186991 2018-06-24 23:44:42 -0700 Different output compared with v8 and spidermonkey 2020-05-07 15:40:13 -0700 1 1 1 Unclassified WebKit JavaScriptCore WebKit Local Build Unspecified Unspecified RESOLVED DUPLICATE 184267 https://bugs.webkit.org/show_bug.cgi?id=186993 https://bugs.webkit.org/show_bug.cgi?id=186992 P2 Normal --- 1 sunlili webkit-unassigned ashvayka nth10sd sunlili ysuzuki oldest_to_newest 1435993 0 sunlili 2018-06-24 23:44:42 -0700 Hello, The following code behaves incorrectly (inconsistent with the standard and other engines). arr0 = [ 1, 2, 3 ]; arr1 = [ 4, 5, 6 ]; handler1 = { get: function (oTarget, sKey) { print('arg ' + '1' + ':get ' + sKey.toString()); if (sKey.toString() == 'Symbol(Symbol.isConcatSpreadable)') { arr1['length'] = 4294967294; } if (sKey.toString() == 'length') { arr1['length'] = 10; } if (Number(sKey.toString()) != NaN) { ; } return Reflect.get(oTarget, sKey); }, has: function (oTarget, sKey) { print('arg ' + '1' + ':has ' + sKey.toString()); if (Number(sKey.toString()) != NaN) { return Symbol.search; } return Reflect.has(oTarget, sKey); } }; var proxy1 = new Proxy(arr1, handler1); func = Array.prototype.concat.bind(arr0, proxy1); arr2 = func(); print(arr2); The output is: arg 1:get Symbol(Symbol.isConcatSpreadable) arg 1:get Symbol(Symbol.toPrimitive) arg 1:get toString arg 1:get join arg 1:get length arg 1:get 0 arg 1:get 1 arg 1:get 2 arg 1:get 3 arg 1:get 4 arg 1:get 5 arg 1:get 6 arg 1:get 7 arg 1:get 8 arg 1:get 9 1,2,3,4,5,6,,,,,,, However, it should be: arg 1:get Symbol(Symbol.isConcatSpreadable) arg 1:get length arg 1:has 0 arg 1:get 0 arg 1:has 1 arg 1:get 1 arg 1:has 2 arg 1:get 2 arg 1:has 3 arg 1:get 3 arg 1:has 4 arg 1:get 4 arg 1:has 5 arg 1:get 5 arg 1:has 6 arg 1:get 6 arg 1:has 7 arg 1:get 7 arg 1:has 8 arg 1:get 8 arg 1:has 9 arg 1:get 9 1,2,3,4,5,6,,,,,,, BT group 2018.6.25 1644200 1 nth10sd 2020-04-21 21:38:35 -0700 I re-ran the testcase in comment #0 with git rev eb42a8967d53ebb95bd59b6d89662ac7fdf95a8b and it seems to show the intended output. It shows the wrong output with a build from mid-2017, or rev 011c994d52cc30bdec69aebed8ec1a025966b34a. I then ran a bisection using robobisect, and it seems to point to the following commit as a possible fix to this bug: commit e580b9a5fa9b5013b749e72f1c10946cb14af9aa Author: caitp Date: Tue May 29 16:56:29 2018 +0000 [JSC] Fix Array.prototype.concat fast case when single argument is Proxy https://bugs.webkit.org/show_bug.cgi?id=184267 Reviewed by Saam Barati. </snip> git-svn-id: https://svn.webkit.org/repository/webkit/trunk@232261 268f45cc-cd09-0410-ab3c-d52691b4dbfc Is bug 184267 a likely fix? 1650363 2 ashvayka 2020-05-07 15:11:25 -0700 (In reply to Gary Kwong [:gkw] [:nth10sd] from comment #1) > Is bug 184267 a likely fix? Thank you for tracking it down, Gary! *** This bug has been marked as a duplicate of bug 184267 ***