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Simplify empty pattern logic a bit

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This commit is contained in:
Nadrieril 2024-01-10 22:47:52 +01:00
parent edb27a306a
commit de77f1a86e
1 changed files with 13 additions and 14 deletions
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27
compiler/rustc_pattern_analysis/src/usefulness.rs
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@ -1441,21 +1441,20 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
debug!("ty: {ty:?}");
let pcx = &PlaceCtxt { mcx, ty };
let ctors_for_ty = pcx.ctors_for_ty()?;
// Whether the place/column we are inspecting is known to contain valid data.
let place_validity = matrix.place_validity[0];
// 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();
// Analyze the constructors present in this column.
let ctors = matrix.heads().map(|p| p.ctor());
let ctors_for_ty = pcx.ctors_for_ty()?;
let is_integers = matches!(ctors_for_ty, ConstructorSet::Integers { .. }); // For diagnostics.
let mut split_set = ctors_for_ty.split(ctors);
// We have now grouped all the constructors into 3 buckets: present, missing, missing_empty.
// In the absence of the `exhaustive_patterns` feature however, we don't count nested empty
// types as empty. Only non-nested `!` or `enum Foo {}` are considered empty.
if !pcx.mcx.tycx.is_exhaustive_patterns_feature_on()
&& !(is_top_level && matches!(ctors_for_ty, ConstructorSet::NoConstructors))
{
if !can_omit_empty_arms {
// Treat all missing constructors as nonempty.
// This clears `missing_empty`.
split_set.missing.append(&mut split_set.missing_empty);
@ -1463,17 +1462,17 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
let all_missing = split_set.present.is_empty();
// Build the set of constructors we will specialize with. It must cover the whole type.
// We need to iterate over a full set of constructors, so we add `Missing` to represent the
// missing ones. This is explained under "Constructor Splitting" at the top of this file.
let mut split_ctors = split_set.present;
if !split_set.missing.is_empty() {
// We need to iterate over a full set of constructors, so we add `Missing` to represent the
// missing ones. This is explained under "Constructor Splitting" at the top of this file.
split_ctors.push(Constructor::Missing);
} else if !split_set.missing_empty.is_empty() && !place_validity.is_known_valid() {
// The missing empty constructors are reachable if the place can contain invalid data.
if !(split_set.missing.is_empty()
&& (split_set.missing_empty.is_empty() || place_validity.is_known_valid()))
{
split_ctors.push(Constructor::Missing);
}
// Decide what constructors to report.
let is_integers = matches!(ctors_for_ty, ConstructorSet::Integers { .. });
let always_report_all = is_top_level && !is_integers;
// Whether we should report "Enum::A and Enum::C are missing" or "_ is missing".
let report_individual_missing_ctors = always_report_all || !all_missing;