Fix #11790 FP functionConst with template function (#5187)

Author: chrchr-github

lib/checkclass.cpp

@@ -2098,6 +2098,17 @@ void CheckClass::checkConst()
 
             const bool returnsPtrOrRef = isPointerOrReference(func.retDef, func.tokenDef);
 
+            if (Function::returnsPointer(&func, /*unknown*/ true) || Function::returnsReference(&func, /*unknown*/ true, /*includeRValueRef*/ true)) { // returns const/non-const depending on template arg
+                bool isTemplateArg = false;
+                for (const Token* tok2 = func.retDef; precedes(tok2, func.token); tok2 = tok2->next())
+                    if (tok2->isTemplateArg() && tok2->str() == "const") {
+                        isTemplateArg = true;
+                        break;
+                    }
+                if (isTemplateArg)
+                    continue;
+            }
+
             if (func.isOperator()) { // Operator without return type: conversion operator
                 const std::string& opName = func.tokenDef->str();
                 if (opName.compare(8, 5, "const") != 0 && (endsWith(opName,'&') || endsWith(opName,'*')))

test/testclass.cpp

@@ -180,6 +180,7 @@ class TestClass : public TestFixture {
         TEST_CASE(const88);
         TEST_CASE(const89);
         TEST_CASE(const90);
+        TEST_CASE(const91);
 
         TEST_CASE(const_handleDefaultParameters);
         TEST_CASE(const_passThisToMemberOfOtherClass);
@@ -6595,6 +6596,20 @@ class TestClass : public TestFixture {
                       errout.str());
     }
 
+    void const91() { // #11790
+        checkConst("struct S {\n"
+                   "    char* p;\n"
+                   "    template <typename T>\n"
+                   "    T* get() {\n"
+                   "        return reinterpret_cast<T*>(p);\n"
+                   "    }\n"
+                   "};\n"
+                   "const int* f(S& s) {\n"
+                   "    return s.get<const int>();\n"
+                   "}\n");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void const_handleDefaultParameters() {
         checkConst("struct Foo {\n"
                    "    void foo1(int i, int j = 0) {\n"