E0379: Make diagnostic more precise

13 files changed, 31 insertions, 20 deletions

diff --git a/compiler/rustc_ast_passes/messages.ftl b/compiler/rustc_ast_passes/messages.ftl
index b5612c1820d..b7274db029f 100644
--- a/compiler/rustc_ast_passes/messages.ftl
+++ b/compiler/rustc_ast_passes/messages.ftl
@@ -233,8 +233,14 @@ ast_passes_tilde_const_disallowed = `~const` is not allowed here
     .item = this item cannot have `~const` trait bounds
 
 ast_passes_trait_fn_const =
-    functions in traits cannot be declared const
-    .label = functions in traits cannot be const
+    functions in {$in_impl ->
+        [true] trait impls
+        *[false] traits
+    } cannot be declared const
+    .label = functions in {$in_impl ->
+        [true] trait impls
+        *[false] traits
+    } cannot be const
 
 ast_passes_trait_object_single_bound = only a single explicit lifetime bound is permitted
 
diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index bc5cf463f12..39ea684087e 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -293,7 +293,7 @@ impl<'a> AstValidator<'a> {
 
     fn check_trait_fn_not_const(&self, constness: Const) {
         if let Const::Yes(span) = constness {
-            self.dcx().emit_err(errors::TraitFnConst { span });
+            self.dcx().emit_err(errors::TraitFnConst { span, in_impl: self.in_trait_impl });
         }
     }
 
diff --git a/compiler/rustc_ast_passes/src/errors.rs b/compiler/rustc_ast_passes/src/errors.rs
index 0cec4374be2..ebaa7ccecc9 100644
--- a/compiler/rustc_ast_passes/src/errors.rs
+++ b/compiler/rustc_ast_passes/src/errors.rs
@@ -49,6 +49,7 @@ pub struct TraitFnConst {
     #[primary_span]
     #[label]
     pub span: Span,
+    pub in_impl: bool,
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_error_codes/src/error_codes/E0379.md b/compiler/rustc_error_codes/src/error_codes/E0379.md
index ab438e41447..35f546cfdb7 100644
--- a/compiler/rustc_error_codes/src/error_codes/E0379.md
+++ b/compiler/rustc_error_codes/src/error_codes/E0379.md
@@ -6,6 +6,10 @@ Erroneous code example:
 trait Foo {
     const fn bar() -> u32; // error!
 }
+
+impl Foo for () {
+    const fn bar() -> u32 { 0 } // error!
+}
 ```
 
 Trait methods cannot be declared `const` by design. For more information, see
diff --git a/tests/ui/consts/const-fn-mismatch.rs b/tests/ui/consts/const-fn-mismatch.rs
index 3107b8128e6..b17e4cedd3f 100644
--- a/tests/ui/consts/const-fn-mismatch.rs
+++ b/tests/ui/consts/const-fn-mismatch.rs
@@ -9,7 +9,7 @@ trait Foo {
 
 impl Foo for u32 {
     const fn f() -> u32 {
-        //~^ ERROR functions in traits cannot be declared const
+        //~^ ERROR functions in trait impls cannot be declared const
         22
     }
 }
diff --git a/tests/ui/consts/const-fn-mismatch.stderr b/tests/ui/consts/const-fn-mismatch.stderr
index beaf52c0cfb..7d681c212b9 100644
--- a/tests/ui/consts/const-fn-mismatch.stderr
+++ b/tests/ui/consts/const-fn-mismatch.stderr
@@ -1,8 +1,8 @@
-error[E0379]: functions in traits cannot be declared const
+error[E0379]: functions in trait impls cannot be declared const
   --> $DIR/const-fn-mismatch.rs:11:5
    |
 LL |     const fn f() -> u32 {
-   |     ^^^^^ functions in traits cannot be const
+   |     ^^^^^ functions in trait impls cannot be const
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/feature-gates/feature-gate-min_const_fn.rs b/tests/ui/feature-gates/feature-gate-min_const_fn.rs
index 8f9b433009d..3d61a9eb937 100644
--- a/tests/ui/feature-gates/feature-gate-min_const_fn.rs
+++ b/tests/ui/feature-gates/feature-gate-min_const_fn.rs
@@ -8,7 +8,7 @@ trait Foo {
 }
 
 impl Foo for u32 {
-    const fn foo() -> u32 { 0 } //~ ERROR functions in traits cannot be declared const
+    const fn foo() -> u32 { 0 } //~ ERROR functions in trait impls cannot be declared const
 }
 
 trait Bar {}
diff --git a/tests/ui/feature-gates/feature-gate-min_const_fn.stderr b/tests/ui/feature-gates/feature-gate-min_const_fn.stderr
index d7a58591364..abc9ddabd51 100644
--- a/tests/ui/feature-gates/feature-gate-min_const_fn.stderr
+++ b/tests/ui/feature-gates/feature-gate-min_const_fn.stderr
@@ -10,11 +10,11 @@ error[E0379]: functions in traits cannot be declared const
 LL |     const fn bar() -> u32 { 0 }
    |     ^^^^^ functions in traits cannot be const
 
-error[E0379]: functions in traits cannot be declared const
+error[E0379]: functions in trait impls cannot be declared const
   --> $DIR/feature-gate-min_const_fn.rs:11:5
    |
 LL |     const fn foo() -> u32 { 0 }
-   |     ^^^^^ functions in traits cannot be const
+   |     ^^^^^ functions in trait impls cannot be const
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/mismatched_types/const-fn-in-trait.stderr b/tests/ui/mismatched_types/const-fn-in-trait.stderr
index 7d1fbe45c53..75122237bf5 100644
--- a/tests/ui/mismatched_types/const-fn-in-trait.stderr
+++ b/tests/ui/mismatched_types/const-fn-in-trait.stderr
@@ -4,11 +4,11 @@ error[E0379]: functions in traits cannot be declared const
 LL |     const fn g();
    |     ^^^^^ functions in traits cannot be const
 
-error[E0379]: functions in traits cannot be declared const
+error[E0379]: functions in trait impls cannot be declared const
   --> $DIR/const-fn-in-trait.rs:7:5
    |
 LL |     const fn f() -> u32 { 22 }
-   |     ^^^^^ functions in traits cannot be const
+   |     ^^^^^ functions in trait impls cannot be const
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/parser/fn-header-semantic-fail.rs b/tests/ui/parser/fn-header-semantic-fail.rs
index f8b58cad7c1..f01e1c2277c 100644
--- a/tests/ui/parser/fn-header-semantic-fail.rs
+++ b/tests/ui/parser/fn-header-semantic-fail.rs
@@ -26,10 +26,10 @@ fn main() {
     impl X for Y {
         async fn ft1() {} // OK.
         unsafe fn ft2() {} // OK.
-        const fn ft3() {} //~ ERROR functions in traits cannot be declared const
+        const fn ft3() {} //~ ERROR functions in trait impls cannot be declared const
         extern "C" fn ft4() {}
         const async unsafe extern "C" fn ft5() {}
-        //~^ ERROR functions in traits cannot be declared const
+        //~^ ERROR functions in trait impls cannot be declared const
         //~| ERROR functions cannot be both `const` and `async`
     }
 
diff --git a/tests/ui/parser/fn-header-semantic-fail.stderr b/tests/ui/parser/fn-header-semantic-fail.stderr
index cdf01e0c5df..1f280424cf3 100644
--- a/tests/ui/parser/fn-header-semantic-fail.stderr
+++ b/tests/ui/parser/fn-header-semantic-fail.stderr
@@ -28,17 +28,17 @@ LL |         const async unsafe extern "C" fn ft5();
    |         |     `async` because of this
    |         `const` because of this
 
-error[E0379]: functions in traits cannot be declared const
+error[E0379]: functions in trait impls cannot be declared const
   --> $DIR/fn-header-semantic-fail.rs:29:9
    |
 LL |         const fn ft3() {}
-   |         ^^^^^ functions in traits cannot be const
+   |         ^^^^^ functions in trait impls cannot be const
 
-error[E0379]: functions in traits cannot be declared const
+error[E0379]: functions in trait impls cannot be declared const
   --> $DIR/fn-header-semantic-fail.rs:31:9
    |
 LL |         const async unsafe extern "C" fn ft5() {}
-   |         ^^^^^ functions in traits cannot be const
+   |         ^^^^^ functions in trait impls cannot be const
 
 error: functions cannot be both `const` and `async`
   --> $DIR/fn-header-semantic-fail.rs:31:9
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.rs b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.rs
index 40e8bfdcc17..0d1c926fef5 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.rs
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.rs
@@ -7,7 +7,7 @@ trait Trait {
 }
 
 impl const Trait for () {
-    const fn fun() {}  //~ ERROR functions in traits cannot be declared const
+    const fn fun() {}  //~ ERROR functions in trait impls cannot be declared const
 }
 
 fn main() {}
diff --git a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.stderr b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.stderr
index 09fe580ae5c..cf8a2772d89 100644
--- a/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.stderr
+++ b/tests/ui/rfcs/rfc-2632-const-trait-impl/effects/trait-fn-const.stderr
@@ -4,11 +4,11 @@ error[E0379]: functions in traits cannot be declared const
 LL |     const fn fun();
    |     ^^^^^ functions in traits cannot be const
 
-error[E0379]: functions in traits cannot be declared const
+error[E0379]: functions in trait impls cannot be declared const
   --> $DIR/trait-fn-const.rs:10:5
    |
 LL |     const fn fun() {}
-   |     ^^^^^ functions in traits cannot be const
+   |     ^^^^^ functions in trait impls cannot be const
 
 error: aborting due to 2 previous errors