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Implement feature gate logic

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Nadrieril 2024-01-18 19:22:44 +01:00
parent 886108b9fe
commit 95a14d43d7
7 changed files with 806 additions and 158 deletions
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26
compiler/rustc_pattern_analysis/src/usefulness.rs
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@ -548,11 +548,12 @@
//! [`ValidityConstraint::specialize`].
//!
//! Having said all that, in practice we don't fully follow what's been presented in this section.
//! Under `exhaustive_patterns`, we allow omitting empty arms even in `!known_valid` places, for
//! backwards-compatibility until we have a better alternative. Without `exhaustive_patterns`, we
//! mostly treat empty types as inhabited, except specifically a non-nested `!` or empty enum. In
//! this specific case we also allow the empty match regardless of place validity, for
//! backwards-compatibility. Hopefully we can eventually deprecate this.
//! Let's call "toplevel exception" the case where the match scrutinee itself has type `!` or
//! `EmptyEnum`. First, on stable rust, we require `_` patterns for empty types in all cases apart
//! from the toplevel exception. The `exhaustive_patterns` and `min_exaustive_patterns` allow
//! omitting patterns in the cases described above. There's a final detail: in the toplevel
//! exception or with the `exhaustive_patterns` feature, we ignore place validity when checking
//! whether a pattern is required for exhaustiveness. I (Nadrieril) hope to deprecate this behavior.
//!
//!
//!
@ -1440,10 +1441,17 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
// We treat match scrutinees of type `!` or `EmptyEnum` differently.
let is_toplevel_exception =
is_top_level && matches!(ctors_for_ty, ConstructorSet::NoConstructors);
// Whether empty patterns can be omitted for exhaustiveness.
let can_omit_empty_arms = is_toplevel_exception || mcx.tycx.is_exhaustive_patterns_feature_on();
// Whether empty patterns are counted as useful or not.
let empty_arms_are_unreachable = place_validity.is_known_valid() && can_omit_empty_arms;
// Whether empty patterns are counted as useful or not. We only warn an empty arm unreachable if
// it is guaranteed unreachable by the opsem (i.e. if the place is `known_valid`).
let empty_arms_are_unreachable = place_validity.is_known_valid()
&& (is_toplevel_exception
|| mcx.tycx.is_exhaustive_patterns_feature_on()
|| mcx.tycx.is_min_exhaustive_patterns_feature_on());
// Whether empty patterns can be omitted for exhaustiveness. We ignore place validity in the
// toplevel exception and `exhaustive_patterns` cases for backwards compatibility.
let can_omit_empty_arms = empty_arms_are_unreachable
|| is_toplevel_exception
|| mcx.tycx.is_exhaustive_patterns_feature_on();
// Analyze the constructors present in this column.
let ctors = matrix.heads().map(|p| p.ctor());