1 use proc_macro2::{Delimiter, Group, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
2 use quote::{format_ident, quote, quote_spanned, ToTokens};
3 use std::collections::BTreeSet as Set;
4 use syn::parse::discouraged::Speculative;
5 use syn::parse::{End, ParseStream};
6 use syn::{
7 braced, bracketed, parenthesized, token, Attribute, Error, ExprPath, Ident, Index, LitFloat,
8 LitInt, LitStr, Meta, Result, Token,
9 };
10
11 pub struct Attrs<'a> {
12 pub display: Option<Display<'a>>,
13 pub source: Option<Source<'a>>,
14 pub backtrace: Option<&'a Attribute>,
15 pub from: Option<From<'a>>,
16 pub transparent: Option<Transparent<'a>>,
17 pub fmt: Option<Fmt<'a>>,
18 }
19
20 #[derive(Clone)]
21 pub struct Display<'a> {
22 pub original: &'a Attribute,
23 pub fmt: LitStr,
24 pub args: TokenStream,
25 pub requires_fmt_machinery: bool,
26 pub has_bonus_display: bool,
27 pub infinite_recursive: bool,
28 pub implied_bounds: Set<(usize, Trait)>,
29 pub bindings: Vec<(Ident, TokenStream)>,
30 }
31
32 #[derive(Copy, Clone)]
33 pub struct Source<'a> {
34 pub original: &'a Attribute,
35 pub span: Span,
36 }
37
38 #[derive(Copy, Clone)]
39 pub struct From<'a> {
40 pub original: &'a Attribute,
41 pub span: Span,
42 }
43
44 #[derive(Copy, Clone)]
45 pub struct Transparent<'a> {
46 pub original: &'a Attribute,
47 pub span: Span,
48 }
49
50 #[derive(Clone)]
51 pub struct Fmt<'a> {
52 pub original: &'a Attribute,
53 pub path: ExprPath,
54 }
55
56 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug)]
57 pub enum Trait {
58 Debug,
59 Display,
60 Octal,
61 LowerHex,
62 UpperHex,
63 Pointer,
64 Binary,
65 LowerExp,
66 UpperExp,
67 }
68
get(input: &[Attribute]) -> Result<Attrs>69 pub fn get(input: &[Attribute]) -> Result<Attrs> {
70 let mut attrs = Attrs {
71 display: None,
72 source: None,
73 backtrace: None,
74 from: None,
75 transparent: None,
76 fmt: None,
77 };
78
79 for attr in input {
80 if attr.path().is_ident("error") {
81 parse_error_attribute(&mut attrs, attr)?;
82 } else if attr.path().is_ident("source") {
83 attr.meta.require_path_only()?;
84 if attrs.source.is_some() {
85 return Err(Error::new_spanned(attr, "duplicate #[source] attribute"));
86 }
87 let span = (attr.pound_token.span)
88 .join(attr.bracket_token.span.join())
89 .unwrap_or(attr.path().get_ident().unwrap().span());
90 attrs.source = Some(Source {
91 original: attr,
92 span,
93 });
94 } else if attr.path().is_ident("backtrace") {
95 attr.meta.require_path_only()?;
96 if attrs.backtrace.is_some() {
97 return Err(Error::new_spanned(attr, "duplicate #[backtrace] attribute"));
98 }
99 attrs.backtrace = Some(attr);
100 } else if attr.path().is_ident("from") {
101 match attr.meta {
102 Meta::Path(_) => {}
103 Meta::List(_) | Meta::NameValue(_) => {
104 // Assume this is meant for derive_more crate or something.
105 continue;
106 }
107 }
108 if attrs.from.is_some() {
109 return Err(Error::new_spanned(attr, "duplicate #[from] attribute"));
110 }
111 let span = (attr.pound_token.span)
112 .join(attr.bracket_token.span.join())
113 .unwrap_or(attr.path().get_ident().unwrap().span());
114 attrs.from = Some(From {
115 original: attr,
116 span,
117 });
118 }
119 }
120
121 Ok(attrs)
122 }
123
parse_error_attribute<'a>(attrs: &mut Attrs<'a>, attr: &'a Attribute) -> Result<()>124 fn parse_error_attribute<'a>(attrs: &mut Attrs<'a>, attr: &'a Attribute) -> Result<()> {
125 mod kw {
126 syn::custom_keyword!(transparent);
127 syn::custom_keyword!(fmt);
128 }
129
130 attr.parse_args_with(|input: ParseStream| {
131 let lookahead = input.lookahead1();
132 let fmt = if lookahead.peek(LitStr) {
133 input.parse::<LitStr>()?
134 } else if lookahead.peek(kw::transparent) {
135 let kw: kw::transparent = input.parse()?;
136 if attrs.transparent.is_some() {
137 return Err(Error::new_spanned(
138 attr,
139 "duplicate #[error(transparent)] attribute",
140 ));
141 }
142 attrs.transparent = Some(Transparent {
143 original: attr,
144 span: kw.span,
145 });
146 return Ok(());
147 } else if lookahead.peek(kw::fmt) {
148 input.parse::<kw::fmt>()?;
149 input.parse::<Token![=]>()?;
150 let path: ExprPath = input.parse()?;
151 if attrs.fmt.is_some() {
152 return Err(Error::new_spanned(
153 attr,
154 "duplicate #[error(fmt = ...)] attribute",
155 ));
156 }
157 attrs.fmt = Some(Fmt {
158 original: attr,
159 path,
160 });
161 return Ok(());
162 } else {
163 return Err(lookahead.error());
164 };
165
166 let args = if input.is_empty() || input.peek(Token![,]) && input.peek2(End) {
167 input.parse::<Option<Token![,]>>()?;
168 TokenStream::new()
169 } else {
170 parse_token_expr(input, false)?
171 };
172
173 let requires_fmt_machinery = !args.is_empty();
174
175 let display = Display {
176 original: attr,
177 fmt,
178 args,
179 requires_fmt_machinery,
180 has_bonus_display: false,
181 infinite_recursive: false,
182 implied_bounds: Set::new(),
183 bindings: Vec::new(),
184 };
185 if attrs.display.is_some() {
186 return Err(Error::new_spanned(
187 attr,
188 "only one #[error(...)] attribute is allowed",
189 ));
190 }
191 attrs.display = Some(display);
192 Ok(())
193 })
194 }
195
parse_token_expr(input: ParseStream, mut begin_expr: bool) -> Result<TokenStream>196 fn parse_token_expr(input: ParseStream, mut begin_expr: bool) -> Result<TokenStream> {
197 let mut tokens = Vec::new();
198 while !input.is_empty() {
199 if input.peek(token::Group) {
200 let group: TokenTree = input.parse()?;
201 tokens.push(group);
202 begin_expr = false;
203 continue;
204 }
205
206 if begin_expr && input.peek(Token![.]) {
207 if input.peek2(Ident) {
208 input.parse::<Token![.]>()?;
209 begin_expr = false;
210 continue;
211 } else if input.peek2(LitInt) {
212 input.parse::<Token![.]>()?;
213 let int: Index = input.parse()?;
214 tokens.push({
215 let ident = format_ident!("_{}", int.index, span = int.span);
216 TokenTree::Ident(ident)
217 });
218 begin_expr = false;
219 continue;
220 } else if input.peek2(LitFloat) {
221 let ahead = input.fork();
222 ahead.parse::<Token![.]>()?;
223 let float: LitFloat = ahead.parse()?;
224 let repr = float.to_string();
225 let mut indices = repr.split('.').map(syn::parse_str::<Index>);
226 if let (Some(Ok(first)), Some(Ok(second)), None) =
227 (indices.next(), indices.next(), indices.next())
228 {
229 input.advance_to(&ahead);
230 tokens.push({
231 let ident = format_ident!("_{}", first, span = float.span());
232 TokenTree::Ident(ident)
233 });
234 tokens.push({
235 let mut punct = Punct::new('.', Spacing::Alone);
236 punct.set_span(float.span());
237 TokenTree::Punct(punct)
238 });
239 tokens.push({
240 let mut literal = Literal::u32_unsuffixed(second.index);
241 literal.set_span(float.span());
242 TokenTree::Literal(literal)
243 });
244 begin_expr = false;
245 continue;
246 }
247 }
248 }
249
250 begin_expr = input.peek(Token![break])
251 || input.peek(Token![continue])
252 || input.peek(Token![if])
253 || input.peek(Token![in])
254 || input.peek(Token![match])
255 || input.peek(Token![mut])
256 || input.peek(Token![return])
257 || input.peek(Token![while])
258 || input.peek(Token![+])
259 || input.peek(Token![&])
260 || input.peek(Token![!])
261 || input.peek(Token![^])
262 || input.peek(Token![,])
263 || input.peek(Token![/])
264 || input.peek(Token![=])
265 || input.peek(Token![>])
266 || input.peek(Token![<])
267 || input.peek(Token![|])
268 || input.peek(Token![%])
269 || input.peek(Token![;])
270 || input.peek(Token![*])
271 || input.peek(Token![-]);
272
273 let token: TokenTree = if input.peek(token::Paren) {
274 let content;
275 let delimiter = parenthesized!(content in input);
276 let nested = parse_token_expr(&content, true)?;
277 let mut group = Group::new(Delimiter::Parenthesis, nested);
278 group.set_span(delimiter.span.join());
279 TokenTree::Group(group)
280 } else if input.peek(token::Brace) {
281 let content;
282 let delimiter = braced!(content in input);
283 let nested = parse_token_expr(&content, true)?;
284 let mut group = Group::new(Delimiter::Brace, nested);
285 group.set_span(delimiter.span.join());
286 TokenTree::Group(group)
287 } else if input.peek(token::Bracket) {
288 let content;
289 let delimiter = bracketed!(content in input);
290 let nested = parse_token_expr(&content, true)?;
291 let mut group = Group::new(Delimiter::Bracket, nested);
292 group.set_span(delimiter.span.join());
293 TokenTree::Group(group)
294 } else {
295 input.parse()?
296 };
297 tokens.push(token);
298 }
299 Ok(TokenStream::from_iter(tokens))
300 }
301
302 impl ToTokens for Display<'_> {
to_tokens(&self, tokens: &mut TokenStream)303 fn to_tokens(&self, tokens: &mut TokenStream) {
304 if self.infinite_recursive {
305 let span = self.fmt.span();
306 tokens.extend(quote_spanned! {span=>
307 #[warn(unconditional_recursion)]
308 fn _fmt() { _fmt() }
309 });
310 }
311
312 let fmt = &self.fmt;
313 let args = &self.args;
314
315 // Currently `write!(f, "text")` produces less efficient code than
316 // `f.write_str("text")`. We recognize the case when the format string
317 // has no braces and no interpolated values, and generate simpler code.
318 let write = if self.requires_fmt_machinery {
319 quote! {
320 ::core::write!(__formatter, #fmt #args)
321 }
322 } else {
323 quote! {
324 __formatter.write_str(#fmt)
325 }
326 };
327
328 tokens.extend(if self.bindings.is_empty() {
329 write
330 } else {
331 let locals = self.bindings.iter().map(|(local, _value)| local);
332 let values = self.bindings.iter().map(|(_local, value)| value);
333 quote! {
334 match (#(#values,)*) {
335 (#(#locals,)*) => #write
336 }
337 }
338 });
339 }
340 }
341
342 impl ToTokens for Trait {
to_tokens(&self, tokens: &mut TokenStream)343 fn to_tokens(&self, tokens: &mut TokenStream) {
344 let trait_name = match self {
345 Trait::Debug => "Debug",
346 Trait::Display => "Display",
347 Trait::Octal => "Octal",
348 Trait::LowerHex => "LowerHex",
349 Trait::UpperHex => "UpperHex",
350 Trait::Pointer => "Pointer",
351 Trait::Binary => "Binary",
352 Trait::LowerExp => "LowerExp",
353 Trait::UpperExp => "UpperExp",
354 };
355 let ident = Ident::new(trait_name, Span::call_site());
356 tokens.extend(quote!(::core::fmt::#ident));
357 }
358 }
359