Fix FN unusedStructMember with member functions, inheritance (#4978)

* Fix #551 Detect unused Private member variables

* Fix FN unusedStructMember when there are member functions

* Unused member

* Warn for unused private variables in base class

* Warn for private inheritance, add test

lib/checkstl.cpp

@@ -919,7 +919,7 @@ struct InvalidContainerAnalyzer {
             const Token* ftok;
         };
         std::unordered_map<int, Reference> expressions;
-        ErrorPath errorPath;
+
         void add(const std::vector<Reference>& refs) {
             for (const Reference& r : refs) {
                 add(r);

lib/checkunusedvar.cpp

@@ -1455,25 +1455,20 @@ void CheckUnusedVar::checkStructMemberUsage()
                 continue;
         }
 
-        // Bail out if struct/union contains any functions
-        if (!scope.functionList.empty())
-            continue;
-
         // Bail out for template struct, members might be used in non-matching instantiations
         if (scope.className.find('<') != std::string::npos)
             continue;
 
         // bail out if struct is inherited
-        bool bailout = std::any_of(symbolDatabase->scopeList.cbegin(), symbolDatabase->scopeList.cend(), [&](const Scope& derivedScope) {
+        const bool isInherited = std::any_of(symbolDatabase->scopeList.cbegin(), symbolDatabase->scopeList.cend(), [&](const Scope& derivedScope) {
             const Type* dType = derivedScope.definedType;
             return dType && std::any_of(dType->derivedFrom.cbegin(), dType->derivedFrom.cend(), [&](const Type::BaseInfo& derivedFrom) {
-                return derivedFrom.type == scope.definedType;
+                return derivedFrom.type == scope.definedType && derivedFrom.access != AccessControl::Private;
             });
         });
-        if (bailout)
-            continue;
 
         // bail out for extern/global struct
+        bool bailout = false;
         for (const Variable* var : symbolDatabase->variableList()) {
             if (var && (var->isExtern() || (var->isGlobal() && !var->isStatic())) && var->typeEndToken()->str() == scope.className) {
                 bailout = true;
@@ -1510,6 +1505,8 @@ void CheckUnusedVar::checkStructMemberUsage()
             // only warn for variables without side effects
             if (!var.typeStartToken()->isStandardType() && !var.isPointer() && !astIsContainer(var.nameToken()) && !isRecordTypeWithoutSideEffects(var.type()))
                 continue;
+            if (isInherited && !var.isPrivate())
+                continue;
 
             // Check if the struct member variable is used anywhere in the file
             bool use = false;

test/testunusedvar.cpp

@@ -1876,6 +1876,34 @@ private:
                                "    int i{};\n"
                                "};\n");
         ASSERT_EQUALS("[test.cpp:2]: (style) class member 'C::i' is never used.\n", errout.str());
+
+        checkStructMemberUsage("class C {\n"
+                               "    int i{}, j{};\n"
+                               "public:\n"
+                               "    int& get() { return i; }\n"
+                               "};\n");
+        ASSERT_EQUALS("[test.cpp:2]: (style) class member 'C::j' is never used.\n", errout.str());
+
+        checkStructMemberUsage("class C {\n"
+                               "private:\n"
+                               "    int i;\n"
+                               "};\n"
+                               "class D : public C {};\n");
+        ASSERT_EQUALS("[test.cpp:3]: (style) class member 'C::i' is never used.\n", errout.str());
+
+        checkStructMemberUsage("class C {\n"
+                               "public:\n"
+                               "    int i;\n"
+                               "};\n"
+                               "class D : C {};\n");
+        ASSERT_EQUALS("[test.cpp:3]: (style) class member 'C::i' is never used.\n", errout.str());
+
+        checkStructMemberUsage("class C {\n"
+                               "public:\n"
+                               "    int i;\n"
+                               "};\n"
+                               "class D : public C {};\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void functionVariableUsage_(const char* file, int line, const char code[], const char filename[] = "test.cpp") {