Turn eager normalization errors to delayed errors

When normalizing `union`s with fields coming from associated types that
don't satisfy trait bounds, avoid ICEing by using `delay_span_bug()`
instead of `bug!()`.

Fix #81199.

compiler/rustc_passes/src/stability.rs

@@ -835,7 +835,13 @@ impl Visitor<'tcx> for Checker<'tcx> {
                 let ty = self.tcx.type_of(item.def_id);
                 let (adt_def, substs) = match ty.kind() {
                     ty::Adt(adt_def, substs) => (adt_def, substs),
-                    _ => bug!(),
+                    _ => {
+                        self.tcx.sess.delay_span_bug(
+                            item.span,
+                            &format!("unexpected type kind {:?} (`{:?}`)", ty, ty.kind()),
+                        );
+                        return;
+                    }
                 };
 
                 // Non-`Copy` fields are unstable, except for `ManuallyDrop`.

compiler/rustc_traits/src/normalize_erasing_regions.rs

@@ -2,6 +2,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt, TypeFoldable};
+use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::query::normalize::AtExt;
 use rustc_trait_selection::traits::{Normalized, ObligationCause};
 use std::sync::atomic::Ordering;
@@ -51,7 +52,13 @@ fn normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq + Cop
                 debug_assert!(!erased.needs_infer(), "{:?}", erased);
                 erased
             }
-            Err(NoSolution) => bug!("could not fully normalize `{:?}`", value),
+            Err(NoSolution) => {
+                infcx
+                    .tcx
+                    .sess
+                    .delay_span_bug(DUMMY_SP, &format!("could not fully normalize `{:?}`", value));
+                value
+            }
         }
     })
 }

src/test/ui/union/normalization-failure-issue-81199-autofix.fixed

@@ -0,0 +1,21 @@
+// run-rustfix
+#[allow(dead_code)]
+#[repr(C)]
+union PtrRepr<T: ?Sized + Pointee> {
+    const_ptr: *const T,
+    mut_ptr: *mut T,
+    components: std::mem::ManuallyDrop<PtrComponents<T>>,
+    //~^ ERROR the trait bound `T: Pointee` is not satisfied
+}
+
+#[repr(C)]
+struct PtrComponents<T: Pointee + ?Sized> {
+    data_address: *const (),
+    metadata: <T as Pointee>::Metadata,
+}
+
+pub trait Pointee {
+   type Metadata;
+}
+
+fn main() {}

src/test/ui/union/normalization-failure-issue-81199-autofix.rs

@@ -0,0 +1,21 @@
+// run-rustfix
+#[allow(dead_code)]
+#[repr(C)]
+union PtrRepr<T: ?Sized> {
+    const_ptr: *const T,
+    mut_ptr: *mut T,
+    components: std::mem::ManuallyDrop<PtrComponents<T>>,
+    //~^ ERROR the trait bound `T: Pointee` is not satisfied
+}
+
+#[repr(C)]
+struct PtrComponents<T: Pointee + ?Sized> {
+    data_address: *const (),
+    metadata: <T as Pointee>::Metadata,
+}
+
+pub trait Pointee {
+   type Metadata;
+}
+
+fn main() {}

src/test/ui/union/normalization-failure-issue-81199-autofix.stderr

@@ -0,0 +1,19 @@
+error[E0277]: the trait bound `T: Pointee` is not satisfied
+  --> $DIR/normalization-failure-issue-81199-autofix.rs:7:40
+   |
+LL |     components: std::mem::ManuallyDrop<PtrComponents<T>>,
+   |                                        ^^^^^^^^^^^^^^^^ the trait `Pointee` is not implemented for `T`
+   |
+note: required by a bound in `PtrComponents`
+  --> $DIR/normalization-failure-issue-81199-autofix.rs:12:25
+   |
+LL | struct PtrComponents<T: Pointee + ?Sized> {
+   |                         ^^^^^^^ required by this bound in `PtrComponents`
+help: consider further restricting this bound
+   |
+LL | union PtrRepr<T: ?Sized + Pointee> {
+   |                         +++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/union/normalization-failure-issue-81199-min.rs

@@ -0,0 +1,12 @@
+union PtrRepr<T: ?Sized> {
+    const_ptr: *const T,
+    mut_ptr: *mut T,
+    components: <T as Pointee>::Metadata
+    //~^ ERROR the trait bound `T: Pointee` is not satisfied
+}
+
+pub trait Pointee {
+   type Metadata;
+}
+
+fn main() {}

src/test/ui/union/normalization-failure-issue-81199-min.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the trait bound `T: Pointee` is not satisfied
+  --> $DIR/normalization-failure-issue-81199-min.rs:4:17
+   |
+LL |     components: <T as Pointee>::Metadata
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Pointee` is not implemented for `T`
+   |
+help: consider further restricting this bound
+   |
+LL | union PtrRepr<T: ?Sized + Pointee> {
+   |                         +++++++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/union/normalization-failure-issue-81199.rs

@@ -0,0 +1,19 @@
+#[repr(C)]
+union PtrRepr<T: ?Sized> {
+    const_ptr: *const T,
+    mut_ptr: *mut T,
+    components: PtrComponents<T>,
+    //~^ ERROR the trait bound `T: Pointee` is not satisfied in `PtrComponents<T>`
+}
+
+#[repr(C)]
+struct PtrComponents<T: Pointee + ?Sized> {
+    data_address: *const (),
+    metadata: <T as Pointee>::Metadata,
+}
+
+pub trait Pointee {
+   type Metadata;
+}
+
+fn main() {}

src/test/ui/union/normalization-failure-issue-81199.stderr

@@ -0,0 +1,29 @@
+error[E0277]: the trait bound `T: Pointee` is not satisfied in `PtrComponents<T>`
+  --> $DIR/normalization-failure-issue-81199.rs:5:17
+   |
+LL |     components: PtrComponents<T>,
+   |                 ^^^^^^^^^^^^^^^^ within `PtrComponents<T>`, the trait `Pointee` is not implemented for `T`
+   |
+note: required because it appears within the type `PtrComponents<T>`
+  --> $DIR/normalization-failure-issue-81199.rs:10:8
+   |
+LL | struct PtrComponents<T: Pointee + ?Sized> {
+   |        ^^^^^^^^^^^^^
+   = 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: consider further restricting this bound
+   |
+LL | union PtrRepr<T: ?Sized + Pointee> {
+   |                         +++++++++
+help: borrowed types always have a statically known size
+   |
+LL |     components: &PtrComponents<T>,
+   |                 +
+help: the `Box` type always has a statically known size and allocates its contents in the heap
+   |
+LL |     components: Box<PtrComponents<T>>,
+   |                 ++++                +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.