Fix #14643, #10965, #11704: false positive: unreadVariable for constructors with unknown side effects (#8420)

Author: ludviggunne

lib/checkunusedvar.cpp

@@ -1359,6 +1359,14 @@ void CheckUnusedVar::checkFunctionVariableUsage()
             if (tok->previous() && tok->previous()->variable() && tok->previous()->variable()->nameToken()->scope()->type == ScopeType::eUnion)
                 continue;
 
+            if (expr->valueType() &&
+                expr->valueType()->type == ValueType::RECORD &&
+                !expr->valueType()->pointer &&
+                expr->valueType()->typeScope &&
+                expr->valueType()->typeScope->definedType &&
+                !symbolDatabase->isRecordTypeWithoutSideEffects(expr->valueType()->typeScope->definedType))
+                continue;
+
             FwdAnalysis fwdAnalysis(*mSettings);
             const Token* scopeEnd = ValueFlow::getEndOfExprScope(expr, scope, /*smallest*/ false);
             if (fwdAnalysis.unusedValue(expr, start, scopeEnd)) {

test/testunusedvar.cpp

@@ -6681,6 +6681,34 @@ class TestUnusedVar : public TestFixture {
                               "    C c(12);\n"
                               "}");
         ASSERT_EQUALS("", errout_str());
+
+        // #14643
+        functionVariableUsage("class S { S(int); };\n"
+                              "void f() { S s = 0; }\n");
+        ASSERT_EQUALS("", errout_str());
+
+        // #10965
+        functionVariableUsage("class A {\n"
+                              "public:\n"
+                              "    A();\n"
+                              "};\n"
+                              "extern A cb();\n"
+                              "void f() { const A c = cb(); }\n");
+        ASSERT_EQUALS("", errout_str());
+
+        // #11704
+        functionVariableUsage("class S {\n"
+                              "public:\n"
+                              "    S();\n"
+                              "};\n"
+                              "class C {\n"
+                              "    S &s();\n"
+                              "    void f() {\n"
+                              "        const S s1 = s(); // warning\n"
+                              "        const S s2; // no warning\n"
+                              "    }\n"
+                              "};\n");
+        ASSERT_EQUALS("", errout_str());
     }
 
     void localVarSmartPtr() {