From a336c076632e1c46e9156a641ed27094b1a9d822 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Marjam=C3=A4ki?= <daniel.marjamaki@gmail.com>
Date: Mon, 12 Jul 2021 15:31:21 +0200
Subject: [PATCH] missing return; False positive when goto jumps back

---
 lib/checkfunctions.cpp | 17 +++++++++++++++++
 test/testfunctions.cpp |  9 +++++++++
 2 files changed, 26 insertions(+)

diff --git a/lib/checkfunctions.cpp b/lib/checkfunctions.cpp
index b7d2a6762..4e17c5787 100644
--- a/lib/checkfunctions.cpp
+++ b/lib/checkfunctions.cpp
@@ -269,6 +269,19 @@ void CheckFunctions::checkMissingReturn()
     }
 }
 
+static bool isForwardJump(const Token *gotoToken)
+{
+    if (!Token::Match(gotoToken, "goto %name% ;"))
+        return false;
+    for (const Token *prev = gotoToken; gotoToken; gotoToken = gotoToken->previous()) {
+        if (Token::Match(prev, "%name% :") && prev->str() == gotoToken->next()->str())
+            return true;
+        if (prev->str() == "{" && prev->scope()->type == Scope::eFunction)
+            return false;
+    }
+    return false;
+}
+
 static const Token *checkMissingReturnScope(const Token *tok, const Library &library)
 {
     const Token *lastStatement = nullptr;
@@ -279,6 +292,8 @@ static const Token *checkMissingReturnScope(const Token *tok, const Library &lib
             for (const Token *prev = tok->link()->previous(); prev && prev->scope() == tok->scope() && !Token::Match(prev, "[;{}]"); prev = prev->previous()) {
                 if (prev->isKeyword() && Token::Match(prev, "return|throw"))
                     return nullptr;
+                if (prev->str() == "goto" && !isForwardJump(prev))
+                    return nullptr;
             }
             if (tok->scope()->type == Scope::ScopeType::eSwitch) {
                 // find reachable break / !default
@@ -316,6 +331,8 @@ static const Token *checkMissingReturnScope(const Token *tok, const Library &lib
         }
         if (tok->isKeyword() && Token::Match(tok, "return|throw"))
             return nullptr;
+        if (tok->str() == "goto" && !isForwardJump(tok))
+            return nullptr;
         if (Token::Match(tok, "%name% (") && library.isnoreturn(tok))
             return nullptr;
         if (Token::Match(tok, "[;{}] %name% :"))
diff --git a/test/testfunctions.cpp b/test/testfunctions.cpp
index 78217f383..7cd843bd5 100644
--- a/test/testfunctions.cpp
+++ b/test/testfunctions.cpp
@@ -1379,6 +1379,15 @@ private:
         check("auto foo4() -> void {}");
         ASSERT_EQUALS("", errout.str());
 
+        check("int f() {\n"
+              "back:\n"
+              "    return 0;\n"
+              "ng:\n"
+              "    x=y;\n"
+              "    goto back;\n"
+              "}\n");
+        ASSERT_EQUALS("", errout.str());
+
         // unreachable code..
         check("int foo(int x) {\n"
               "  return 1;\n"