use crate::mbe::macro_parser::count_metavar_decls; use crate::mbe::{Delimited, KleeneOp, KleeneToken, MetaVarExpr, SequenceRepetition, TokenTree}; use rustc_ast::token::{self, Delimiter, Token}; use rustc_ast::{tokenstream, NodeId}; use rustc_ast_pretty::pprust; use rustc_feature::Features; use rustc_session::parse::{feature_err, ParseSess}; use rustc_span::symbol::{kw, sym, Ident}; use rustc_span::edition::Edition; use rustc_span::Span; const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \ `ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, \ `literal`, `path`, `meta`, `tt`, `item` and `vis`"; /// Takes a `tokenstream::TokenStream` and returns a `Vec`. Specifically, this /// takes a generic `TokenStream`, such as is used in the rest of the compiler, and returns a /// collection of `TokenTree` for use in parsing a macro. /// /// # Parameters /// /// - `input`: a token stream to read from, the contents of which we are parsing. /// - `parsing_patterns`: `parse` can be used to parse either the "patterns" or the "body" of a /// macro. Both take roughly the same form _except_ that: /// - In a pattern, metavars are declared with their "matcher" type. For example `$var:expr` or /// `$id:ident`. In this example, `expr` and `ident` are "matchers". They are not present in the /// body of a macro rule -- just in the pattern. /// - Metavariable expressions are only valid in the "body", not the "pattern". /// - `sess`: the parsing session. Any errors will be emitted to this session. /// - `node_id`: the NodeId of the macro we are parsing. /// - `features`: language features so we can do feature gating. /// /// # Returns /// /// A collection of `self::TokenTree`. There may also be some errors emitted to `sess`. pub(super) fn parse( input: &tokenstream::TokenStream, parsing_patterns: bool, sess: &ParseSess, node_id: NodeId, features: &Features, edition: Edition, ) -> Vec { // Will contain the final collection of `self::TokenTree` let mut result = Vec::new(); // For each token tree in `input`, parse the token into a `self::TokenTree`, consuming // additional trees if need be. let mut trees = input.trees(); while let Some(tree) = trees.next() { // Given the parsed tree, if there is a metavar and we are expecting matchers, actually // parse out the matcher (i.e., in `$id:ident` this would parse the `:` and `ident`). let tree = parse_tree(tree, &mut trees, parsing_patterns, sess, node_id, features, edition); match tree { TokenTree::MetaVar(start_sp, ident) if parsing_patterns => { let span = match trees.next() { Some(&tokenstream::TokenTree::Token(Token { kind: token::Colon, span }, _)) => { match trees.next() { Some(tokenstream::TokenTree::Token(token, _)) => match token.ident() { Some((frag, _)) => { let span = token.span.with_lo(start_sp.lo()); let kind = token::NonterminalKind::from_symbol(frag.name, || { // FIXME(#85708) - once we properly decode a foreign // crate's `SyntaxContext::root`, then we can replace // this with just `span.edition()`. A // `SyntaxContext::root()` from the current crate will // have the edition of the current crate, and a // `SyntaxContext::root()` from a foreign crate will // have the edition of that crate (which we manually // retrieve via the `edition` parameter). if span.ctxt().is_root() { edition } else { span.edition() } }) .unwrap_or_else( || { let msg = format!( "invalid fragment specifier `{}`", frag.name ); sess.dcx .struct_span_err(span, msg) .help(VALID_FRAGMENT_NAMES_MSG) .emit(); token::NonterminalKind::Ident }, ); result.push(TokenTree::MetaVarDecl(span, ident, Some(kind))); continue; } _ => token.span, }, tree => tree.map_or(span, tokenstream::TokenTree::span), } } tree => tree.map_or(start_sp, tokenstream::TokenTree::span), }; result.push(TokenTree::MetaVarDecl(span, ident, None)); } // Not a metavar or no matchers allowed, so just return the tree _ => result.push(tree), } } result } /// Asks for the `macro_metavar_expr` feature if it is not already declared fn maybe_emit_macro_metavar_expr_feature(features: &Features, sess: &ParseSess, span: Span) { if !features.macro_metavar_expr { let msg = "meta-variable expressions are unstable"; feature_err(sess, sym::macro_metavar_expr, span, msg).emit(); } } /// Takes a `tokenstream::TokenTree` and returns a `self::TokenTree`. Specifically, this takes a /// generic `TokenTree`, such as is used in the rest of the compiler, and returns a `TokenTree` /// for use in parsing a macro. /// /// Converting the given tree may involve reading more tokens. /// /// # Parameters /// /// - `tree`: the tree we wish to convert. /// - `outer_trees`: an iterator over trees. We may need to read more tokens from it in order to finish /// converting `tree` /// - `parsing_patterns`: same as [parse]. /// - `sess`: the parsing session. Any errors will be emitted to this session. /// - `features`: language features so we can do feature gating. fn parse_tree<'a>( tree: &'a tokenstream::TokenTree, outer_trees: &mut impl Iterator, parsing_patterns: bool, sess: &ParseSess, node_id: NodeId, features: &Features, edition: Edition, ) -> TokenTree { // Depending on what `tree` is, we could be parsing different parts of a macro match tree { // `tree` is a `$` token. Look at the next token in `trees` &tokenstream::TokenTree::Token(Token { kind: token::Dollar, span }, _) => { // FIXME: Handle `Invisible`-delimited groups in a more systematic way // during parsing. let mut next = outer_trees.next(); let mut trees: Box>; if let Some(tokenstream::TokenTree::Delimited(.., Delimiter::Invisible, tts)) = next { trees = Box::new(tts.trees()); next = trees.next(); } else { trees = Box::new(outer_trees); } match next { // `tree` is followed by a delimited set of token trees. Some(&tokenstream::TokenTree::Delimited(delim_span, _, delim, ref tts)) => { if parsing_patterns { if delim != Delimiter::Parenthesis { span_dollar_dollar_or_metavar_in_the_lhs_err( sess, &Token { kind: token::OpenDelim(delim), span: delim_span.entire() }, ); } } else { match delim { Delimiter::Brace => { // The delimiter is `{`. This indicates the beginning // of a meta-variable expression (e.g. `${count(ident)}`). // Try to parse the meta-variable expression. match MetaVarExpr::parse(tts, delim_span.entire(), sess) { Err(mut err) => { err.emit(); // Returns early the same read `$` to avoid spanning // unrelated diagnostics that could be performed afterwards return TokenTree::token(token::Dollar, span); } Ok(elem) => { maybe_emit_macro_metavar_expr_feature( features, sess, delim_span.entire(), ); return TokenTree::MetaVarExpr(delim_span, elem); } } } Delimiter::Parenthesis => {} _ => { let tok = pprust::token_kind_to_string(&token::OpenDelim(delim)); let msg = format!("expected `(` or `{{`, found `{tok}`"); sess.dcx.span_err(delim_span.entire(), msg); } } } // If we didn't find a metavar expression above, then we must have a // repetition sequence in the macro (e.g. `$(pat)*`). Parse the // contents of the sequence itself let sequence = parse(tts, parsing_patterns, sess, node_id, features, edition); // Get the Kleene operator and optional separator let (separator, kleene) = parse_sep_and_kleene_op(&mut trees, delim_span.entire(), sess); // Count the number of captured "names" (i.e., named metavars) let num_captures = if parsing_patterns { count_metavar_decls(&sequence) } else { 0 }; TokenTree::Sequence( delim_span, SequenceRepetition { tts: sequence, separator, kleene, num_captures }, ) } // `tree` is followed by an `ident`. This could be `$meta_var` or the `$crate` // special metavariable that names the crate of the invocation. Some(tokenstream::TokenTree::Token(token, _)) if token.is_ident() => { let (ident, is_raw) = token.ident().unwrap(); let span = ident.span.with_lo(span.lo()); if ident.name == kw::Crate && !is_raw { TokenTree::token(token::Ident(kw::DollarCrate, is_raw), span) } else { TokenTree::MetaVar(span, ident) } } // `tree` is followed by another `$`. This is an escaped `$`. Some(&tokenstream::TokenTree::Token(Token { kind: token::Dollar, span }, _)) => { if parsing_patterns { span_dollar_dollar_or_metavar_in_the_lhs_err( sess, &Token { kind: token::Dollar, span }, ); } else { maybe_emit_macro_metavar_expr_feature(features, sess, span); } TokenTree::token(token::Dollar, span) } // `tree` is followed by some other token. This is an error. Some(tokenstream::TokenTree::Token(token, _)) => { let msg = format!("expected identifier, found `{}`", pprust::token_to_string(token),); sess.dcx.span_err(token.span, msg); TokenTree::MetaVar(token.span, Ident::empty()) } // There are no more tokens. Just return the `$` we already have. None => TokenTree::token(token::Dollar, span), } } // `tree` is an arbitrary token. Keep it. tokenstream::TokenTree::Token(token, _) => TokenTree::Token(token.clone()), // `tree` is the beginning of a delimited set of tokens (e.g., `(` or `{`). We need to // descend into the delimited set and further parse it. &tokenstream::TokenTree::Delimited(span, spacing, delim, ref tts) => TokenTree::Delimited( span, spacing, Delimited { delim, tts: parse(tts, parsing_patterns, sess, node_id, features, edition), }, ), } } /// Takes a token and returns `Some(KleeneOp)` if the token is `+` `*` or `?`. Otherwise, return /// `None`. fn kleene_op(token: &Token) -> Option { match token.kind { token::BinOp(token::Star) => Some(KleeneOp::ZeroOrMore), token::BinOp(token::Plus) => Some(KleeneOp::OneOrMore), token::Question => Some(KleeneOp::ZeroOrOne), _ => None, } } /// Parse the next token tree of the input looking for a KleeneOp. Returns /// /// - Ok(Ok((op, span))) if the next token tree is a KleeneOp /// - Ok(Err(tok, span)) if the next token tree is a token but not a KleeneOp /// - Err(span) if the next token tree is not a token fn parse_kleene_op<'a>( input: &mut impl Iterator, span: Span, ) -> Result, Span> { match input.next() { Some(tokenstream::TokenTree::Token(token, _)) => match kleene_op(token) { Some(op) => Ok(Ok((op, token.span))), None => Ok(Err(token.clone())), }, tree => Err(tree.map_or(span, tokenstream::TokenTree::span)), } } /// Attempt to parse a single Kleene star, possibly with a separator. /// /// For example, in a pattern such as `$(a),*`, `a` is the pattern to be repeated, `,` is the /// separator, and `*` is the Kleene operator. This function is specifically concerned with parsing /// the last two tokens of such a pattern: namely, the optional separator and the Kleene operator /// itself. Note that here we are parsing the _macro_ itself, rather than trying to match some /// stream of tokens in an invocation of a macro. /// /// This function will take some input iterator `input` corresponding to `span` and a parsing /// session `sess`. If the next one (or possibly two) tokens in `input` correspond to a Kleene /// operator and separator, then a tuple with `(separator, KleeneOp)` is returned. Otherwise, an /// error with the appropriate span is emitted to `sess` and a dummy value is returned. fn parse_sep_and_kleene_op<'a>( input: &mut impl Iterator, span: Span, sess: &ParseSess, ) -> (Option, KleeneToken) { // We basically look at two token trees here, denoted as #1 and #2 below let span = match parse_kleene_op(input, span) { // #1 is a `?`, `+`, or `*` KleeneOp Ok(Ok((op, span))) => return (None, KleeneToken::new(op, span)), // #1 is a separator followed by #2, a KleeneOp Ok(Err(token)) => match parse_kleene_op(input, token.span) { // #2 is the `?` Kleene op, which does not take a separator (error) Ok(Ok((KleeneOp::ZeroOrOne, span))) => { // Error! sess.dcx.span_err( token.span, "the `?` macro repetition operator does not take a separator", ); // Return a dummy return (None, KleeneToken::new(KleeneOp::ZeroOrMore, span)); } // #2 is a KleeneOp :D Ok(Ok((op, span))) => return (Some(token), KleeneToken::new(op, span)), // #2 is a random token or not a token at all :( Ok(Err(Token { span, .. })) | Err(span) => span, }, // #1 is not a token Err(span) => span, }; // If we ever get to this point, we have experienced an "unexpected token" error sess.dcx.span_err(span, "expected one of: `*`, `+`, or `?`"); // Return a dummy (None, KleeneToken::new(KleeneOp::ZeroOrMore, span)) } // `$$` or a meta-variable is the lhs of a macro but shouldn't. // // For example, `macro_rules! foo { ( ${length()} ) => {} }` fn span_dollar_dollar_or_metavar_in_the_lhs_err(sess: &ParseSess, token: &Token) { sess.dcx.span_err(token.span, format!("unexpected token: {}", pprust::token_to_string(token))); sess.dcx.span_note( token.span, "`$$` and meta-variable expressions are not allowed inside macro parameter definitions", ); }