Scalable SIMD tests for disallowing scalable types in types.

Tests to ensure that scalable SIMD types can't exist in
struct, union, enum variants and compound types.

This also changes the well formed checking of types to improve the
error message when scalable SIMD types are included. The previous
implementation would also allow a scalable SIMD type as the last
element within a struct in some cases which we currently don't want to
allow.

compiler/rustc_error_codes/src/error_codes/E0799.md

@@ -0,0 +1,9 @@
+A scalable SIMD type was used in a context where they cannot exist. Scalable
+SIMD types exist in a place that is somewhere between `Sized` and `Unsized`
+therefore have restrictions on the uses. A scalable SIMD type can't exist in any
+of the following:
+
+* Struct
+* Enum variant
+* Union
+* Compound type.

compiler/rustc_error_codes/src/lib.rs

@@ -535,6 +535,7 @@ E0795: 0795,
 E0796: 0796,
 E0797: 0797,
 E0798: 0798,
+E0799: 0799,
         );
     )
 }

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1114,10 +1114,9 @@ fn check_type_defn<'tcx>(
             };
             // 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
-                variant.fields.raw[..variant.fields.len() - unsized_len].iter().enumerate()
-            {
+            let unsized_len =
+                if all_sized { variant.fields.len() } else { variant.fields.len() - 1 };
+            for (idx, field) in variant.fields.raw.iter().enumerate() {
                 let last = idx == variant.fields.len() - 1;
                 let field_id = field.did.expect_local();
                 let hir::FieldDef { ty: hir_ty, .. } =
@@ -1127,28 +1126,45 @@ fn check_type_defn<'tcx>(
                     None,
                     tcx.type_of(field.did).instantiate_identity(),
                 );
-                wfcx.register_bound(
-                    traits::ObligationCause::new(
+                if matches!(ty.kind(), ty::Adt(def, _) if def.repr().scalable()) {
+                    struct_span_code_err!(
+                        tcx.dcx(),
                         hir_ty.span,
-                        wfcx.body_def_id,
-                        traits::FieldSized {
-                            adt_kind: match &item.kind {
-                                ItemKind::Struct(..) => AdtKind::Struct,
-                                ItemKind::Union(..) => AdtKind::Union,
-                                ItemKind::Enum(..) => AdtKind::Enum,
-                                kind => span_bug!(
-                                    item.span,
-                                    "should be wfchecking an ADT, got {kind:?}"
-                                ),
+                        E0799,
+                        "Scalable simd types cannot exist within {}",
+                        match &item.kind {
+                            ItemKind::Struct(..) => "a struct",
+                            ItemKind::Union(..) => "a union",
+                            ItemKind::Enum(..) => "enum variants",
+                            kind =>
+                                span_bug!(item.span, "should be wfchecking an ADT, got {kind:?}"),
+                        }
+                    )
+                    .emit();
+                } else if idx < unsized_len {
+                    wfcx.register_bound(
+                        traits::ObligationCause::new(
+                            hir_ty.span,
+                            wfcx.body_def_id,
+                            traits::FieldSized {
+                                adt_kind: match &item.kind {
+                                    ItemKind::Struct(..) => AdtKind::Struct,
+                                    ItemKind::Union(..) => AdtKind::Union,
+                                    ItemKind::Enum(..) => AdtKind::Enum,
+                                    kind => span_bug!(
+                                        item.span,
+                                        "should be wfchecking an ADT, got {kind:?}"
+                                    ),
+                                },
+                                span: hir_ty.span,
+                                last,
                             },
-                            span: hir_ty.span,
-                            last,
-                        },
-                    ),
-                    wfcx.param_env,
-                    ty,
-                    tcx.require_lang_item(LangItem::Sized, None),
-                );
+                        ),
+                        wfcx.param_env,
+                        ty,
+                        tcx.require_lang_item(LangItem::Sized, None),
+                    );
+                }
             }
 
             // Explicit `enum` discriminant values must const-evaluate successfully.

tests/ui/simd/scalable/disallow-array.rs

@@ -0,0 +1,10 @@
+#![feature(repr_simd, repr_scalable)]
+
+#[repr(simd, scalable(4))]
+pub struct ScalableSimdFloat {
+    _ty: [f32]
+}
+
+fn main() {
+    let x: [ScalableSimdFloat; 2]; //~ ERROR E0277
+}

tests/ui/simd/scalable/disallow-array.stderr

@@ -0,0 +1,17 @@
+error[E0277]: the size for values of type `[f32]` cannot be known at compilation time
+  --> $DIR/disallow-array.rs:9:12
+   |
+LL |     let x: [ScalableSimdFloat; 2];
+   |            ^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: within `ScalableSimdFloat`, the trait `Sized` is not implemented for `[f32]`, which is required by `ScalableSimdFloat: Sized`
+note: required because it appears within the type `ScalableSimdFloat`
+  --> $DIR/disallow-array.rs:4:12
+   |
+LL | pub struct ScalableSimdFloat {
+   |            ^^^^^^^^^^^^^^^^^
+   = note: slice and array elements must have `Sized` type
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/simd/scalable/disallow-enum.rs

@@ -0,0 +1,14 @@
+#![feature(repr_simd, repr_scalable)]
+
+#[repr(simd, scalable(4))]
+pub struct ScalableSimdFloat {
+    _ty: [f32]
+}
+
+pub enum Invalid {
+    Scalable(ScalableSimdFloat), //~ ERROR E0799
+    Int(i32),
+}
+
+fn main() {
+}

tests/ui/simd/scalable/disallow-enum.stderr

@@ -0,0 +1,9 @@
+error[E0799]: Scalable simd types cannot exist within enum variants
+  --> $DIR/disallow-enum.rs:9:14
+   |
+LL |     Scalable(ScalableSimdFloat),
+   |              ^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0799`.

tests/ui/simd/scalable/disallow-struct.rs

@@ -0,0 +1,17 @@
+#![feature(repr_simd, repr_scalable)]
+
+#[repr(simd, scalable(4))]
+pub struct ScalableSimdFloat {
+    _ty: [f32]
+}
+
+pub struct Invalid {
+    x: ScalableSimdFloat, //~ ERROR E0799
+    last: i32,
+}
+
+#[repr(transparent)]
+struct Wrap(ScalableSimdFloat); //~ ERROR E0799
+
+fn main() {
+}

tests/ui/simd/scalable/disallow-struct.stderr

@@ -0,0 +1,15 @@
+error[E0799]: Scalable simd types cannot exist within a struct
+  --> $DIR/disallow-struct.rs:9:8
+   |
+LL |     x: ScalableSimdFloat,
+   |        ^^^^^^^^^^^^^^^^^
+
+error[E0799]: Scalable simd types cannot exist within a struct
+  --> $DIR/disallow-struct.rs:14:13
+   |
+LL | struct Wrap(ScalableSimdFloat);
+   |             ^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0799`.

tests/ui/simd/scalable/disallow-union.rs

@@ -0,0 +1,14 @@
+#![feature(repr_simd, repr_scalable)]
+
+#[repr(simd, scalable(4))]
+pub struct ScalableSimdFloat {
+    _ty: [f32]
+}
+
+pub union Invalid {
+    x: ScalableSimdFloat, //~ ERROR E0799
+    other: i32,
+}
+
+fn main() {
+}

tests/ui/simd/scalable/disallow-union.stderr

@@ -0,0 +1,9 @@
+error[E0799]: Scalable simd types cannot exist within a union
+  --> $DIR/disallow-union.rs:9:8
+   |
+LL |     x: ScalableSimdFloat,
+   |        ^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0799`.