Fix false positive from issue 8612 (#1285)

Author: pfultz2

lib/checkother.cpp

@@ -1949,7 +1949,18 @@ void CheckOther::checkDuplicateExpression()
                         isSameExpression(_tokenizer->isCPP(), true, tok->next(), nextAssign->next(), _settings->library, true) &&
                         isSameExpression(_tokenizer->isCPP(), true, tok->astOperand2(), nextAssign->astOperand2(), _settings->library, true) &&
                         !isUniqueExpression(tok->astOperand2())) {
-                        duplicateAssignExpressionError(var1, var2);
+                        bool assigned = false;
+                        const Scope * varScope = var1->scope() ? var1->scope() : &*scope;
+                        for (const Token *assignTok = Token::findsimplematch(var2, ";"); assignTok && assignTok != varScope->bodyEnd; assignTok = assignTok->next()) {
+                            if(Token::Match(assignTok, "%varid% = %var%", var1->varId()) && Token::Match(assignTok, "%var% = %varid%", var2->varId())) {
+                                assigned = true;
+                            }
+                            if(Token::Match(assignTok, "%varid% = %var%", var2->varId()) && Token::Match(assignTok, "%var% = %varid%", var1->varId())) {
+                                assigned = true;
+                            }
+                        }
+                        if(!assigned)
+                            duplicateAssignExpressionError(var1, var2);
                     }
                 }
             }

test/testother.cpp

@@ -134,6 +134,7 @@ class TestOther : public TestFixture {
         TEST_CASE(oppositeExpression);
         TEST_CASE(duplicateVarExpression);
         TEST_CASE(duplicateVarExpressionUnique);
+        TEST_CASE(duplicateVarExpressionAssign);
 
         TEST_CASE(checkSignOfUnsignedVariable);
         TEST_CASE(checkSignOfPointer);
@@ -4173,6 +4174,57 @@ class TestOther : public TestFixture {
         ASSERT_EQUALS("", errout.str());
     }
 
+    void duplicateVarExpressionAssign() {
+        check("struct A { int x; int y; };"
+              "void use(int);\n"
+              "void test(A a) {\n"
+              "    int i = a.x;\n"
+              "    int j = a.x;\n"
+              "    use(i);\n"
+              "    i = j;\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        check("struct A { int x; int y; };"
+              "void use(int);\n"
+              "void test(A a) {\n"
+              "    int i = a.x;\n"
+              "    int j = a.x;\n"
+              "    use(j);\n"
+              "    j = i;\n"
+              "}");
+        ASSERT_EQUALS("", errout.str());
+
+        // Issue #8612
+        check("struct P\n"
+              "{\n"
+              "    void func();\n"
+              "    bool operator==(const P&) const;\n"
+              "};\n"
+              "struct X\n"
+              "{\n"
+              "    P first;\n"
+              "    P second;\n"
+              "};\n"
+              "bool bar();\n"
+              "void baz(const P&);\n"
+              "void foo(const X& x)\n"
+              "{\n"
+              "    P current = x.first;\n"
+              "    P previous = x.first;\n"
+              "    while (true)\n"
+              "    {\n"
+              "        baz(current);\n"
+              "        if (bar() && previous == current)\n"
+              "        {\n"
+              "            current.func();\n"
+              "        }\n"
+              "        previous = current;\n"
+              "    }\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void checkSignOfUnsignedVariable() {
         check(
             "void foo() {\n"