rustc_expand/mbe/quoted.rs
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use rustc_ast::token::{self, Delimiter, IdentIsRaw, NonterminalKind, Token};
use rustc_ast::{NodeId, tokenstream};
use rustc_ast_pretty::pprust;
use rustc_feature::Features;
use rustc_session::Session;
use rustc_session::parse::feature_err;
use rustc_span::Span;
use rustc_span::edition::Edition;
use rustc_span::symbol::{Ident, kw, sym};
use crate::errors;
use crate::mbe::macro_parser::count_metavar_decls;
use crate::mbe::{Delimited, KleeneOp, KleeneToken, MetaVarExpr, SequenceRepetition, TokenTree};
pub(crate) const VALID_FRAGMENT_NAMES_MSG: &str = "valid fragment specifiers are \
`ident`, `block`, `stmt`, `expr`, `pat`, `ty`, `lifetime`, `literal`, `path`, \
`meta`, `tt`, `item` and `vis`, along with `expr_2021` and `pat_param` for edition compatibility";
/// Takes a `tokenstream::TokenStream` and returns a `Vec<self::TokenTree>`. 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: &Session,
node_id: NodeId,
features: &Features,
edition: Edition,
) -> Vec<TokenTree> {
// 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().peekable();
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 => {
// Not consuming the next token immediately, as it may not be a colon
let span = match trees.peek() {
Some(&tokenstream::TokenTree::Token(
Token { kind: token::Colon, span: colon_span },
_,
)) => {
// Consume the colon first
trees.next();
// It's ok to consume the next tree no matter how,
// since if it's not a token then it will be an invalid declaration.
match trees.next() {
Some(tokenstream::TokenTree::Token(token, _)) => match token.ident() {
Some((fragment, _)) => {
let span = token.span.with_lo(start_sp.lo());
let edition = || {
// 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.from_expansion() {
edition
} else {
span.edition()
}
};
let kind = NonterminalKind::from_symbol(fragment.name, edition)
.unwrap_or_else(|| {
sess.dcx().emit_err(errors::InvalidFragmentSpecifier {
span,
fragment,
help: VALID_FRAGMENT_NAMES_MSG.into(),
});
NonterminalKind::Ident
});
result.push(TokenTree::MetaVarDecl(span, ident, Some(kind)));
continue;
}
_ => token.span,
},
// Invalid, return a nice source location
_ => colon_span.with_lo(start_sp.lo()),
}
}
// Whether it's none or some other tree, it doesn't belong to
// the current meta variable, returning the original span.
_ => start_sp,
};
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 enabled
fn maybe_emit_macro_metavar_expr_feature(features: &Features, sess: &Session, span: Span) {
if !features.macro_metavar_expr() {
let msg = "meta-variable expressions are unstable";
feature_err(sess, sym::macro_metavar_expr, span, msg).emit();
}
}
fn maybe_emit_macro_metavar_expr_concat_feature(features: &Features, sess: &Session, span: Span) {
if !features.macro_metavar_expr_concat() {
let msg = "the `concat` meta-variable expression is unstable";
feature_err(sess, sym::macro_metavar_expr_concat, 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<Item = &'a tokenstream::TokenTree>,
parsing_patterns: bool,
sess: &Session,
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: dollar_span }, _) => {
// FIXME: Handle `Invisible`-delimited groups in a more systematic way
// during parsing.
let mut next = outer_trees.next();
let mut trees: Box<dyn Iterator<Item = &tokenstream::TokenTree>>;
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. `${count(ident)}`).
// Try to parse the meta-variable expression.
match MetaVarExpr::parse(tts, delim_span.entire(), &sess.psess) {
Err(err) => {
err.emit();
// Returns early the same read `$` to avoid spanning
// unrelated diagnostics that could be performed afterwards
return TokenTree::token(token::Dollar, dollar_span);
}
Ok(elem) => {
if let MetaVarExpr::Concat(_) = elem {
maybe_emit_macro_metavar_expr_concat_feature(
features,
sess,
delim_span.entire(),
);
} else {
maybe_emit_macro_metavar_expr_feature(
features,
sess,
delim_span.entire(),
);
}
return TokenTree::MetaVarExpr(delim_span, elem);
}
}
}
Delimiter::Parenthesis => {}
_ => {
let token = pprust::token_kind_to_string(&token::OpenDelim(delim));
sess.dcx().emit_err(errors::ExpectedParenOrBrace {
span: delim_span.entire(),
token,
});
}
}
}
// 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 `$crate`
// special metavariable that names the crate of the invocation.
Some(tokenstream::TokenTree::Token(token, _)) if token.is_ident() => {
let (ident, is_raw) = token.ident().unwrap();
let span = ident.span.with_lo(dollar_span.lo());
if ident.name == kw::Crate && matches!(is_raw, IdentIsRaw::No) {
TokenTree::token(token::Ident(kw::DollarCrate, is_raw), span)
} else {
TokenTree::MetaVar(span, ident)
}
}
// `tree` is followed by another `$`. This is an escaped `$`.
Some(&tokenstream::TokenTree::Token(
Token { kind: token::Dollar, span: dollar_span2 },
_,
)) => {
if parsing_patterns {
span_dollar_dollar_or_metavar_in_the_lhs_err(sess, &Token {
kind: token::Dollar,
span: dollar_span2,
});
} else {
maybe_emit_macro_metavar_expr_feature(features, sess, dollar_span2);
}
TokenTree::token(token::Dollar, dollar_span2)
}
// `tree` is followed by some other token. This is an error.
Some(tokenstream::TokenTree::Token(token, _)) => {
let msg =
format!("expected identifier, found `{}`", pprust::token_to_string(token),);
sess.dcx().span_err(token.span, msg);
TokenTree::MetaVar(token.span, Ident::empty())
}
// There are no more tokens. Just return the `$` we already have.
None => TokenTree::token(token::Dollar, 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<KleeneOp> {
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<Item = &'a tokenstream::TokenTree>,
span: Span,
) -> Result<Result<(KleeneOp, Span), Token>, 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<Item = &'a tokenstream::TokenTree>,
span: Span,
sess: &Session,
) -> (Option<Token>, 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))
}
// `$$` or a meta-variable is the lhs of a macro but shouldn't.
//
// For example, `macro_rules! foo { ( ${len()} ) => {} }`
fn span_dollar_dollar_or_metavar_in_the_lhs_err(sess: &Session, token: &Token) {
sess.dcx()
.span_err(token.span, format!("unexpected token: {}", pprust::token_to_string(token)));
sess.dcx().span_note(
token.span,
"`$$` and meta-variable expressions are not allowed inside macro parameter definitions",
);
}