Fix #14098 FN nullPointer constructing std::string from known function result (regression) (danmar#8141)

Author: chrchr-github

lib/checknullpointer.cpp

@@ -223,10 +223,10 @@ bool CheckNullPointer::isPointerDeRef(const Token *tok, bool &unknown, const Set
         return true;
 
     // std::string dereferences nullpointers
-    if (Token::Match(parent->tokAt(-3), "std :: string|wstring (|{ %name% )|}"))
+    if (Token::Match(parent->tokAt(-3), "std :: string|wstring (|{"))
         return true;
-    if (Token::Match(parent->previous(), "%name% (|{ %name% )|}")) {
-        const Variable* var = tok->tokAt(-2)->variable();
+    if (Token::Match(parent->previous(), "%name% (|{")) {
+        const Variable* var = parent->previous()->variable();
         if (var && !var->isPointer() && !var->isArray() && var->isStlStringType())
             return true;
     }

test/testnullpointer.cpp

@@ -3944,6 +3944,15 @@ class TestNullPointer : public TestFixture {
               "void f() { std::string s = g(0L); }\n");
         ASSERT_EQUALS("[test.cpp:2:29]: (error) Null pointer dereference: g(0L) [nullPointer]\n",
                       errout_str());
+
+        check("const char* g() { return nullptr; }\n" // #14098
+              "std::string f() {\n"
+              "    std::string s{ g() };\n"
+              "    return s + std::string(g());\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:3:21]: (error) Null pointer dereference: g() [nullPointer]\n"
+                      "[test.cpp:4:29]: (error) Null pointer dereference: g() [nullPointer]\n",
+                      errout_str());
     }
 
     void nullpointerStdStream() {