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 897873838006; Tue, 24 May 2022 15:29:58 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 897873838006
From: "andij.cr at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/105720] New: std::views::split_view wrong behaviour
 in case of partial match
Date: Tue, 24 May 2022 15:29:58 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: libstdc++
X-Bugzilla-Version: 10.3.1
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: andij.cr at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-105720-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Tue, 24 May 2022 15:29:58 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105720

            Bug ID: 105720
           Summary: std::views::split_view wrong behaviour in case of
                    partial match
           Product: gcc
           Version: 10.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: andij.cr at gmail dot com
  Target Milestone: ---

compiled with=20
g++-10 -std=3Dc++20 split_view_wrong.cpp -lfmt

godbolt link https://gcc.godbolt.org/z/47TxWovd4

fmtlib used for exposition only

    #include <fmt/printf.h>
    #include <fmt/ranges.h>
    #include <ranges>
    #include <string_view>

    auto words_no_bug =3D std::string_view{"Hello-_-C++-_-20-_-!-_-"};
    auto words_bug =3D std::string_view{"Hello--_-C++-_-20-_-!-_-"};
    auto delim =3D std::string_view{"-_-"};

    // needed because split_view is lazy in gcc 10.3
    auto range_to_str =3D [](auto &&r) {
      return fmt::format("{}", fmt::join(r, ""));
    };

    int main() {
      fmt::print("no bug: '{}' tokens: {}\n", words_no_bug,
                     words_no_bug | std::views::split(delim) |
                     std::views::transform(range_to_str));

      fmt::print("bug: '{}' tokens: {}\n", words_bug,
                     words_bug | std::views::split(delim) |
                     std::views::transform(range_to_str));
    }

this code applies split to tokenize a text

compiled with gcc-10.3 it wrongly produces

    no bug: 'Hello-_-C++-_-20-_-!-_-' tokens: ["Hello", "C++", "20", "!"]
    bug: 'Hello--_-C++-_-20-_-!-_-' tokens: ["Hello-", "20", "!"]

while compiled with gcc-11.3 is correctly produces=20

    no bug: 'Hello-_-C++-_-20-_-!-_-' tokens: ["Hello", "C++", "20", "!"]
    bug: 'Hello--_-C++-_-20-_-!-_-' tokens: ["Hello-", "C++", "20", "!"]


notice how the substring "--_-C++" instead of being split in ["-", "C++"]
is split as ["-"], skipping the "C++" token.

it's fixed from gcc-11, but i couldn't find a mention in the release notes
about it=