Fixed #4168 (False positive: (style) struct or union member 'super::x' is never used)

lib/checkunusedvar.cpp

@@ -1082,6 +1082,18 @@ void CheckUnusedVar::checkStructMemberUsage()
             if (Token::findmatch(tok, s.c_str()))
                 structname.clear();
 
+            // Bail out if instance is initialized with {}..
+            if (!structname.empty()) {
+                const std::string pattern1(structname + " %var% ;");
+                const Token *tok2 = tok;
+                while (NULL != (tok2 = Token::findmatch(tok2->next(), pattern1.c_str()))) {
+                    if (Token::simpleMatch(tok2->tokAt(3), (tok2->strAt(1) + " = {").c_str())) {
+                        structname.clear();
+                        break;
+                    }
+                }
+            }
+
             // Try to prevent false positives when struct members are not used directly.
             if (Token::findmatch(tok, (structname + " *").c_str()))
                 structname.clear();

test/testunusedvar.cpp

@@ -45,6 +45,7 @@ private:
         TEST_CASE(structmember9);  // #2017 - struct is inherited
         TEST_CASE(structmember_extern); // No false positives for extern structs
         TEST_CASE(structmember10);
+        TEST_CASE(structmember11); // #4168 - initialization with {} / passed by address to unknown function
 
         TEST_CASE(localvar1);
         TEST_CASE(localvar2);
@@ -333,6 +334,18 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void structmember11() { // #4168
+        checkStructMemberUsage("struct abc { int x; };\n"
+                               "struct abc s = {0};\n"
+                               "void f() { do_something(&s); }\n");
+        ASSERT_EQUALS("", errout.str());
+
+        checkStructMemberUsage("struct abc { int x; };\n"
+                               "struct abc s = {0};\n"
+                               "void f() { }\n");
+        TODO_ASSERT_EQUALS("abc::x is not used", "", errout.str());
+    }
+
     void structmember_extern() {
         // extern struct => no false positive
         checkStructMemberUsage("extern struct AB\n"