Fixed #5860: Don't show returnTempReference for calculations on unknown types

lib/checkautovariables.cpp

@@ -327,6 +327,34 @@ bool CheckAutoVariables::returnTemporary(const Token *tok) const
 
 //---------------------------------------------------------------------------
 
+static bool astHasAutoResult(const Token *tok)
+{
+    if (tok->astOperand1() && !astHasAutoResult(tok->astOperand1()))
+        return false;
+    if (tok->astOperand2() && !astHasAutoResult(tok->astOperand2()))
+        return false;
+
+    if (tok->isOp())
+        return true;
+
+    if (tok->isLiteral())
+        return true;
+
+    if (tok->isName()) {
+        // TODO: check function calls, struct members, arrays, etc also
+        if (!tok->variable())
+            return false;
+        if (tok->variable()->isStlType() && !Token::Match(tok->astParent(), "<<|>>"))
+            return true;
+        if (tok->variable()->isClass() || tok->variable()->isPointer() || tok->variable()->isReference()) // TODO: Properly handle pointers/references to classes in symbol database
+            return false;
+
+        return true;
+    }
+
+    return false;
+}
+
 void CheckAutoVariables::returnReference()
 {
     const SymbolDatabase *symbolDatabase = _tokenizer->getSymbolDatabase();
@@ -377,7 +405,7 @@ void CheckAutoVariables::returnReference()
                 }
 
                 // Return reference to a literal or the result of a calculation
-                else if (tok2->astOperand1() && (tok2->astOperand1()->isCalculation() || tok2->next()->isLiteral())) {
+                else if (tok2->astOperand1() && (tok2->astOperand1()->isCalculation() || tok2->next()->isLiteral()) && astHasAutoResult(tok2->astOperand1())) {
                     errorReturnTempReference(tok2);
                 }
             }

lib/templatesimplifier.cpp

@@ -254,7 +254,7 @@ unsigned int TemplateSimplifier::templateParameters(const Token *tok)
         // Skip casts
         if (tok->str() == "(") {
             tok = tok->link();
-            if(tok)
+            if (tok)
                 tok = tok->next();
         }
 

test/testautovariables.cpp

@@ -867,6 +867,16 @@ private:
               "}");
         ASSERT_EQUALS("[test.cpp:2]: (error) Reference to temporary returned.\n", errout.str());
 
+        check("std::ostream& operator<<(std::ostream& out, const std::string& path) {\n"
+              "    return out << path;\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check("Unknown1& operator<<(Unknown1 out, Unknown2 path) {\n"
+              "    return out << path;\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
         check("int& a(int b) {\n"
               "    return 2*(b+1);\n"
               "}");