Include macro name in 'local ambiguity' error

compiler/rustc_expand/src/lib.rs

@@ -1,6 +1,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]
 #![feature(destructuring_assignment)]
+#![feature(format_args_capture)]
 #![feature(iter_zip)]
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_internals)]

compiler/rustc_expand/src/mbe/macro_parser.rs

@@ -85,6 +85,7 @@ use smallvec::{smallvec, SmallVec};
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::Lrc;
+use rustc_span::symbol::Ident;
 use std::borrow::Cow;
 use std::collections::hash_map::Entry::{Occupied, Vacant};
 use std::mem;
@@ -615,7 +616,11 @@ fn inner_parse_loop<'root, 'tt>(
 
 /// Use the given sequence of token trees (`ms`) as a matcher. Match the token
 /// stream from the given `parser` against it and return the match.
-pub(super) fn parse_tt(parser: &mut Cow<'_, Parser<'_>>, ms: &[TokenTree]) -> NamedParseResult {
+pub(super) fn parse_tt(
+    parser: &mut Cow<'_, Parser<'_>>,
+    ms: &[TokenTree],
+    macro_name: Ident,
+) -> NamedParseResult {
     // A queue of possible matcher positions. We initialize it with the matcher position in which
     // the "dot" is before the first token of the first token tree in `ms`. `inner_parse_loop` then
     // processes all of these possible matcher positions and produces possible next positions into
@@ -711,7 +716,7 @@ pub(super) fn parse_tt(parser: &mut Cow<'_, Parser<'_>>, ms: &[TokenTree]) -> Na
             return Error(
                 parser.token.span,
                 format!(
-                    "local ambiguity: multiple parsing options: {}",
+                    "local ambiguity when calling macro `{macro_name}`: multiple parsing options: {}",
                     match next_items.len() {
                         0 => format!("built-in NTs {}.", nts),
                         1 => format!("built-in NTs {} or 1 other option.", nts),

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -245,7 +245,7 @@ fn generic_extension<'cx>(
         // are not recorded. On the first `Success(..)`ful matcher, the spans are merged.
         let mut gated_spans_snapshot = mem::take(&mut *sess.gated_spans.spans.borrow_mut());
 
-        match parse_tt(&mut Cow::Borrowed(&parser), lhs_tt) {
+        match parse_tt(&mut Cow::Borrowed(&parser), lhs_tt, name) {
             Success(named_matches) => {
                 // The matcher was `Success(..)`ful.
                 // Merge the gated spans from parsing the matcher with the pre-existing ones.
@@ -338,7 +338,7 @@ fn generic_extension<'cx>(
                 _ => continue,
             };
             if let Success(_) =
-                parse_tt(&mut Cow::Borrowed(&parser_from_cx(sess, arg.clone())), lhs_tt)
+                parse_tt(&mut Cow::Borrowed(&parser_from_cx(sess, arg.clone())), lhs_tt, name)
             {
                 if comma_span.is_dummy() {
                     err.note("you might be missing a comma");
@@ -432,7 +432,7 @@ pub fn compile_declarative_macro(
     ];
 
     let parser = Parser::new(&sess.parse_sess, body, true, rustc_parse::MACRO_ARGUMENTS);
-    let argument_map = match parse_tt(&mut Cow::Borrowed(&parser), &argument_gram) {
+    let argument_map = match parse_tt(&mut Cow::Borrowed(&parser), &argument_gram, def.ident) {
         Success(m) => m,
         Failure(token, msg) => {
             let s = parse_failure_msg(&token);

src/test/ui/macros/local-ambiguity-multiple-parsing-options.stderr

@@ -1,10 +1,10 @@
-error: local ambiguity: multiple parsing options: built-in NTs ident ('i') or ident ('j').
+error: local ambiguity when calling macro `ambiguity`: multiple parsing options: built-in NTs ident ('i') or ident ('j').
   --> $DIR/local-ambiguity-multiple-parsing-options.rs:7:12
    |
 LL | ambiguity!(error);
    |            ^^^^^
 
-error: local ambiguity: multiple parsing options: built-in NTs ident ('i') or ident ('j').
+error: local ambiguity when calling macro `ambiguity`: multiple parsing options: built-in NTs ident ('i') or ident ('j').
   --> $DIR/local-ambiguity-multiple-parsing-options.rs:8:12
    |
 LL | ambiguity!(error);