feat(unused_var): analyze global variables inside function body (#2944)

lib/checkunusedvar.cpp

@@ -1609,17 +1609,33 @@ bool CheckUnusedVar::isFunctionWithoutSideEffects(const Function& func, const To
     }
 
     bool sideEffectReturnFound = false;
+    std::set<const Variable*> pointersToGlobals;
     for (Token* bodyToken = func.functionScope->bodyStart->next(); bodyToken != func.functionScope->bodyEnd;
-         bodyToken = bodyToken->next()) {
+            bodyToken = bodyToken->next())
+    {
+        // check variable inside function body
         const Variable* bodyVariable = bodyToken->variable();
         if (bodyVariable) {
-            // check variable for side-effects
             if (!isVariableWithoutSideEffects(*bodyVariable)) {
                 return false;
             }
             // check if global variable is changed
-            if (bodyVariable->isGlobal()) {
+            if (bodyVariable->isGlobal() || (pointersToGlobals.find(bodyVariable) != pointersToGlobals.end()) ) {
-                return false; // TODO: analyze global variable usage
+                if (bodyVariable->isPointer() || bodyVariable->isArray()) {
+                    return false; // TODO: Update astutils.cpp:1544 isVariableChanged() and remove this. Unhandled case: `*(global_arr + 1) = new_val`
+                }
+                const int depth = 20;
+                if (isVariableChanged(bodyToken, depth, mSettings, mTokenizer->isCPP())) {
+                    return false;
+                }
+                // check if pointer to global variable assigned to another variable (another_var = &global_var)
+                if (Token::simpleMatch(bodyToken->tokAt(-1), "&") && Token::simpleMatch(bodyToken->tokAt(-2), "=")) {
+                    const Token* assigned_var_token = bodyToken->tokAt(-3);
+                    if (assigned_var_token && assigned_var_token->variable())
+                    {
+                        pointersToGlobals.insert(assigned_var_token->variable());
+                    }
+                }
             }
         }
 

test/testunusedvar.cpp

@@ -615,7 +615,7 @@ private:
             "void f() {\n"
             "   C c;\n"
             "}");
-        TODO_ASSERT_EQUALS("[test.cpp:11]: (style) Unused variable: c\n", "", errout.str());
+        ASSERT_EQUALS("[test.cpp:11]: (style) Unused variable: c\n", errout.str());
 
         // changing global variable in return
         functionVariableUsage(
@@ -698,6 +698,23 @@ private:
             "}");
         ASSERT_EQUALS("", errout.str());
 
+        // global variable use in function body without change
+        functionVariableUsage(
+            "int global = 1;\n"
+            "int func() {\n"
+            "   int x = global + 1;\n"
+            "   return x;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        ASSERT_EQUALS("[test.cpp:12]: (style) Unused variable: c\n", errout.str());
+
         // changing global array variable in function body
         functionVariableUsage(
             "int x[] = {0, 1, 3};\n"
@@ -715,6 +732,38 @@ private:
             "}");
         ASSERT_EQUALS("", errout.str());
 
+        functionVariableUsage(
+            "int x[] = {0, 1, 3};\n"
+            "int func() {\n"
+            "   *x = 2;\n"
+            "   return 1;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
+        functionVariableUsage(
+            "int x[] = {0, 1, 3};\n"
+            "int func() {\n"
+            "   *(x + 1) = 2;\n"
+            "   return 1;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
         // changing local variable
         functionVariableUsage(
             "int func() {\n"
@@ -985,7 +1034,7 @@ private:
         functionVariableUsage(
             "int global = 1;\n"
             "int func() {\n"
-            "   int *p = &global;\n"
+            "   int* p = &global;\n"
             "   *p = 0;\n"
             "   return 1;\n"
             "}\n"
@@ -999,11 +1048,30 @@ private:
             "}");
         ASSERT_EQUALS("", errout.str());
 
-        // global struct variable
+        // global variable assigning to local pointer, but not modifying
+        functionVariableUsage(
+            "int global = 1;\n"
+            "int func() {\n"
+            "   int* p = &global;\n"
+            "   (void) p;\n"
+            "   return 1;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        // TODO: see TODO for global vars under CheckUnusedVar::isFunctionWithoutSideEffects()
+        TODO_ASSERT_EQUALS("[test.cpp:13]: (style) Unused variable: c\n", "", errout.str());
+
+        // global struct variable modification
         functionVariableUsage(
             "struct S { int x; } s;\n"
             "int func() {\n"
-            "   s.x = 1;;\n"
+            "   s.x = 1;\n"
             "   return 1;\n"
             "}\n"
             "class C {\n"
@@ -1015,6 +1083,60 @@ private:
             "   C c;\n"
             "}");
         ASSERT_EQUALS("", errout.str());
+
+        // global struct variable without modification
+        functionVariableUsage(
+            "struct S { int x; } s;\n"
+            "int func() {\n"
+            "   int y = s.x + 1;\n"
+            "   return y;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        ASSERT_EQUALS("[test.cpp:12]: (style) Unused variable: c\n", errout.str());
+
+        // global pointer to struct variable modification
+        functionVariableUsage(
+            "struct S { int x; };\n"
+            "struct S* s = new(struct S);\n"
+            "int func() {\n"
+            "   s->x = 1;\n"
+            "   return 1;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
+        // global pointer to struct variable without modification
+        functionVariableUsage(
+            "struct S { int x; };\n"
+            "struct S* s = new(struct S);\n"
+            "int func() {\n"
+            "   int y = s->x + 1;\n"
+            "   return y;\n"
+            "}\n"
+            "class C {\n"
+            "public:\n"
+            "   C() : x(func()) {}\n"
+            "   int x;\n"
+            "};\n"
+            "void f() {\n"
+            "   C c;\n"
+            "}");
+        // TODO: see TODO for global vars under CheckUnusedVar::isFunctionWithoutSideEffects()
+        TODO_ASSERT_EQUALS("[test.cpp:13]: (style) Unused variable: c\n", "", errout.str());
     }
 
     // #5355 - False positive: Variable is not assigned a value.