Fix #14005 FP: returnDanglingLifetime while returning reference to struct field (danmar#7661)

Co-authored-by: chrchr-github <noreply@github.com>

Author: chrchr-github

lib/valueflow.cpp

@@ -3166,6 +3166,14 @@ static void valueFlowLifetime(TokenList &tokenlist, ErrorLogger &errorLogger, co
         else if (tok->isUnaryOp("&")) {
             if (Token::simpleMatch(tok->astParent(), "*"))
                 continue;
+            if (Token::simpleMatch(tok->astOperand1(), "[")) {
+                const Token* const op1 = tok->astOperand1()->astOperand1();
+                const Token* tok2 = op1;
+                while (Token::simpleMatch(tok2, "."))
+                    tok2 = tok2->astOperand2();
+                if (tok2 && tok2 != op1 && (!tok2->variable() || !tok2->variable()->isArray()) && !(tok2->valueType() && tok2->valueType()->container))
+                    continue;
+            }
             for (const ValueFlow::LifetimeToken& lt : ValueFlow::getLifetimeTokens(tok->astOperand1(), settings)) {
                 if (!settings.certainty.isEnabled(Certainty::inconclusive) && lt.inconclusive)
                     continue;

test/testautovariables.cpp

@@ -78,6 +78,7 @@ class TestAutoVariables : public TestFixture {
         TEST_CASE(testautovar_return3);
         TEST_CASE(testautovar_return4);
         TEST_CASE(testautovar_return5);
+        TEST_CASE(testautovar_return6);
         TEST_CASE(testautovar_extern);
         TEST_CASE(testautovar_reassigned);
         TEST_CASE(testinvaliddealloc);
@@ -624,6 +625,26 @@ class TestAutoVariables : public TestFixture {
         ASSERT_EQUALS("", errout_str());
     }
 
+    void testautovar_return6() { // #14005
+        check("struct S;\n"
+              "struct T { const struct S *s; };\n"
+              "extern struct T factory();\n"
+              "const struct S* f() {\n"
+              "    struct T t = factory();\n"
+              "    return &t.s[0];\n"
+              "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        check("struct S;\n"
+              "struct T { std::vector<struct S> v; };\n"
+              "extern struct T factory();\n"
+              "const struct S* f() {\n"
+              "    struct T t = factory();\n"
+              "    return &t.v[0];\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:6:12] -> [test.cpp:5:14] -> [test.cpp:6:12]: (error) Returning pointer to local variable 't' that will be invalid when returning. [returnDanglingLifetime]\n", errout_str());
+    }
+
     void testautovar_extern() {
         check("struct foo *f()\n"
               "{\n"