constStatementError: don't warn for casts with possible side effects,… (#3885)

* constStatementError: don't warn for casts with possible side effects, handle bool constants

* Recursive call, add tests

* Restore test

* Don't warn for C++ casts to void

* Don't warn for cast to void*

lib/checkother.cpp

@@ -1739,7 +1739,7 @@ static bool isVarDeclOp(const Token* tok)
     return isType(typetok, Token::Match(vartok, "%var%"));
 }
 
-static bool isConstStatement(const Token *tok)
+static bool isConstStatement(const Token *tok, bool cpp)
 {
     if (!tok)
         return false;
@@ -1759,11 +1759,13 @@ static bool isConstStatement(const Token *tok)
     if (Token::simpleMatch(tok->previous(), "sizeof ("))
         return true;
     if (isCPPCast(tok))
-        return isConstStatement(tok->astOperand2());
+        return isWithoutSideEffects(cpp, tok) && isConstStatement(tok->astOperand2(), cpp);
+    else if (tok->isCast())
+        return isWithoutSideEffects(cpp, tok->astOperand1()) && isConstStatement(tok->astOperand1(), cpp);
     if (Token::Match(tok, "( %type%"))
-        return isConstStatement(tok->astOperand1());
+        return isConstStatement(tok->astOperand1(), cpp);
     if (Token::simpleMatch(tok, ","))
-        return isConstStatement(tok->astOperand2());
+        return isConstStatement(tok->astOperand2(), cpp);
     return false;
 }
 
@@ -1771,6 +1773,8 @@ static bool isVoidStmt(const Token *tok)
 {
     if (Token::simpleMatch(tok, "( void"))
         return true;
+    if (isCPPCast(tok) && tok->astOperand1() && Token::Match(tok->astOperand1()->next(), "< void *| >"))
+        return true;
     const Token *tok2 = tok;
     while (tok2->astOperand1())
         tok2 = tok2->astOperand1();
@@ -1838,7 +1842,7 @@ void CheckOther::checkIncompleteStatement()
         // Skip statement expressions
         if (Token::simpleMatch(rtok, "; } )"))
             continue;
-        if (!isConstStatement(tok))
+        if (!isConstStatement(tok, mTokenizer->isCPP()))
             continue;
         if (isVoidStmt(tok))
             continue;
@@ -1864,8 +1868,14 @@ void CheckOther::constStatementError(const Token *tok, const std::string &type,
         msg = "Found suspicious operator '" + tok->str() + "'";
     else if (Token::Match(tok, "%var%"))
         msg = "Unused variable value '" + tok->str() + "'";
-    else if (Token::Match(valueTok, "%str%|%num%"))
+    else if (Token::Match(valueTok, "%str%|%num%|%bool%")) {
-        msg = "Redundant code: Found a statement that begins with " + std::string(valueTok->isNumber() ? "numeric" : "string") + " constant.";
+        std::string typeStr("string");
+        if (valueTok->isNumber())
+            typeStr = "numeric";
+        else if (valueTok->isBoolean())
+            typeStr = "bool";
+        msg = "Redundant code: Found a statement that begins with " + typeStr + " constant.";
+    }
     else if (!tok)
         msg = "Redundant code: Found a statement that begins with " + type + " constant.";
     else if (tok->isCast() && tok->tokType() == Token::Type::eExtendedOp) {

test/testincompletestatement.cpp

@@ -386,6 +386,36 @@ private:
 
         check("void f(int x) { static_cast<unsigned>(x); }");
         ASSERT_EQUALS("[test.cpp:1]: (warning) Found unused cast of expression 'x'.\n", errout.str());
+
+        check("void f(int x, int* p) {\n"
+              "    static_cast<void>(x);\n"
+              "    (void)x;\n"
+              "    static_cast<void*>(p);\n"
+              "    (void*)p;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
+        check("void f() { false; }"); // #10856
+        ASSERT_EQUALS("[test.cpp:1]: (warning) Redundant code: Found a statement that begins with bool constant.\n", errout.str());
+
+        check("void f(int i) {\n"
+              "    (float)(char)i;\n"
+              "    static_cast<float>((char)i);\n"
+              "    (char)static_cast<float>(i);\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:2]: (warning) Found unused cast of expression 'i'.\n"
+                      "[test.cpp:3]: (warning) Found unused cast of expression 'i'.\n"
+                      "[test.cpp:4]: (warning) Found unused cast of expression 'i'.\n",
+                      errout.str());
+
+        check("struct S; struct T; struct U;\n"
+              "void f() {\n"
+              "    T t;\n"
+              "    (S)(U)t;\n"
+              "    (S)static_cast<U>(t);\n"
+              "    static_cast<S>((U)t);\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
     }
 
     void vardecl() {