Do not allow safe usafe on static and fn items

Author: spastorino

compiler/rustc_ast_passes/messages.ftl

@@ -167,6 +167,9 @@ ast_passes_invalid_unnamed_field_ty =
     unnamed fields can only have struct or union types
     .label = not a struct or union
 
+ast_passes_item_invalid_safety = items cannot be declared with `safe` safety qualifier
+    .suggestion = remove safe to this item
+
 ast_passes_item_underscore = `{$kind}` items in this context need a name
     .label = `_` is not a valid name for this `{$kind}` item
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -456,6 +456,12 @@ impl<'a> AstValidator<'a> {
         }
     }
 
+    fn check_item_safety(&self, span: Span, safety: Safety) {
+        if matches!(safety, Safety::Safe(_)) {
+            self.dcx().emit_err(errors::InvalidSafetyOnItem { span });
+        }
+    }
+
     fn check_foreign_item_safety(&self, item_span: Span, safety: Safety) {
         if matches!(safety, Safety::Unsafe(_) | Safety::Safe(_))
             && (self.extern_mod_safety == Some(Safety::Default)
@@ -1015,6 +1021,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
             }
             ItemKind::Fn(box Fn { defaultness, sig, generics, body }) => {
                 self.check_defaultness(item.span, *defaultness);
+                self.check_item_safety(item.span, sig.header.safety);
 
                 if body.is_none() {
                     self.dcx().emit_err(errors::FnWithoutBody {
@@ -1174,11 +1181,15 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     });
                 }
             }
-            ItemKind::Static(box StaticItem { expr: None, .. }) => {
-                self.dcx().emit_err(errors::StaticWithoutBody {
-                    span: item.span,
-                    replace_span: self.ending_semi_or_hi(item.span),
-                });
+            ItemKind::Static(box StaticItem { expr, safety, .. }) => {
+                self.check_item_safety(item.span, *safety);
+
+                if expr.is_none() {
+                    self.dcx().emit_err(errors::StaticWithoutBody {
+                        span: item.span,
+                        replace_span: self.ending_semi_or_hi(item.span),
+                    });
+                }
             }
             ItemKind::TyAlias(
                 ty_alias @ box TyAlias { defaultness, bounds, where_clauses, ty, .. },

compiler/rustc_ast_passes/src/errors.rs

@@ -225,6 +225,13 @@ pub struct InvalidSafetyOnExtern {
     pub block: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(ast_passes_item_invalid_safety)]
+pub struct InvalidSafetyOnItem {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(ast_passes_bound_in_context)]
 pub struct BoundInContext<'a> {

tests/ui/rust-2024/safe-outside-extern.rs

@@ -0,0 +1,7 @@
+safe fn foo() {}
+//~^ ERROR: items cannot be declared with `safe` safety qualifier
+
+safe static FOO: i32 = 1;
+//~^ ERROR: items cannot be declared with `safe` safety qualifier
+
+fn main() {}

tests/ui/rust-2024/safe-outside-extern.stderr

@@ -0,0 +1,14 @@
+error: items cannot be declared with `safe` safety qualifier
+  --> $DIR/safe-outside-extern.rs:1:1
+   |
+LL | safe fn foo() {}
+   | ^^^^^^^^^^^^^^^^
+
+error: items cannot be declared with `safe` safety qualifier
+  --> $DIR/safe-outside-extern.rs:4:1
+   |
+LL | safe static FOO: i32 = 1;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+