Auto merge of rust-lang#117818 - fmease:properly-reject-defaultness-on-free-consts, r=cjgillot

Properly reject `default` on free const items

Fixes rust-lang#117791.

Technically speaking, this is a breaking change but I doubt it will lead to any real-world regressions (maybe in some macro-trickery crates?). Doing a crater run probably isn't worth it.

Author: bors

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1028,12 +1028,14 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     _ => {}
                 }
             }
-            ItemKind::Const(box ConstItem { defaultness, expr: None, .. }) => {
+            ItemKind::Const(box ConstItem { defaultness, expr, .. }) => {
                 self.check_defaultness(item.span, *defaultness);
-                self.session.emit_err(errors::ConstWithoutBody {
-                    span: item.span,
-                    replace_span: self.ending_semi_or_hi(item.span),
-                });
+                if expr.is_none() {
+                    self.session.emit_err(errors::ConstWithoutBody {
+                        span: item.span,
+                        replace_span: self.ending_semi_or_hi(item.span),
+                    });
+                }
             }
             ItemKind::Static(box StaticItem { expr: None, .. }) => {
                 self.session.emit_err(errors::StaticWithoutBody {

tests/ui/parser/trait-item-with-defaultness-fail-semantic.rs renamed to tests/ui/parser/defaultness-invalid-places-fail-semantic.rs

@@ -10,3 +10,7 @@ trait X {
     default fn f1(); //~ ERROR `default` is only allowed on items in trait impls
     default fn f2() {} //~ ERROR `default` is only allowed on items in trait impls
 }
+
+default const E: u8 = 0; //~ ERROR `default` is only allowed on items in trait impls
+default type F = (); //~ ERROR `default` is only allowed on items in trait impls
+default fn h() {} //~ ERROR `default` is only allowed on items in trait impls

tests/ui/parser/trait-item-with-defaultness-fail-semantic.stderr renamed to tests/ui/parser/defaultness-invalid-places-fail-semantic.stderr

@@ -1,53 +1,77 @@
 error: `default` is only allowed on items in trait impls
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:6:5
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:6:5
    |
 LL |     default const A: u8;
    |     -------^^^^^^^^^^^^^
    |     |
    |     `default` because of this
 
 error: `default` is only allowed on items in trait impls
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:7:5
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:7:5
    |
 LL |     default const B: u8 = 0;
    |     -------^^^^^^^^^^^^^^^^^
    |     |
    |     `default` because of this
 
 error: `default` is only allowed on items in trait impls
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:8:5
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:8:5
    |
 LL |     default type D;
    |     -------^^^^^^^^
    |     |
    |     `default` because of this
 
 error: `default` is only allowed on items in trait impls
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:9:5
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:9:5
    |
 LL |     default type C: Ord;
    |     -------^^^^^^^^^^^^^
    |     |
    |     `default` because of this
 
 error: `default` is only allowed on items in trait impls
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:10:5
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:10:5
    |
 LL |     default fn f1();
    |     -------^^^^^^^^^
    |     |
    |     `default` because of this
 
 error: `default` is only allowed on items in trait impls
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:11:5
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:11:5
    |
 LL |     default fn f2() {}
    |     -------^^^^^^^^
    |     |
    |     `default` because of this
 
+error: `default` is only allowed on items in trait impls
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:14:1
+   |
+LL | default const E: u8 = 0;
+   | -------^^^^^^^^^^^^^^^^^
+   | |
+   | `default` because of this
+
+error: `default` is only allowed on items in trait impls
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:15:1
+   |
+LL | default type F = ();
+   | -------^^^^^^^^^^^^^
+   | |
+   | `default` because of this
+
+error: `default` is only allowed on items in trait impls
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:16:1
+   |
+LL | default fn h() {}
+   | -------^^^^^^^
+   | |
+   | `default` because of this
+
 warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/trait-item-with-defaultness-fail-semantic.rs:1:12
+  --> $DIR/defaultness-invalid-places-fail-semantic.rs:1:12
    |
 LL | #![feature(specialization)]
    |            ^^^^^^^^^^^^^^
@@ -56,5 +80,5 @@ LL | #![feature(specialization)]
    = help: consider using `min_specialization` instead, which is more stable and complete
    = note: `#[warn(incomplete_features)]` on by default
 
-error: aborting due to 6 previous errors; 1 warning emitted
+error: aborting due to 9 previous errors; 1 warning emitted