[PATCH] Detect suspicious use of semicolon after 'if/for/while'

statements if they are followed by a {..} block.

Examples are:

for (int i = 0; i < 10; ++i);
{
   printf("i)";
}

or

if (i == 100);
{
   die("Wrong argument");
}

This new check is active if you enable inconclusive checks.

lib/checkother.cpp

@@ -264,6 +264,39 @@ void CheckOther::bitwiseOnBooleanError(const Token *tok, const std::string &varn
                             "Boolean variable '" + varname + "' is used in bitwise operation. Did you mean " + op + " ?");
 }
 
+void CheckOther::checkSuspiciousSemicolon()
+{
+    if (!_settings->inconclusive || !_settings->isEnabled("style"))
+        return;
+
+    for (const Token *tok = _tokenizer->tokens(); tok; tok = tok->next())
+    {
+        // Look for "if(); {}", "for(); {}" or "while(); {}"
+        if (Token::Match(tok, "if|for|while ("))
+        {
+            const Token *end = tok->next()->link();
+            if (!end)
+                continue;
+
+            // Ensure the semicolon is at the same line number as the if/for/while statement
+            // and the {..} block follows it without an extra empty line.
+            if (Token::simpleMatch(end, ") { ; } {") &&
+                end->linenr() == end->tokAt(2)->linenr()
+                && end->linenr()+1 >= end->tokAt(4)->linenr())
+            {
+                SuspiciousSemicolonError(tok);
+            }
+        }
+    }
+}
+
+void CheckOther::SuspiciousSemicolonError(const Token* tok)
+{
+    reportInconclusiveError(tok, Severity::warning, "suspiciousSemicolon",
+                "Suspicious use of ; at the end of 'if/for/while' statement.");
+}
+
+
 //---------------------------------------------------------------------------
 //---------------------------------------------------------------------------
 void CheckOther::warningOldStylePointerCast()

lib/checkother.h

@@ -66,6 +66,7 @@ public:
         checkOther.checkDuplicateBranch();
         checkOther.checkDuplicateExpression();
         checkOther.checkDuplicateBreak();
+        checkOther.checkSuspiciousSemicolon();
 
         // information checks
         checkOther.checkVariableScope();
@@ -233,6 +234,9 @@ public:
     /** @brief %Check for comparing a bool expression with an integer other than 0 or 1 */
     void checkComparisonOfBoolExpressionWithInt();
 
+    /** @brief %Check for suspicious use of semicolon */
+    void checkSuspiciousSemicolon();
+
     // Error messages..
     void cstyleCastError(const Token *tok);
     void dangerousUsageStrtolError(const Token *tok);
@@ -271,6 +275,7 @@ public:
     void unsignedPositiveError(const Token *tok, const std::string &varname);
     void bitwiseOnBooleanError(const Token *tok, const std::string &varname, const std::string &op);
     void comparisonOfBoolExpressionWithIntError(const Token *tok);
+    void SuspiciousSemicolonError(const Token *tok);
 
     void getErrorMessages(ErrorLogger *errorLogger, const Settings *settings)
     {
@@ -321,6 +326,7 @@ public:
         c.unsignedPositiveError(0, "varname");
         c.bitwiseOnBooleanError(0, "varname", "&&");
         c.comparisonOfBoolExpressionWithIntError(0);
+        c.SuspiciousSemicolonError(0);
     }
 
     std::string myName() const
@@ -371,6 +377,7 @@ public:
                "* testing if unsigned variable is negative\n"
                "* testing is unsigned variable is positive\n"
                "* using bool in bitwise expression\n"
+               "* Suspicious use of ; at the end of 'if/for/while' statement.\n"
 
                // optimisations
                "* optimisation: detect post increment/decrement\n";

test/testother.cpp

@@ -140,6 +140,9 @@ private:
 
         TEST_CASE(alwaysTrueFalseStringCompare);
         TEST_CASE(checkSignOfUnsignedVariable);
+
+        TEST_CASE(checkForSuspiciousSemicolon1);
+        TEST_CASE(checkForSuspiciousSemicolon2);
     }
 
     void check(const char code[], const char *filename = NULL)
@@ -170,6 +173,7 @@ private:
         checkOther.checkDuplicateExpression();
         checkOther.checkBitwiseOnBoolean();
         checkOther.checkComparisonOfBoolExpressionWithInt();
+        checkOther.checkSuspiciousSemicolon();
 
         // Simplify token list..
         tokenizer.simplifyTokenList();
@@ -3645,7 +3649,88 @@ private:
             "}");
         ASSERT_EQUALS("", errout.str());
     }
+
+    void checkForSuspiciousSemicolon1()
+    {
+        check(
+            "void foo() {\n"
+            "  for(int i = 0; i < 10; ++i);\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
+        // Empty block
+        check(
+            "void foo() {\n"
+            "  for(int i = 0; i < 10; ++i); {\n"
+            "  }\n"
+            "}");
+        ASSERT_EQUALS("[test.cpp:2]: (warning) Suspicious use of ; at the end of 'if/for/while' statement.\n", errout.str());
+
+        // Block with some tokens to make sure the tokenizer output
+        // stays the same for "for(); {}"
+        check(
+            "void foo() {\n"
+            "  for(int i = 0; i < 10; ++i); {\n"
+            "  int j = 123;\n"
+            "  }\n"
+            "}");
+        ASSERT_EQUALS("[test.cpp:2]: (warning) Suspicious use of ; at the end of 'if/for/while' statement.\n", errout.str());
+
+        check(
+            "void foo() {\n"
+            "  while (!quit); {\n"
+            "    do_something();\n"
+            "  }\n"
+            "}");
+        ASSERT_EQUALS("[test.cpp:2]: (warning) Suspicious use of ; at the end of 'if/for/while' statement.\n", errout.str());
+    }
+
+    void checkForSuspiciousSemicolon2()
+    {
+        check(
+            "void foo() {\n"
+            "  if (i == 1); {\n"
+            "    do_something();\n"
+            "  }\n"
+            "}");
+        ASSERT_EQUALS("[test.cpp:2]: (warning) Suspicious use of ; at the end of 'if/for/while' statement.\n", errout.str());
+
+        // Seen this in the wild
+        check(
+            "void foo() {\n"
+            "  if (Match());\n"
+            "  do_something();\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check(
+            "void foo() {\n"
+            "  if (Match());\n"
+            "  else\n"
+            "    do_something();\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check(
+            "void foo() {\n"
+            "  if (i == 1)\n"
+            "       ;\n"
+            "  {\n"
+            "    do_something();\n"
+            "  }\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check(
+            "void foo() {\n"
+            "  if (i == 1);\n"
+            "\n"
+            "  {\n"
+            "    do_something();\n"
+            "  }\n"
+            "}");
+        ASSERT_EQUALS("", errout.str());
+    }
 };
 
 REGISTER_TEST(TestOther)
-