Rollup merge of rust-lang#97780 - compiler-errors:field-wfcheck-before-sized, r=jackh726

Check ADT field is well-formed before checking it is sized

Fixes rust-lang#96810.

There is one diagnostics regression, in [`src/test/ui/generic-associated-types/bugs/issue-80626.stderr`](https://github.com/rust-lang/rust/pull/97780/files#diff-53795946378e78a0af23a10277c628ff79091c18090fdc385801ee70c1ba6963). I am not super concerned about it, since it's GAT related.
We _could_ fix it, possibly by using the `FieldSized` obligation cause code instead of `BuiltinDerivedObligation`. But that would require changing `Sized` trait confirmation and the `adt_sized_constraint` query.

Author: matthiaskrgr

compiler/rustc_middle/src/traits/mod.rs

@@ -406,7 +406,7 @@ pub enum ObligationCauseCode<'tcx> {
     QuestionMark,
 
     /// Well-formed checking. If a `WellFormedLoc` is provided,
-    /// then it will be used to eprform HIR-based wf checking
+    /// then it will be used to perform HIR-based wf checking
     /// after an error occurs, in order to generate a more precise error span.
     /// This is purely for diagnostic purposes - it is always
     /// correct to use `MiscObligation` instead, or to specify

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -990,6 +990,15 @@ fn check_type_defn<'tcx, F>(
         let packed = tcx.adt_def(item.def_id).repr().packed();
 
         for variant in &variants {
+            // All field types must be well-formed.
+            for field in &variant.fields {
+                fcx.register_wf_obligation(
+                    field.ty.into(),
+                    field.span,
+                    ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(field.def_id))),
+                )
+            }
+
             // For DST, or when drop needs to copy things around, all
             // intermediate types must be sized.
             let needs_drop_copy = || {
@@ -1006,6 +1015,7 @@ fn check_type_defn<'tcx, F>(
                     }
                 }
             };
+            // All fields (except for possibly the last) should be sized.
             let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
             let unsized_len = if all_sized { 0 } else { 1 };
             for (idx, field) in
@@ -1030,15 +1040,6 @@ fn check_type_defn<'tcx, F>(
                 );
             }
 
-            // All field types must be well-formed.
-            for field in &variant.fields {
-                fcx.register_wf_obligation(
-                    field.ty.into(),
-                    field.span,
-                    ObligationCauseCode::WellFormed(Some(WellFormedLoc::Ty(field.def_id))),
-                )
-            }
-
             // Explicit `enum` discriminant values must const-evaluate successfully.
             if let Some(discr_def_id) = variant.explicit_discr {
                 let discr_substs = InternalSubsts::identity_for_item(tcx, discr_def_id.to_def_id());

src/test/ui/generic-associated-types/bugs/issue-80626.stderr

@@ -4,16 +4,11 @@ error[E0275]: overflow evaluating the requirement `LinkedList<A>: Sized`
 LL |     Next(A::Allocated<Self>)
    |          ^^^^^^^^^^^^^^^^^^
    |
-   = note: no field of an enum variant 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
+note: required by a bound in `Allocator::Allocated`
+  --> $DIR/issue-80626.rs:9:20
    |
-LL |     Next(&A::Allocated<Self>)
-   |          +
-help: the `Box` type always has a statically known size and allocates its contents in the heap
-   |
-LL |     Next(Box<A::Allocated<Self>>)
-   |          ++++                  +
+LL |     type Allocated<T>;
+   |                    ^ required by this bound in `Allocator::Allocated`
 
 error: aborting due to previous error
 

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

@@ -1,28 +1,18 @@
-error[E0277]: the trait bound `T: Pointee` is not satisfied in `PtrComponents<T>`
+error[E0277]: the trait bound `T: Pointee` is not satisfied
   --> $DIR/issue-81199.rs:5:17
    |
 LL |     components: PtrComponents<T>,
-   |                 ^^^^^^^^^^^^^^^^ within `PtrComponents<T>`, the trait `Pointee` is not implemented for `T`
+   |                 ^^^^^^^^^^^^^^^^ the trait `Pointee` is not implemented for `T`
    |
-note: required because it appears within the type `PtrComponents<T>`
-  --> $DIR/issue-81199.rs:10:8
+note: required by a bound in `PtrComponents`
+  --> $DIR/issue-81199.rs:10:25
    |
 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
+   |                         ^^^^^^^ required by this bound in `PtrComponents`
 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
 

src/test/ui/wf/issue-96810.rs

@@ -0,0 +1,12 @@
+struct S<T: Tr>(T::Assoc);
+
+trait Tr {
+    type Assoc;
+}
+
+struct Hoge<K> {
+    s: S<K>, //~ ERROR the trait bound `K: Tr` is not satisfied
+    a: u32,
+}
+
+fn main() {}

src/test/ui/wf/issue-96810.stderr

@@ -0,0 +1,19 @@
+error[E0277]: the trait bound `K: Tr` is not satisfied
+  --> $DIR/issue-96810.rs:8:8
+   |
+LL |     s: S<K>,
+   |        ^^^^ the trait `Tr` is not implemented for `K`
+   |
+note: required by a bound in `S`
+  --> $DIR/issue-96810.rs:1:13
+   |
+LL | struct S<T: Tr>(T::Assoc);
+   |             ^^ required by this bound in `S`
+help: consider restricting type parameter `K`
+   |
+LL | struct Hoge<K: Tr> {
+   |              ++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.