Incorrect pattern matching results using OTP 19.0.x on some platforms

[scouten]

I've identified what looks like a bug in pattern matching (function head selection) in OTP 19.0.x, but only on some platforms.

Environment

• Elixir versions tested: 1.2, 1.3.0, 1.3.2, 1.3.4 (happens in all versions)
• OTP versions tested: 18.0, 19.0, 19.1, 19.2 (happens only in OTP 19.0)
• Operating systems tested: Ubuntu 12.04.5 LTS, Mac OS 10.11.6 (happens only on Ubuntu)

Current behavior

A minimal repro case (one file, one test) is available at https://github.com/scouten/otp-pattern-match. This is a very stripped down version of sqlitex, where I first encountered the bug.

If you examine the Travis CI build logs at https://travis-ci.org/scouten/otp-pattern-match/builds/186425073, you'll see that the test fails on OTP 19.0, but succeeds on 18.0, 19.1, and 19.2.

The bug is essentially that the code fails to match the translate_value clause at https://github.com/scouten/otp-pattern-match/blob/master/lib/pattern_match_bug.ex#L11 in my example. It instead falls through to the catch-all clause at line 23 and thus generates an unwanted result.

Expected behavior

Test matches https://github.com/scouten/otp-pattern-match/blob/master/lib/pattern_match_bug.ex#L11 on all OTP versions.

[scouten]

This is likely an OTP bug (and could well be closed as such), but wanted to make sure Elixir core team was aware of it.

I will discontinue testing my code on OTP 19.0 for now. 🙂

[josevalim]

It is a known bug that has been fixed. Here is the test case added to OTP: erlang/otp@8b83bc0

Since it was fixed on later 19.0 releases, I believe the OS difference is caused by the version in the OS package manager.

Thanks for the report!