[clang][Lex] Fix a crash on malformed string literals

Differential Revision: https://reviews.llvm.org/D135161

Author: kadircet

clang/lib/Lex/LiteralSupport.cpp

@@ -545,7 +545,6 @@ static bool ProcessNamedUCNEscape(const char *ThisTokBegin,
            diag::err_delimited_escape_missing_brace)
           << StringRef(&ThisTokBuf[-1], 1);
     }
-    ThisTokBuf++;
     return false;
   }
   ThisTokBuf++;

clang/test/Lexer/char-escapes-delimited.c

@@ -94,7 +94,7 @@ void named(void) {
 
   unsigned h = U'\N{LOTUS}';                      // ext-warning {{extension}} cxx2b-warning {{C++2b}}
   unsigned i = u'\N{GREEK CAPITAL LETTER DELTA}'; // ext-warning {{extension}} cxx2b-warning {{C++2b}}
-  char j = '\NN';                                 // expected-error {{expected '{' after '\N' escape sequence}}
+  char j = '\NN';                                 // expected-error {{expected '{' after '\N' escape sequence}} expected-warning {{multi-character character constant}}
   unsigned k = u'\N{LOTUS';                       // expected-error {{incomplete universal character name}}
 }
 

clang/unittests/Lex/LexerTest.cpp

@@ -18,6 +18,7 @@
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/HeaderSearchOptions.h"
+#include "clang/Lex/LiteralSupport.h"
 #include "clang/Lex/MacroArgs.h"
 #include "clang/Lex/MacroInfo.h"
 #include "clang/Lex/ModuleLoader.h"
@@ -659,4 +660,11 @@ TEST_F(LexerTest, RawAndNormalLexSameForLineComments) {
   }
   EXPECT_TRUE(ToksView.empty());
 }
+
+TEST_F(LexerTest, BrokenStringLiteral) {
+  const llvm::StringLiteral Source = R"cpp("\N")cpp";
+  // Make sure this isn't crashing.
+  StringLiteralParser P(Lex(Source), *PP);
+  EXPECT_TRUE(P.hadError);
+}
 } // anonymous namespace