rustc_expand/mbe/quoted.rs
1use rustc_ast::token::{self, Delimiter, IdentIsRaw, NonterminalKind, Token};
2use rustc_ast::tokenstream::TokenStreamIter;
3use rustc_ast::{NodeId, tokenstream};
4use rustc_ast_pretty::pprust;
5use rustc_feature::Features;
6use rustc_session::Session;
7use rustc_session::parse::feature_err;
8use rustc_span::edition::Edition;
9use rustc_span::{Ident, Span, kw, sym};
10
11use crate::errors;
12use crate::mbe::macro_parser::count_metavar_decls;
13use crate::mbe::{Delimited, KleeneOp, KleeneToken, MetaVarExpr, SequenceRepetition, TokenTree};
14
15pub(crate) const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
16 `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, `literal`, `path`, \
17 `meta`, `tt`, `item` and `vis`, along with `expr_2021` and `pat_param` for edition compatibility";
18
19/// Takes a `tokenstream::TokenStream` and returns a `Vec<self::TokenTree>`. Specifically, this
20/// takes a generic `TokenStream`, such as is used in the rest of the compiler, and returns a
21/// collection of `TokenTree` for use in parsing a macro.
22///
23/// # Parameters
24///
25/// - `input`: a token stream to read from, the contents of which we are parsing.
26/// - `parsing_patterns`: `parse` can be used to parse either the "patterns" or the "body" of a
27/// macro. Both take roughly the same form _except_ that:
28/// - In a pattern, metavars are declared with their "matcher" type. For example `$var:expr` or
29/// `$id:ident`. In this example, `expr` and `ident` are "matchers". They are not present in the
30/// body of a macro rule -- just in the pattern.
31/// - Metavariable expressions are only valid in the "body", not the "pattern".
32/// - `sess`: the parsing session. Any errors will be emitted to this session.
33/// - `node_id`: the NodeId of the macro we are parsing.
34/// - `features`: language features so we can do feature gating.
35///
36/// # Returns
37///
38/// A collection of `self::TokenTree`. There may also be some errors emitted to `sess`.
39pub(super) fn parse(
40 input: &tokenstream::TokenStream,
41 parsing_patterns: bool,
42 sess: &Session,
43 node_id: NodeId,
44 features: &Features,
45 edition: Edition,
46) -> Vec<TokenTree> {
47 // Will contain the final collection of `self::TokenTree`
48 let mut result = Vec::new();
49
50 // For each token tree in `input`, parse the token into a `self::TokenTree`, consuming
51 // additional trees if need be.
52 let mut iter = input.iter();
53 while let Some(tree) = iter.next() {
54 // Given the parsed tree, if there is a metavar and we are expecting matchers, actually
55 // parse out the matcher (i.e., in `$id:ident` this would parse the `:` and `ident`).
56 let tree = parse_tree(tree, &mut iter, parsing_patterns, sess, node_id, features, edition);
57 match tree {
58 TokenTree::MetaVar(start_sp, ident) if parsing_patterns => {
59 // Not consuming the next token immediately, as it may not be a colon
60 let span = match iter.peek() {
61 Some(&tokenstream::TokenTree::Token(
62 Token { kind: token::Colon, span: colon_span },
63 _,
64 )) => {
65 // Consume the colon first
66 iter.next();
67
68 // It's ok to consume the next tree no matter how,
69 // since if it's not a token then it will be an invalid declaration.
70 match iter.next() {
71 Some(tokenstream::TokenTree::Token(token, _)) => match token.ident() {
72 Some((fragment, _)) => {
73 let span = token.span.with_lo(start_sp.lo());
74 let edition = || {
75 // FIXME(#85708) - once we properly decode a foreign
76 // crate's `SyntaxContext::root`, then we can replace
77 // this with just `span.edition()`. A
78 // `SyntaxContext::root()` from the current crate will
79 // have the edition of the current crate, and a
80 // `SyntaxContext::root()` from a foreign crate will
81 // have the edition of that crate (which we manually
82 // retrieve via the `edition` parameter).
83 if !span.from_expansion() {
84 edition
85 } else {
86 span.edition()
87 }
88 };
89 let kind = NonterminalKind::from_symbol(fragment.name, edition)
90 .unwrap_or_else(|| {
91 sess.dcx().emit_err(errors::InvalidFragmentSpecifier {
92 span,
93 fragment,
94 help: VALID_FRAGMENT_NAMES_MSG.into(),
95 });
96 NonterminalKind::Ident
97 });
98 result.push(TokenTree::MetaVarDecl(span, ident, Some(kind)));
99 continue;
100 }
101 _ => token.span,
102 },
103 // Invalid, return a nice source location
104 _ => colon_span.with_lo(start_sp.lo()),
105 }
106 }
107 // Whether it's none or some other tree, it doesn't belong to
108 // the current meta variable, returning the original span.
109 _ => start_sp,
110 };
111
112 result.push(TokenTree::MetaVarDecl(span, ident, None));
113 }
114
115 // Not a metavar or no matchers allowed, so just return the tree
116 _ => result.push(tree),
117 }
118 }
119 result
120}
121
122/// Asks for the `macro_metavar_expr` feature if it is not enabled
123fn maybe_emit_macro_metavar_expr_feature(features: &Features, sess: &Session, span: Span) {
124 if !features.macro_metavar_expr() {
125 let msg = "meta-variable expressions are unstable";
126 feature_err(sess, sym::macro_metavar_expr, span, msg).emit();
127 }
128}
129
130fn maybe_emit_macro_metavar_expr_concat_feature(features: &Features, sess: &Session, span: Span) {
131 if !features.macro_metavar_expr_concat() {
132 let msg = "the `concat` meta-variable expression is unstable";
133 feature_err(sess, sym::macro_metavar_expr_concat, span, msg).emit();
134 }
135}
136
137/// Takes a `tokenstream::TokenTree` and returns a `self::TokenTree`. Specifically, this takes a
138/// generic `TokenTree`, such as is used in the rest of the compiler, and returns a `TokenTree`
139/// for use in parsing a macro.
140///
141/// Converting the given tree may involve reading more tokens.
142///
143/// # Parameters
144///
145/// - `tree`: the tree we wish to convert.
146/// - `outer_iter`: an iterator over trees. We may need to read more tokens from it in order to finish
147/// converting `tree`
148/// - `parsing_patterns`: same as [parse].
149/// - `sess`: the parsing session. Any errors will be emitted to this session.
150/// - `features`: language features so we can do feature gating.
151fn parse_tree<'a>(
152 tree: &'a tokenstream::TokenTree,
153 outer_iter: &mut TokenStreamIter<'a>,
154 parsing_patterns: bool,
155 sess: &Session,
156 node_id: NodeId,
157 features: &Features,
158 edition: Edition,
159) -> TokenTree {
160 // Depending on what `tree` is, we could be parsing different parts of a macro
161 match tree {
162 // `tree` is a `$` token. Look at the next token in `trees`
163 &tokenstream::TokenTree::Token(Token { kind: token::Dollar, span: dollar_span }, _) => {
164 // FIXME: Handle `Invisible`-delimited groups in a more systematic way
165 // during parsing.
166 let mut next = outer_iter.next();
167 let mut iter_storage;
168 let mut iter: &mut TokenStreamIter<'_> = match next {
169 Some(tokenstream::TokenTree::Delimited(.., delim, tts)) if delim.skip() => {
170 iter_storage = tts.iter();
171 next = iter_storage.next();
172 &mut iter_storage
173 }
174 _ => outer_iter,
175 };
176
177 match next {
178 // `tree` is followed by a delimited set of token trees.
179 Some(&tokenstream::TokenTree::Delimited(delim_span, _, delim, ref tts)) => {
180 if parsing_patterns {
181 if delim != Delimiter::Parenthesis {
182 span_dollar_dollar_or_metavar_in_the_lhs_err(
183 sess,
184 &Token {
185 kind: delim.as_open_token_kind(),
186 span: delim_span.entire(),
187 },
188 );
189 }
190 } else {
191 match delim {
192 Delimiter::Brace => {
193 // The delimiter is `{`. This indicates the beginning
194 // of a meta-variable expression (e.g. `${count(ident)}`).
195 // Try to parse the meta-variable expression.
196 match MetaVarExpr::parse(tts, delim_span.entire(), &sess.psess) {
197 Err(err) => {
198 err.emit();
199 // Returns early the same read `$` to avoid spanning
200 // unrelated diagnostics that could be performed afterwards
201 return TokenTree::token(token::Dollar, dollar_span);
202 }
203 Ok(elem) => {
204 if let MetaVarExpr::Concat(_) = elem {
205 maybe_emit_macro_metavar_expr_concat_feature(
206 features,
207 sess,
208 delim_span.entire(),
209 );
210 } else {
211 maybe_emit_macro_metavar_expr_feature(
212 features,
213 sess,
214 delim_span.entire(),
215 );
216 }
217 return TokenTree::MetaVarExpr(delim_span, elem);
218 }
219 }
220 }
221 Delimiter::Parenthesis => {}
222 _ => {
223 let token =
224 pprust::token_kind_to_string(&delim.as_open_token_kind());
225 sess.dcx().emit_err(errors::ExpectedParenOrBrace {
226 span: delim_span.entire(),
227 token,
228 });
229 }
230 }
231 }
232 // If we didn't find a metavar expression above, then we must have a
233 // repetition sequence in the macro (e.g. `$(pat)*`). Parse the
234 // contents of the sequence itself
235 let sequence = parse(tts, parsing_patterns, sess, node_id, features, edition);
236 // Get the Kleene operator and optional separator
237 let (separator, kleene) =
238 parse_sep_and_kleene_op(&mut iter, delim_span.entire(), sess);
239 // Count the number of captured "names" (i.e., named metavars)
240 let num_captures =
241 if parsing_patterns { count_metavar_decls(&sequence) } else { 0 };
242 TokenTree::Sequence(
243 delim_span,
244 SequenceRepetition { tts: sequence, separator, kleene, num_captures },
245 )
246 }
247
248 // `tree` is followed by an `ident`. This could be `$meta_var` or the `$crate`
249 // special metavariable that names the crate of the invocation.
250 Some(tokenstream::TokenTree::Token(token, _)) if token.is_ident() => {
251 let (ident, is_raw) = token.ident().unwrap();
252 let span = ident.span.with_lo(dollar_span.lo());
253 if ident.name == kw::Crate && matches!(is_raw, IdentIsRaw::No) {
254 TokenTree::token(token::Ident(kw::DollarCrate, is_raw), span)
255 } else {
256 TokenTree::MetaVar(span, ident)
257 }
258 }
259
260 // `tree` is followed by another `$`. This is an escaped `$`.
261 Some(&tokenstream::TokenTree::Token(
262 Token { kind: token::Dollar, span: dollar_span2 },
263 _,
264 )) => {
265 if parsing_patterns {
266 span_dollar_dollar_or_metavar_in_the_lhs_err(
267 sess,
268 &Token { kind: token::Dollar, span: dollar_span2 },
269 );
270 } else {
271 maybe_emit_macro_metavar_expr_feature(features, sess, dollar_span2);
272 }
273 TokenTree::token(token::Dollar, dollar_span2)
274 }
275
276 // `tree` is followed by some other token. This is an error.
277 Some(tokenstream::TokenTree::Token(token, _)) => {
278 let msg =
279 format!("expected identifier, found `{}`", pprust::token_to_string(token),);
280 sess.dcx().span_err(token.span, msg);
281 TokenTree::MetaVar(token.span, Ident::dummy())
282 }
283
284 // There are no more tokens. Just return the `$` we already have.
285 None => TokenTree::token(token::Dollar, dollar_span),
286 }
287 }
288
289 // `tree` is an arbitrary token. Keep it.
290 tokenstream::TokenTree::Token(token, _) => TokenTree::Token(*token),
291
292 // `tree` is the beginning of a delimited set of tokens (e.g., `(` or `{`). We need to
293 // descend into the delimited set and further parse it.
294 &tokenstream::TokenTree::Delimited(span, spacing, delim, ref tts) => TokenTree::Delimited(
295 span,
296 spacing,
297 Delimited {
298 delim,
299 tts: parse(tts, parsing_patterns, sess, node_id, features, edition),
300 },
301 ),
302 }
303}
304
305/// Takes a token and returns `Some(KleeneOp)` if the token is `+` `*` or `?`. Otherwise, return
306/// `None`.
307fn kleene_op(token: &Token) -> Option<KleeneOp> {
308 match token.kind {
309 token::Star => Some(KleeneOp::ZeroOrMore),
310 token::Plus => Some(KleeneOp::OneOrMore),
311 token::Question => Some(KleeneOp::ZeroOrOne),
312 _ => None,
313 }
314}
315
316/// Parse the next token tree of the input looking for a KleeneOp. Returns
317///
318/// - Ok(Ok((op, span))) if the next token tree is a KleeneOp
319/// - Ok(Err(tok, span)) if the next token tree is a token but not a KleeneOp
320/// - Err(span) if the next token tree is not a token
321fn parse_kleene_op(
322 iter: &mut TokenStreamIter<'_>,
323 span: Span,
324) -> Result<Result<(KleeneOp, Span), Token>, Span> {
325 match iter.next() {
326 Some(tokenstream::TokenTree::Token(token, _)) => match kleene_op(token) {
327 Some(op) => Ok(Ok((op, token.span))),
328 None => Ok(Err(*token)),
329 },
330 tree => Err(tree.map_or(span, tokenstream::TokenTree::span)),
331 }
332}
333
334/// Attempt to parse a single Kleene star, possibly with a separator.
335///
336/// For example, in a pattern such as `$(a),*`, `a` is the pattern to be repeated, `,` is the
337/// separator, and `*` is the Kleene operator. This function is specifically concerned with parsing
338/// the last two tokens of such a pattern: namely, the optional separator and the Kleene operator
339/// itself. Note that here we are parsing the _macro_ itself, rather than trying to match some
340/// stream of tokens in an invocation of a macro.
341///
342/// This function will take some input iterator `iter` corresponding to `span` and a parsing
343/// session `sess`. If the next one (or possibly two) tokens in `iter` correspond to a Kleene
344/// operator and separator, then a tuple with `(separator, KleeneOp)` is returned. Otherwise, an
345/// error with the appropriate span is emitted to `sess` and a dummy value is returned.
346fn parse_sep_and_kleene_op(
347 iter: &mut TokenStreamIter<'_>,
348 span: Span,
349 sess: &Session,
350) -> (Option<Token>, KleeneToken) {
351 // We basically look at two token trees here, denoted as #1 and #2 below
352 let span = match parse_kleene_op(iter, span) {
353 // #1 is a `?`, `+`, or `*` KleeneOp
354 Ok(Ok((op, span))) => return (None, KleeneToken::new(op, span)),
355
356 // #1 is a separator followed by #2, a KleeneOp
357 Ok(Err(token)) => match parse_kleene_op(iter, token.span) {
358 // #2 is the `?` Kleene op, which does not take a separator (error)
359 Ok(Ok((KleeneOp::ZeroOrOne, span))) => {
360 // Error!
361 sess.dcx().span_err(
362 token.span,
363 "the `?` macro repetition operator does not take a separator",
364 );
365
366 // Return a dummy
367 return (None, KleeneToken::new(KleeneOp::ZeroOrMore, span));
368 }
369
370 // #2 is a KleeneOp :D
371 Ok(Ok((op, span))) => return (Some(token), KleeneToken::new(op, span)),
372
373 // #2 is a random token or not a token at all :(
374 Ok(Err(Token { span, .. })) | Err(span) => span,
375 },
376
377 // #1 is not a token
378 Err(span) => span,
379 };
380
381 // If we ever get to this point, we have experienced an "unexpected token" error
382 sess.dcx().span_err(span, "expected one of: `*`, `+`, or `?`");
383
384 // Return a dummy
385 (None, KleeneToken::new(KleeneOp::ZeroOrMore, span))
386}
387
388// `$$` or a meta-variable is the lhs of a macro but shouldn't.
389//
390// For example, `macro_rules! foo { ( ${len()} ) => {} }`
391fn span_dollar_dollar_or_metavar_in_the_lhs_err(sess: &Session, token: &Token) {
392 sess.dcx()
393 .span_err(token.span, format!("unexpected token: {}", pprust::token_to_string(token)));
394 sess.dcx().span_note(
395 token.span,
396 "`$$` and meta-variable expressions are not allowed inside macro parameter definitions",
397 );
398}