?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// You can also pass in multiple parameters and get a result back
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn foo(add: &Func, mut store: Store<()>) -> anyhow::Result<()> {
    /// let typed = add.typed::<(i32, i64), f32, _>(&store)?;
    /// assert_eq!(typed.call(&mut store, (1, 2))?, 3.0);
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// and similarly if a function has multiple results you can bind that too
    ///
    /// ```
    /// # use wasmtime::*;
    /// # fn foo(add_with_overflow: &Func, mut store: Store<()>) -> anyhow::Result<()> {
    /// let typed = add_with_overflow.typed::<(u32, u32), (u32, i32), _>(&store)?;
    /// let (result, overflow) = typed.call(&mut store, (u32::max_value(), 2))?;
    /// assert_eq!(result, 1);
    /// assert_eq!(overflow, 1);
    /// # Ok(())
    /// # }
    /// ```
    pub fn typed<Params, Results, S>(&self, store: S) -> Result<TypedFunc<Params, Results>>
    where
        Params: WasmParams,
        Results: WasmResults,
        S: AsContext,
    {
        // Type-check that the params/results are all valid
        let ty = self.ty(store);
        Params::typecheck(ty.params()).context("type mismatch with parameters")?;
        Results::typecheck(ty.results()).context("type mismatch with results")?;

        // and then we can construct the typed version of this function
        // (unsafely), which should be safe since we just did the type check above.
        unsafe { Ok(TypedFunc::new_unchecked(*self)) }
    }
}

/// Prepares for entrance into WebAssembly.
///
/// This function will set up context such that `closure` is allowed to call a
/// raw trampoline or a raw WebAssembly function. This *must* be called to do
/// things like catch traps and set up GC properly.
///
/// The `closure` provided receives a default "caller" `VMContext` parameter it
/// can pass to the called wasm function, if desired.
pub(crate) fn invoke_wasm_and_catch_traps<T>(
    store: &mut StoreContextMut<'_, T>,
    closure: impl FnMut(*mut VMContext),
) -> Result<(), Trap> {
    unsafe {
        let exit = enter_wasm(store);

        if let Err(trap) = store.0.call_hook(CallHook::CallingWasm) {
            exit_wasm(store, exit);
            return Err(trap);
        }
        let result = wasmtime_runtime::catch_traps(
            store.0.signal_handler(),
            store.0.engine().config().wasm_backtrace,
            store.0.default_caller(),
            closure,
        );
        exit_wasm(store, exit);
        store.0.call_hook(CallHook::ReturningFromWasm)?;
        result.map_err(|t| Trap::from_runtime_box(store.0, t))
    }
}

/// This function is called to register state within `Store` whenever
/// WebAssembly is entered within the `Store`.
///
/// This function sets up various limits such as:
///
/// * The stack limit. This is what ensures that we limit the stack space
///   allocated by WebAssembly code and it's relative to the initial stack
///   pointer that called into wasm.
///
/// This function may fail if the the stack limit can't be set because an
/// interrupt already happened.
fn enter_wasm<T>(store: &mut StoreContextMut<'_, T>) -> Option<usize> {
    // If this is a recursive call, e.g. our stack limit is already set, then
    // we may be able to skip this function.
    //
    // For synchronous stores there's nothing else to do because all wasm calls
    // happen synchronously and on the same stack. This means that the previous
    // stack limit will suffice for the next recursive call.
    //
    // For asynchronous stores then each call happens on a separate native
    // stack. This means that the previous stack limit is no longer relevant
    // because we're on a separate stack.
    if unsafe { *store.0.runtime_limits().stack_limit.get() } != usize::MAX
        && !store.0.async_support()
    {
        return None;
    }

    let stack_pointer = psm::stack_pointer() as usize;

    // Determine the stack pointer where, after which, any wasm code will
    // immediately trap. This is checked on the entry to all wasm functions.
    //
    // Note that this isn't 100% precise. We are requested to give wasm
    // `max_wasm_stack` bytes, but what we're actually doing is giving wasm
    // probably a little less than `max_wasm_stack` because we're
    // calculating the limit relative to this function's approximate stack
    // pointer. Wasm will be executed on a frame beneath this one (or next
    // to it). In any case it's expected to be at most a few hundred bytes
    // of slop one way or another. When wasm is typically given a MB or so
    // (a million bytes) the slop shouldn't matter too much.
    //
    // After we've got the stack limit then we store it into the `stack_limit`
    // variable.
    let wasm_stack_limit = stack_pointer - store.engine().config().max_wasm_stack;
    let prev_stack = unsafe {
        mem::replace(
            &mut *store.0.runtime_limits().stack_limit.get(),
            wasm_stack_limit,
        )
    };

    Some(prev_stack)
}

fn exit_wasm<T>(store: &mut StoreContextMut<'_, T>, prev_stack: Option<usize>) {
    // If we don't have a previous stack pointer to restore, then there's no
    // cleanup we need to perform here.
    let prev_stack = match prev_stack {
        Some(stack) => stack,
        None => return,
    };

    unsafe {
        *store.0.runtime_limits().stack_limit.get() = prev_stack;
    }
}

/// A trait implemented for types which can be returned from closures passed to
/// [`Func::wrap`] and friends.
///
/// This trait should not be implemented by user types. This trait may change at
/// any time internally. The types which implement this trait, however, are
/// stable over time.
///
/// For more information see [`Func::wrap`]
pub unsafe trait WasmRet {
    // Same as `WasmTy::Abi`.
    #[doc(hidden)]
    type Abi: Copy;
    #[doc(hidden)]
    type Retptr: Copy;

    // Same as `WasmTy::compatible_with_store`.
    #[doc(hidden)]
    fn compatible_with_store(&self, store: &StoreOpaque) -> bool;

    // Similar to `WasmTy::into_abi_for_arg` but used when host code is
    // returning a value into Wasm, rather than host code passing an argument to
    // a Wasm call. Unlike `into_abi_for_arg`, implementors of this method can
    // raise traps, which means that callers must ensure that
    // `invoke_wasm_and_catch_traps` is on the stack, and therefore this method
    // is unsafe.
    #[doc(hidden)]
    unsafe fn into_abi_for_ret(
        self,
        store: &mut StoreOpaque,
        ptr: Self::Retptr,
    ) -> Result<Self::Abi, Trap>;

    #[doc(hidden)]
    fn func_type(params: impl Iterator<Item = ValType>) -> FuncType;

    #[doc(hidden)]
    unsafe fn wrap_trampoline(ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi);

    // Utilities used to convert an instance of this type to a `Result`
    // explicitly, used when wrapping async functions which always bottom-out
    // in a function that returns a trap because futures can be cancelled.
    #[doc(hidden)]
    type Fallible: WasmRet<Abi = Self::Abi, Retptr = Self::Retptr>;
    #[doc(hidden)]
    fn into_fallible(self) -> Self::Fallible;
    #[doc(hidden)]
    fn fallible_from_trap(trap: Trap) -> Self::Fallible;
}

unsafe impl<T> WasmRet for T
where
    T: WasmTy,
{
    type Abi = <T as WasmTy>::Abi;
    type Retptr = ();
    type Fallible = Result<T, Trap>;

    fn compatible_with_store(&self, store: &StoreOpaque) -> bool {
        <Self as WasmTy>::compatible_with_store(self, store)
    }

    unsafe fn into_abi_for_ret(
        self,
        store: &mut StoreOpaque,
        _retptr: (),
    ) -> Result<Self::Abi, Trap> {
        Ok(<Self as WasmTy>::into_abi(self, store))
    }

    fn func_type(params: impl Iterator<Item = ValType>) -> FuncType {
        FuncType::new(params, Some(<Self as WasmTy>::valtype()))
    }

    unsafe fn wrap_trampoline(ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi) {
        T::abi_into_raw(f(()), ptr);
    }

    fn into_fallible(self) -> Result<T, Trap> {
        Ok(self)
    }

    fn fallible_from_trap(trap: Trap) -> Result<T, Trap> {
        Err(trap)
    }
}

unsafe impl<T> WasmRet for Result<T, Trap>
where
    T: WasmRet,
{
    type Abi = <T as WasmRet>::Abi;
    type Retptr = <T as WasmRet>::Retptr;
    type Fallible = Self;

    fn compatible_with_store(&self, store: &StoreOpaque) -> bool {
        match self {
            Ok(x) => <T as WasmRet>::compatible_with_store(x, store),
            Err(_) => true,
        }
    }

    unsafe fn into_abi_for_ret(
        self,
        store: &mut StoreOpaque,
        retptr: Self::Retptr,
    ) -> Result<Self::Abi, Trap> {
        self.and_then(|val| val.into_abi_for_ret(store, retptr))
    }

    fn func_type(params: impl Iterator<Item = ValType>) -> FuncType {
        T::func_type(params)
    }

    unsafe fn wrap_trampoline(ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi) {
        T::wrap_trampoline(ptr, f)
    }

    fn into_fallible(self) -> Result<T, Trap> {
        self
    }

    fn fallible_from_trap(trap: Trap) -> Result<T, Trap> {
        Err(trap)
    }
}

macro_rules! impl_wasm_host_results {
    ($n:tt $($t:ident)*) => (
        #[allow(non_snake_case)]
        unsafe impl<$($t),*> WasmRet for ($($t,)*)
        where
            $($t: WasmTy,)*
            ($($t::Abi,)*): HostAbi,
        {
            type Abi = <($($t::Abi,)*) as HostAbi>::Abi;
            type Retptr = <($($t::Abi,)*) as HostAbi>::Retptr;
            type Fallible = Result<Self, Trap>;

            #[inline]
            fn compatible_with_store(&self, _store: &StoreOpaque) -> bool {
                let ($($t,)*) = self;
                $( $t.compatible_with_store(_store) && )* true
            }

            #[inline]
            unsafe fn into_abi_for_ret(self, _store: &mut StoreOpaque, ptr: Self::Retptr) -> Result<Self::Abi, Trap> {
                let ($($t,)*) = self;
                let abi = ($($t.into_abi(_store),)*);
                Ok(<($($t::Abi,)*) as HostAbi>::into_abi(abi, ptr))
            }

            fn func_type(params: impl Iterator<Item = ValType>) -> FuncType {
                FuncType::new(
                    params,
                    IntoIterator::into_iter([$($t::valtype(),)*]),
                )
            }

            #[allow(unused_assignments)]
            unsafe fn wrap_trampoline(mut _ptr: *mut ValRaw, f: impl FnOnce(Self::Retptr) -> Self::Abi) {
                let ($($t,)*) = <($($t::Abi,)*) as HostAbi>::call(f);
                $(
                    $t::abi_into_raw($t, _ptr);
                    _ptr = _ptr.add(1);
                )*
            }

            #[inline]
            fn into_fallible(self) -> Result<Self, Trap> {
                Ok(self)
            }

            #[inline]
            fn fallible_from_trap(trap: Trap) -> Result<Self, Trap> {
                Err(trap)
            }
        }
    )
}

for_each_function_signature!(impl_wasm_host_results);

// Internal trait representing how to communicate tuples of return values across
// an ABI boundary. This internally corresponds to the "wasmtime" ABI inside of
// cranelift itself. Notably the first element of each tuple is returned via the
// typical system ABI (e.g. systemv or fastcall depending on platform) and all
// other values are returned packed via the stack.
//
// This trait helps to encapsulate all the details of that.
#[doc(hidden)]
pub trait HostAbi {
    // A value returned from native functions which return `Self`
    type Abi: Copy;
    // A return pointer, added to the end of the argument list, for native
    // functions that return `Self`. Note that a 0-sized type here should get
    // elided at the ABI level.
    type Retptr: Copy;

    // Converts a value of `self` into its components. Stores necessary values
    // into `ptr` and then returns whatever needs to be returned from the
    // function.
    unsafe fn into_abi(self, ptr: Self::Retptr) -> Self::Abi;

    // Calls `f` with a suitably sized return area and requires `f` to return
    // the raw abi value of the first element of our tuple. This will then
    // unpack the `Retptr` and assemble it with `Self::Abi` to return an
    // instance of the whole tuple.
    unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self;
}

macro_rules! impl_host_abi {
    // Base case, everything is `()`
    (0) => {
        impl HostAbi for () {
            type Abi = ();
            type Retptr = ();

            #[inline]
            unsafe fn into_abi(self, _ptr: Self::Retptr) -> Self::Abi {}

            #[inline]
            unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self {
                f(())
            }
        }
    };

    // In the 1-case the retptr is not present, so it's a 0-sized value.
    (1 $a:ident) => {
        impl<$a: Copy> HostAbi for ($a,) {
            type Abi = $a;
            type Retptr = ();

            unsafe fn into_abi(self, _ptr: Self::Retptr) -> Self::Abi {
                self.0
            }

            unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self {
                (f(()),)
            }
        }
    };

    // This is where the more interesting case happens. The first element of the
    // tuple is returned via `Abi` and all other elements are returned via
    // `Retptr`. We create a `TupleRetNN` structure to represent all of the
    // return values here.
    //
    // Also note that this isn't implemented for the old backend right now due
    // to the original author not really being sure how to implement this in the
    // old backend.
    ($n:tt $t:ident $($u:ident)*) => {paste::paste!{
        #[doc(hidden)]
        #[allow(non_snake_case)]
        #[repr(C)]
        pub struct [<TupleRet $n>]<$($u,)*> {
            $($u: $u,)*
        }

        #[allow(non_snake_case, unused_assignments)]
        impl<$t: Copy, $($u: Copy,)*> HostAbi for ($t, $($u,)*) {
            type Abi = $t;
            type Retptr = *mut [<TupleRet $n>]<$($u,)*>;

            unsafe fn into_abi(self, ptr: Self::Retptr) -> Self::Abi {
                let ($t, $($u,)*) = self;
                // Store the tail of our tuple into the return pointer...
                $((*ptr).$u = $u;)*
                // ... and return the head raw.
                $t
            }

            unsafe fn call(f: impl FnOnce(Self::Retptr) -> Self::Abi) -> Self {
                // Create space to store all the return values and then invoke
                // the function.
                let mut space = std::mem::MaybeUninit::uninit();
                let t = f(space.as_mut_ptr());
                let space = space.assume_init();

                // Use the return value as the head of the tuple and unpack our
                // return area to get the rest of the tuple.
                (t, $(space.$u,)*)
            }
        }
    }};
}

for_each_function_signature!(impl_host_abi);

/// Internal trait implemented for all arguments that can be passed to
/// [`Func::wrap`] and [`Linker::func_wrap`](crate::Linker::func_wrap).
///
/// This trait should not be implemented by external users, it's only intended
/// as an implementation detail of this crate.
pub trait IntoFunc<T, Params, Results>: Send + Sync + 'static {
    #[doc(hidden)]
    fn into_func(
        self,
        engine: &Engine,
    ) -> (Box<VMHostFuncContext>, VMSharedSignatureIndex, VMTrampoline);
}

/// A structure representing the caller's context when creating a function
/// via [`Func::wrap`].
///
/// This structure can be taken as the first parameter of a closure passed to
/// [`Func::wrap`] or other constructors, and serves two purposes:
///
/// * First consumers can use [`Caller<'_, T>`](crate::Caller) to get access to
///   [`StoreContextMut<'_, T>`](crate::StoreContextMut) and/or get access to
///   `T` itself. This means that the [`Caller`] type can serve as a proxy to
///   the original [`Store`](crate::Store) itself and is used to satisfy
///   [`AsContext`] and [`AsContextMut`] bounds.
///
/// * Second a [`Caller`] can be used as the name implies, learning about the
///   caller's context, namely it's exported memory and exported functions. This
///   allows functions which take pointers as arguments to easily read the
///   memory the pointers point into, or if a function is expected to call
///   malloc in the wasm module to reserve space for the output you can do that.
///
/// Host functions which want access to [`Store`](crate::Store)-level state are
/// recommended to use this type.
pub struct Caller<'a, T> {
    pub(crate) store: StoreContextMut<'a, T>,
    caller: &'a InstanceHandle,
}

impl<T> Caller<'_, T> {
    unsafe fn with<R>(caller: *mut VMContext, f: impl FnOnce(Caller<'_, T>) -> R) -> R {
        assert!(!caller.is_null());
        let instance = InstanceHandle::from_vmctx(caller);
        let store = StoreContextMut::from_raw(instance.store());
        f(Caller {
            store,
            caller: &instance,
        })
    }

    fn sub_caller(&mut self) -> Caller<'_, T> {
        Caller {
            store: self.store.as_context_mut(),
            caller: self.caller,
        }
    }

    /// Looks up an export from the caller's module by the `name` given.
    ///
    /// Note that when accessing and calling exported functions, one should
    /// adhere to the guidelines of the interface types proposal.  This method
    /// is a temporary mechanism for accessing the caller's information until
    /// interface types has been fully standardized and implemented. The
    /// interface types proposal will obsolete this type and this will be
    /// removed in the future at some point after interface types is
    /// implemented. If you're relying on this method type it's recommended to
    /// become familiar with interface types to ensure that your use case is
    /// covered by the proposal.
    ///
    /// # Return
    ///
    /// If a memory or function export with the `name` provided was found, then it is
    /// returned as a `Memory`. There are a number of situations, however, where
    /// the memory or function may not be available:
    ///
    /// * The caller instance may not have an export named `name`
    /// * The export named `name` may not be an exported memory
    /// * There may not be a caller available, for example if `Func` was called
    ///   directly from host code.
    ///
    /// It's recommended to take care when calling this API and gracefully
    /// handling a `None` return value.
    pub fn get_export(&mut self, name: &str) -> Option<Extern> {
        // All instances created have a `host_state` with a pointer pointing
        // back to themselves. If this caller doesn't have that `host_state`
        // then it probably means it was a host-created object like `Func::new`
        // which doesn't have any exports we want to return anyway.
        self.caller
            .host_state()
            .downcast_ref::<Instance>()?
            .get_export(&mut self.store, name)
    }

    /// Access the underlying data owned by this `Store`.
    ///
    /// Same as [`Store::data`](crate::Store::data)
    pub fn data(&self) -> &T {
        self.store.data()
    }

    /// Access the underlying data owned by this `Store`.
    ///
    /// Same as [`Store::data_mut`](crate::Store::data_mut)
    pub fn data_mut(&mut self) -> &mut T {
        self.store.data_mut()
    }

    /// Returns the underlying [`Engine`] this store is connected to.
    pub fn engine(&self) -> &Engine {
        self.store.engine()
    }

    /// Perform garbage collection of `ExternRef`s.
    ///
    /// Same as [`Store::gc`](crate::Store::gc).
    pub fn gc(&mut self) {
        self.store.gc()
    }

    /// Returns the fuel consumed by this store.
    ///
    /// For more information see [`Store::fuel_consumed`](crate::Store::fuel_consumed)
    pub fn fuel_consumed(&self) -> Option<u64> {
        self.store.fuel_consumed()
    }

    /// Inject more fuel into this store to be consumed when executing wasm code.
    ///
    /// For more information see [`Store::add_fuel`](crate::Store::add_fuel)
    pub fn add_fuel(&mut self, fuel: u64) -> Result<()> {
        self.store.add_fuel(fuel)
    }

    /// Synthetically consumes fuel from the store.
    ///
    /// For more information see [`Store::consume_fuel`](crate::Store::consume_fuel)
    pub fn consume_fuel(&mut self, fuel: u64) -> Result<u64> {
        self.store.consume_fuel(fuel)
    }

    /// Configures this `Store` to trap whenever fuel runs out.
    ///
    /// For more information see
    /// [`Store::out_of_fuel_trap`](crate::Store::out_of_fuel_trap)
    pub fn out_of_fuel_trap(&mut self) {
        self.store.out_of_fuel_trap()
    }

    /// Configures this `Store` to yield while executing futures whenever fuel
    /// runs out.
    ///
    /// For more information see
    /// [`Store::out_of_fuel_async_yield`](crate::Store::out_of_fuel_async_yield)
    pub fn out_of_fuel_async_yield(&mut self, injection_count: u64, fuel_to_inject: u64) {
        self.store
            .out_of_fuel_async_yield(injection_count, fuel_to_inject)
    }
}

impl<T> AsContext for Caller<'_, T> {
    type Data = T;
    fn as_context(&self) -> StoreContext<'_, T> {
        self.store.as_context()
    }
}

impl<T> AsContextMut for Caller<'_, T> {
    fn as_context_mut(&mut self) -> StoreContextMut<'_, T> {
        self.store.as_context_mut()
    }
}

macro_rules! impl_into_func {
    ($num:tt $($args:ident)*) => {
        // Implement for functions without a leading `&Caller` parameter,
        // delegating to the implementation below which does have the leading
        // `Caller` parameter.
        #[allow(non_snake_case)]
        impl<T, F, $($args,)* R> IntoFunc<T, ($($args,)*), R> for F
        where
            F: Fn($($args),*) -> R + Send + Sync + 'static,
            $($args: WasmTy,)*
            R: WasmRet,
        {
            fn into_func(self, engine: &Engine) -> (Box<VMHostFuncContext>, VMSharedSignatureIndex, VMTrampoline) {
                let f = move |_: Caller<'_, T>, $($args:$args),*| {
                    self($($args),*)
                };

                f.into_func(engine)
            }
        }

        #[allow(non_snake_case)]
        impl<T, F, $($args,)* R> IntoFunc<T, (Caller<'_, T>, $($args,)*), R> for F
        where
            F: Fn(Caller<'_, T>, $($args),*) -> R + Send + Sync + 'static,
            $($args: WasmTy,)*
            R: WasmRet,
        {
            fn into_func(self, engine: &Engine) -> (Box<VMHostFuncContext>, VMSharedSignatureIndex, VMTrampoline) {
                /// This shim is called by Wasm code, constructs a `Caller`,
                /// calls the wrapped host function, and returns the translated
                /// result back to Wasm.
                ///
                /// Note that this shim's ABI must *exactly* match that expected
                /// by Cranelift, since Cranelift is generating raw function
                /// calls directly to this function.
                unsafe extern "C" fn wasm_to_host_shim<T, F, $($args,)* R>(
                    vmctx: *mut VMOpaqueContext,
                    caller_vmctx: *mut VMContext,
                    $( $args: $args::Abi, )*
                    retptr: R::Retptr,
                ) -> R::Abi
                where
                    F: Fn(Caller<'_, T>, $( $args ),*) -> R + 'static,
                    $( $args: WasmTy, )*
                    R: WasmRet,
                {
                    enum CallResult<U> {
                        Ok(U),
                        Trap(anyhow::Error),
                        Panic(Box<dyn std::any::Any + Send>),
                    }

                    // Note that this `result` is intentionally scoped into a
                    // separate block. Handling traps and panics will involve
                    // longjmp-ing from this function which means we won't run
                    // destructors. As a result anything requiring a destructor
                    // should be part of this block, and the long-jmp-ing
                    // happens after the block in handling `CallResult`.
                    let result = Caller::with(caller_vmctx, |mut caller| {
                        let vmctx = VMHostFuncContext::from_opaque(vmctx);
                        let state = (*vmctx).host_state();

                        // Double-check ourselves in debug mode, but we control
                        // the `Any` here so an unsafe downcast should also
                        // work.
                        debug_assert!(state.is::<F>());
                        let func = &*(state as *const _ as *const F);

                        let ret = {
                            panic::catch_unwind(AssertUnwindSafe(|| {
                                if let Err(trap) = caller.store.0.call_hook(CallHook::CallingHost) {
                                    return R::fallible_from_trap(trap);
                                }
                                $(let $args = $args::from_abi($args, caller.store.0);)*
                                let r = func(
                                    caller.sub_caller(),
                                    $( $args, )*
                                );
                                if let Err(trap) = caller.store.0.call_hook(CallHook::ReturningFromHost) {
                                    return R::fallible_from_trap(trap);
                                }
                                r.into_fallible()
                            }))
                        };

                        // Note that we need to be careful when dealing with traps
                        // here. Traps are implemented with longjmp/setjmp meaning
                        // that it's not unwinding and consequently no Rust
                        // destructors are run. We need to be careful to ensure that
                        // nothing on the stack needs a destructor when we exit
                        // abnormally from this `match`, e.g. on `Err`, on
                        // cross-store-issues, or if `Ok(Err)` is raised.
                        match ret {
                            Err(panic) => CallResult::Panic(panic),
                            Ok(ret) => {
                                // Because the wrapped function is not `unsafe`, we
                                // can't assume it returned a value that is
                                // compatible with this store.
                                if !ret.compatible_with_store(caller.store.0) {
                                    CallResult::Trap(anyhow::anyhow!("host function attempted to return cross-`Store` value to Wasm"))
                                } else {
                                    match ret.into_abi_for_ret(caller.store.0, retptr) {
                                        Ok(val) => CallResult::Ok(val),
                                        Err(trap) => CallResult::Trap(trap.into()),
                                    }
                                }

                            }
                        }
                    });

                    match result {
                        CallResult::Ok(val) => val,
                        CallResult::Trap(trap) => raise_user_trap(trap),
                        CallResult::Panic(panic) => wasmtime_runtime::resume_panic(panic),
                    }
                }

                /// This trampoline allows host code to indirectly call the
                /// wrapped function (e.g. via `Func::call` on a `funcref` that
                /// happens to reference our wrapped function).
                ///
                /// It reads the arguments out of the incoming `args` array,
                /// calls the given function pointer, and then stores the result
                /// back into the `args` array.
                unsafe extern "C" fn host_to_wasm_trampoline<$($args,)* R>(
                    callee_vmctx: *mut VMOpaqueContext,
                    caller_vmctx: *mut VMContext,
                    ptr: *const VMFunctionBody,
                    args: *mut ValRaw,
                )
                where
                    $($args: WasmTy,)*
                    R: WasmRet,
                {
                    let ptr = mem::transmute::<
                        *const VMFunctionBody,
                        unsafe extern "C" fn(
                            *mut VMOpaqueContext,
                            *mut VMContext,
                            $( $args::Abi, )*
                            R::Retptr,
                        ) -> R::Abi,
                    >(ptr);

                    let mut _n = 0;
                    $(
                        let $args = $args::abi_from_raw(args.add(_n));
                        _n += 1;
                    )*
                    R::wrap_trampoline(args, |retptr| {
                        ptr(callee_vmctx, caller_vmctx, $( $args, )* retptr)
                    });
                }

                let ty = R::func_type(
                    None::<ValType>.into_iter()
                        $(.chain(Some($args::valtype())))*
                );

                let shared_signature_id = engine.signatures().register(ty.as_wasm_func_type());

                let trampoline = host_to_wasm_trampoline::<$($args,)* R>;

                let ctx = unsafe {
                    VMHostFuncContext::new(
                        NonNull::new(wasm_to_host_shim::<T, F, $($args,)* R> as *mut _).unwrap(),
                        shared_signature_id,
                        Box::new(self),
                    )
                };

                (ctx, shared_signature_id, trampoline)
            }
        }
    }
}

for_each_function_signature!(impl_into_func);

/// Representation of a host-defined function.
///
/// This is used for `Func::new` but also for `Linker`-defined functions. For
/// `Func::new` this is stored within a `Store`, and for `Linker`-defined
/// functions they wrap this up in `Arc` to enable shared ownership of this
/// across many stores.
///
/// Technically this structure needs a `<T>` type parameter to connect to the
/// `Store<T>` itself, but that's an unsafe contract of using this for now
/// rather than part of the struct type (to avoid `Func<T>` in the API).
pub(crate) struct HostFunc {
    // The host function context that is shared with our host-to-Wasm
    // trampoline.
    ctx: Box<VMHostFuncContext>,

    // The index for this function's signature within the engine-wide shared
    // signature registry.
    signature: VMSharedSignatureIndex,

    // Trampoline to enter this function from Rust.
    host_to_wasm_trampoline: VMTrampoline,

    // Stored to unregister this function's signature with the engine when this
    // is dropped.
    engine: Engine,
}

impl HostFunc {
    /// Analog of [`Func::new`]
    #[cfg(compiler)]
    pub fn new<T>(
        engine: &Engine,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, &[Val], &mut [Val]) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let ty_clone = ty.clone();
        unsafe {
            HostFunc::new_unchecked(engine, ty, move |caller, values| {
                Func::invoke(caller, &ty_clone, values, &func)
            })
        }
    }

    /// Analog of [`Func::new_unchecked`]
    #[cfg(compiler)]
    pub unsafe fn new_unchecked<T>(
        engine: &Engine,
        ty: FuncType,
        func: impl Fn(Caller<'_, T>, &mut [ValRaw]) -> Result<(), Trap> + Send + Sync + 'static,
    ) -> Self {
        let func = move |caller_vmctx, values: &mut [ValRaw]| {
            Caller::<T>::with(caller_vmctx, |mut caller| {
                caller.store.0.call_hook(CallHook::CallingHost)?;
                let result = func(caller.sub_caller(), values)?;
                caller.store.0.call_hook(CallHook::ReturningFromHost)?;
                Ok(result)
            })
        };
        let (ctx, signature, trampoline) = crate::trampoline::create_function(&ty, func, engine)
            .expect("failed to create function");
        HostFunc::_new(engine, ctx, signature, trampoline)
    }

    /// Analog of [`Func::wrap`]
    pub fn wrap<T, Params, Results>(
        engine: &Engine,
        func: impl IntoFunc<T, Params, Results>,
    ) -> Self {
        let (ctx, signature, trampoline) = func.into_func(engine);
        HostFunc::_new(engine, ctx, signature, trampoline)
    }

    /// Requires that this function's signature is already registered within
    /// `Engine`. This happens automatically during the above two constructors.
    fn _new(
        engine: &Engine,
        ctx: Box<VMHostFuncContext>,
        signature: VMSharedSignatureIndex,
        trampoline: VMTrampoline,
    ) -> Self {
        HostFunc {
            ctx,
            signature,
            host_to_wasm_trampoline: trampoline,
            engine: engine.clone(),
        }
    }

    /// Inserts this `HostFunc` into a `Store`, returning the `Func` pointing to
    /// it.
    ///
    /// # Unsafety
    ///
    /// Can only be inserted into stores with a matching `T` relative to when
    /// this `HostFunc` was first created.
    pub unsafe fn to_func(self: &Arc<Self>, store: &mut StoreOpaque) -> Func {
        self.validate_store(store);
        let me = self.clone();
        Func::from_func_kind(FuncKind::SharedHost(me), store)
    }

    /// Inserts this `HostFunc` into a `Store`, returning the `Func` pointing to
    /// it.
    ///
    /// This function is similar to, but not equivalent, to `HostFunc::to_func`.
    /// Notably this function requires that the `Arc<Self>` pointer is otherwise
    /// rooted within the `StoreOpaque` via another means. When in doubt use
    /// `to_func` above as it's safer.
    ///
    /// # Unsafety
    ///
    /// Can only be inserted into stores with a matching `T` relative to when
    /// this `HostFunc` was first created.
    ///
    /// Additionally the `&Arc<Self>` is not cloned in this function. Instead a
    /// raw pointer to `Self` is stored within the `Store` for this function.
    /// The caller must arrange for the `Arc<Self>` to be "rooted" in the store
    /// provided via another means, probably by pushing to
    /// `StoreOpaque::rooted_host_funcs`.
    pub unsafe fn to_func_store_rooted(self: &Arc<Self>, store: &mut StoreOpaque) -> Func {
        self.validate_store(store);
        Func::from_func_kind(FuncKind::RootedHost(RootedHostFunc::new(self)), store)
    }

    /// Same as [`HostFunc::to_func`], different ownership.
    unsafe fn into_func(self, store: &mut StoreOpaque) -> Func {
        self.validate_store(store);
        Func::from_func_kind(FuncKind::Host(Box::new(self)), store)
    }

    fn validate_store(&self, store: &mut StoreOpaque) {
        // This assert is required to ensure that we can indeed safely insert
        // `self` into the `store` provided, otherwise the type information we
        // have listed won't be correct. This is possible to hit with the public
        // API of Wasmtime, and should be documented in relevant functions.
        assert!(
            Engine::same(&self.engine, store.engine()),
            "cannot use a store with a different engine than a linker was created with",
        );
    }

    pub(crate) fn sig_index(&self) -> VMSharedSignatureIndex {
        self.signature
    }

    fn export_func(&self) -> ExportFunction {
        ExportFunction {
            anyfunc: self.ctx.wasm_to_host_trampoline(),
        }
    }
}

impl Drop for HostFunc {
    fn drop(&mut self) {
        unsafe {
            self.engine.signatures().unregister(self.signature);
        }
    }
}

impl FuncData {
    #[inline]
    pub(crate) fn trampoline(&self) -> VMTrampoline {
        match &self.kind {
            FuncKind::StoreOwned { trampoline, .. } => *trampoline,
            FuncKind::SharedHost(host) => host.host_to_wasm_trampoline,
            FuncKind::RootedHost(host) => host.host_to_wasm_trampoline,
            FuncKind::Host(host) => host.host_to_wasm_trampoline,
        }
    }

    #[inline]
    fn export(&self) -> ExportFunction {
        self.kind.export()
    }

    pub(crate) fn sig_index(&self) -> VMSharedSignatureIndex {
        unsafe { self.export().anyfunc.as_ref().type_index }
    }
}

impl FuncKind {
    #[inline]
    fn export(&self) -> ExportFunction {
        match self {
            FuncKind::StoreOwned { export, .. } => *export,
            FuncKind::SharedHost(host) => host.export_func(),
            FuncKind::RootedHost(host) => host.export_func(),
            FuncKind::Host(host) => host.export_func(),
        }
    }
}

use self::rooted::*;

/// An inner module is used here to force unsafe construction of
/// `RootedHostFunc` instead of accidentally safely allowing access to its
/// constructor.
mod rooted {
    use super::HostFunc;
    use std::ops::Deref;
    use std::ptr::NonNull;
    use std::sync::Arc;

    /// A variant of a pointer-to-a-host-function used in `FuncKind::RootedHost`
    /// above.
    ///
    /// For more documentation see `FuncKind::RootedHost`, `InstancePre`, and
    /// `HostFunc::to_func_store_rooted`.
    pub(crate) struct RootedHostFunc(NonNull<HostFunc>);

    // These are required due to the usage of `NonNull` but should be safe
    // because `HostFunc` is itself send/sync.
    unsafe impl Send for RootedHostFunc where HostFunc: Send {}
    unsafe impl Sync for RootedHostFunc where HostFunc: Sync {}

    impl RootedHostFunc {
        /// Note that this is `unsafe` because this wrapper type allows safe
        /// access to the pointer given at any time, including outside the
        /// window of validity of `func`, so callers must not use the return
        /// value past the lifetime of the provided `func`.
        pub(crate) unsafe fn new(func: &Arc<HostFunc>) -> RootedHostFunc {
            RootedHostFunc(NonNull::from(&**func))
        }
    }

    impl Deref for RootedHostFunc {
        type Target = HostFunc;

        fn deref(&self) -> &HostFunc {
            unsafe { self.0.as_ref() }
        }
    }
}