bjoernager/rust
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Add an error path to the algorithm

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This commit is contained in:
Nadrieril 2024-01-07 21:20:16 +01:00
parent d8b44d2802
commit 07d5f19426
5 changed files with 40 additions and 28 deletions
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21
compiler/rustc_pattern_analysis/src/usefulness.rs
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@ -1341,14 +1341,14 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
mcx: MatchCtxt<'a, 'p, Cx>,
matrix: &mut Matrix<'p, Cx>,
is_top_level: bool,
) -> WitnessMatrix<Cx> {
) -> Result<WitnessMatrix<Cx>, Cx::Error> {
debug_assert!(matrix.rows().all(|r| r.len() == matrix.column_count()));
if !matrix.wildcard_row_is_relevant && matrix.rows().all(|r| !r.pats.relevant) {
// Here we know that nothing will contribute further to exhaustiveness or usefulness. This
// is purely an optimization: skipping this check doesn't affect correctness. See the top of
// the file for details.
return WitnessMatrix::empty();
return Ok(WitnessMatrix::empty());
}
let Some(ty) = matrix.head_ty() else {
@ -1360,16 +1360,16 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
// When there's an unguarded row, the match is exhaustive and any subsequent row is not
// useful.
if !row.is_under_guard {
return WitnessMatrix::empty();
return Ok(WitnessMatrix::empty());
}
}
// No (unguarded) rows, so the match is not exhaustive. We return a new witness unless
// irrelevant.
return if matrix.wildcard_row_is_relevant {
WitnessMatrix::unit_witness()
Ok(WitnessMatrix::unit_witness())
} else {
// We choose to not report anything here; see at the top for details.
WitnessMatrix::empty()
Ok(WitnessMatrix::empty())
};
};
@ -1422,7 +1422,7 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
let mut spec_matrix = matrix.specialize_constructor(pcx, &ctor, ctor_is_relevant);
let mut witnesses = ensure_sufficient_stack(|| {
compute_exhaustiveness_and_usefulness(mcx, &mut spec_matrix, false)
});
})?;
// Transform witnesses for `spec_matrix` into witnesses for `matrix`.
witnesses.apply_constructor(pcx, &missing_ctors, &ctor, report_individual_missing_ctors);
@ -1443,7 +1443,7 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
}
}
ret
Ok(ret)
}
/// Indicates whether or not a given arm is useful.
@ -1474,9 +1474,10 @@ pub fn compute_match_usefulness<'p, Cx: TypeCx>(
arms: &[MatchArm<'p, Cx>],
scrut_ty: Cx::Ty,
scrut_validity: ValidityConstraint,
) -> UsefulnessReport<'p, Cx> {
) -> Result<UsefulnessReport<'p, Cx>, Cx::Error> {
let mut matrix = Matrix::new(arms, scrut_ty, scrut_validity);
let non_exhaustiveness_witnesses = compute_exhaustiveness_and_usefulness(cx, &mut matrix, true);
let non_exhaustiveness_witnesses =
compute_exhaustiveness_and_usefulness(cx, &mut matrix, true)?;
let non_exhaustiveness_witnesses: Vec<_> = non_exhaustiveness_witnesses.single_column();
let arm_usefulness: Vec<_> = arms
@ -1493,5 +1494,5 @@ pub fn compute_match_usefulness<'p, Cx: TypeCx>(
(arm, usefulness)
})
.collect();
UsefulnessReport { arm_usefulness, non_exhaustiveness_witnesses }
Ok(UsefulnessReport { arm_usefulness, non_exhaustiveness_witnesses })
}