Rollup merge of #68586 - Centril:repr-deny, r=pnkfelix

Make conflicting_repr_hints a deny-by-default c-future-compat lint

Closes https://github.com/rust-lang/rust/issues/68428.
cc https://github.com/rust-lang/rust/issues/68585.

r? @petrochenkov @pnkfelix

src/librustc/hir/check_attr.rs

@@ -14,7 +14,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::DUMMY_HIR_ID;
 use rustc_hir::{self, HirId, Item, ItemKind, TraitItem, TraitItemKind};
-use rustc_session::lint::builtin::UNUSED_ATTRIBUTES;
+use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 use syntax::ast::Attribute;
@@ -196,7 +196,7 @@ impl CheckAttrVisitor<'tcx> {
             self.tcx.codegen_fn_attrs(self.tcx.hir().local_def_id(hir_id));
         }
 
-        self.check_repr(attrs, span, target, item);
+        self.check_repr(attrs, span, target, item, hir_id);
         self.check_used(attrs, target);
     }
 
@@ -357,6 +357,7 @@ impl CheckAttrVisitor<'tcx> {
         span: &Span,
         target: Target,
         item: Option<&Item<'_>>,
+        hir_id: HirId,
     ) {
         // Extract the names of all repr hints, e.g., [foo, bar, align] for:
         // ```
@@ -446,12 +447,14 @@ impl CheckAttrVisitor<'tcx> {
             || (is_simd && is_c)
             || (int_reprs == 1 && is_c && item.map_or(false, |item| is_c_like_enum(item)))
         {
-            struct_span_err!(
-                self.tcx.sess,
+            self.tcx
+                .struct_span_lint_hir(
+                    CONFLICTING_REPR_HINTS,
+                    hir_id,
                     hint_spans.collect::<Vec<Span>>(),
-                E0566,
                     "conflicting representation hints",
                 )
+                .code(rustc_errors::error_code!(E0566))
                 .emit();
         }
     }

src/librustc_session/lint/builtin.rs

@@ -18,6 +18,16 @@ declare_lint! {
     };
 }
 
+declare_lint! {
+    pub CONFLICTING_REPR_HINTS,
+    Deny,
+    "conflicts between `#[repr(..)]` hints that were previously accepted and used in practice",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #68585 <https://github.com/rust-lang/rust/issues/68585>",
+        edition: None,
+    };
+}
+
 declare_lint! {
     pub META_VARIABLE_MISUSE,
     Allow,
@@ -520,6 +530,7 @@ declare_lint_pass! {
         MACRO_USE_EXTERN_CRATE,
         MACRO_EXPANDED_MACRO_EXPORTS_ACCESSED_BY_ABSOLUTE_PATHS,
         ILL_FORMED_ATTRIBUTE_INPUT,
+        CONFLICTING_REPR_HINTS,
         META_VARIABLE_MISUSE,
         DEPRECATED_IN_FUTURE,
         AMBIGUOUS_ASSOCIATED_ITEMS,

src/test/ui/conflicting-repr-hints.rs

@@ -11,11 +11,13 @@ enum B {
 }
 
 #[repr(C, u64)] //~ ERROR conflicting representation hints
+//~^ WARN this was previously accepted
 enum C {
     C,
 }
 
 #[repr(u32, u64)] //~ ERROR conflicting representation hints
+//~^ WARN this was previously accepted
 enum D {
     D,
 }

src/test/ui/conflicting-repr-hints.stderr

@@ -3,45 +3,52 @@ error[E0566]: conflicting representation hints
    |
 LL | #[repr(C, u64)]
    |        ^  ^^^
+   |
+   = note: `#[deny(conflicting_repr_hints)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
 
 error[E0566]: conflicting representation hints
-  --> $DIR/conflicting-repr-hints.rs:18:8
+  --> $DIR/conflicting-repr-hints.rs:19:8
    |
 LL | #[repr(u32, u64)]
    |        ^^^  ^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
 
 error[E0587]: type has conflicting packed and align representation hints
-  --> $DIR/conflicting-repr-hints.rs:27:1
+  --> $DIR/conflicting-repr-hints.rs:29:1
    |
 LL | struct F(i32);
    | ^^^^^^^^^^^^^^
 
 error[E0587]: type has conflicting packed and align representation hints
-  --> $DIR/conflicting-repr-hints.rs:31:1
+  --> $DIR/conflicting-repr-hints.rs:33:1
    |
 LL | struct G(i32);
    | ^^^^^^^^^^^^^^
 
 error[E0587]: type has conflicting packed and align representation hints
-  --> $DIR/conflicting-repr-hints.rs:35:1
+  --> $DIR/conflicting-repr-hints.rs:37:1
    |
 LL | struct H(i32);
    | ^^^^^^^^^^^^^^
 
 error[E0634]: type has conflicting packed representation hints
-  --> $DIR/conflicting-repr-hints.rs:38:1
+  --> $DIR/conflicting-repr-hints.rs:40:1
    |
 LL | struct I(i32);
    | ^^^^^^^^^^^^^^
 
 error[E0634]: type has conflicting packed representation hints
-  --> $DIR/conflicting-repr-hints.rs:42:1
+  --> $DIR/conflicting-repr-hints.rs:44:1
    |
 LL | struct J(i32);
    | ^^^^^^^^^^^^^^
 
 error[E0587]: type has conflicting packed and align representation hints
-  --> $DIR/conflicting-repr-hints.rs:48:1
+  --> $DIR/conflicting-repr-hints.rs:50:1
    |
 LL | / union X {
 LL | |
@@ -50,7 +57,7 @@ LL | | }
    | |_^
 
 error[E0587]: type has conflicting packed and align representation hints
-  --> $DIR/conflicting-repr-hints.rs:55:1
+  --> $DIR/conflicting-repr-hints.rs:57:1
    |
 LL | / union Y {
 LL | |
@@ -59,7 +66,7 @@ LL | | }
    | |_^
 
 error[E0587]: type has conflicting packed and align representation hints
-  --> $DIR/conflicting-repr-hints.rs:62:1
+  --> $DIR/conflicting-repr-hints.rs:64:1
    |
 LL | / union Z {
 LL | |

src/test/ui/feature-gates/feature-gate-repr-simd.rs

@@ -2,6 +2,7 @@
 struct Foo(u64, u64);
 
 #[repr(C)] //~ ERROR conflicting representation hints
+//~^ WARN this was previously accepted
 #[repr(simd)] //~ error: SIMD types are experimental
 struct Bar(u64, u64);
 

src/test/ui/feature-gates/feature-gate-repr-simd.stderr

@@ -8,7 +8,7 @@ LL | #[repr(simd)]
    = help: add `#![feature(repr_simd)]` to the crate attributes to enable
 
 error[E0658]: SIMD types are experimental and possibly buggy
-  --> $DIR/feature-gate-repr-simd.rs:5:1
+  --> $DIR/feature-gate-repr-simd.rs:6:1
    |
 LL | #[repr(simd)]
    | ^^^^^^^^^^^^^
@@ -21,8 +21,13 @@ error[E0566]: conflicting representation hints
    |
 LL | #[repr(C)]
    |        ^
+LL |
 LL | #[repr(simd)]
    |        ^^^^
+   |
+   = note: `#[deny(conflicting_repr_hints)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
 
 error: aborting due to 3 previous errors
 

src/test/ui/issues/issue-47094.rs

@@ -1,10 +1,12 @@
 #[repr(C, u8)] //~ ERROR conflicting representation hints
+//~^ WARN this was previously accepted
 enum Foo {
     A,
     B,
 }
 
 #[repr(C)] //~ ERROR conflicting representation hints
+//~^ WARN this was previously accepted
 #[repr(u8)]
 enum Bar {
     A,

src/test/ui/issues/issue-47094.stderr

@@ -3,14 +3,22 @@ error[E0566]: conflicting representation hints
    |
 LL | #[repr(C, u8)]
    |        ^  ^^
+   |
+   = note: `#[deny(conflicting_repr_hints)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
 
 error[E0566]: conflicting representation hints
-  --> $DIR/issue-47094.rs:7:8
+  --> $DIR/issue-47094.rs:8:8
    |
 LL | #[repr(C)]
    |        ^
+LL |
 LL | #[repr(u8)]
    |        ^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #68585 <https://github.com/rust-lang/rust/issues/68585>
 
 error: aborting due to 2 previous errors