From a64a5cf77c9685aa623ec69168e7f50324a102b9 Mon Sep 17 00:00:00 2001
From: Arthur Cohen <arthur.cohen@embecosm.com>
Date: Fri, 18 Mar 2022 11:34:39 +0100
Subject: [PATCH] macros: Do not propagate parse errors in match repetitions

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.
---
 gcc/rust/expand/rust-macro-expand.cc  | 11 +++++++----
 gcc/rust/parse/rust-parse.h           |  3 ++-
 gcc/testsuite/rust/compile/macro25.rs |  9 +++++++++
 gcc/testsuite/rust/compile/macro9.rs  |  1 -
 4 files changed, 18 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/rust/compile/macro25.rs

diff --git a/gcc/rust/expand/rust-macro-expand.cc b/gcc/rust/expand/rust-macro-expand.cc
index 3bdb8c685e6..6b26f98dede 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
diff --git a/gcc/rust/parse/rust-parse.h b/gcc/rust/parse/rust-parse.h
index 588061629e9..9a31fb6d625 100644
--- a/gcc/rust/parse/rust-parse.h
+++ b/gcc/rust/parse/rust-parse.h
@@ -649,7 +649,6 @@ private:
   bool done_end_of_file ();
 
   void add_error (Error error) { error_table.push_back (std::move (error)); }
-  void clear_errors () { error_table.clear (); }
 
 public:
   // Construct parser with specified "managed" token source.
@@ -668,6 +667,8 @@ public:
 
   // Returns whether any parsing errors have occurred.
   bool has_errors () const { return !error_table.empty (); }
+  // Remove all parsing errors from the table
+  void clear_errors () { error_table.clear (); }
 
   // Get a reference to the list of errors encountered
   std::vector<Error> &get_errors () { return error_table; }
diff --git a/gcc/testsuite/rust/compile/macro25.rs b/gcc/testsuite/rust/compile/macro25.rs
new file mode 100644
index 00000000000..d92534c0747
--- /dev/null
+++ b/gcc/testsuite/rust/compile/macro25.rs
@@ -0,0 +1,9 @@
+macro_rules! valid {
+    ($($a:literal)* $i:ident) => {{}};
+}
+
+fn main() {
+    valid!(1 one_lit);
+    valid!(identifier_only);
+    valid!(1 2 two_lits);
+}
diff --git a/gcc/testsuite/rust/compile/macro9.rs b/gcc/testsuite/rust/compile/macro9.rs
index a06a093dc30..9a59089b1e4 100644
--- a/gcc/testsuite/rust/compile/macro9.rs
+++ b/gcc/testsuite/rust/compile/macro9.rs
@@ -12,7 +12,6 @@ fn main() -> i32 {
     let b = add!(15);
     let b = add!(15 14); // { dg-error "Failed to match any rule within macro" }
     let b = add!(15, 14,); // { dg-error "Failed to match any rule within macro" }
-                           // { dg-error "found unexpected token" "" { target *-*-* } .-1 }
 
     0
 }