Merge #1040

1040: Do not propagate parse errors in match repetitions r=CohenArthur a=CohenArthur

Since parsing repetitions is very eager, the parser might accumulate
bogus errors by trying to match more repetitions than there are. We can
avoid this by clearing the parsing errors if parsing repetitions
returned a valid result. This should not be an issue for previous
matchers erroring out, as they would immediately return upon failure and
not reach inside other match functions.

We need to figure out the best way to emit parser errors, as we do not always want to emit them in `match_fragment`. I think for now the easiest is to just *not* emit parse errors and simply error out with "failed to match macro rule". We will need to think about adding a bunch of hints too in order to make using macros easier.

Fixes #958 

Co-authored-by: Arthur Cohen <arthur.cohen@embecosm.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/gcc/rust/expand/rust-macro-expand.cc b/gcc/rust/expand/rust-macro-expand.cc
index 3bdb8c6..6b26f98 100644
--- a/gcc/rust/expand/rust-macro-expand.cc
+++ b/gcc/rust/expand/rust-macro-expand.cc
@@ -505,9 +505,6 @@ MacroExpander::match_fragment (Parser<MacroInvocLexer> &parser,
       return false;
     }
 
-  for (const auto &error : parser.get_errors ())
-    error.emit_error ();
-
   // it matches if the parser did not produce errors trying to parse that type
   // of item
   return !parser.has_errors ();
@@ -714,7 +711,13 @@ MacroExpander::match_n_matches (Parser<MacroInvocLexer> &parser,
   bool did_meet_lo_bound = match_amount >= lo_bound;
   bool did_meet_hi_bound = hi_bound ? match_amount <= hi_bound : true;
 
-  return did_meet_lo_bound && did_meet_hi_bound;
+  // If the end-result is valid, then we can clear the parse errors: Since
+  // repetitions are parsed eagerly, it is okay to fail in some cases
+  auto res = did_meet_lo_bound && did_meet_hi_bound;
+  if (res)
+    parser.clear_errors ();
+
+  return res;
 }
 
 bool