test: regression test for #118179

check for `{type error}` being leaked in user-facing messages,
particularly when using the `adt_const_params` feature

Author: onkoe

tests/ui/generic-const-items/wfcheck_err_leak_issue_118179.rs

@@ -0,0 +1,7 @@
+//! Regression test for #118179: `adt_const_params` feature shouldn't leak
+//! `{type error}` in error messages.
+
+struct G<T, const N: Vec<T>>(T);
+//~^ ERROR the type of const parameters must not depend on other generic parameters
+
+fn main() {}

tests/ui/generic-const-items/wfcheck_err_leak_issue_118179.stderr

@@ -0,0 +1,11 @@
+error[E0770]: the type of const parameters must not depend on other generic parameters
+  --> $DIR/wfcheck_err_leak_issue_118179.rs:4:26
+   |
+LL | struct G<T, const N: Vec<T>>(T);
+   |                          ^ the type must not depend on the parameter `T`
+   |
+   = note: type parameters may not be used in the type of const parameters
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0770`.