ERL-923: 22.0 release candidates cause Yaws test to fail

[OTP-Maintainer]

Original reporter: vinoski
Affected version: OTP-22.0
Component: compiler
Migrated from: https://bugs.erlang.org/browse/ERL-923

---

The Yaws web server supports a binding feature that allows web page content to contain variables that Yaws replaces with values prior to returning the content to the client. The Yaws unit test request_bindings in yaws_compile_SUITE.erl helps verify that Yaws parses variable bindings correctly.

All 3 release candidates for 22.0 fail this test, apparently due to a change in the compiler. I bisected to find the failing change:


{noformat}
commit 7d941c529dc9db016af30cdace2df089d1648dbf
Merge: 08ef38b2c9 afa36d2081
Author: John Högberg <john@erlang.org>
Date:   Fri Sep 28 14:08:23 2018 +0200

    Merge pull request #1958 from jhogberg/john/compiler/ssa-bsm-opt

    Rewrite BSM optimizations in the new SSA-based intermediate format

{noformat}

Within the git branch noted in this merge commit, commit cf5094c, the first one in the branch, passes, but the commits after that on the branch fail.

If I compile Yaws with 21.3 and run it under a 22.0 release candidate, the test does not fail.

Unfortunately, I haven't been able to devise a smaller test case to reproduce this. The approach I've been using is to follow these steps to build Yaws in an Ubuntu docker container (assuming Erlang/OTP is already built/installed there):


{noformat}
    sudo apt-get build-dep yaws
    git clone https://github.com/klacke/yaws.git
    cd yaws
    autoreconf -fi
    ./configure
    make -j8
    sudo make install
{noformat}

I then use erlc to compile this module:


{code:erlang}
-module(comptest).
-export([start/0]).

start() ->
    application:load(yaws),
    application:start(yaws),
    {ok,GC,_} = yaws_api:getconf(),
    put(gc,GC),
    {ok,0,[{data,V}|_]} = yaws_compile:compile_file("comptest-data"),
    application:stop(yaws),
    erlang:halt(case V of
                    5 -> 0;
                    _ -> 1
                end).

{code}

where the input file comptest-data required by the module contains the following:

{noformat}
%%%%<%%x%%>
{noformat}

After compiling the module, I run it with


{noformat}
erl -noshell -noinput -s comptest start
{noformat}

If this exits with a 0 status, the test passed.

The error occurs within the Yaws source file src/yaws_compile.erl. From what I can tell, something is compiled incorrectly within the many clauses of yaws_compile:compile_file/4, particularly those involving yaws_compile:parse_binding/1,2.

[OTP-Maintainer]

john said:

Thanks for your report, I've narrowed down the issue and hope to have it resolved early next week.

[OTP-Maintainer]

vinoski said:

Great, thanks! Once you have a branch ready, I'd be happy to test it. Let me know when it's available and I'll pull it and try it out.

[OTP-Maintainer]

john said:

https://github.com/jhogberg/otp/tree/john/compiler/fix-missing-match-reposition/ERL-923

There's a lot of polish left (I'll get around to that on Monday), but it ought to work.

[OTP-Maintainer]

vinoski said:

Thanks, I verified the failing Yaws test case now passes against your branch.

[OTP-Maintainer]

john said:

I've merged a fix to master, thanks again for your report!