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Implement macro meta-variable expressions #93545
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,180 @@ | ||
| use std::fmt::Display; | ||
| use std::str::FromStr; | ||
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| use rustc_ast::token::{self, Lit}; | ||
| use rustc_ast::tokenstream; | ||
| use rustc_ast_pretty::pprust; | ||
| use rustc_errors::{Applicability, PResult}; | ||
| use rustc_session::parse::ParseSess; | ||
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| use rustc_span::symbol::Ident; | ||
| use rustc_span::Span; | ||
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| /// A meta-variable expression, for expansions based on properties of meta-variables. | ||
| #[derive(Debug, Clone, PartialEq, Encodable, Decodable)] | ||
| crate enum MetaVarExpr { | ||
| /// The number of repetitions of an identifier, optionally limited to a number | ||
| /// of outer-most repetition depths. If the depth limit is `None` then the depth is unlimited. | ||
| Count(Ident, Option<usize>), | ||
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| /// Ignore a meta-variable for repetition without expansion. | ||
| Ignore(Ident), | ||
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| /// The index of the repetition at a particular depth, where 0 is the inner-most | ||
| /// repetition. The `usize` is the depth. | ||
| Index(usize), | ||
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| /// The length of the repetition at a particular depth, where 0 is the inner-most | ||
| /// repetition. The `usize` is the depth. | ||
| Length(usize), | ||
| } | ||
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| impl MetaVarExpr { | ||
| /// Attempt to parse a meta-variable expression from a token stream. | ||
| crate fn parse<'sess>( | ||
| input: &tokenstream::TokenStream, | ||
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| sess: &'sess ParseSess, | ||
| ) -> PResult<'sess, MetaVarExpr> { | ||
| let mut tts = input.trees(); | ||
| match tts.next() { | ||
| Some(tokenstream::TokenTree::Token(token)) if let Some((ident, false)) = token.ident() => { | ||
| let Some(tokenstream::TokenTree::Delimited(_, token::Paren, args)) = tts.next() else { | ||
| let msg = "meta-variable expression paramter must be wrapped in parentheses"; | ||
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| return Err(sess.span_diagnostic.struct_span_err(ident.span, msg)); | ||
| }; | ||
| let mut iter = args.trees(); | ||
| let rslt = match &*ident.as_str() { | ||
| "count" => parse_count(&mut iter, sess, ident.span)?, | ||
| "ignore" => MetaVarExpr::Ignore(parse_ident(&mut iter, sess, ident.span)?), | ||
| "index" => MetaVarExpr::Index(parse_depth(&mut iter, sess, ident.span)?), | ||
| "length" => MetaVarExpr::Length(parse_depth(&mut iter, sess, ident.span)?), | ||
| _ => { | ||
| let msg = "unrecognised meta-variable expression. Supported expressions \ | ||
| are count, ignore, index and length"; | ||
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| return Err(sess.span_diagnostic.struct_span_err(ident.span, msg)); | ||
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| } | ||
| }; | ||
| if let Some(arg) = iter.next() { | ||
| let msg = "unexpected meta-variable expression argument"; | ||
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| return Err(sess.span_diagnostic.struct_span_err(arg.span(), msg)); | ||
| } | ||
| Ok(rslt) | ||
| } | ||
| Some(tokenstream::TokenTree::Token(token)) => { | ||
| return Err(sess.span_diagnostic.struct_span_err( | ||
| token.span, | ||
| &format!( | ||
| "expected meta-variable expression, found `{}`", | ||
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| pprust::token_to_string(&token), | ||
| ), | ||
| )); | ||
| } | ||
| _ => return Err(sess.span_diagnostic.struct_err("expected meta-variable expression")) | ||
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| } | ||
| } | ||
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| crate fn ident(&self) -> Option<&Ident> { | ||
| match self { | ||
| MetaVarExpr::Count(ident, _) | MetaVarExpr::Ignore(ident) => Some(&ident), | ||
| MetaVarExpr::Index(..) | MetaVarExpr::Length(..) => None, | ||
| } | ||
| } | ||
| } | ||
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| /// Tries to convert a literal to an arbitrary type | ||
| fn convert_literal<T>(lit: Lit, sess: &ParseSess, span: Span) -> PResult<'_, T> | ||
| where | ||
| T: FromStr, | ||
| <T as FromStr>::Err: Display, | ||
| { | ||
| if lit.suffix.is_some() { | ||
| let msg = "literal suffixes are not supported in meta-variable expressions"; | ||
| return Err(sess.span_diagnostic.struct_span_err(span, msg)); | ||
| } | ||
| lit.symbol.as_str().parse::<T>().map_err(|e| { | ||
| sess.span_diagnostic.struct_span_err( | ||
| span, | ||
| &format!("failed to parse meta-variable expression argument: {}", e), | ||
| ) | ||
| }) | ||
| } | ||
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| /// Parse a meta-variable `count` expression: `count(ident[, depth])` | ||
| fn parse_count<'sess>( | ||
| iter: &mut tokenstream::Cursor, | ||
| sess: &'sess ParseSess, | ||
| span: Span, | ||
| ) -> PResult<'sess, MetaVarExpr> { | ||
| let ident = parse_ident(iter, sess, span)?; | ||
| let depth = if try_eat_comma(iter) { Some(parse_depth(iter, sess, span)?) } else { None }; | ||
| Ok(MetaVarExpr::Count(ident, depth)) | ||
| } | ||
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| /// Parses the depth used by index(depth) and length(depth). | ||
| fn parse_depth<'sess>( | ||
| iter: &mut tokenstream::Cursor, | ||
| sess: &'sess ParseSess, | ||
| span: Span, | ||
| ) -> PResult<'sess, usize> { | ||
| let Some(tt) = iter.next() else { return Ok(0) }; | ||
| let tokenstream::TokenTree::Token(token::Token { | ||
| kind: token::TokenKind::Literal(lit), | ||
| span: literal_span, | ||
| }) = tt else { | ||
| return Err(sess.span_diagnostic.struct_span_err( | ||
| span, | ||
| "meta-expression depth must be a literal" | ||
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| )); | ||
| }; | ||
| convert_literal::<usize>(lit, sess, literal_span) | ||
| } | ||
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| /// Parses an generic ident | ||
| fn parse_ident<'sess>( | ||
| iter: &mut tokenstream::Cursor, | ||
| sess: &'sess ParseSess, | ||
| span: Span, | ||
| ) -> PResult<'sess, Ident> { | ||
| let err_fn = | ||
| || sess.span_diagnostic.struct_span_err(span, "could not find an expected `ident` element"); | ||
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| if let Some(tt) = iter.next() { | ||
| match tt { | ||
| tokenstream::TokenTree::Token(token) => { | ||
| if let Some((elem, false)) = token.ident() { | ||
| return Ok(elem); | ||
| } | ||
| let mut err = err_fn(); | ||
| err.span_suggestion( | ||
| token.span, | ||
| &format!("Try removing `{}`", pprust::token_to_string(&token)), | ||
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| <_>::default(), | ||
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| Applicability::MaybeIncorrect, | ||
| ); | ||
| return Err(err); | ||
| } | ||
| tokenstream::TokenTree::Delimited(delim_span, _, _) => { | ||
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| let mut err = err_fn(); | ||
| err.span_suggestion( | ||
| delim_span.entire(), | ||
| "Try removing the delimiter", | ||
| <_>::default(), | ||
| Applicability::MaybeIncorrect, | ||
| ); | ||
| return Err(err); | ||
| } | ||
| } | ||
| } | ||
| Err(err_fn()) | ||
| } | ||
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| /// Tries to move the iterator forward returning `true` if there is a comma. If not, then the | ||
| /// iterator is not modified and the result is `false`. | ||
| fn try_eat_comma(iter: &mut tokenstream::Cursor) -> bool { | ||
| if let Some(tokenstream::TokenTree::Token(token::Token { kind: token::Comma, .. })) = | ||
| iter.look_ahead(0) | ||
| { | ||
| let _ = iter.next(); | ||
| return true; | ||
| } | ||
| false | ||
| } | ||
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