[clang-tidy] TwineLocalCheck: add param # checking

[yawanng]

Summary

The statement getArg tries to get the first one without checking, which may cause segmentation fault.

[yawanng]

Add more tests.

[chh]

LGTM. Leave approval to bkramer.

[bkramer]

looks good, thanks!

clang-tidy/llvm/TwineLocalCheck.cpp

auto Diag = diag(VD->getLocation(),
                    "twine variables are prone to use-after-free bugs");
 
   // If this VarDecl has an initializer try to fix it.
   if (VD->hasInit()) {
     // Peel away implicit constructors and casts so we can see the actual type
     // of the initializer.
     const Expr *C = VD->getInit()->IgnoreImplicit();
 
-    while (isa<CXXConstructExpr>(C))
+    while (isa<CXXConstructExpr>(C)) {
+      if (cast<CXXConstructExpr>(C)->getNumArgs() == 0)
+        break;
       C = cast<CXXConstructExpr>(C)->getArg(0)->IgnoreParenImpCasts();
+    }
 
     SourceRange TypeRange =
         VD->getTypeSourceInfo()->getTypeLoc().getSourceRange();
 
     // A real Twine, turn it into a std::string.
     if (VD->getType()->getCanonicalTypeUnqualified() ==
         C->getType()->getCanonicalTypeUnqualified()) {
       SourceLocation EndLoc = Lexer::getLocForEndOfToken(

test/clang-tidy/llvm-twine-local.cpp

 // RUN: %check_clang_tidy %s llvm-twine-local %t
 
 namespace llvm {
 class Twine {
 public:
   Twine(const char *);
   Twine(int);
+  Twine();
   Twine &operator+(const Twine &);
 };
 }
 
 using namespace llvm;
 
 void foo(const Twine &x);
 
 static Twine Moo = Twine("bark") + "bah";
 // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: twine variables are prone to use-after-free bugs
 // CHECK-MESSAGES: note: FIX-IT applied suggested code changes
 // CHECK-FIXES: static std::string Moo = (Twine("bark") + "bah").str();
 
 int main() {
   const Twine t = Twine("a") + "b" + Twine(42);
 // CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
 // CHECK-MESSAGES: note: FIX-IT applied suggested code changes
 // CHECK-FIXES: std::string t = (Twine("a") + "b" + Twine(42)).str();
   foo(Twine("a") + "b");
 
   Twine Prefix = false ? "__INT_FAST" : "__UINT_FAST";
 // CHECK-MESSAGES: :[[@LINE-1]]:9: warning: twine variables are prone to use-after-free bugs
 // CHECK-MESSAGES: note: FIX-IT applied suggested code changes
 // CHECK-FIXES: const char * Prefix = false ? "__INT_FAST" : "__UINT_FAST";
+
+  const Twine t2 = Twine();
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
+// CHECK-MESSAGES: note: FIX-IT applied suggested code changes
+// CHECK-FIXES: std::string t2 = (Twine()).str();
+  foo(Twine() + "b");
+
+  const Twine t3 = Twine(42);
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
+// CHECK-MESSAGES: note: FIX-IT applied suggested code changes
+// CHECK-FIXES: std::string t3 = (Twine(42)).str();
+
+  const Twine t4 = Twine(42) + "b";
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
+// CHECK-MESSAGES: note: FIX-IT applied suggested code changes
+// CHECK-FIXES: std::string t4 = (Twine(42) + "b").str();
+
+  const Twine t5 = Twine() + "b";
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
+// CHECK-MESSAGES: note: FIX-IT applied suggested code changes
+// CHECK-FIXES: std::string t5 = (Twine() + "b").str();
+
+  const Twine t6 = true ? Twine() : Twine(42);
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
+// CHECK-MESSAGES: note: FIX-IT applied suggested code changes
+// CHECK-FIXES: std::string t6 = (true ? Twine() : Twine(42)).str();
+
+  const Twine t7 = false ? Twine() : Twine("b");
+// CHECK-MESSAGES: :[[@LINE-1]]:15: warning: twine variables are prone to use-after-free bugs
+// CHECK-MESSAGES: note: FIX-IT applied suggested code changes
+// CHECK-FIXES: std::string t7 = (false ? Twine() : Twine("b")).str();
 }