[analyzer] Fix a crash in SyntaxCString checker when given a custom strncat.

Fixes PR13476

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179228 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 7 insertions, 0 deletions

diff --git a/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp b/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
index 3a57a56aea..92c0eef3e8 100644
--- a/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/CStringSyntaxChecker.cpp
@@ -101,6 +101,8 @@ public:
 //   - strncat(dst, src, sizeof(dst) - 1);
 //   - strncat(dst, src, sizeof(dst));
 bool WalkAST::containsBadStrncatPattern(const CallExpr *CE) {
+  if (CE->getNumArgs() != 3)
+    return false;
   const Expr *DstArg = CE->getArg(0);
   const Expr *SrcArg = CE->getArg(1);
   const Expr *LenArg = CE->getArg(2);
diff --git a/test/Analysis/cstring-syntax-cxx.cpp b/test/Analysis/cstring-syntax-cxx.cpp
index bae3d0a164..39c978ab60 100644
--- a/test/Analysis/cstring-syntax-cxx.cpp
+++ b/test/Analysis/cstring-syntax-cxx.cpp
@@ -15,3 +15,8 @@ void test(X a, X b) {
   X c = a + b;
 }
 
+// Ensure we don't crash on custom-defined strncat.
+char strncat ();
+int main () {
+  return strncat ();
+}
\ No newline at end of file