clang-format: Prevent exponential runtime in token annotator.

llvm-svn: 236577

clang/lib/Format/TokenAnnotator.cpp

@@ -15,6 +15,7 @@
 
 #include "TokenAnnotator.h"
 #include "clang/Basic/SourceManager.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/Debug.h"
 
 #define DEBUG_TYPE "format-token-annotator"
@@ -495,13 +496,15 @@ private:
         return false;
       break;
     case tok::less:
-      if ((!Tok->Previous ||
+      if (!NonTemplateLess.count(Tok) &&
+          (!Tok->Previous ||
            (!Tok->Previous->Tok.isLiteral() &&
             !(Tok->Previous->is(tok::r_paren) && Contexts.size() > 1))) &&
           parseAngle()) {
         Tok->Type = TT_TemplateOpener;
       } else {
         Tok->Type = TT_BinaryOperator;
+        NonTemplateLess.insert(Tok);
         CurrentToken = Tok;
         next();
       }
@@ -648,6 +651,7 @@ private:
 
 public:
   LineType parseLine() {
+    NonTemplateLess.clear();
     if (CurrentToken->is(tok::hash))
       return parsePreprocessorDirective();
 
@@ -1160,6 +1164,12 @@ private:
   FormatToken *CurrentToken;
   bool AutoFound;
   const AdditionalKeywords &Keywords;
+
+  // Set of "<" tokens that do not open a template parameter list. If parseAngle
+  // determines that a specific token can't be a template opener, it will make
+  // same decision irrespective of the decisions for tokens leading up to it.
+  // Store this information to prevent this from causing exponential runtime.
+  llvm::SmallPtrSet<FormatToken *, 16> NonTemplateLess;
 };
 
 static const int PrecedenceUnaryOperator = prec::PointerToMember + 1;

clang/unittests/Format/FormatTest.cpp

@@ -5155,6 +5155,7 @@ TEST_F(FormatTest, UnderstandsTemplateParameters) {
                getLLVMStyleWithColumns(60));
   verifyFormat("static_assert(is_convertible<A &&, B>::value, \"AAA\");");
   verifyFormat("Constructor(A... a) : a_(X<A>{std::forward<A>(a)}...) {}");
+  verifyFormat("< < < < < < < < < < < < < < < < < < < < < < < < < < < < < <");
 }
 
 TEST_F(FormatTest, UnderstandsBinaryOperators) {