Fix #9805 (False positive; Unused function (template)) (#2871)

* Add test
* Ignore templates with trailing return type as well

lib/checkunusedfunctions.cpp

@@ -65,13 +65,8 @@ void CheckUnusedFunctions::parseTokens(const Tokenizer &tokenizer, const char Fi
             continue;
 
         // Don't care about templates
-        if (tokenizer.isCPP()) {
+        if (tokenizer.isCPP() && func->templateDef != nullptr)
-            const Token *retDef = func->retDef;
-            while (retDef && retDef->isName())
-                retDef = retDef->previous();
-            if (retDef && retDef->str() == ">")
             continue;
-        }
 
         mFunctionDecl.emplace_back(func);
 

test/testunusedfunctions.cpp

@@ -46,6 +46,7 @@ private:
         TEST_CASE(template1);
         TEST_CASE(template2);
         TEST_CASE(template3);
+        TEST_CASE(template4); // #9805
         TEST_CASE(throwIsNotAFunction);
         TEST_CASE(unusedError);
         TEST_CASE(unusedMain);
@@ -229,6 +230,26 @@ private:
         ASSERT_EQUALS("[test.cpp:3]: (style) The function 'bar' is never used.\n", errout.str());
     }
 
+    void template4() { // #9805
+        check("struct A {\n"
+              "    int a = 0;\n"
+              "    void f() { a = 1; }\n"
+              "    template <typename T, typename... Args> auto call(const Args &... args) -> T {\n"
+              "        a = 2;\n"
+              "        return T{};\n"
+              "    }\n"
+              "};\n"
+              "\n"
+              "struct B : public A {\n"
+              "    void test() {\n"
+              "        f();\n"
+              "        call<int>(1, 2, 3);\n"
+              "        test();\n"
+              "    }\n"
+              "};");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void throwIsNotAFunction() {
         check("struct A {void f() const throw () {}}; int main() {A a; a.f();}");
         ASSERT_EQUALS("", errout.str());