diff options
| -rw-r--r-- | compiler/rustc_middle/src/mir/syntax.rs | 4 | ||||
| -rw-r--r-- | compiler/rustc_mir_transform/src/validate.rs | 26 | ||||
| -rw-r--r-- | src/tools/miri/tests/panic/mir-validation.stderr | 2 |
3 files changed, 26 insertions, 6 deletions
diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs index 2b28496faec..2d485211433 100644 --- a/compiler/rustc_middle/src/mir/syntax.rs +++ b/compiler/rustc_middle/src/mir/syntax.rs @@ -1008,8 +1008,8 @@ pub type AssertMessage<'tcx> = AssertKind<Operand<'tcx>>; /// element: /// /// - [`Downcast`](ProjectionElem::Downcast): This projection sets the place's variant index to the -/// given one, and makes no other changes. A `Downcast` projection on a place with its variant -/// index already set is not well-formed. +/// given one, and makes no other changes. A `Downcast` projection must always be followed +/// immediately by a `Field` projection. /// - [`Field`](ProjectionElem::Field): `Field` projections take their parent place and create a /// place referring to one of the fields of the type. The resulting address is the parent /// address, plus the offset of the field. The type becomes the type of the field. If the parent diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs index 66cc65de647..6df32169eec 100644 --- a/compiler/rustc_mir_transform/src/validate.rs +++ b/compiler/rustc_mir_transform/src/validate.rs @@ -689,8 +689,10 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> { if Some(adt_def.did()) == self.tcx.lang_items().dyn_metadata() { self.fail( location, - format!("You can't project to field {f:?} of `DynMetadata` because \ - layout is weird and thinks it doesn't have fields."), + format!( + "You can't project to field {f:?} of `DynMetadata` because \ + layout is weird and thinks it doesn't have fields." + ), ); } @@ -839,7 +841,25 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> { && cntxt != PlaceContext::NonUse(NonUseContext::VarDebugInfo) && place.projection[1..].contains(&ProjectionElem::Deref) { - self.fail(location, format!("{place:?}, has deref at the wrong place")); + self.fail( + location, + format!("place {place:?} has deref as a later projection (it is only permitted as the first projection)"), + ); + } + + // Ensure all downcast projections are followed by field projections. + let mut projections_iter = place.projection.iter(); + while let Some(proj) = projections_iter.next() { + if matches!(proj, ProjectionElem::Downcast(..)) { + if !matches!(projections_iter.next(), Some(ProjectionElem::Field(..))) { + self.fail( + location, + format!( + "place {place:?} has `Downcast` projection not followed by `Field`" + ), + ); + } + } } self.super_place(place, cntxt, location); diff --git a/src/tools/miri/tests/panic/mir-validation.stderr b/src/tools/miri/tests/panic/mir-validation.stderr index d5dd53d7b4e..534e2d5881f 100644 --- a/src/tools/miri/tests/panic/mir-validation.stderr +++ b/src/tools/miri/tests/panic/mir-validation.stderr @@ -1,6 +1,6 @@ thread 'rustc' panicked at compiler/rustc_mir_transform/src/validate.rs:LL:CC: broken MIR in Item(DefId) (after phase change to runtime-optimized) at bb0[1]: -(*(_2.0: *mut i32)), has deref at the wrong place +place (*(_2.0: *mut i32)) has deref as a later projection (it is only permitted as the first projection) stack backtrace: error: the compiler unexpectedly panicked. this is a bug. |