1use crate::ast::{Enum, Field, Input, Struct};
2use crate::attr::Trait;
3use crate::generics::InferredBounds;
4use crate::span::MemberSpan;
5use proc_macro2::TokenStream;
6use quote::{format_ident, quote, quote_spanned, ToTokens};
7use std::collections::BTreeSet as Set;
8use syn::{DeriveInput, GenericArgument, Member, PathArguments, Result, Token, Type};
9
10pub fn derive(input: &DeriveInput) -> TokenStream {
11 match try_expand(input) {
12 Ok(expanded) => expanded,
13 Err(error) => fallback(input, error),
17 }
18}
19
20fn try_expand(input: &DeriveInput) -> Result<TokenStream> {
21 let input = Input::from_syn(input)?;
22 input.validate()?;
23 Ok(match input {
24 Input::Struct(input) => impl_struct(input),
25 Input::Enum(input) => impl_enum(input),
26 })
27}
28
29fn fallback(input: &DeriveInput, error: syn::Error) -> TokenStream {
30 let ty = &input.ident;
31 let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
32
33 let error = error.to_compile_error();
34
35 quote! {
36 #error
37
38 #[allow(unused_qualifications)]
39 impl #impl_generics std::error::Error for #ty #ty_generics #where_clause
40 where
41 for<'workaround> #ty #ty_generics: ::core::fmt::Debug,
44 {}
45
46 #[allow(unused_qualifications)]
47 impl #impl_generics ::core::fmt::Display for #ty #ty_generics #where_clause {
48 fn fmt(&self, __formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
49 ::core::unreachable!()
50 }
51 }
52 }
53}
54
55fn impl_struct(input: Struct) -> TokenStream {
56 let ty = &input.ident;
57 let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
58 let mut error_inferred_bounds = InferredBounds::new();
59
60 let source_body = if let Some(transparent_attr) = &input.attrs.transparent {
61 let only_field = &input.fields[0];
62 if only_field.contains_generic {
63 error_inferred_bounds.insert(only_field.ty, quote!(std::error::Error));
64 }
65 let member = &only_field.member;
66 Some(quote_spanned! {transparent_attr.span=>
67 std::error::Error::source(self.#member.as_dyn_error())
68 })
69 } else if let Some(source_field) = input.source_field() {
70 let source = &source_field.member;
71 if source_field.contains_generic {
72 let ty = unoptional_type(source_field.ty);
73 error_inferred_bounds.insert(ty, quote!(std::error::Error + 'static));
74 }
75 let asref = if type_is_option(source_field.ty) {
76 Some(quote_spanned!(source.member_span()=> .as_ref()?))
77 } else {
78 None
79 };
80 let dyn_error = quote_spanned! {source_field.source_span()=>
81 self.#source #asref.as_dyn_error()
82 };
83 Some(quote! {
84 ::core::option::Option::Some(#dyn_error)
85 })
86 } else {
87 None
88 };
89 let source_method = source_body.map(|body| {
90 quote! {
91 fn source(&self) -> ::core::option::Option<&(dyn std::error::Error + 'static)> {
92 use thiserror::__private::AsDynError as _;
93 #body
94 }
95 }
96 });
97
98 let provide_method = input.backtrace_field().map(|backtrace_field| {
99 let request = quote!(request);
100 let backtrace = &backtrace_field.member;
101 let body = if let Some(source_field) = input.source_field() {
102 let source = &source_field.member;
103 let source_provide = if type_is_option(source_field.ty) {
104 quote_spanned! {source.member_span()=>
105 if let ::core::option::Option::Some(source) = &self.#source {
106 source.thiserror_provide(#request);
107 }
108 }
109 } else {
110 quote_spanned! {source.member_span()=>
111 self.#source.thiserror_provide(#request);
112 }
113 };
114 let self_provide = if source == backtrace {
115 None
116 } else if type_is_option(backtrace_field.ty) {
117 Some(quote! {
118 if let ::core::option::Option::Some(backtrace) = &self.#backtrace {
119 #request.provide_ref::<std::backtrace::Backtrace>(backtrace);
120 }
121 })
122 } else {
123 Some(quote! {
124 #request.provide_ref::<std::backtrace::Backtrace>(&self.#backtrace);
125 })
126 };
127 quote! {
128 use thiserror::__private::ThiserrorProvide as _;
129 #source_provide
130 #self_provide
131 }
132 } else if type_is_option(backtrace_field.ty) {
133 quote! {
134 if let ::core::option::Option::Some(backtrace) = &self.#backtrace {
135 #request.provide_ref::<std::backtrace::Backtrace>(backtrace);
136 }
137 }
138 } else {
139 quote! {
140 #request.provide_ref::<std::backtrace::Backtrace>(&self.#backtrace);
141 }
142 };
143 quote! {
144 fn provide<'_request>(&'_request self, #request: &mut std::error::Request<'_request>) {
145 #body
146 }
147 }
148 });
149
150 let mut display_implied_bounds = Set::new();
151 let display_body = if input.attrs.transparent.is_some() {
152 let only_field = &input.fields[0].member;
153 display_implied_bounds.insert((0, Trait::Display));
154 Some(quote! {
155 ::core::fmt::Display::fmt(&self.#only_field, __formatter)
156 })
157 } else if let Some(display) = &input.attrs.display {
158 display_implied_bounds = display.implied_bounds.clone();
159 let use_as_display = use_as_display(display.has_bonus_display);
160 let pat = fields_pat(&input.fields);
161 Some(quote! {
162 #use_as_display
163 #[allow(unused_variables, deprecated)]
164 let Self #pat = self;
165 #display
166 })
167 } else {
168 None
169 };
170 let display_impl = display_body.map(|body| {
171 let mut display_inferred_bounds = InferredBounds::new();
172 for (field, bound) in display_implied_bounds {
173 let field = &input.fields[field];
174 if field.contains_generic {
175 display_inferred_bounds.insert(field.ty, bound);
176 }
177 }
178 let display_where_clause = display_inferred_bounds.augment_where_clause(input.generics);
179 quote! {
180 #[allow(unused_qualifications)]
181 impl #impl_generics ::core::fmt::Display for #ty #ty_generics #display_where_clause {
182 #[allow(clippy::used_underscore_binding)]
183 fn fmt(&self, __formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
184 #body
185 }
186 }
187 }
188 });
189
190 let from_impl = input.from_field().map(|from_field| {
191 let backtrace_field = input.distinct_backtrace_field();
192 let from = unoptional_type(from_field.ty);
193 let body = from_initializer(from_field, backtrace_field);
194 quote! {
195 #[allow(unused_qualifications)]
196 impl #impl_generics ::core::convert::From<#from> for #ty #ty_generics #where_clause {
197 #[allow(deprecated)]
198 fn from(source: #from) -> Self {
199 #ty #body
200 }
201 }
202 }
203 });
204
205 if input.generics.type_params().next().is_some() {
206 let self_token = <Token![Self]>::default();
207 error_inferred_bounds.insert(self_token, Trait::Debug);
208 error_inferred_bounds.insert(self_token, Trait::Display);
209 }
210 let error_where_clause = error_inferred_bounds.augment_where_clause(input.generics);
211
212 if crate::use_std() {
213 quote! {
214 #[allow(unused_qualifications)]
215 impl #impl_generics std::error::Error for #ty #ty_generics #error_where_clause {
216 #source_method
217 #provide_method
218 }
219 #display_impl
220 #from_impl
221 }
222 } else {
223 quote! {
224 #display_impl
225 #from_impl
226 }
227 }
228}
229
230fn impl_enum(input: Enum) -> TokenStream {
231 let ty = &input.ident;
232 let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
233 let mut error_inferred_bounds = InferredBounds::new();
234
235 let source_method = if input.has_source() {
236 let arms = input.variants.iter().map(|variant| {
237 let ident = &variant.ident;
238 if let Some(transparent_attr) = &variant.attrs.transparent {
239 let only_field = &variant.fields[0];
240 if only_field.contains_generic {
241 error_inferred_bounds.insert(only_field.ty, quote!(std::error::Error));
242 }
243 let member = &only_field.member;
244 let source = quote_spanned! {transparent_attr.span=>
245 std::error::Error::source(transparent.as_dyn_error())
246 };
247 quote! {
248 #ty::#ident {#member: transparent} => #source,
249 }
250 } else if let Some(source_field) = variant.source_field() {
251 let source = &source_field.member;
252 if source_field.contains_generic {
253 let ty = unoptional_type(source_field.ty);
254 error_inferred_bounds.insert(ty, quote!(std::error::Error + 'static));
255 }
256 let asref = if type_is_option(source_field.ty) {
257 Some(quote_spanned!(source.member_span()=> .as_ref()?))
258 } else {
259 None
260 };
261 let varsource = quote!(source);
262 let dyn_error = quote_spanned! {source_field.source_span()=>
263 #varsource #asref.as_dyn_error()
264 };
265 quote! {
266 #ty::#ident {#source: #varsource, ..} => ::core::option::Option::Some(#dyn_error),
267 }
268 } else {
269 quote! {
270 #ty::#ident {..} => ::core::option::Option::None,
271 }
272 }
273 });
274 Some(quote! {
275 fn source(&self) -> ::core::option::Option<&(dyn std::error::Error + 'static)> {
276 use thiserror::__private::AsDynError as _;
277 #[allow(deprecated)]
278 match self {
279 #(#arms)*
280 }
281 }
282 })
283 } else {
284 None
285 };
286
287 let provide_method = if input.has_backtrace() {
288 let request = quote!(request);
289 let arms = input.variants.iter().map(|variant| {
290 let ident = &variant.ident;
291 match (variant.backtrace_field(), variant.source_field()) {
292 (Some(backtrace_field), Some(source_field))
293 if backtrace_field.attrs.backtrace.is_none() =>
294 {
295 let backtrace = &backtrace_field.member;
296 let source = &source_field.member;
297 let varsource = quote!(source);
298 let source_provide = if type_is_option(source_field.ty) {
299 quote_spanned! {source.member_span()=>
300 if let ::core::option::Option::Some(source) = #varsource {
301 source.thiserror_provide(#request);
302 }
303 }
304 } else {
305 quote_spanned! {source.member_span()=>
306 #varsource.thiserror_provide(#request);
307 }
308 };
309 let self_provide = if type_is_option(backtrace_field.ty) {
310 quote! {
311 if let ::core::option::Option::Some(backtrace) = backtrace {
312 #request.provide_ref::<std::backtrace::Backtrace>(backtrace);
313 }
314 }
315 } else {
316 quote! {
317 #request.provide_ref::<std::backtrace::Backtrace>(backtrace);
318 }
319 };
320 quote! {
321 #ty::#ident {
322 #backtrace: backtrace,
323 #source: #varsource,
324 ..
325 } => {
326 use thiserror::__private::ThiserrorProvide as _;
327 #source_provide
328 #self_provide
329 }
330 }
331 }
332 (Some(backtrace_field), Some(source_field))
333 if backtrace_field.member == source_field.member =>
334 {
335 let backtrace = &backtrace_field.member;
336 let varsource = quote!(source);
337 let source_provide = if type_is_option(source_field.ty) {
338 quote_spanned! {backtrace.member_span()=>
339 if let ::core::option::Option::Some(source) = #varsource {
340 source.thiserror_provide(#request);
341 }
342 }
343 } else {
344 quote_spanned! {backtrace.member_span()=>
345 #varsource.thiserror_provide(#request);
346 }
347 };
348 quote! {
349 #ty::#ident {#backtrace: #varsource, ..} => {
350 use thiserror::__private::ThiserrorProvide as _;
351 #source_provide
352 }
353 }
354 }
355 (Some(backtrace_field), _) => {
356 let backtrace = &backtrace_field.member;
357 let body = if type_is_option(backtrace_field.ty) {
358 quote! {
359 if let ::core::option::Option::Some(backtrace) = backtrace {
360 #request.provide_ref::<std::backtrace::Backtrace>(backtrace);
361 }
362 }
363 } else {
364 quote! {
365 #request.provide_ref::<std::backtrace::Backtrace>(backtrace);
366 }
367 };
368 quote! {
369 #ty::#ident {#backtrace: backtrace, ..} => {
370 #body
371 }
372 }
373 }
374 (None, _) => quote! {
375 #ty::#ident {..} => {}
376 },
377 }
378 });
379 Some(quote! {
380 fn provide<'_request>(&'_request self, #request: &mut std::error::Request<'_request>) {
381 #[allow(deprecated)]
382 match self {
383 #(#arms)*
384 }
385 }
386 })
387 } else {
388 None
389 };
390
391 let display_impl = if input.has_display() {
392 let mut display_inferred_bounds = InferredBounds::new();
393 let has_bonus_display = input.variants.iter().any(|v| {
394 v.attrs
395 .display
396 .as_ref()
397 .map_or(false, |display| display.has_bonus_display)
398 });
399 let use_as_display = use_as_display(has_bonus_display);
400 let void_deref = if input.variants.is_empty() {
401 Some(quote!(*))
402 } else {
403 None
404 };
405 let arms = input.variants.iter().map(|variant| {
406 let mut display_implied_bounds = Set::new();
407 let display = match &variant.attrs.display {
408 Some(display) => {
409 display_implied_bounds = display.implied_bounds.clone();
410 display.to_token_stream()
411 }
412 None => {
413 let only_field = match &variant.fields[0].member {
414 Member::Named(ident) => ident.clone(),
415 Member::Unnamed(index) => format_ident!("_{}", index),
416 };
417 display_implied_bounds.insert((0, Trait::Display));
418 quote!(::core::fmt::Display::fmt(#only_field, __formatter))
419 }
420 };
421 for (field, bound) in display_implied_bounds {
422 let field = &variant.fields[field];
423 if field.contains_generic {
424 display_inferred_bounds.insert(field.ty, bound);
425 }
426 }
427 let ident = &variant.ident;
428 let pat = fields_pat(&variant.fields);
429 quote! {
430 #ty::#ident #pat => #display
431 }
432 });
433 let arms = arms.collect::<Vec<_>>();
434 let display_where_clause = display_inferred_bounds.augment_where_clause(input.generics);
435 Some(quote! {
436 #[allow(unused_qualifications)]
437 impl #impl_generics ::core::fmt::Display for #ty #ty_generics #display_where_clause {
438 fn fmt(&self, __formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
439 #use_as_display
440 #[allow(unused_variables, deprecated, clippy::used_underscore_binding)]
441 match #void_deref self {
442 #(#arms,)*
443 }
444 }
445 }
446 })
447 } else {
448 None
449 };
450
451 let from_impls = input.variants.iter().filter_map(|variant| {
452 let from_field = variant.from_field()?;
453 let backtrace_field = variant.distinct_backtrace_field();
454 let variant = &variant.ident;
455 let from = unoptional_type(from_field.ty);
456 let body = from_initializer(from_field, backtrace_field);
457 Some(quote! {
458 #[allow(unused_qualifications)]
459 impl #impl_generics ::core::convert::From<#from> for #ty #ty_generics #where_clause {
460 #[allow(deprecated)]
461 fn from(source: #from) -> Self {
462 #ty::#variant #body
463 }
464 }
465 })
466 });
467
468 if input.generics.type_params().next().is_some() {
469 let self_token = <Token![Self]>::default();
470 error_inferred_bounds.insert(self_token, Trait::Debug);
471 error_inferred_bounds.insert(self_token, Trait::Display);
472 }
473 let error_where_clause = error_inferred_bounds.augment_where_clause(input.generics);
474
475 if crate::use_std() {
476 quote! {
477 #[allow(unused_qualifications)]
478 impl #impl_generics std::error::Error for #ty #ty_generics #error_where_clause {
479 #source_method
480 #provide_method
481 }
482 #display_impl
483 #(#from_impls)*
484 }
485 } else {
486 quote! {
487 #display_impl
488 #(#from_impls)*
489 }
490 }
491}
492
493fn fields_pat(fields: &[Field]) -> TokenStream {
494 let mut members = fields.iter().map(|field| &field.member).peekable();
495 match members.peek() {
496 Some(Member::Named(_)) => quote!({ #(#members),* }),
497 Some(Member::Unnamed(_)) => {
498 let vars = members.map(|member| match member {
499 Member::Unnamed(member) => format_ident!("_{}", member),
500 Member::Named(_) => unreachable!(),
501 });
502 quote!((#(#vars),*))
503 }
504 None => quote!({}),
505 }
506}
507
508fn use_as_display(needs_as_display: bool) -> Option<TokenStream> {
509 if needs_as_display {
510 Some(quote! {
511 use thiserror::__private::AsDisplay as _;
512 })
513 } else {
514 None
515 }
516}
517
518fn from_initializer(from_field: &Field, backtrace_field: Option<&Field>) -> TokenStream {
519 let from_member = &from_field.member;
520 let some_source = if type_is_option(from_field.ty) {
521 quote!(::core::option::Option::Some(source))
522 } else {
523 quote!(source)
524 };
525 let backtrace = backtrace_field.map(|backtrace_field| {
526 let backtrace_member = &backtrace_field.member;
527 if type_is_option(backtrace_field.ty) {
528 quote! {
529 #backtrace_member: ::core::option::Option::Some(std::backtrace::Backtrace::capture()),
530 }
531 } else {
532 quote! {
533 #backtrace_member: ::core::convert::From::from(std::backtrace::Backtrace::capture()),
534 }
535 }
536 });
537 quote!({
538 #from_member: #some_source,
539 #backtrace
540 })
541}
542
543fn type_is_option(ty: &Type) -> bool {
544 type_parameter_of_option(ty).is_some()
545}
546
547fn unoptional_type(ty: &Type) -> TokenStream {
548 let unoptional = type_parameter_of_option(ty).unwrap_or(ty);
549 quote!(#unoptional)
550}
551
552fn type_parameter_of_option(ty: &Type) -> Option<&Type> {
553 let path = match ty {
554 Type::Path(ty) => &ty.path,
555 _ => return None,
556 };
557
558 let last = path.segments.last().unwrap();
559 if last.ident != "Option" {
560 return None;
561 }
562
563 let bracketed = match &last.arguments {
564 PathArguments::AngleBracketed(bracketed) => bracketed,
565 _ => return None,
566 };
567
568 if bracketed.args.len() != 1 {
569 return None;
570 }
571
572 match &bracketed.args[0] {
573 GenericArgument::Type(arg) => Some(arg),
574 _ => None,
575 }
576}