Fix diagnostic suggests adding type [type error]

Fixes #79040

Unresolved questions:

Why does this change output the diagnostic twice?

Why does the CI fail when the errors are pointed out (UI tests)?

Author: henryboisdequin

compiler/rustc_typeck/src/collect/type_of.rs

@@ -659,7 +659,7 @@ fn infer_placeholder_type(
                 format!("{}: {}", item_ident, ty),
                 Applicability::MachineApplicable,
             )
-            .emit();
+            .emit_unless(matches!(ty.kind(), ty::Error(_)));
         }
         None => {
             let mut diag = bad_placeholder_type(tcx, vec![span]);

src/test/ui/79040.rs

@@ -0,0 +1,5 @@
+fn main() {
+    const FOO = "hello" + 1;
+    //^~ ERROR cannot add `{integer}` to `&str`
+    println!("{}", FOO);
+}

src/test/ui/79040.stderr

@@ -0,0 +1,19 @@
+error[E0369]: cannot add `{integer}` to `&str`
+  --> $DIR/79040.rs:2:25
+   |
+LL |     const FOO = "hello" + 1;
+   |                 ------- ^ - {integer}
+   |                 |
+   |                 &str
+
+error[E0369]: cannot add `{integer}` to `&str`
+  --> $DIR/79040.rs:2:25
+   |
+LL |     const FOO = "hello" + 1;
+   |                 ------- ^ - {integer}
+   |                 |
+   |                 &str
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0369`.

src/test/ui/parser/item-free-const-no-body-semantic-fail.stderr

@@ -14,11 +14,5 @@ LL | const B;
    |        |
    |        help: provide a definition for the constant: `= <expr>;`
 
-error: missing type for `const` item
-  --> $DIR/item-free-const-no-body-semantic-fail.rs:6:7
-   |
-LL | const B;
-   |       ^ help: provide a type for the item: `B: [type error]`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

src/test/ui/parser/item-free-static-no-body-semantic-fail.stderr

@@ -30,17 +30,5 @@ LL | static mut D;
    |             |
    |             help: provide a definition for the static: `= <expr>;`
 
-error: missing type for `static` item
-  --> $DIR/item-free-static-no-body-semantic-fail.rs:6:8
-   |
-LL | static B;
-   |        ^ help: provide a type for the item: `B: [type error]`
-
-error: missing type for `static mut` item
-  --> $DIR/item-free-static-no-body-semantic-fail.rs:10:12
-   |
-LL | static mut D;
-   |            ^ help: provide a type for the item: `D: [type error]`
-
-error: aborting due to 6 previous errors
+error: aborting due to 4 previous errors