diff options
| -rw-r--r-- | compiler/rustc_middle/src/ty/layout.rs | 21 | ||||
| -rw-r--r-- | tests/ui/layout/debug.rs | 5 | ||||
| -rw-r--r-- | tests/ui/layout/debug.stderr | 8 | ||||
| -rw-r--r-- | tests/ui/layout/normalization-failure.rs | 57 | ||||
| -rw-r--r-- | tests/ui/layout/normalization-failure.stderr | 12 |
5 files changed, 102 insertions, 1 deletions
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs index bbb8a9fa671..2a058addf15 100644 --- a/compiler/rustc_middle/src/ty/layout.rs +++ b/compiler/rustc_middle/src/ty/layout.rs @@ -229,11 +229,32 @@ impl fmt::Display for ValidityRequirement { #[derive(Copy, Clone, Debug, HashStable, TyEncodable, TyDecodable)] pub enum LayoutError<'tcx> { + /// A type doesn't have a sensible layout. + /// + /// This variant is used for layout errors that don't necessarily cause + /// compile errors. + /// + /// For example, this can happen if a struct contains an unsized type in a + /// non-tail field, but has an unsatisfiable bound like `str: Sized`. Unknown(Ty<'tcx>), + /// The size of a type exceeds [`TargetDataLayout::obj_size_bound`]. SizeOverflow(Ty<'tcx>), + /// The layout can vary due to a generic parameter. + /// + /// Unlike `Unknown`, this variant is a "soft" error and indicates that the layout + /// may become computable after further instantiating the generic parameter(s). TooGeneric(Ty<'tcx>), + /// An alias failed to normalize. + /// + /// This variant is necessary, because, due to trait solver incompleteness, it is + /// possible than an alias that was rigid during analysis fails to normalize after + /// revealing opaque types. + /// + /// See `tests/ui/layout/normalization-failure.rs` for an example. NormalizationFailure(Ty<'tcx>, NormalizationError<'tcx>), + /// A non-layout error is reported elsewhere. ReferencesError(ErrorGuaranteed), + /// A type has cyclic layout, i.e. the type contains itself without indirection. Cycle(ErrorGuaranteed), } diff --git a/tests/ui/layout/debug.rs b/tests/ui/layout/debug.rs index 81dc7285254..c0adf9ec677 100644 --- a/tests/ui/layout/debug.rs +++ b/tests/ui/layout/debug.rs @@ -82,3 +82,8 @@ type Impossible = (str, str); //~ ERROR: cannot be known at compilation time #[rustc_layout(debug)] union EmptyUnion {} //~ ERROR: has an unknown layout //~^ ERROR: unions cannot have zero fields + +// Test the error message of `LayoutError::TooGeneric` +// (this error is never emitted to users). +#[rustc_layout(debug)] +type TooGeneric<T> = T; //~ ERROR: does not have a fixed size diff --git a/tests/ui/layout/debug.stderr b/tests/ui/layout/debug.stderr index 319c0de26a9..d64dee4e27f 100644 --- a/tests/ui/layout/debug.stderr +++ b/tests/ui/layout/debug.stderr @@ -596,12 +596,18 @@ error: the type has an unknown layout LL | union EmptyUnion {} | ^^^^^^^^^^^^^^^^ +error: `T` does not have a fixed size + --> $DIR/debug.rs:89:1 + | +LL | type TooGeneric<T> = T; + | ^^^^^^^^^^^^^^^^^^ + error: `#[rustc_layout]` can only be applied to `struct`/`enum`/`union` declarations and type aliases --> $DIR/debug.rs:75:5 | LL | const C: () = (); | ^^^^^^^^^^^ -error: aborting due to 19 previous errors +error: aborting due to 20 previous errors For more information about this error, try `rustc --explain E0277`. diff --git a/tests/ui/layout/normalization-failure.rs b/tests/ui/layout/normalization-failure.rs new file mode 100644 index 00000000000..c0f8710c03c --- /dev/null +++ b/tests/ui/layout/normalization-failure.rs @@ -0,0 +1,57 @@ +//! This test demonstrates how `LayoutError::NormalizationFailure` can happen and why +//! it is necessary. +//! +//! This code does not cause an immediate normalization error in typeck, because we +//! don't reveal the hidden type returned by `opaque<T>` in the analysis typing mode. +//! Instead, `<{opaque} as Project2>::Assoc2` is a *rigid projection*, because we know +//! that `{opaque}: Project2` holds, due to the opaque type's `impl Project2` bound, +//! but cannot normalize `<{opaque} as Project2>::Assoc2` any further. +//! +//! However, in the post-analysis typing mode, which is used for the layout computation, +//! the opaque's hidden type is revealed to be `PhantomData<T>`, and now we fail to +//! normalize `<PhantomData<T> as Project2>::Assoc2` if there is a `T: Project1` bound +//! in the param env! This happens, because `PhantomData<T>: Project2` only holds if +//! `<T as Project1>::Assoc1 == ()` holds. This would usually be satisfied by the +//! blanket `impl<T> Project1 for T`, but due to the `T: Project1` bound we do not +//! normalize `<T as Project1>::Assoc1` via the impl and treat it as rigid instead. +//! Therefore, `PhantomData<T>: Project2` does NOT hold and normalizing +//! `<PhantomData<T> as Project2>::Assoc2` fails. +//! +//! Note that this layout error can only happen when computing the layout in a generic +//! context, which is not required for codegen, but may happen for lints, MIR optimizations, +//! and the transmute check. + +use std::marker::PhantomData; + +trait Project1 { + type Assoc1; +} + +impl<T> Project1 for T { + type Assoc1 = (); +} + +trait Project2 { + type Assoc2; + fn get(self) -> Self::Assoc2; +} + +impl<T: Project1<Assoc1 = ()>> Project2 for PhantomData<T> { + type Assoc2 = (); + fn get(self) -> Self::Assoc2 {} +} + +fn opaque<T>() -> impl Project2 { + PhantomData::<T> +} + +fn check<T: Project1>() { + unsafe { + std::mem::transmute::<_, ()>(opaque::<T>().get()); + //~^ ERROR: cannot transmute + //~| NOTE: (unable to determine layout for `<impl Project2 as Project2>::Assoc2` because `<impl Project2 as Project2>::Assoc2` cannot be normalized) + //~| NOTE: (0 bits) + } +} + +fn main() {} diff --git a/tests/ui/layout/normalization-failure.stderr b/tests/ui/layout/normalization-failure.stderr new file mode 100644 index 00000000000..5fe38d4403a --- /dev/null +++ b/tests/ui/layout/normalization-failure.stderr @@ -0,0 +1,12 @@ +error[E0512]: cannot transmute between types of different sizes, or dependently-sized types + --> $DIR/normalization-failure.rs:50:9 + | +LL | std::mem::transmute::<_, ()>(opaque::<T>().get()); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | + = note: source type: `<impl Project2 as Project2>::Assoc2` (unable to determine layout for `<impl Project2 as Project2>::Assoc2` because `<impl Project2 as Project2>::Assoc2` cannot be normalized) + = note: target type: `()` (0 bits) + +error: aborting due to 1 previous error + +For more information about this error, try `rustc --explain E0512`. |