From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id D15873858D20; Thu, 30 May 2024 10:24:07 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D15873858D20
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1717064647;
	bh=bnn7JRrQyO1z5by4jmE+uq1IOCoxo7ci6zmB5nPuAQE=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=TmELc8c6oq4Pj5gWSFokQddA5cpjedIPEldLwTy3/1AX81jlIm6Z0VXf+JMGUVTww
	 w50V0b/A/JDn2lPS5pC6gRCN6Trr43RnUy8HUqgAy9i3qq6sHbxHxJr/qrMueaMLLG
	 QS219bBsCwxwn6a7dqffyx9sJFytDOhaBL/baTTs=
From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/115285] [12/13/14/15 Regression] std::unordered_set
 can have duplicate value
Date: Thu, 30 May 2024 10:24:07 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 15.0
X-Bugzilla-Keywords: needs-bisection
X-Bugzilla-Severity: normal
X-Bugzilla-Who: redi at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 12.4
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-115285-4-tLzScfMUiL@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-115285-4@http.gcc.gnu.org/bugzilla/>
References: <bug-115285-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115285

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #7)
> I am suspecting it was
> https://gcc.gnu.org/git/?p=3Dgcc.git;a=3Dcommit;
> h=3D2c43f5ec9db163696de8691eb529df06c4999bcc which caused the issue.

Ah no, I think you're right about this.

The problem is not std::equal_to, but in std::hash<TrimmedStr>, because it
takes an argument of type std::string not TrimmedStr.

This means that hashing "foo "s does not convert to a TrimmedStr first, so =
it
hashes the un-trimmed string.

This fixes the code:

template<> struct hash<TrimmedStr> {
  bool operator()(const TrimmedStr& s) const noexcept
  { return std::hash<std::string>{}(s); }
};

I'm not sure if the code is valid or not. It certainly seems like a problem
that a plain std::string can be compared to a TrimmedStr using
std::equal_to<TrimmedStr> *and* can be hashed using std::hash<TrimmedStr>, =
when
a plain std::string is *not* a TrimmedStr.

Using inheritance this way is a bad idea, certainly for the std::hash
specialization. IMHO also for the TrimmedStr itself.=