stash API: remove panic to fix ICE.

src/librustc_errors/lib.rs

@@ -444,22 +444,12 @@ impl Handler {
     }
 
     /// Stash a given diagnostic with the given `Span` and `StashKey` as the key for later stealing.
-    /// If the diagnostic with this `(span, key)` already exists, this will result in an ICE.
     pub fn stash_diagnostic(&self, span: Span, key: StashKey, diag: Diagnostic) {
         let mut inner = self.inner.borrow_mut();
-        if let Some(mut old_diag) = inner.stashed_diagnostics.insert((span, key), diag) {
-            // We are removing a previously stashed diagnostic which should not happen.
-            old_diag.level = Bug;
-            old_diag.note(&format!(
-                "{}:{}: already existing stashed diagnostic with (span = {:?}, key = {:?})",
-                file!(),
-                line!(),
-                span,
-                key
-            ));
-            inner.emit_diag_at_span(old_diag, span);
-            panic!(ExplicitBug);
-        }
+        // FIXME(Centril, #69537): Consider reintroducing panic on overwriting a stashed diagnostic
+        // if/when we have a more robust macro-friendly replacement for `(span, key)` as a key.
+        // See the PR for a discussion.
+        inner.stashed_diagnostics.insert((span, key), diag);
     }
 
     /// Steal a previously stashed diagnostic with the given `Span` and `StashKey` as the key.

src/test/ui/issues/issue-69396-const-no-type-in-macro.rs

@@ -0,0 +1,17 @@
+macro_rules! suite {
+    ( $( $fn:ident; )* ) => {
+        $(
+            const A = "A".$fn();
+            //~^ ERROR the name `A` is defined multiple times
+            //~| ERROR missing type for `const` item
+            //~| ERROR the type placeholder `_` is not allowed within types
+        )*
+    }
+}
+
+suite! {
+    len;
+    is_empty;
+}
+
+fn main() {}

src/test/ui/issues/issue-69396-const-no-type-in-macro.stderr

@@ -0,0 +1,53 @@
+error[E0428]: the name `A` is defined multiple times
+  --> $DIR/issue-69396-const-no-type-in-macro.rs:4:13
+   |
+LL |               const A = "A".$fn();
+   |               ^^^^^^^^^^^^^^^^^^^^
+   |               |
+   |               `A` redefined here
+   |               previous definition of the value `A` here
+...
+LL | / suite! {
+LL | |     len;
+LL | |     is_empty;
+LL | | }
+   | |_- in this macro invocation
+   |
+   = note: `A` must be defined only once in the value namespace of this module
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: missing type for `const` item
+  --> $DIR/issue-69396-const-no-type-in-macro.rs:4:19
+   |
+LL |               const A = "A".$fn();
+   |                     ^ help: provide a type for the item: `A: usize`
+...
+LL | / suite! {
+LL | |     len;
+LL | |     is_empty;
+LL | | }
+   | |_- in this macro invocation
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/issue-69396-const-no-type-in-macro.rs:4:19
+   |
+LL |               const A = "A".$fn();
+   |                     ^
+   |                     |
+   |                     not allowed in type signatures
+   |                     help: replace `_` with the correct type: `bool`
+...
+LL | / suite! {
+LL | |     len;
+LL | |     is_empty;
+LL | | }
+   | |_- in this macro invocation
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0121, E0428.
+For more information about an error, try `rustc --explain E0121`.