[clang-tidy] bugprone-string-constructor: Catch string from nullptr.

Summary: Context: https://twitter.com/willkirkby/status/1084219580799741953

Subscribers: xazax.hun, cfe-commits

Differential Revision: https://reviews.llvm.org/D56657

1 files changed, 11 insertions, 0 deletions

diff --git a/clang-tools-extra/test/clang-tidy/bugprone-string-constructor.cpp b/clang-tools-extra/test/clang-tidy/bugprone-string-constructor.cpp
index 51d91305882..3ab4f424087 100644
--- a/clang-tools-extra/test/clang-tidy/bugprone-string-constructor.cpp
+++ b/clang-tools-extra/test/clang-tidy/bugprone-string-constructor.cpp
@@ -9,6 +9,7 @@ template <typename C, typename T = std::char_traits<C>, typename A = std::alloca
 struct basic_string {
   basic_string();
   basic_string(const C*, unsigned int size);
+  basic_string(const C *, const A &allocator = A());
   basic_string(unsigned int size, C c);
 };
 typedef basic_string<char> string;
@@ -45,6 +46,15 @@ void Test() {
   // CHECK-MESSAGES: [[@LINE-1]]:15: warning: length is bigger then string literal size
   std::string q5(kText3,  0x1000000);
   // CHECK-MESSAGES: [[@LINE-1]]:15: warning: suspicious large length parameter
+  std::string q6(nullptr);
+  // CHECK-MESSAGES: [[@LINE-1]]:15: warning: constructing string from nullptr is undefined behaviour
+  std::string q7 = 0;
+  // CHECK-MESSAGES: [[@LINE-1]]:20: warning: constructing string from nullptr is undefined behaviour
+}
+
+std::string StringFromZero() {
+  return 0;
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: constructing string from nullptr is undefined behaviour
 }
 
 void Valid() {
@@ -53,4 +63,5 @@ void Valid() {
   std::wstring wstr(4, L'x');
   std::string s1("test", 4);
   std::string s2("test", 3);
+  std::string s3("test");
 }