Fix ICE when passing DefId-creating args to legacy_const_generics.

compiler/rustc_ast_lowering/src/errors.rs

@@ -451,3 +451,26 @@ pub(crate) struct YieldInClosure {
     #[suggestion(code = "#[coroutine] ", applicability = "maybe-incorrect", style = "verbose")]
     pub suggestion: Option<Span>,
 }
+
+#[derive(Diagnostic)]
+#[diag(ast_lowering_invalid_legacy_const_generic_arg)]
+pub(crate) struct InvalidLegacyConstGenericArg {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub suggestion: UseConstGenericArg,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(
+    ast_lowering_invalid_legacy_const_generic_arg_suggestion,
+    applicability = "maybe-incorrect"
+)]
+pub(crate) struct UseConstGenericArg {
+    #[suggestion_part(code = "::<{const_args}>")]
+    pub end_of_fn: Span,
+    pub const_args: String,
+    pub other_args: String,
+    #[suggestion_part(code = "{other_args}")]
+    pub call_args: Span,
+}