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Cleanup the reporting of unreachable patterns

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This commit is contained in:
Nadrieril 2021-09-13 15:49:57 +01:00
parent 003bbcb799
commit ff90c6353b
1 changed files with 14 additions and 20 deletions
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34
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
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@ -190,20 +190,16 @@ impl<'tcx> MatchVisitor<'_, 'tcx> {
let scrut_ty = self.typeck_results.expr_ty_adjusted(scrut);
let report = compute_match_usefulness(&cx, &arms, scrut.hir_id, scrut_ty);
report_arm_reachability(&cx, &report, |arm_span, arm_hir_id, catchall| {
match source {
hir::MatchSource::ForLoopDesugar | hir::MatchSource::Normal => {
unreachable_pattern(cx.tcx, arm_span, arm_hir_id, catchall);
}
// Unreachable patterns in try and await expressions occur when one of
// the arms are an uninhabited type. Which is OK.
hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {}
match source {
hir::MatchSource::ForLoopDesugar | hir::MatchSource::Normal => {
report_arm_reachability(&cx, &report)
}
});
// Unreachable patterns in try and await expressions occur when one of
// the arms are an uninhabited type. Which is OK.
hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {}
}
// Check if the match is exhaustive.
// Note: An empty match isn't the same as an empty matrix for diagnostics purposes,
// since an empty matrix can occur when there are arms, if those arms all have guards.
let is_empty_match = arms.is_empty();
let witnesses = report.non_exhaustiveness_witnesses;
if !witnesses.is_empty() {
@ -434,9 +430,10 @@ fn check_let_reachability<'p, 'tcx>(
let arms = [MatchArm { pat, hir_id: pat_id, has_guard: false }];
let report = compute_match_usefulness(&cx, &arms, pat_id, pat.ty);
report_arm_reachability(&cx, &report, |arm_span, arm_hir_id, _| {
unreachable_pattern(cx.tcx, arm_span, arm_hir_id, None)
});
// Report if the pattern is unreachable, which can only occur when the type is uninhabited.
// This also reports unreachable sub-patterns though, so we can't just replace it with an
// `is_uninhabited` check.
report_arm_reachability(&cx, &report);
if report.non_exhaustiveness_witnesses.is_empty() {
// The match is exhaustive, i.e. the `if let` pattern is irrefutable.
@ -445,18 +442,15 @@ fn check_let_reachability<'p, 'tcx>(
}
/// Report unreachable arms, if any.
fn report_arm_reachability<'p, 'tcx, F>(
fn report_arm_reachability<'p, 'tcx>(
cx: &MatchCheckCtxt<'p, 'tcx>,
report: &UsefulnessReport<'p, 'tcx>,
unreachable: F,
) where
F: Fn(Span, HirId, Option<Span>),
{
) {
use Reachability::*;
let mut catchall = None;
for (arm, is_useful) in report.arm_usefulness.iter() {
match is_useful {
Unreachable => unreachable(arm.pat.span, arm.hir_id, catchall),
Unreachable => unreachable_pattern(cx.tcx, arm.pat.span, arm.hir_id, catchall),
Reachable(unreachables) if unreachables.is_empty() => {}
// The arm is reachable, but contains unreachable subpatterns (from or-patterns).
Reachable(unreachables) => {