feat: add modulo of one check (#9528) (#2650)

lib/checkother.cpp

@@ -3105,3 +3105,25 @@ void CheckOther::comparePointersError(const Token *tok, const ValueFlow::Value *
     reportError(
         errorPath, Severity::error, "comparePointers", verb + " pointers that point to different objects", CWE570, false);
 }
+
+void CheckOther::checkModuloOfOne()
+{
+    for (const Token *tok = mTokenizer->tokens(); tok; tok = tok->next()) {
+        if (!tok->astOperand2() || !tok->astOperand1())
+            continue;
+        if (tok->str() != "%")
+            continue;
+        if (!tok->valueType() || !tok->valueType()->isIntegral())
+            continue;
+
+        // Value flow..
+        const ValueFlow::Value *value = tok->astOperand2()->getValue(1LL);
+        if (value && value->isKnown())
+            checkModuloOfOneError(tok);
+    }
+}
+
+void CheckOther::checkModuloOfOneError(const Token *tok)
+{
+    reportError(tok, Severity::style, "moduloofone", "Modulo of one is always equal to zero");
+}

lib/checkother.h

@@ -100,6 +100,7 @@ public:
         checkOther.checkCastIntToCharAndBack();
         checkOther.checkMisusedScopedObject();
         checkOther.checkAccessOfMovedVariable();
+        checkOther.checkModuloOfOne();
     }
 
     /** @brief Clarify calculation for ".. a * b ? .." */
@@ -215,6 +216,8 @@ public:
 
     void checkComparePointers();
 
+    void checkModuloOfOne();
+
 private:
     // Error messages..
     void checkComparisonFunctionIsAlwaysTrueOrFalseError(const Token* tok, const std::string &functionName, const std::string &varName, const bool result);
@@ -271,6 +274,7 @@ private:
     void shadowError(const Token *var, const Token *shadowed, std::string type);
     void knownArgumentError(const Token *tok, const Token *ftok, const ValueFlow::Value *value);
     void comparePointersError(const Token *tok, const ValueFlow::Value *v1, const ValueFlow::Value *v2);
+    void checkModuloOfOneError(const Token *tok);
 
     void getErrorMessages(ErrorLogger *errorLogger, const Settings *settings) const OVERRIDE {
         CheckOther c(nullptr, settings, errorLogger);
@@ -342,6 +346,7 @@ private:
 
         const std::vector<const Token *> nullvec;
         c.funcArgOrderDifferent("function", nullptr, nullptr, nullvec, nullvec);
+        c.checkModuloOfOneError(nullptr);
     }
 
     static std::string myName() {
@@ -402,7 +407,8 @@ private:
                "- function declaration and definition argument names different.\n"
                "- function declaration and definition argument order different.\n"
                "- shadow variable.\n"
-               "- variable can be declared const.\n";
+               "- variable can be declared const.\n"
+               "- calculating modulo of one.\n";
     }
 };
 /// @}

test/testother.cpp

@@ -239,6 +239,8 @@ private:
         TEST_CASE(checkComparePointers);
 
         TEST_CASE(unusedVariableValueTemplate); // #8994
+
+        TEST_CASE(moduloOfOne);
     }
 
     void check(const char code[], const char *filename = nullptr, bool experimental = false, bool inconclusive = true, bool runSimpleChecks=true, bool verbose=false, Settings* settings = nullptr) {
@@ -8565,6 +8567,20 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void moduloOfOne() {
+        check("void f(unsigned int x) {\n"
+              "  int y = x % 1;\n"
+              "}");
+        ASSERT_EQUALS("[test.cpp:2]: (style) Modulo of one is always equal to zero\n", errout.str());
+
+        check("void f() {\n"
+              "  for (int x = 1; x < 10; x++) {\n"
+              "    int y = 100 % x;\n"
+              "  }\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+    }
+
 };
 
 REGISTER_TEST(TestOther)