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Rollup merge of #139628 - makai410:suggest-vis, r=compiler-errors

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Suggest remove redundant `$()?` around `vis`

Resolves: #139480 .
This commit is contained in:
Jacob Pratt 2025-04-13 17:37:54 -04:00 • committed by GitHub
commit a04a03720e
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4 changed files with 128 additions and 6 deletions
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44
compiler/rustc_expand/src/mbe/macro_rules.rs
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@ -12,7 +12,7 @@ use rustc_ast::{self as ast, DUMMY_NODE_ID, NodeId};
use rustc_ast_pretty::pprust;
use rustc_attr_parsing::{AttributeKind, find_attr};
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_errors::{Applicability, ErrorGuaranteed};
use rustc_errors::{Applicability, Diag, ErrorGuaranteed};
use rustc_feature::Features;
use rustc_hir as hir;
use rustc_lint_defs::BuiltinLintDiag;
@ -27,19 +27,18 @@ use rustc_span::hygiene::Transparency;
use rustc_span::{Ident, MacroRulesNormalizedIdent, Span, kw, sym};
use tracing::{debug, instrument, trace, trace_span};
use super::diagnostics;
use super::macro_parser::{NamedMatches, NamedParseResult};
use super::{SequenceRepetition, diagnostics};
use crate::base::{
DummyResult, ExpandResult, ExtCtxt, MacResult, MacroExpanderResult, SyntaxExtension,
SyntaxExtensionKind, TTMacroExpander,
};
use crate::expand::{AstFragment, AstFragmentKind, ensure_complete_parse, parse_ast_fragment};
use crate::mbe;
use crate::mbe::diagnostics::{annotate_doc_comment, parse_failure_msg};
use crate::mbe::macro_check;
use crate::mbe::macro_parser::NamedMatch::*;
use crate::mbe::macro_parser::{Error, ErrorReported, Failure, MatcherLoc, Success, TtParser};
use crate::mbe::transcribe::transcribe;
use crate::mbe::{self, KleeneOp, macro_check};
pub(crate) struct ParserAnyMacro<'a> {
parser: Parser<'a>,
@ -640,6 +639,37 @@ fn is_empty_token_tree(sess: &Session, seq: &mbe::SequenceRepetition) -> bool {
}
}
/// Checks if a `vis` nonterminal fragment is unnecessarily wrapped in an optional repetition.
///
/// When a `vis` fragment (which can already be empty) is wrapped in `$(...)?`,
/// this suggests removing the redundant repetition syntax since it provides no additional benefit.
fn check_redundant_vis_repetition(
err: &mut Diag<'_>,
sess: &Session,
seq: &SequenceRepetition,
span: &DelimSpan,
) {
let is_zero_or_one: bool = seq.kleene.op == KleeneOp::ZeroOrOne;
let is_vis = seq.tts.first().map_or(false, |tt| {
matches!(tt, mbe::TokenTree::MetaVarDecl(_, _, Some(NonterminalKind::Vis)))
});
if is_vis && is_zero_or_one {
err.note("a `vis` fragment can already be empty");
err.multipart_suggestion(
"remove the `$(` and `)?`",
vec![
(
sess.source_map().span_extend_to_prev_char_before(span.open, '$', true),
"".to_string(),
),
(span.close.with_hi(seq.kleene.span.hi()), "".to_string()),
],
Applicability::MaybeIncorrect,
);
}
}
/// Checks that the lhs contains no repetition which could match an empty token
/// tree, because then the matcher would hang indefinitely.
fn check_lhs_no_empty_seq(sess: &Session, tts: &[mbe::TokenTree]) -> Result<(), ErrorGuaranteed> {
@ -654,8 +684,10 @@ fn check_lhs_no_empty_seq(sess: &Session, tts: &[mbe::TokenTree]) -> Result<(),
TokenTree::Sequence(span, seq) => {
if is_empty_token_tree(sess, seq) {
let sp = span.entire();
let guar = sess.dcx().span_err(sp, "repetition matches empty token tree");
return Err(guar);
let mut err =
sess.dcx().struct_span_err(sp, "repetition matches empty token tree");
check_redundant_vis_repetition(&mut err, sess, seq, span);
return Err(err.emit());
}
check_lhs_no_empty_seq(sess, &seq.tts)?
}