Fix danmar#7458 (FP unusedStructMember with struct in union) (danmar#7844)

Author: danmar

lib/checkunusedvar.cpp

@@ -1599,6 +1599,23 @@ void CheckUnusedVar::checkStructMemberUsage()
         if (bailout)
             continue;
 
+        // #7458 - if struct is declared inside union and any struct member is used,
+        // then don't warn about other struct members
+        if (scope.type == ScopeType::eStruct && scope.nestedIn && scope.nestedIn->type == ScopeType::eUnion) {
+            bool structMemberUsed = false;
+
+            for (const Token *tok = scope.nestedIn->bodyStart; tok; tok = tok->next()) {
+                if (tok->variable() && tok != tok->variable()->nameToken() && tok->variable()->scope() == &scope) {
+                    structMemberUsed = true;
+                    break;
+                }
+            }
+
+            // Skip reporting unused members if this struct is in a union and any member is used
+            if (structMemberUsed)
+                continue;
+        }
+
         for (const Variable &var : scope.varlist) {
             // only warn for variables without side effects
             if (!var.typeStartToken()->isStandardType() && !var.isPointer() && !astIsContainer(var.nameToken()) && !isRecordTypeWithoutSideEffects(var.type()))

test/testunusedvar.cpp

@@ -1411,6 +1411,22 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("[test.cpp:3:9]: (style) union member 'abc::a' is never used. [unusedStructMember]\n"
                       "[test.cpp:4:9]: (style) union member 'abc::b' is never used. [unusedStructMember]\n"
                       "[test.cpp:5:9]: (style) union member 'abc::c' is never used. [unusedStructMember]\n", errout_str());
+
+        // #7458 - union with anonymous struct should not cause false positive
+        checkStructMemberUsage("union DoubleInt {\n"
+                               "    double asDouble;\n"
+                               "    uint64_t asInt;\n"
+                               "    struct {\n"
+                               "        uint32_t lo, hi;\n" // <- no FP about lo because hi is used
+                               "    } asIntel;\n"
+                               "};\n"
+                               "void f() {\n"
+                               "    union DoubleInt di;\n"
+                               "    di.asIntel.hi = 3;\n"
+                               "}");
+        ASSERT_EQUALS("[test.cpp:2:12]: (style) union member 'DoubleInt::asDouble' is never used. [unusedStructMember]\n"
+                      "[test.cpp:3:14]: (style) union member 'DoubleInt::asInt' is never used. [unusedStructMember]\n",
+                      errout_str());
     }
 
     void structmember2() {