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| 1 | +use rustc_ast::token; |
| 2 | +use rustc_ast::tokenstream::{Cursor, TokenStream, TokenTree}; |
| 3 | +use rustc_ast::{LitIntType, LitKind}; |
| 4 | +use rustc_ast_pretty::pprust; |
| 5 | +use rustc_errors::{Applicability, PResult}; |
| 6 | +use rustc_session::parse::ParseSess; |
| 7 | +use rustc_span::symbol::Ident; |
| 8 | +use rustc_span::Span; |
| 9 | + |
| 10 | +/// A meta-variable expression, for expansions based on properties of meta-variables. |
| 11 | +#[derive(Debug, Clone, PartialEq, Encodable, Decodable)] |
| 12 | +crate enum MetaVarExpr { |
| 13 | + /// The number of repetitions of an identifier, optionally limited to a number |
| 14 | + /// of outer-most repetition depths. If the depth limit is `None` then the depth is unlimited. |
| 15 | + Count(Ident, Option<usize>), |
| 16 | + |
| 17 | + /// Ignore a meta-variable for repetition without expansion. |
| 18 | + Ignore(Ident), |
| 19 | + |
| 20 | + /// The index of the repetition at a particular depth, where 0 is the inner-most |
| 21 | + /// repetition. The `usize` is the depth. |
| 22 | + Index(usize), |
| 23 | + |
| 24 | + /// The length of the repetition at a particular depth, where 0 is the inner-most |
| 25 | + /// repetition. The `usize` is the depth. |
| 26 | + Length(usize), |
| 27 | +} |
| 28 | + |
| 29 | +impl MetaVarExpr { |
| 30 | + /// Attempt to parse a meta-variable expression from a token stream. |
| 31 | + crate fn parse<'sess>( |
| 32 | + input: &TokenStream, |
| 33 | + outer_span: Span, |
| 34 | + sess: &'sess ParseSess, |
| 35 | + ) -> PResult<'sess, MetaVarExpr> { |
| 36 | + let mut tts = input.trees(); |
| 37 | + let ident = parse_ident(&mut tts, sess, outer_span)?; |
| 38 | + let Some(TokenTree::Delimited(_, token::Paren, args)) = tts.next() else { |
| 39 | + let msg = "meta-variable expression parameter must be wrapped in parentheses"; |
| 40 | + return Err(sess.span_diagnostic.struct_span_err(ident.span, msg)); |
| 41 | + }; |
| 42 | + check_trailing_token(&mut tts, sess)?; |
| 43 | + let mut iter = args.trees(); |
| 44 | + let rslt = match &*ident.as_str() { |
| 45 | + "count" => parse_count(&mut iter, sess, ident.span)?, |
| 46 | + "ignore" => MetaVarExpr::Ignore(parse_ident(&mut iter, sess, ident.span)?), |
| 47 | + "index" => MetaVarExpr::Index(parse_depth(&mut iter, sess, ident.span)?), |
| 48 | + "length" => MetaVarExpr::Length(parse_depth(&mut iter, sess, ident.span)?), |
| 49 | + _ => { |
| 50 | + let err_msg = "unrecognized meta-variable expression"; |
| 51 | + let mut err = sess.span_diagnostic.struct_span_err(ident.span, err_msg); |
| 52 | + err.span_suggestion( |
| 53 | + ident.span, |
| 54 | + "supported expressions are count, ignore, index and length", |
| 55 | + String::new(), |
| 56 | + Applicability::MachineApplicable, |
| 57 | + ); |
| 58 | + return Err(err); |
| 59 | + } |
| 60 | + }; |
| 61 | + check_trailing_token(&mut iter, sess)?; |
| 62 | + Ok(rslt) |
| 63 | + } |
| 64 | + |
| 65 | + crate fn ident(&self) -> Option<&Ident> { |
| 66 | + match self { |
| 67 | + MetaVarExpr::Count(ident, _) | MetaVarExpr::Ignore(ident) => Some(&ident), |
| 68 | + MetaVarExpr::Index(..) | MetaVarExpr::Length(..) => None, |
| 69 | + } |
| 70 | + } |
| 71 | +} |
| 72 | + |
| 73 | +// Checks if there are any remaining tokens. For example, `${ignore(ident ... a b c ...)}` |
| 74 | +fn check_trailing_token<'sess>(iter: &mut Cursor, sess: &'sess ParseSess) -> PResult<'sess, ()> { |
| 75 | + if let Some(tt) = iter.next() { |
| 76 | + let mut diag = sess.span_diagnostic.struct_span_err( |
| 77 | + tt.span(), |
| 78 | + &format!("unexpected token: {}", pprust::tt_to_string(&tt)), |
| 79 | + ); |
| 80 | + diag.span_note(tt.span(), "meta-variable expression must not have trailing tokens"); |
| 81 | + Err(diag) |
| 82 | + } else { |
| 83 | + Ok(()) |
| 84 | + } |
| 85 | +} |
| 86 | + |
| 87 | +/// Parse a meta-variable `count` expression: `count(ident[, depth])` |
| 88 | +fn parse_count<'sess>( |
| 89 | + iter: &mut Cursor, |
| 90 | + sess: &'sess ParseSess, |
| 91 | + span: Span, |
| 92 | +) -> PResult<'sess, MetaVarExpr> { |
| 93 | + let ident = parse_ident(iter, sess, span)?; |
| 94 | + let depth = if try_eat_comma(iter) { Some(parse_depth(iter, sess, span)?) } else { None }; |
| 95 | + Ok(MetaVarExpr::Count(ident, depth)) |
| 96 | +} |
| 97 | + |
| 98 | +/// Parses the depth used by index(depth) and length(depth). |
| 99 | +fn parse_depth<'sess>( |
| 100 | + iter: &mut Cursor, |
| 101 | + sess: &'sess ParseSess, |
| 102 | + span: Span, |
| 103 | +) -> PResult<'sess, usize> { |
| 104 | + let Some(tt) = iter.next() else { return Ok(0) }; |
| 105 | + let TokenTree::Token(token::Token { |
| 106 | + kind: token::TokenKind::Literal(lit), .. |
| 107 | + }) = tt else { |
| 108 | + return Err(sess.span_diagnostic.struct_span_err( |
| 109 | + span, |
| 110 | + "meta-variable expression depth must be a literal" |
| 111 | + )); |
| 112 | + }; |
| 113 | + if let Ok(lit_kind) = LitKind::from_lit_token(lit) |
| 114 | + && let LitKind::Int(n_u128, LitIntType::Unsuffixed) = lit_kind |
| 115 | + && let Ok(n_usize) = usize::try_from(n_u128) |
| 116 | + { |
| 117 | + Ok(n_usize) |
| 118 | + } |
| 119 | + else { |
| 120 | + let msg = "only unsuffixes integer literals are supported in meta-variable expressions"; |
| 121 | + Err(sess.span_diagnostic.struct_span_err(span, msg)) |
| 122 | + } |
| 123 | +} |
| 124 | + |
| 125 | +/// Parses an generic ident |
| 126 | +fn parse_ident<'sess>( |
| 127 | + iter: &mut Cursor, |
| 128 | + sess: &'sess ParseSess, |
| 129 | + span: Span, |
| 130 | +) -> PResult<'sess, Ident> { |
| 131 | + let err_fn = |msg| sess.span_diagnostic.struct_span_err(span, msg); |
| 132 | + if let Some(tt) = iter.next() && let TokenTree::Token(token) = tt { |
| 133 | + if let Some((elem, false)) = token.ident() { |
| 134 | + return Ok(elem); |
| 135 | + } |
| 136 | + let token_str = pprust::token_to_string(&token); |
| 137 | + let mut err = err_fn(&format!("expected identifier, found `{}`", &token_str)); |
| 138 | + err.span_suggestion( |
| 139 | + token.span, |
| 140 | + &format!("try removing `{}`", &token_str), |
| 141 | + String::new(), |
| 142 | + Applicability::MaybeIncorrect, |
| 143 | + ); |
| 144 | + return Err(err); |
| 145 | + } |
| 146 | + Err(err_fn("expected identifier")) |
| 147 | +} |
| 148 | + |
| 149 | +/// Tries to move the iterator forward returning `true` if there is a comma. If not, then the |
| 150 | +/// iterator is not modified and the result is `false`. |
| 151 | +fn try_eat_comma(iter: &mut Cursor) -> bool { |
| 152 | + if let Some(TokenTree::Token(token::Token { kind: token::Comma, .. })) = iter.look_ahead(0) { |
| 153 | + let _ = iter.next(); |
| 154 | + return true; |
| 155 | + } |
| 156 | + false |
| 157 | +} |
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