make "invalid fragment specifier" translatable

Author: tshepang

compiler/rustc_expand/messages.ftl

@@ -61,6 +61,11 @@ expand_invalid_cfg_multiple_predicates = multiple `cfg` predicates are specified
 expand_invalid_cfg_no_parens = `cfg` is not followed by parentheses
 expand_invalid_cfg_no_predicate = `cfg` predicate is not specified
 expand_invalid_cfg_predicate_literal = `cfg` predicate key cannot be a literal
+
+expand_invalid_fragment_specifier =
+    invalid fragment specifier `{$name}`
+    .help = {$help}
+
 expand_macro_body_stability =
     macros cannot have body stability attributes
     .label = invalid body stability attribute

compiler/rustc_expand/src/errors.rs

@@ -408,3 +408,13 @@ pub struct DuplicateMatcherBinding {
     #[label(expand_label2)]
     pub prev: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(expand_invalid_fragment_specifier)]
+#[help]
+pub struct InvalidFragmentSpecifier {
+    #[primary_span]
+    pub span: Span,
+    pub name: String,
+    pub help: String,
+}

compiler/rustc_expand/src/mbe/quoted.rs

@@ -1,3 +1,4 @@
+use crate::errors;
 use crate::mbe::macro_parser::count_metavar_decls;
 use crate::mbe::{Delimited, KleeneOp, KleeneToken, MetaVarExpr, SequenceRepetition, TokenTree};
 
@@ -81,14 +82,13 @@ pub(super) fn parse(
                                         })
                                         .unwrap_or_else(
                                             || {
-                                                let msg = format!(
-                                                    "invalid fragment specifier `{}`",
-                                                    frag.name
+                                                sess.dcx().emit_err(
+                                                    errors::InvalidFragmentSpecifier {
+                                                        span,
+                                                        name: frag.name.to_string(),
+                                                        help: VALID_FRAGMENT_NAMES_MSG.into(),
+                                                    },
                                                 );
-                                                sess.dcx()
-                                                    .struct_span_err(span, msg)
-                                                    .with_help(VALID_FRAGMENT_NAMES_MSG)
-                                                    .emit();
                                                 token::NonterminalKind::Ident
                                             },
                                         );