rustc_expand: make diagnostic translatable

Author: Xiretza

compiler/rustc_expand/messages.ftl

@@ -10,6 +10,10 @@ expand_attribute_meta_item =
 expand_attribute_single_word =
     attribute must only be a single word
 
+expand_attributes_on_expressions_experimental =
+    attributes on expressions are experimental
+    .help_outer_doc = `///` is for documentation comments. For a plain comment, use `//`.
+
 expand_attributes_wrong_form =
     attribute must be of form: `attributes(foo, bar)`
 

compiler/rustc_expand/src/config.rs

@@ -383,11 +383,11 @@ impl<'a> StripUnconfigured<'a> {
                 &self.sess,
                 sym::stmt_expr_attributes,
                 attr.span,
-                "attributes on expressions are experimental",
+                crate::fluent_generated::expand_attributes_on_expressions_experimental,
             );
 
             if attr.is_doc_comment() {
-                err.help("`///` is for documentation comments. For a plain comment, use `//`.");
+                err.help(crate::fluent_generated::expand_help_outer_doc);
             }
 
             err.emit();