From 2c34e660b3c3570fa6d26b53d3250e4818abbd5c Mon Sep 17 00:00:00 2001
From: vilarion <vilarion@illarion.org>
Date: Sun, 1 Nov 2020 15:10:02 +0100
Subject: [PATCH] Fix #9805 (False positive; Unused function (template))
 (#2871)

* Add test
* Ignore templates with trailing return type as well
---
 lib/checkunusedfunctions.cpp |  9 ++-------
 test/testunusedfunctions.cpp | 21 +++++++++++++++++++++
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/lib/checkunusedfunctions.cpp b/lib/checkunusedfunctions.cpp
index d884834fd..5dba2eda0 100644
--- a/lib/checkunusedfunctions.cpp
+++ b/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()) {
-            const Token *retDef = func->retDef;
-            while (retDef && retDef->isName())
-                retDef = retDef->previous();
-            if (retDef && retDef->str() == ">")
-                continue;
-        }
+        if (tokenizer.isCPP() && func->templateDef != nullptr)
+            continue;
 
         mFunctionDecl.emplace_back(func);
 
diff --git a/test/testunusedfunctions.cpp b/test/testunusedfunctions.cpp
index 8382a98b9..ef6280f55 100644
--- a/test/testunusedfunctions.cpp
+++ b/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());