fix #13107: FP unusedStructMember with structured binding (#7177)

Author: ludviggunne

lib/checkunusedvar.cpp

@@ -1534,6 +1534,40 @@ void CheckUnusedVar::checkStructMemberUsage()
         if (bailout)
             continue;
 
+        // Bailout if struct is used in structured binding
+        for (const Variable *var : symbolDatabase->variableList()) {
+            if (!var || !Token::Match(var->typeStartToken(), "auto &|&&| [ %varid%", var->declarationId()))
+                continue;
+
+            const Token *tok = var->nameToken()->linkAt(-1);
+            if (Token::Match(tok, "] %assign%"))
+            {
+                tok = tok->next()->astOperand2();
+                const ValueType *valueType = tok->valueType();
+
+                if (valueType && valueType->typeScope == &scope) {
+                    bailout = true;
+                    break;
+                }
+            }
+
+            if (Token::simpleMatch(tok, "] :")) {
+                tok = tok->next()->astOperand2();
+                const ValueType *valueType = tok->valueType();
+
+                if (!valueType->containerTypeToken)
+                    continue;
+
+                const Type *type = valueType->containerTypeToken->type();
+                if (type && type->classScope == &scope) {
+                    bailout = true;
+                    break;
+                }
+            }
+        }
+        if (bailout)
+            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

@@ -74,6 +74,7 @@ class TestUnusedVar : public TestFixture {
         TEST_CASE(structmember27); // #13367
         TEST_CASE(structmember_macro);
         TEST_CASE(classmember);
+        TEST_CASE(structmemberStructuredBinding); // #13107
 
         TEST_CASE(localvar1);
         TEST_CASE(localvar2);
@@ -2024,6 +2025,30 @@ class TestUnusedVar : public TestFixture {
         ASSERT_EQUALS("", errout_str());
     }
 
+    void structmemberStructuredBinding() { // #13107
+        checkStructMemberUsage("struct S { int a, b; };\n"
+                               "void f(S &s) {\n"
+                               "    auto& [x, y] = s;\n"
+                               "    x = y;\n"
+                               "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        checkStructMemberUsage("struct S { int a, b; };\n"
+                               "struct T { S s; };\n"
+                               "void f(T &t) {\n"
+                               "    auto& [x, y] = t.s;\n"
+                               "    x = y;\n"
+                               "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        checkStructMemberUsage("struct S { int a, b; };\n"
+                               "void f(std::vector<S> &sv) {\n"
+                               "    for (auto& [x, y] : sv)\n"
+                               "        x = y;\n"
+                               "}\n");
+        ASSERT_EQUALS("", errout_str());
+    }
+
     void functionVariableUsage_(const char* file, int line, const char code[], bool cpp = true) {
         // Tokenize..
         SimpleTokenizer tokenizer(settings, *this);