Fix leakNoVarFunctionCall FP (#4523)

Author: chrchr-github

cfg/std.cfg

@@ -4976,7 +4976,7 @@ The obsolete function 'gets' is called. With 'gets' you'll get a buffer overrun
   </function>
   <!-- char *strncpy(char *s, const char *ct, size_t n); -->
   <function name="strncpy,std::strncpy">
-    <returnValue type="char *"/>
+    <returnValue type="char *">arg1</returnValue>
     <noreturn>false</noreturn>
     <leak-ignore/>
     <not-overlapping-data ptr1-arg="1" ptr2-arg="2" size-arg="3"/>

lib/checkmemoryleak.cpp

@@ -997,9 +997,9 @@ void CheckMemoryLeakNoVar::checkForUnreleasedInputArgument(const Scope *scope)
 
         // check if the output of the function is assigned
         const Token* tok2 = tok->next()->astParent();
-        while (tok2 && tok2->isCast())
+        while (tok2 && (tok2->isCast() || Token::Match(tok2, "?|:")))
             tok2 = tok2->astParent();
-        if (Token::Match(tok2, "%assign%"))
+        if (Token::Match(tok2, "%assign%")) // TODO: check if function returns allocated resource
             continue;
         if (Token::simpleMatch(tok->astTop(), "return"))
             continue;

test/testmemleak.cpp

@@ -2446,6 +2446,12 @@ class TestMemleakNoVar : public TestFixture {
               "    u.reset(strcpy(new char[n], s.c_str()));\n"
               "};\n");
         ASSERT_EQUALS("", errout.str());
+
+        check("struct S { char* p; };\n"
+              "void f(S* s, int N) {\n"
+              "    s->p = s->p ? strcpy(new char[N], s->p) : nullptr;\n"
+              "};\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void missingAssignment() {