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Rollup merge of #120097 - Nadrieril:consistent_unreachable_subpats, r=compiler-errors

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Report unreachable subpatterns consistently

We weren't reporting unreachable subpatterns in function arguments and `let` expressions. This wasn't very important, but never patterns make it more relevant: a user might write `let (Ok(x) | Err(!)) = ...` in a case where `let Ok(x) = ...` is accepted, so we should report the `Err(!)` as redundant.

r? ```@compiler-errors```
This commit is contained in:
Matthias Krüger 2024-01-22 16:54:58 +01:00 • committed by GitHub
commit f194a84ce2
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6 changed files with 182 additions and 40 deletions
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88
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
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@ -1,9 +1,8 @@
use rustc_pattern_analysis::errors::Uncovered;
use rustc_pattern_analysis::rustc::{
Constructor, DeconstructedPat, RustcMatchCheckCtxt as MatchCheckCtxt, Usefulness,
Constructor, DeconstructedPat, MatchArm, RustcMatchCheckCtxt as MatchCheckCtxt, Usefulness,
UsefulnessReport, WitnessPat,
};
use rustc_pattern_analysis::{analyze_match, MatchArm};
use crate::errors::*;
@ -390,6 +389,34 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
}
}
fn analyze_patterns(
&mut self,
cx: &MatchCheckCtxt<'p, 'tcx>,
arms: &[MatchArm<'p, 'tcx>],
scrut_ty: Ty<'tcx>,
) -> Result<UsefulnessReport<'p, 'tcx>, ErrorGuaranteed> {
let report =
rustc_pattern_analysis::analyze_match(&cx, &arms, scrut_ty).map_err(|err| {
self.error = Err(err);
err
})?;
// Warn unreachable subpatterns.
for (arm, is_useful) in report.arm_usefulness.iter() {
if let Usefulness::Useful(redundant_subpats) = is_useful
&& !redundant_subpats.is_empty()
{
let mut redundant_subpats = redundant_subpats.clone();
// Emit lints in the order in which they occur in the file.
redundant_subpats.sort_unstable_by_key(|pat| pat.data().unwrap().span);
for pat in redundant_subpats {
report_unreachable_pattern(cx, arm.arm_data, pat.data().unwrap().span, None)
}
}
}
Ok(report)
}
#[instrument(level = "trace", skip(self))]
fn check_let(&mut self, pat: &'p Pat<'tcx>, scrutinee: Option<ExprId>, span: Span) {
assert!(self.let_source != LetSource::None);
@ -435,14 +462,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
}
}
let scrut_ty = scrut.ty;
let report = match analyze_match(&cx, &tarms, scrut_ty) {
Ok(report) => report,
Err(err) => {
self.error = Err(err);
return;
}
};
let Ok(report) = self.analyze_patterns(&cx, &tarms, scrut.ty) else { return };
match source {
// Don't report arm reachability of desugared `match $iter.into_iter() { iter => .. }`
@ -474,7 +494,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
);
} else {
self.error = Err(report_non_exhaustive_match(
&cx, self.thir, scrut_ty, scrut.span, witnesses, arms, expr_span,
&cx, self.thir, scrut.ty, scrut.span, witnesses, arms, expr_span,
));
}
}
@ -556,7 +576,7 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
let cx = self.new_cx(refutability, None, scrut, pat.span);
let pat = self.lower_pattern(&cx, pat)?;
let arms = [MatchArm { pat, arm_data: self.lint_level, has_guard: false }];
let report = analyze_match(&cx, &arms, pat.ty().inner())?;
let report = self.analyze_patterns(&cx, &arms, pat.ty().inner())?;
Ok((cx, report))
}
@ -567,7 +587,6 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
) -> Result<RefutableFlag, ErrorGuaranteed> {
let (cx, report) = self.analyze_binding(pat, Refutable, scrut)?;
// Report if the pattern is unreachable, which can only occur when the type is uninhabited.
// This also reports unreachable sub-patterns.
report_arm_reachability(&cx, &report);
// If the list of witnesses is empty, the match is exhaustive, i.e. the `if let` pattern is
// irrefutable.
@ -850,39 +869,30 @@ fn report_irrefutable_let_patterns(
}
}
/// Report unreachable arms, if any.
fn report_unreachable_pattern<'p, 'tcx>(
cx: &MatchCheckCtxt<'p, 'tcx>,
hir_id: HirId,
span: Span,
catchall: Option<Span>,
) {
cx.tcx.emit_spanned_lint(
UNREACHABLE_PATTERNS,
hir_id,
span,
UnreachablePattern { span: if catchall.is_some() { Some(span) } else { None }, catchall },
);
}
/// Report unreachable arms, if any.
fn report_arm_reachability<'p, 'tcx>(
cx: &MatchCheckCtxt<'p, 'tcx>,
report: &UsefulnessReport<'p, 'tcx>,
) {
let report_unreachable_pattern = |span, hir_id, catchall: Option<Span>| {
cx.tcx.emit_spanned_lint(
UNREACHABLE_PATTERNS,
hir_id,
span,
UnreachablePattern {
span: if catchall.is_some() { Some(span) } else { None },
catchall,
},
);
};
let mut catchall = None;
for (arm, is_useful) in report.arm_usefulness.iter() {
match is_useful {
Usefulness::Redundant => {
report_unreachable_pattern(arm.pat.data().unwrap().span, arm.arm_data, catchall)
}
Usefulness::Useful(redundant_subpats) if redundant_subpats.is_empty() => {}
// The arm is reachable, but contains redundant subpatterns (from or-patterns).
Usefulness::Useful(redundant_subpats) => {
let mut redundant_subpats = redundant_subpats.clone();
// Emit lints in the order in which they occur in the file.
redundant_subpats.sort_unstable_by_key(|pat| pat.data().unwrap().span);
for pat in redundant_subpats {
report_unreachable_pattern(pat.data().unwrap().span, arm.arm_data, None);
}
}
if matches!(is_useful, Usefulness::Redundant) {
report_unreachable_pattern(cx, arm.arm_data, arm.pat.data().unwrap().span, catchall)
}
if !arm.has_guard && catchall.is_none() && pat_is_catchall(arm.pat) {
catchall = Some(arm.pat.data().unwrap().span);