Consider more erroneous layouts as LayoutError::ReferencesError to suppress spurious errors

compiler/rustc_ty_utils/src/layout.rs

@@ -105,21 +105,27 @@ fn map_error<'tcx>(
             // See `tests/ui/layout/trivial-bounds-sized.rs` for an example.
             assert!(field.layout.is_unsized(), "invalid layout error {err:#?}");
             if !field.ty.is_sized(cx.tcx(), cx.typing_env) {
-                cx.tcx().dcx().delayed_bug(format!(
+                let guar = cx.tcx().dcx().delayed_bug(format!(
                     "encountered unexpected unsized field in layout of {ty:?}: {field:#?}"
                 ));
+                LayoutError::ReferencesError(guar)
+            } else {
+                LayoutError::Unknown(ty)
             }
-            LayoutError::Unknown(ty)
         }
         LayoutCalculatorError::EmptyUnion => {
             // This is always a compile error.
-            cx.tcx().dcx().delayed_bug(format!("computed layout of empty union: {ty:?}"));
-            LayoutError::Unknown(ty)
+            let guar =
+                cx.tcx().dcx().delayed_bug(format!("computed layout of empty union: {ty:?}"));
+            LayoutError::ReferencesError(guar)
         }
         LayoutCalculatorError::ReprConflict => {
             // packed enums are the only known trigger of this, but others might arise
-            cx.tcx().dcx().delayed_bug(format!("computed impossible repr (packed enum?): {ty:?}"));
-            LayoutError::Unknown(ty)
+            let guar = cx
+                .tcx()
+                .dcx()
+                .delayed_bug(format!("computed impossible repr (packed enum?): {ty:?}"));
+            LayoutError::ReferencesError(guar)
         }
     };
     error(cx, err)
@@ -432,8 +438,10 @@ fn layout_of_uncached<'tcx>(
         ty::Adt(def, args) if def.repr().simd() => {
             if !def.is_struct() {
                 // Should have yielded E0517 by now.
-                tcx.dcx().delayed_bug("#[repr(simd)] was applied to an ADT that is not a struct");
-                return Err(error(cx, LayoutError::Unknown(ty)));
+                let guar = tcx
+                    .dcx()
+                    .delayed_bug("#[repr(simd)] was applied to an ADT that is not a struct");
+                return Err(error(cx, LayoutError::ReferencesError(guar)));
             }
 
             let fields = &def.non_enum_variant().fields;
@@ -459,10 +467,10 @@ fn layout_of_uncached<'tcx>(
             // (should be caught by typeck)
             for fi in fields {
                 if fi.ty(tcx, args) != f0_ty {
-                    tcx.dcx().delayed_bug(
+                    let guar = tcx.dcx().delayed_bug(
                         "#[repr(simd)] was applied to an ADT with heterogeneous field type",
                     );
-                    return Err(error(cx, LayoutError::Unknown(ty)));
+                    return Err(error(cx, LayoutError::ReferencesError(guar)));
                 }
             }
 
@@ -567,11 +575,11 @@ fn layout_of_uncached<'tcx>(
 
             if def.is_union() {
                 if def.repr().pack.is_some() && def.repr().align.is_some() {
-                    tcx.dcx().span_delayed_bug(
+                    let guar = tcx.dcx().span_delayed_bug(
                         tcx.def_span(def.did()),
                         "union cannot be packed and aligned",
                     );
-                    return Err(error(cx, LayoutError::Unknown(ty)));
+                    return Err(error(cx, LayoutError::ReferencesError(guar)));
                 }
 
                 return Ok(tcx.mk_layout(

tests/ui/enum-discriminant/eval-error.rs

@@ -0,0 +1,37 @@
+union Foo {
+    a: str,
+    //~^ ERROR the size for values of type `str` cannot be known at compilation time
+    //~| ERROR field must implement `Copy` or be wrapped in `ManuallyDrop<...>`
+}
+
+enum Bar {
+    Boo = {
+        let _: Option<Foo> = None;
+        0
+    },
+}
+
+union Foo2 {}
+//~^ ERROR unions cannot have zero fields
+
+enum Bar2 {
+    Boo = {
+        let _: Option<Foo2> = None;
+        0
+    },
+}
+
+#[repr(u8, packed)]
+//~^ ERROR attribute should be applied to a struct or union
+enum Foo3 {
+    A
+}
+
+enum Bar3 {
+    Boo = {
+        let _: Option<Foo3> = None;
+        0
+    },
+}
+
+fn main() {}

tests/ui/enum-discriminant/eval-error.stderr

@@ -0,0 +1,51 @@
+error: unions cannot have zero fields
+  --> $DIR/eval-error.rs:14:1
+   |
+LL | union Foo2 {}
+   | ^^^^^^^^^^^^^
+
+error[E0517]: attribute should be applied to a struct or union
+  --> $DIR/eval-error.rs:24:12
+   |
+LL |   #[repr(u8, packed)]
+   |              ^^^^^^
+LL |
+LL | / enum Foo3 {
+LL | |     A
+LL | | }
+   | |_- not a struct or union
+
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/eval-error.rs:2:8
+   |
+LL |     a: str,
+   |        ^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = note: no field of a union may have a dynamically sized type
+   = help: change the field's type to have a statically known size
+help: borrowed types always have a statically known size
+   |
+LL |     a: &str,
+   |        +
+help: the `Box` type always has a statically known size and allocates its contents in the heap
+   |
+LL |     a: Box<str>,
+   |        ++++   +
+
+error[E0740]: field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union
+  --> $DIR/eval-error.rs:2:5
+   |
+LL |     a: str,
+   |     ^^^^^^
+   |
+   = note: union fields must not have drop side-effects, which is currently enforced via either `Copy` or `ManuallyDrop<...>`
+help: wrap the field type in `ManuallyDrop<...>`
+   |
+LL |     a: std::mem::ManuallyDrop<str>,
+   |        +++++++++++++++++++++++   +
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0277, E0517, E0740.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/layout/base-layout-is-sized-ice-123078.rs

@@ -8,7 +8,6 @@ struct S {
 }
 
 const C: S = unsafe { std::mem::transmute(()) };
-//~^ ERROR cannot transmute between types of different sizes, or dependently-sized types
 const _: [(); {
     C;
     0

tests/ui/layout/base-layout-is-sized-ice-123078.stderr

@@ -16,16 +16,6 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL |     a: Box<[u8]>,
    |        ++++    +
 
-error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
-  --> $DIR/base-layout-is-sized-ice-123078.rs:10:23
-   |
-LL | const C: S = unsafe { std::mem::transmute(()) };
-   |                       ^^^^^^^^^^^^^^^^^^^
-   |
-   = note: source type: `()` (0 bits)
-   = note: target type: `S` (size can vary because of [u8])
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0277, E0512.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0277`.

tests/ui/layout/debug.stderr

@@ -590,7 +590,7 @@ LL | type Impossible = (str, str);
    = help: the trait `Sized` is not implemented for `str`
    = note: only the last element of a tuple may have a dynamically sized type
 
-error: the type `EmptyUnion` has an unknown layout
+error: the type has an unknown layout
   --> $DIR/debug.rs:83:1
    |
 LL | union EmptyUnion {}