lisette-emit 0.3.4

Little language inspired by Rust that compiles to Go
Documentation 
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

//! Lowered body IR: the typed vocabulary `plan::lower` produces and `render/`
//! consumes. `RawGo` is a transitional node holding pre-rendered Go.

use crate::plan::values::ValuePlan;
use syntax::types::Type;

/// Destination for a lowered block's tail. The enclosing function's return
/// context (for nested `return`/`?`) is read from the scope stack via
/// `Planner::return_ctx`; `Return` is also the tail target.
pub(crate) enum PlacePlan<'a> {
    Statement,
    Return,
    Assign {
        local: &'a str,
        target_ty: Option<&'a Type>,
    },
}

impl PlacePlan<'_> {
    pub(crate) fn is_return(&self) -> bool {
        matches!(self, PlacePlan::Return)
    }
}

pub(crate) struct LoweredBlock {
    pub(crate) statements: Vec<LoweredStatement>,
}

pub(crate) enum LoweredStatement {
    If(IfPlan),
    Loop(LoopPlan),
    Block(LoweredBlock),
    Break {
        directive: String,
        label: Option<String>,
    },
    Continue {
        directive: String,
        label: Option<String>,
    },
    Const(ConstPlan),
    Return(ReturnStatementPlan),
    BreakValue(BreakValuePlan),
    Let(LetPlan),
    Assign(AssignPlan),
    Expression(ExpressionStatementPlan),
    Match(MatchStatementPlan),
    Select(SelectStatementPlan),
    Switch(SwitchStatementPlan),
    WhileLet(WhileLetPlan),
    /// Eval-order temp capture: `name := value`.
    TempBind {
        name: String,
        value: String,
    },
    /// `name := <closure_open><body><closure_close>` (try-block IIFE,
    /// recover-block closure). `closure_open`/`close` are opaque Go text.
    ClosureBind {
        name: String,
        closure_open: String,
        body: LoweredBlock,
        closure_close: String,
    },
    RawGo(String),
    /// Raw Go whose tail diverges (a never-typed call such as `panic(...)`).
    /// Tracked separately from `RawGo` so divergence is structural rather than
    /// re-derived by scanning text.
    DivergingRawGo(String),
    /// `panic("unreachable")` tail after a non-exhaustive branch in return
    /// position — a structured diverging leaf.
    UnreachablePanic,
}

/// A source `const` (or `var` when the value is not Go-const-eligible).
pub(crate) struct ConstPlan {
    pub(crate) directive: String,
    pub(crate) is_const: bool,
    pub(crate) name: String,
    pub(crate) ty_str: String,
    pub(crate) value: ValuePlan,
}

/// A source `return expr` statement, classified by `ReturnForm`.
pub(crate) struct ReturnStatementPlan {
    pub(crate) directive: String,
    pub(crate) form: ReturnForm,
}

pub(crate) enum ReturnForm {
    Plain {
        value: ValuePlan,
    },
    /// Bare `return` for a unit-typed function. `side_effect` is run first
    /// when the returned expression is impure.
    Unit {
        side_effect: Option<LoweredBlock>,
    },
    /// `return v0, v1, ...` for a lowered multi-value ABI return.
    Multi {
        values: Vec<String>,
    },
    /// `PartialTuple`/`Tuple` tail destructure: tag-check `IfPlan`s and
    /// `Return` leaves built by `abi_transition`.
    LoweredAbi {
        body: LoweredBlock,
    },
    /// `Result`/`Option`-wrapped return through `FalliblePlanner`.
    Wrapped {
        body: LoweredBlock,
    },
}

/// `break value` statement. `disposition` decides how the value text
/// reaches the loop-result slot (or is discarded); a trailing `break`
/// terminates unless the value already diverged.
pub(crate) struct BreakValuePlan {
    pub(crate) directive: String,
    pub(crate) value: ValuePlan,
    pub(crate) disposition: BreakValueDisposition,
    pub(crate) label: Option<String>,
}

/// What to do with the value of a `break value` statement after its setup
/// has run.
pub(crate) enum BreakValueDisposition {
    /// The value diverged (empty `Propagate`); no further code is emitted
    /// and the `break` is skipped because the value already terminates.
    Diverged,
    /// Inside a loop with a result slot, when the value is a unit-typed
    /// call: emit `<value>` as a side-effect statement (skipped if value
    /// text is empty), then `<result_var> = struct{}{}`, then break.
    UnitCallIntoResult { result_var: String },
    /// Inside a loop with a result slot: emit `<result_var> = <value>`
    /// (skipped if value text is empty), then break.
    AssignToResult { result_var: String },
    /// No result slot: emit `_ = <value>` (skipped if value text is empty),
    /// then break.
    Discard,
}

/// A `let` binding, classified by shape.
pub(crate) struct LetPlan {
    pub(crate) directive: String,
    pub(crate) form: LetForm,
}

pub(crate) enum LetForm {
    /// `!`-typed value. `declaration` is the optional `var X T` line so dead code
    /// can still reference the binding.
    Never {
        declaration: Option<String>,
        body: LoweredBlock,
    },
    /// `let x = value` (single identifier), including `let x = expr?`.
    SimpleIdentifier {
        body: LoweredBlock,
    },
    /// `let _ = value` or all-unused tuple destructure.
    Discard {
        body: LoweredBlock,
    },
    ComplexPattern {
        body: LoweredBlock,
    },
    /// `let (a, b) = go_call()`.
    MultiValueCall {
        body: LoweredBlock,
    },
    LetElse {
        body: LoweredBlock,
    },
}

impl LetForm {
    pub(crate) fn body(&self) -> &LoweredBlock {
        match self {
            LetForm::Never { body, .. }
            | LetForm::SimpleIdentifier { body }
            | LetForm::Discard { body }
            | LetForm::ComplexPattern { body }
            | LetForm::MultiValueCall { body }
            | LetForm::LetElse { body } => body,
        }
    }
}

/// An assignment statement, structured by shape.
pub(crate) struct AssignPlan {
    pub(crate) directive: String,
    pub(crate) form: AssignForm,
}

pub(crate) enum AssignForm {
    /// `target++`, `target--`, or `target op= rhs`.
    Compound {
        target_capture: Vec<LoweredStatement>,
        target_str: String,
        kind: CompoundKind,
    },
    /// `target = value`.
    Simple {
        target_capture: Vec<LoweredStatement>,
        target_str: String,
        value: ValuePlan,
    },
    /// `target = nil` — clearing a Go-imported nullable field with `None`.
    NilClear {
        target_capture: Vec<LoweredStatement>,
        target_str: String,
    },
    /// `_ = expr` discard (drops lowered multi-return values).
    Discard { body: LoweredBlock },
    /// The RHS diverges (never-typed); emitted as a statement.
    NeverTyped { body: LoweredBlock },
}

pub(crate) enum CompoundKind {
    Increment,
    Decrement,
    /// `target op= rhs`. `op_text` is the rendered Go operator.
    OpAssign {
        op_text: String,
        rhs: ValuePlan,
    },
}

/// A bare expression statement.
pub(crate) struct ExpressionStatementPlan {
    pub(crate) directive: String,
    pub(crate) form: ExpressionStatementForm,
}

pub(crate) enum ExpressionStatementForm {
    /// `go <value>` / `defer <value>` at statement position.
    Async {
        value: ValuePlan,
    },
    /// `<keyword> func() { <body> }()` IIFE wrapper for Task/Defer block
    /// forms and inner expressions requiring an IIFE (`needs_iife_for_async`).
    AsyncBlock {
        keyword: String,
        body: LoweredBlock,
    },
    /// `expr?` in statement position (discards the ok value).
    Propagate {
        body: LoweredBlock,
    },
    Discard {
        body: LoweredBlock,
    },
}

pub(crate) struct MatchStatementPlan {
    pub(crate) directive: String,
    pub(crate) body: LoweredBlock,
}

/// A `switch` statement (value or type switch). The renderer owns the
/// `switch`/`case`/`default:` syntax.
pub(crate) struct SwitchStatementPlan {
    pub(crate) directive: String,
    pub(crate) kind: SwitchKind,
    pub(crate) cases: Vec<SwitchCasePlan>,
    pub(crate) default: Option<LoweredBlock>,
    /// Statements after the switch, such as an unreachable panic.
    pub(crate) postlude: Vec<LoweredStatement>,
}

pub(crate) enum SwitchKind {
    /// `switch <subject> {`
    Value { subject: String },
    /// `switch <binding> := <subject>.(type) {` when `binding` is set,
    /// otherwise `switch <subject>.(type) {`.
    Type {
        subject: String,
        binding: Option<String>,
    },
}

/// A single `case <labels>:` plus its body.
pub(crate) struct SwitchCasePlan {
    pub(crate) labels: String,
    pub(crate) body: LoweredBlock,
}

impl SwitchStatementPlan {
    fn ends_with_diverge(&self) -> bool {
        self.postlude
            .last()
            .is_some_and(LoweredStatement::ends_with_diverge)
    }
}

/// A `select` statement: optional retry-loop wrapper around the `select`, an
/// ordered set of arms, plus hoisted setup and a trailing postlude (e.g. an
/// unreachable panic). The renderer owns the `for`/`select`/`case`/`default:`
/// syntax.
pub(crate) struct SelectStatementPlan {
    pub(crate) directive: String,
    /// Side-effecting setup hoisted before the `select` (channel/value temps).
    pub(crate) setup: Vec<LoweredStatement>,
    /// When set, the `select` is wrapped in `for { ... break }` for retry.
    pub(crate) retry_loop: bool,
    pub(crate) arms: Vec<SelectArmPlan>,
    /// Statements after the `select`/retry loop, such as an unreachable panic.
    pub(crate) postlude: Vec<LoweredStatement>,
}

/// A single `select` arm: a `case`/`default:` header plus its body block.
pub(crate) enum SelectArmPlan {
    /// `case <receive_vars> := <-<channel>:`, or `case <-<channel>:` when
    /// `receive_vars` is `None`.
    Receive {
        receive_vars: Option<String>,
        channel: String,
        body: LoweredBlock,
    },
    /// `case <operation>:` where `operation` is `ch <- val` or `<-ch`.
    Send {
        operation: String,
        body: LoweredBlock,
    },
    /// `default:`
    Default { body: LoweredBlock },
}

impl SelectStatementPlan {
    fn ends_with_diverge(&self) -> bool {
        self.postlude
            .last()
            .is_some_and(LoweredStatement::ends_with_diverge)
            || self.all_arms_diverge()
    }

    pub(crate) fn all_arms_diverge(&self) -> bool {
        !self.arms.is_empty() && self.arms.iter().all(|arm| arm.body().ends_with_diverge())
    }
}

impl SelectArmPlan {
    pub(crate) fn body(&self) -> &LoweredBlock {
        match self {
            SelectArmPlan::Receive { body, .. }
            | SelectArmPlan::Send { body, .. }
            | SelectArmPlan::Default { body } => body,
        }
    }
}

pub(crate) struct WhileLetPlan {
    pub(crate) directive: String,
    pub(crate) body: LoweredBlock,
}

/// A statement-position loop. `prologue` is pre-loop setup (a for-loop's
/// iterable capture); `header` is the rendered Go loop opener through the body's
/// opening brace; `label` is the optional break/continue label.
pub(crate) struct LoopPlan {
    pub(crate) directive: String,
    pub(crate) prologue: String,
    pub(crate) label: Option<String>,
    pub(crate) header: String,
    pub(crate) body: LoweredBlock,
}

pub(crate) struct IfPlan {
    /// Empty unless debug; set only on the leading `if`, never on nested
    /// `else if`s.
    pub(crate) directive: String,
    pub(crate) condition_setup: String,
    pub(crate) condition: String,
    pub(crate) then_body: LoweredBlock,
    pub(crate) else_arm: ElseArm,
}

pub(crate) enum ElseArm {
    None,
    ElseIf(Box<IfPlan>),
    /// `inline` is set when the preceding branch diverges so Go would reject
    /// a dead `else`: the body emits unwrapped after `}` instead of `else {}`.
    Else {
        body: LoweredBlock,
        inline: bool,
    },
}

impl LoweredBlock {
    /// Whether the block's last rendered line is `break`, `continue`,
    /// `return`, or `panic(...)`.
    pub(crate) fn ends_with_diverge(&self) -> bool {
        self.statements
            .last()
            .is_some_and(LoweredStatement::ends_with_diverge)
    }

    /// Whether the block has no statements.
    pub(crate) fn is_empty(&self) -> bool {
        self.statements.is_empty()
    }
}

impl LoweredStatement {
    fn ends_with_diverge(&self) -> bool {
        match self {
            LoweredStatement::If(plan) => plan.ends_with_diverge(),
            LoweredStatement::Loop(_) | LoweredStatement::Block(_) | LoweredStatement::Const(_) => {
                false
            }
            LoweredStatement::Break { .. } | LoweredStatement::Continue { .. } => true,
            LoweredStatement::Return(_) => true,
            LoweredStatement::BreakValue(_) => true,
            LoweredStatement::Let(plan) => plan.form.body().ends_with_diverge(),
            LoweredStatement::Assign(plan) => match &plan.form {
                AssignForm::Compound { .. }
                | AssignForm::Simple { .. }
                | AssignForm::NilClear { .. } => false,
                AssignForm::Discard { body } | AssignForm::NeverTyped { body } => {
                    body.ends_with_diverge()
                }
            },
            LoweredStatement::Expression(plan) => match &plan.form {
                ExpressionStatementForm::Async { .. }
                | ExpressionStatementForm::AsyncBlock { .. } => false,
                ExpressionStatementForm::Propagate { body }
                | ExpressionStatementForm::Discard { body } => body.ends_with_diverge(),
            },
            LoweredStatement::Match(plan) => plan.body.ends_with_diverge(),
            LoweredStatement::Select(plan) => plan.ends_with_diverge(),
            LoweredStatement::Switch(plan) => plan.ends_with_diverge(),
            LoweredStatement::WhileLet(plan) => plan.body.ends_with_diverge(),
            LoweredStatement::TempBind { .. } | LoweredStatement::ClosureBind { .. } => false,
            LoweredStatement::RawGo(_) => false,
            LoweredStatement::DivergingRawGo(_) | LoweredStatement::UnreachablePanic => true,
        }
    }

    pub(crate) fn blocks_fallthrough(&self) -> bool {
        !matches!(self, LoweredStatement::WhileLet(_)) && self.ends_with_diverge()
    }
}

impl IfPlan {
    fn ends_with_diverge(&self) -> bool {
        if !self.then_body.ends_with_diverge() {
            return false;
        }
        match &self.else_arm {
            ElseArm::None => false,
            ElseArm::ElseIf(inner) if inner.condition_setup.is_empty() => inner.ends_with_diverge(),
            ElseArm::ElseIf(_) => false,
            ElseArm::Else { body, .. } => body.ends_with_diverge(),
        }
    }
}