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[1/2] Implement macro meta-variable expressions #94368
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Mar 11, 2022
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,157 @@ | ||
| use rustc_ast::token; | ||
| use rustc_ast::tokenstream::{Cursor, TokenStream, TokenTree}; | ||
| use rustc_ast::{LitIntType, LitKind}; | ||
| use rustc_ast_pretty::pprust; | ||
| use rustc_errors::{Applicability, PResult}; | ||
| use rustc_session::parse::ParseSess; | ||
| use rustc_span::symbol::Ident; | ||
| use rustc_span::Span; | ||
|
|
||
| /// 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>), | ||
|
|
||
| /// 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), | ||
| } | ||
|
|
||
| impl MetaVarExpr { | ||
| /// Attempt to parse a meta-variable expression from a token stream. | ||
| crate fn parse<'sess>( | ||
| input: &TokenStream, | ||
| outer_span: Span, | ||
| sess: &'sess ParseSess, | ||
| ) -> PResult<'sess, MetaVarExpr> { | ||
| let mut tts = input.trees(); | ||
| let ident = parse_ident(&mut tts, sess, outer_span)?; | ||
| let Some(TokenTree::Delimited(_, token::Paren, args)) = tts.next() else { | ||
| let msg = "meta-variable expression parameter must be wrapped in parentheses"; | ||
| return Err(sess.span_diagnostic.struct_span_err(ident.span, msg)); | ||
| }; | ||
| check_trailing_token(&mut tts, sess)?; | ||
| 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)?), | ||
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|
||
| _ => { | ||
| let err_msg = "unrecognized meta-variable expression"; | ||
| let mut err = sess.span_diagnostic.struct_span_err(ident.span, err_msg); | ||
| err.span_suggestion( | ||
| ident.span, | ||
| "supported expressions are count, ignore, index and length", | ||
| String::new(), | ||
| Applicability::MachineApplicable, | ||
| ); | ||
| return Err(err); | ||
| } | ||
| }; | ||
| check_trailing_token(&mut iter, sess)?; | ||
| Ok(rslt) | ||
| } | ||
|
|
||
| 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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||
| // Checks if there are any remaining tokens. For example, `${ignore(ident ... a b c ...)}` | ||
| fn check_trailing_token<'sess>(iter: &mut Cursor, sess: &'sess ParseSess) -> PResult<'sess, ()> { | ||
| if let Some(tt) = iter.next() { | ||
| let mut diag = sess.span_diagnostic.struct_span_err( | ||
| tt.span(), | ||
| &format!("unexpected token: {}", pprust::tt_to_string(&tt)), | ||
| ); | ||
| diag.span_note(tt.span(), "meta-variable expression must not have trailing tokens"); | ||
| Err(diag) | ||
| } else { | ||
| Ok(()) | ||
| } | ||
| } | ||
|
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||
| /// Parse a meta-variable `count` expression: `count(ident[, depth])` | ||
| fn parse_count<'sess>( | ||
| iter: &mut 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)) | ||
| } | ||
|
|
||
| /// Parses the depth used by index(depth) and length(depth). | ||
| fn parse_depth<'sess>( | ||
| iter: &mut Cursor, | ||
| sess: &'sess ParseSess, | ||
| span: Span, | ||
| ) -> PResult<'sess, usize> { | ||
| let Some(tt) = iter.next() else { return Ok(0) }; | ||
| let TokenTree::Token(token::Token { | ||
| kind: token::TokenKind::Literal(lit), .. | ||
| }) = tt else { | ||
| return Err(sess.span_diagnostic.struct_span_err( | ||
| span, | ||
| "meta-variable expression depth must be a literal" | ||
| )); | ||
| }; | ||
| if let Ok(lit_kind) = LitKind::from_lit_token(lit) | ||
| && let LitKind::Int(n_u128, LitIntType::Unsuffixed) = lit_kind | ||
| && let Ok(n_usize) = usize::try_from(n_u128) | ||
| { | ||
| Ok(n_usize) | ||
| } | ||
| else { | ||
| let msg = "only unsuffixes integer literals are supported in meta-variable expressions"; | ||
| Err(sess.span_diagnostic.struct_span_err(span, msg)) | ||
| } | ||
| } | ||
|
|
||
| /// Parses an generic ident | ||
| fn parse_ident<'sess>( | ||
| iter: &mut Cursor, | ||
| sess: &'sess ParseSess, | ||
| span: Span, | ||
| ) -> PResult<'sess, Ident> { | ||
| let err_fn = |msg| sess.span_diagnostic.struct_span_err(span, msg); | ||
| if let Some(tt) = iter.next() && let TokenTree::Token(token) = tt { | ||
| if let Some((elem, false)) = token.ident() { | ||
| return Ok(elem); | ||
| } | ||
| let token_str = pprust::token_to_string(&token); | ||
| let mut err = err_fn(&format!("expected identifier, found `{}`", &token_str)); | ||
| err.span_suggestion( | ||
| token.span, | ||
| &format!("try removing `{}`", &token_str), | ||
| String::new(), | ||
| Applicability::MaybeIncorrect, | ||
| ); | ||
| return Err(err); | ||
| } | ||
| Err(err_fn("expected identifier")) | ||
| } | ||
|
|
||
| /// 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 Cursor) -> bool { | ||
| if let Some(TokenTree::Token(token::Token { kind: token::Comma, .. })) = iter.look_ahead(0) { | ||
| let _ = iter.next(); | ||
| return true; | ||
| } | ||
| false | ||
| } | ||
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