1 files changed, 39 insertions, 10 deletions
diff --git a/flang/lib/Parser/token-sequence.cpp b/flang/lib/Parser/token-sequence.cpp
index 3ed9d05..55217a9 100644
--- a/flang/lib/Parser/token-sequence.cpp
+++ b/flang/lib/Parser/token-sequence.cpp
@@ -27,6 +27,8 @@ void TokenSequence::clear() {
 }
 
 void TokenSequence::pop_back() {
+  CHECK(!start_.empty());
+  CHECK(nextStart_ > start_.back());
   std::size_t bytes{nextStart_ - start_.back()};
   nextStart_ = start_.back();
   start_.pop_back();
@@ -82,16 +84,6 @@ bool TokenSequence::IsAnythingLeft(std::size_t at) const {
   return false;
 }
 
-void TokenSequence::RemoveLastToken() {
-  CHECK(!start_.empty());
-  CHECK(nextStart_ > start_.back());
-  std::size_t bytes{nextStart_ - start_.back()};
-  nextStart_ = start_.back();
-  start_.pop_back();
-  char_.erase(char_.begin() + nextStart_, char_.end());
-  provenances_.RemoveLastBytes(bytes);
-}
-
 void TokenSequence::Put(const TokenSequence &that) {
   if (nextStart_ < char_.size()) {
     start_.push_back(nextStart_);
@@ -338,4 +330,41 @@ const TokenSequence &TokenSequence::CheckBadFortranCharacters(
   }
   return *this;
 }
+
+const TokenSequence &TokenSequence::CheckBadParentheses(
+    Messages &messages) const {
+  // First, a quick pass with no allocation for the common case
+  int nesting{0};
+  std::size_t tokens{SizeInTokens()};
+  for (std::size_t j{0}; j < tokens; ++j) {
+    CharBlock token{TokenAt(j)};
+    char ch{token.FirstNonBlank()};
+    if (ch == '(') {
+      ++nesting;
+    } else if (ch == ')') {
+      --nesting;
+    }
+  }
+  if (nesting != 0) {
+    // There's an error; diagnose it
+    std::vector<std::size_t> stack;
+    for (std::size_t j{0}; j < tokens; ++j) {
+      CharBlock token{TokenAt(j)};
+      char ch{token.FirstNonBlank()};
+      if (ch == '(') {
+        stack.push_back(j);
+      } else if (ch == ')') {
+        if (stack.empty()) {
+          messages.Say(GetTokenProvenanceRange(j), "Unmatched ')'"_err_en_US);
+          return *this;
+        }
+        stack.pop_back();
+      }
+    }
+    CHECK(!stack.empty());
+    messages.Say(
+        GetTokenProvenanceRange(stack.back()), "Unmatched '('"_err_en_US);
+  }
+  return *this;
+}
 } // namespace Fortran::parser