Fix #13491 FP unreachableCode for declaration in switch (danmar#7194)

Author: chrchr-github

lib/checkother.cpp

@@ -851,6 +851,30 @@ void CheckOther::suspiciousCaseInSwitchError(const Token* tok, const std::string
                 "Using an operator like '" + operatorString + "' in a case label is suspicious. Did you intend to use a bitwise operator, multiple case labels or if/else instead?", CWE398, Certainty::inconclusive);
 }
 
+static bool isNestedInSwitch(const Scope* scope)
+{
+    while (scope) {
+        if (scope->type == Scope::ScopeType::eSwitch)
+            return true;
+        if (scope->type == Scope::ScopeType::eUnconditional) {
+            scope = scope->nestedIn;
+            continue;
+        }
+        break;
+    }
+    return false;
+}
+
+static bool isVardeclInSwitch(const Token* tok)
+{
+    if (!tok)
+        return false;
+    if (!isNestedInSwitch(tok->scope()))
+        return false;
+    const Token* end = Token::findsimplematch(tok, ";");
+    return end && end->previous()->variable() && end->previous()->variable()->nameToken() == end->previous();
+}
+
 //---------------------------------------------------------------------------
 //    Find consecutive return, break, continue, goto or throw statements. e.g.:
 //        break; break;
@@ -958,7 +982,7 @@ void CheckOther::checkUnreachableCode()
                     if (silencedWarning)
                         secondBreak = silencedWarning;
 
-                    if (!labelInFollowingLoop && !silencedCompilerWarningOnly)
+                    if (!labelInFollowingLoop && !silencedCompilerWarningOnly && !isVardeclInSwitch(secondBreak))
                         unreachableCodeError(secondBreak, tok, inconclusive);
                     tok = Token::findmatch(secondBreak, "[}:]");
                 } else if (secondBreak->scope() && secondBreak->scope()->isLoopScope() && secondBreak->str() == "}" && tok->str() == "continue") {

test/testother.cpp

@@ -5677,6 +5677,53 @@ class TestOther : public TestFixture {
         ASSERT_EQUALS("[test.cpp:6]: (style) Consecutive return, break, continue, goto or throw statements are unnecessary.\n"
                       "[test.cpp:1]: (style) Parameter 'argv' can be declared as const array\n",
                       errout_str());
+
+        check("int f(int i) {\n" // #13491
+              "    switch (i) {\n"
+              "    case 0:\n"
+              "        return 0;\n"
+              "        int j;\n"
+              "    case 1:\n"
+              "    case 2:\n"
+              "        j = 5;\n"
+              "        return j + i;\n"
+              "    }\n"
+              "    return 3;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        check("int f(int i) {\n"
+              "    switch (i) {\n"
+              "    {\n"
+              "    case 0:\n"
+              "        return 0;\n"
+              "    }\n"
+              "    {\n"
+              "        int j;\n"
+              "    case 1:\n"
+              "    case 2:\n"
+              "        j = 5;\n"
+              "        return j + i;\n"
+              "    }\n"
+              "    }\n"
+              "    return 3;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout_str());
+
+        check("int f(int i) {\n"
+              "    switch (i) {\n"
+              "    case 0:\n"
+              "        return 0;\n"
+              "        int j;\n"
+              "        dostuff();\n"
+              "    case 1:\n"
+              "    case 2:\n"
+              "        j = 5;\n"
+              "        return j + i;\n"
+              "    }\n"
+              "    return 3;\n"
+              "}\n");
+        TODO_ASSERT_EQUALS("[test.cpp:6]: (style) Statements following 'return' will never be executed.\n", "", errout_str());
     }
 
     void redundantContinue() {