checkLibraryCheckType: handle global scope operator / Fix FN unreadVariable (#5199)

Author: chrchr-github

lib/checkunusedvar.cpp

@@ -1213,7 +1213,7 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                     continue;
                 tok = tok->next();
             }
-            if (tok->astParent() && !tok->astParent()->isAssignmentOp() && tok->str() != "(") {
+            if (!isInitialization && tok->astParent() && !tok->astParent()->isAssignmentOp() && tok->str() != "(") {
                 const Token *parent = tok->astParent();
                 while (Token::Match(parent, "%oror%|%comp%|!|&&"))
                     parent = parent->astParent();
@@ -1268,7 +1268,9 @@ void CheckUnusedVar::checkFunctionVariableUsage()
                     op1Var->isClass() &&
                     (!op1Var->valueType() || op1Var->valueType()->type == ValueType::Type::UNKNOWN_TYPE)) {
                     // Check in the library if we should bailout or not..
-                    const std::string typeName = op1Var->getTypeName();
+                    std::string typeName = op1Var->getTypeName();
+                    if (typeName.compare(0, 2, "::") == 0)
+                        typeName.erase(typeName.begin(), typeName.begin() + 2);
                     switch (mSettings->library.getTypeCheck("unusedvar", typeName)) {
                     case Library::TypeCheck::def:
                         bailoutTypeName = typeName;

test/testunusedvar.cpp

@@ -6197,6 +6197,15 @@ class TestUnusedVar : public TestFixture {
                               "    s[0] = 0;\n"
                               "}\n");
         ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage("struct S {\n"
+                              "    std::mutex m;\n"
+                              "    void f();\n"
+                              "};\n"
+                              "void S::f() {\n"
+                              "    const ::std::lock_guard g(m);\n"
+                              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void localVarClass() {
@@ -6478,6 +6487,11 @@ class TestUnusedVar : public TestFixture {
                               "    std::list<std::list<int>>::value_type a{ 1, 2, 3, 4 };\n"
                               "}\n");
         TODO_ASSERT_EQUALS("", "[test.cpp:2]: (information) --check-library: Provide <type-checks><unusedvar> configuration for std::list::value_type\n", errout.str());
+
+        functionVariableUsage("void f(int* p) {\n"
+                              "    int* q{ p };\n"
+                              "}\n");
+        ASSERT_EQUALS("[test.cpp:2]: (style) Variable 'q' is assigned a value that is never used.\n", errout.str());
     }
 
     void localvarRangeBasedFor() {