diff options
Diffstat (limited to 'compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs')
| -rw-r--r-- | compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs | 65 |
1 files changed, 25 insertions, 40 deletions
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs index c73f8284ca5..b243f1dc8d0 100644 --- a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs +++ b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs @@ -62,21 +62,13 @@ struct ConstToPat<'tcx> { treat_byte_string_as_slice: bool, } -mod fallback_to_const_ref { - #[derive(Debug)] - /// This error type signals that we encountered a non-struct-eq situation behind a reference. - /// We bubble this up in order to get back to the reference destructuring and make that emit - /// a const pattern instead of a deref pattern. This allows us to simply call `PartialEq::eq` - /// on such patterns (since that function takes a reference) and not have to jump through any - /// hoops to get a reference to the value. - pub(super) struct FallbackToConstRef(()); - - pub(super) fn fallback_to_const_ref(c2p: &super::ConstToPat<'_>) -> FallbackToConstRef { - assert!(c2p.behind_reference.get()); - FallbackToConstRef(()) - } -} -use fallback_to_const_ref::{fallback_to_const_ref, FallbackToConstRef}; +/// This error type signals that we encountered a non-struct-eq situation. +/// We bubble this up in order to get back to the reference destructuring and make that emit +/// a const pattern instead of a deref pattern. This allows us to simply call `PartialEq::eq` +/// on such patterns (since that function takes a reference) and not have to jump through any +/// hoops to get a reference to the value. +#[derive(Debug)] +struct FallbackToConstRef; impl<'tcx> ConstToPat<'tcx> { fn new( @@ -236,13 +228,13 @@ impl<'tcx> ConstToPat<'tcx> { let kind = match cv.ty().kind() { ty::Float(_) => { - tcx.emit_spanned_lint( - lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN, - id, - span, - FloatPattern, - ); - PatKind::Constant { value: cv } + tcx.emit_spanned_lint( + lint::builtin::ILLEGAL_FLOATING_POINT_LITERAL_PATTERN, + id, + span, + FloatPattern, + ); + return Err(FallbackToConstRef); } ty::Adt(adt_def, _) if adt_def.is_union() => { // Matching on union fields is unsafe, we can't hide it in constants @@ -289,7 +281,7 @@ impl<'tcx> ConstToPat<'tcx> { // Since we are behind a reference, we can just bubble the error up so we get a // constant at reference type, making it easy to let the fallback call // `PartialEq::eq` on it. - return Err(fallback_to_const_ref(self)); + return Err(FallbackToConstRef); } ty::Adt(adt_def, _) if !self.type_marked_structural(cv.ty()) => { debug!( @@ -393,11 +385,11 @@ impl<'tcx> ConstToPat<'tcx> { self.behind_reference.set(old); val } - // Backwards compatibility hack: support references to non-structural types. - // We'll lower - // this pattern to a `PartialEq::eq` comparison and `PartialEq::eq` takes a - // reference. This makes the rest of the matching logic simpler as it doesn't have - // to figure out how to get a reference again. + // Backwards compatibility hack: support references to non-structural types, + // but hard error if we aren't behind a double reference. We could just use + // the fallback code path below, but that would allow *more* of this fishy + // code to compile, as then it only goes through the future incompat lint + // instead of a hard error. ty::Adt(_, _) if !self.type_marked_structural(*pointee_ty) => { if self.behind_reference.get() { if !self.saw_const_match_error.get() @@ -411,7 +403,7 @@ impl<'tcx> ConstToPat<'tcx> { IndirectStructuralMatch { non_sm_ty: *pointee_ty }, ); } - PatKind::Constant { value: cv } + return Err(FallbackToConstRef); } else { if !self.saw_const_match_error.get() { self.saw_const_match_error.set(true); @@ -435,16 +427,9 @@ impl<'tcx> ConstToPat<'tcx> { PatKind::Wild } else { let old = self.behind_reference.replace(true); - // In case there are structural-match violations somewhere in this subpattern, - // we fall back to a const pattern. If we do not do this, we may end up with - // a !structural-match constant that is not of reference type, which makes it - // very hard to invoke `PartialEq::eq` on it as a fallback. - let val = match self.recur(tcx.deref_mir_constant(self.param_env.and(cv)), false) { - Ok(subpattern) => PatKind::Deref { subpattern }, - Err(_) => PatKind::Constant { value: cv }, - }; + let subpattern = self.recur(tcx.deref_mir_constant(self.param_env.and(cv)), false)?; self.behind_reference.set(old); - val + PatKind::Deref { subpattern } } } }, @@ -452,7 +437,7 @@ impl<'tcx> ConstToPat<'tcx> { PatKind::Constant { value: cv } } ty::RawPtr(pointee) if pointee.ty.is_sized(tcx, param_env) => { - PatKind::Constant { value: cv } + return Err(FallbackToConstRef); } // FIXME: these can have very surprising behaviour where optimization levels or other // compilation choices change the runtime behaviour of the match. @@ -469,7 +454,7 @@ impl<'tcx> ConstToPat<'tcx> { PointerPattern ); } - PatKind::Constant { value: cv } + return Err(FallbackToConstRef); } _ => { self.saw_const_match_error.set(true); |