Fix FP knowConditionTrueFalse (#4419)

* Fix #10426 FN (style) Condition 's.empty()' is always false

* Fix test

* Fix FP knowConditionTrueFalse

* Check for casts

* Fix FP for user-defined functions

* Adjust condition detection

* Tweaks

lib/checkcondition.cpp

@@ -1512,15 +1512,20 @@ void CheckCondition::alwaysTrueFalse()
                     continue;
             }
 
+            const Token* astTop = tok->astTop();
             const bool constIfWhileExpression =
-                tok->astParent() && Token::Match(tok->astTop()->astOperand1(), "if|while") && !tok->astTop()->astOperand1()->isConstexpr() &&
+                tok->astParent() && Token::Match(astTop->astOperand1(), "if|while") && !astTop->astOperand1()->isConstexpr() &&
                 (Token::Match(tok->astParent(), "%oror%|&&") || Token::Match(tok->astParent()->astOperand1(), "if|while"));
             const bool constValExpr = tok->isNumber() && Token::Match(tok->astParent(),"%oror%|&&|?"); // just one number in boolean expression
-            const bool compExpr = Token::Match(tok, "%comp%|!|("); // a compare expression
+            const bool compExpr = Token::Match(tok, "%comp%|!"); // a compare expression
             const bool ternaryExpression = Token::simpleMatch(tok->astParent(), "?");
-            const bool returnExpression = Token::simpleMatch(tok->astTop(), "return") && (tok->isComparisonOp() || Token::Match(tok, "&&|%oror%"));
+            const bool isReturn = Token::simpleMatch(astTop, "return");
-
+            const bool returnExpression = isReturn && (tok->isComparisonOp() || Token::Match(tok, "&&|%oror%"));
-            if (!(constIfWhileExpression || constValExpr || compExpr || ternaryExpression || returnExpression))
+            const bool callExpression = Token::simpleMatch(tok, "(");
+            if (!(constIfWhileExpression || constValExpr || compExpr || ternaryExpression || returnExpression || callExpression))
+                continue;
+            // only warn for functions returning bool
+            if (isReturn && callExpression && !(scope->function && scope->function->retDef && scope->function->retDef->str() == "bool"))
                 continue;
 
             const Token* expr1 = tok->astOperand1(), *expr2 = tok->astOperand2();

test/cfg/qt.cpp

@@ -29,7 +29,7 @@ void QString1(QString s)
     }
 }
 
-int QString2()
+bool QString2()
 {
     QString s;
     // cppcheck-suppress knownConditionTrueFalse

test/testcondition.cpp

@@ -4307,15 +4307,38 @@ private:
         ASSERT_EQUALS("", errout.str());
 
         // #10426
-        check("void f() {\n"
+        check("int f() {\n"
               "    std::string s;\n"
               "    for (; !s.empty();) {}\n"
               "    for (; s.empty();) {}\n"
               "    if (s.empty()) {}\n"
+              "    if ((bool)0) {}\n"
+              "    return s.empty();"
               "}\n");
         ASSERT_EQUALS("[test.cpp:3]: (style) Condition '!s.empty()' is always false\n"
                       "[test.cpp:4]: (style) Condition 's.empty()' is always true\n"
-                      "[test.cpp:5]: (style) Condition 's.empty()' is always true\n",
+                      "[test.cpp:5]: (style) Condition 's.empty()' is always true\n"
+                      "[test.cpp:6]: (style) Condition '(bool)0' is always false\n",
+                      errout.str());
+
+        check("int f(bool b) {\n"
+              "    if (b) return static_cast<int>(1);\n"
+              "    return (int)0;\n"
+              "}\n"
+              "bool g(bool b) {\n"
+              "    if (b) return static_cast<int>(1);\n"
+              "    return (int)0;\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:6]: (style) Condition 'static_cast<int>(1)' is always true\n"
+                      "[test.cpp:7]: (style) Condition '(int)0' is always false\n",
+                      errout.str());
+
+        check("int f() { return 3; }\n"
+              "int g() { return f(); }\n"
+              "int h() { if (f()) {} }\n"
+              "int i() { return f() == 3; }\n");
+        ASSERT_EQUALS("[test.cpp:3]: (style) Condition 'f()' is always true\n"
+                      "[test.cpp:4]: (style) Condition 'f()==3' is always true\n",
                       errout.str());
     }