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Rollup merge of #128033 - Nadrieril:explain-empty-wildcards, r=compiler-errors

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Explain why we require `_` for empty patterns

This adds a note to the "non-exhaustive patterns" diagnostic to explain why we sometimes require extra `_` patterns on empty types. This is one of the two diagnostic improvements I wanted to do before [stabilizing `min_exhaustive_patterns`](https://github.com/rust-lang/rust/pull/122792).

r? ``@compiler-errors``
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Jubilee 2024-07-21 17:44:30 -07:00 committed by GitHub
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4 changed files with 37 additions and 17 deletions
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36
compiler/rustc_mir_build/src/thir/pattern/check_match.rs
View File

@ -16,8 +16,8 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt};
use rustc_pattern_analysis::errors::Uncovered;
use rustc_pattern_analysis::rustc::{
Constructor, DeconstructedPat, MatchArm, RustcPatCtxt as PatCtxt, Usefulness, UsefulnessReport,
WitnessPat,
Constructor, DeconstructedPat, MatchArm, RevealedTy, RustcPatCtxt as PatCtxt, Usefulness,
UsefulnessReport, WitnessPat,
};
use rustc_session::lint::builtin::{
BINDINGS_WITH_VARIANT_NAME, IRREFUTABLE_LET_PATTERNS, UNREACHABLE_PATTERNS,
@ -998,27 +998,31 @@ fn report_non_exhaustive_match<'p, 'tcx>(
err.note(format!("the matched value is of type `{}`", scrut_ty));
if !is_empty_match {
let mut non_exhaustive_tys = FxIndexSet::default();
let mut special_tys = FxIndexSet::default();
// Look at the first witness.
collect_non_exhaustive_tys(cx, &witnesses[0], &mut non_exhaustive_tys);
collect_special_tys(cx, &witnesses[0], &mut special_tys);
for ty in non_exhaustive_tys {
for ty in special_tys {
if ty.is_ptr_sized_integral() {
if ty == cx.tcx.types.usize {
if ty.inner() == cx.tcx.types.usize {
err.note(format!(
"`{ty}` does not have a fixed maximum value, so half-open ranges are necessary to match \
exhaustively",
));
} else if ty == cx.tcx.types.isize {
} else if ty.inner() == cx.tcx.types.isize {
err.note(format!(
"`{ty}` does not have fixed minimum and maximum values, so half-open ranges are necessary to match \
exhaustively",
));
}
} else if ty == cx.tcx.types.str_ {
} else if ty.inner() == cx.tcx.types.str_ {
err.note("`&str` cannot be matched exhaustively, so a wildcard `_` is necessary");
} else if cx.is_foreign_non_exhaustive_enum(cx.reveal_opaque_ty(ty)) {
} else if cx.is_foreign_non_exhaustive_enum(ty) {
err.note(format!("`{ty}` is marked as non-exhaustive, so a wildcard `_` is necessary to match exhaustively"));
} else if cx.is_uninhabited(ty.inner()) && cx.tcx.features().min_exhaustive_patterns {
// The type is uninhabited yet there is a witness: we must be in the `MaybeInvalid`
// case.
err.note(format!("`{ty}` is uninhabited but is not being matched by value, so a wildcard `_` is required"));
}
}
}
@ -1168,22 +1172,22 @@ fn joined_uncovered_patterns<'p, 'tcx>(
}
}
fn collect_non_exhaustive_tys<'tcx>(
/// Collect types that require specific explanations when they show up in witnesses.
fn collect_special_tys<'tcx>(
cx: &PatCtxt<'_, 'tcx>,
pat: &WitnessPat<'_, 'tcx>,
non_exhaustive_tys: &mut FxIndexSet<Ty<'tcx>>,
special_tys: &mut FxIndexSet<RevealedTy<'tcx>>,
) {
if matches!(pat.ctor(), Constructor::NonExhaustive) {
non_exhaustive_tys.insert(pat.ty().inner());
if matches!(pat.ctor(), Constructor::NonExhaustive | Constructor::Never) {
special_tys.insert(*pat.ty());
}
if let Constructor::IntRange(range) = pat.ctor() {
if cx.is_range_beyond_boundaries(range, *pat.ty()) {
// The range denotes the values before `isize::MIN` or the values after `usize::MAX`/`isize::MAX`.
non_exhaustive_tys.insert(pat.ty().inner());
special_tys.insert(*pat.ty());
}
}
pat.iter_fields()
.for_each(|field_pat| collect_non_exhaustive_tys(cx, field_pat, non_exhaustive_tys))
pat.iter_fields().for_each(|field_pat| collect_special_tys(cx, field_pat, special_tys))
}
fn report_adt_defined_here<'tcx>(

8
compiler/rustc_pattern_analysis/src/rustc.rs
View File

@ -40,9 +40,15 @@ pub type WitnessPat<'p, 'tcx> = crate::pat::WitnessPat<RustcPatCtxt<'p, 'tcx>>;
///
/// Use `.inner()` or deref to get to the `Ty<'tcx>`.
#[repr(transparent)]
#[derive(Clone, Copy)]
#[derive(Clone, Copy, PartialEq, Eq, Hash)]
pub struct RevealedTy<'tcx>(Ty<'tcx>);
impl<'tcx> fmt::Display for RevealedTy<'tcx> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
self.0.fmt(fmt)
}
}
impl<'tcx> fmt::Debug for RevealedTy<'tcx> {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
self.0.fmt(fmt)

9
tests/ui/pattern/usefulness/empty-types.min_exh_pats.stderr
View File

@ -204,6 +204,7 @@ note: `Option<Void>` defined here
|
= note: not covered
= note: the matched value is of type `Option<Void>`
= note: `Void` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ None => {},
@ -349,6 +350,7 @@ LL | match slice_never {
| ^^^^^^^^^^^ pattern `&[_, ..]` not covered
|
= note: the matched value is of type `&[!]`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ [] => {},
@ -484,6 +486,7 @@ note: `Option<!>` defined here
|
= note: not covered
= note: the matched value is of type `&Option<!>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ &None => {},
@ -502,6 +505,7 @@ note: `Option<!>` defined here
|
= note: not covered
= note: the matched value is of type `Option<!>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ None => {},
@ -520,6 +524,7 @@ note: `Result<!, !>` defined here
|
= note: not covered
= note: the matched value is of type `Result<!, !>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ Ok(_) => {},
@ -538,6 +543,7 @@ note: `Result<!, !>` defined here
|
= note: not covered
= note: the matched value is of type `Result<!, !>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ Ok(_a) => {},
@ -589,6 +595,7 @@ LL | match ref_never {
| ^^^^^^^^^ pattern `&_` not covered
|
= note: the matched value is of type `&!`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
= note: references are always considered inhabited
= note: match arms with guards don't count towards exhaustivity
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
@ -609,6 +616,7 @@ note: `Result<!, !>` defined here
|
= note: not covered
= note: the matched value is of type `Result<!, !>`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ Err(_) => {},
@ -627,6 +635,7 @@ note: `Option<Result<!, !>>` defined here
|
= note: not covered
= note: the matched value is of type `Option<Result<!, !>>`
= note: `Result<!, !>` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ None => {},

1
tests/ui/pattern/usefulness/slice_of_empty.min_exhaustive_patterns.stderr
View File

@ -5,6 +5,7 @@ LL | match nevers {
| ^^^^^^ pattern `&[_, ..]` not covered
|
= note: the matched value is of type `&[!]`
= note: `!` is uninhabited but is not being matched by value, so a wildcard `_` is required
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
|
LL ~ &[] => (),