Fix issue 8369: False negative: Condition 'condition' is always true (#1325)

* Fix issue 8369: False negative: Condition 'condition' is always true

* Use simpleMatch

* Add iterator header

* Cleanup

* Remove unused variable

lib/valueflow.cpp

@@ -92,6 +92,8 @@
 
 #include <algorithm>
 #include <cstddef>
+#include <functional>
+#include <iterator>
 #include <limits>
 #include <map>
 #include <set>
@@ -1829,6 +1831,22 @@ static bool valueFlowForward(Token * const               startToken,
                     return false;
                 }
 
+                // Forward known values in the else branch
+                if(Token::simpleMatch(end, "} else {")) {
+                    std::list<ValueFlow::Value> knownValues;
+                    std::copy_if(values.begin(), values.end(), std::back_inserter(knownValues), std::mem_fn(&ValueFlow::Value::isKnown));
+                    valueFlowForward(end->tokAt(2),
+                                     end->linkAt(2),
+                                     var,
+                                     varid,
+                                     knownValues,
+                                     constValue,
+                                     subFunction,
+                                     tokenlist,
+                                     errorLogger,
+                                     settings);
+                }
+
                 // Remove conditional values
                 std::list<ValueFlow::Value>::iterator it;
                 for (it = values.begin(); it != values.end();) {

test/testcondition.cpp

@@ -2462,6 +2462,15 @@ private:
 
         check("void f() { if(1) {} }");
         ASSERT_EQUALS("", errout.str());
+
+        check("void f(int i) {\n"
+              "    bool b = false;\n"
+              "    if (i == 0) b = true;\n"
+              "    else if (!b && i == 1) {}\n"
+              "    if (b)\n"
+              "    {}\n"
+              "}\n");
+        ASSERT_EQUALS("[test.cpp:4]: (style) Condition '!b' is always true\n", errout.str());
     }
 
     void checkInvalidTestForOverflow() {

test/testvalueflow.cpp

@@ -80,6 +80,7 @@ private:
         TEST_CASE(valueFlowAfterCondition);
         TEST_CASE(valueFlowForwardCompoundAssign);
         TEST_CASE(valueFlowForwardCorrelatedVariables);
+        TEST_CASE(valueFlowForwardModifiedVariables);
         TEST_CASE(valueFlowForwardFunction);
         TEST_CASE(valueFlowForwardTernary);
         TEST_CASE(valueFlowForwardLambda);
@@ -107,6 +108,24 @@ private:
         TEST_CASE(valueFlowContainerSize);
     }
 
+    bool testValueOfXKnown(const char code[], unsigned int linenr, int value) {
+        // Tokenize..
+        Tokenizer tokenizer(&settings, this);
+        std::istringstream istr(code);
+        tokenizer.tokenize(istr, "test.cpp");
+
+        for (const Token *tok = tokenizer.tokens(); tok; tok = tok->next()) {
+            if (tok->str() == "x" && tok->linenr() == linenr) {
+                for(const ValueFlow::Value& val:tok->values()) {
+                    if(val.isKnown() && val.intvalue == value)
+                        return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
     bool testValueOfX(const char code[], unsigned int linenr, int value) {
         // Tokenize..
         Tokenizer tokenizer(&settings, this);
@@ -2135,6 +2154,27 @@ private:
         ASSERT_EQUALS(false, testValueOfX(code, 4U, 0));
     }
 
+    void valueFlowForwardModifiedVariables() {
+        const char *code;
+
+        code = "void f(bool b) {\n"
+               "  int x = 0;\n"
+               "  if (b) x = 1;\n"
+               "  else b = x;\n"
+               "}";
+        ASSERT_EQUALS(true, testValueOfXKnown(code, 4U, 0));
+
+        code = "void f(int i) {\n"
+               "    int x = 0;\n"
+               "    if (i == 0) \n"
+               "        x = 1;\n"
+               "    else if (!x && i == 1) \n"
+               "        int b = x;\n"
+               "}\n";
+        ASSERT_EQUALS(true, testValueOfXKnown(code, 5U, 0));
+        ASSERT_EQUALS(true, testValueOfXKnown(code, 6U, 0));
+    }
+
     void valueFlowForwardFunction() {
         const char *code;