test/helper.rb: ignore GC compaction on unsupported platforms

[terceiro]

For example, ruby 3.0 on Debian ppc64el architecture does not support GC
compaction. When running the tests, every 20th test crashes like this:

Error:
Minitest::Result#test_parsing_attribute_namespace:
NotImplementedError: Compaction isn't available on this platform
    <internal:gc>:213:in `compact'
    /home/terceiro/ruby-nokogiri-1.13.5+dfsg/test/helper.rb:123:in `teardown'

[flavorjones]

If you look at the method initialize_nokogiri_test_gc_level in test/helper.rb you can see that it checks if GC.compact and GC.verify_compaction_references are defined? before deciding to set the compaction verification. Can you help me understand why that's not working?

[flavorjones]

I'd prefer a PR that did the appropriate checks in initialize_nokogiri_test_gc_level than wrapped these calls in rescue blocks, if that's possible.

[terceiro]

If you look at the method initialize_nokogiri_test_gc_level in test/helper.rb you can see that it checks if GC.compact and GC.verify_compaction_references are defined? before deciding to set the compaction verification. Can you help me understand why that's not working?

When compaction is not supported, those methods are defined, but raise NotImplementedError when called:

irb(main):001:0> defined?(GC.compact)
=> "method"
irb(main):002:0> GC.compact
<internal:gc>:213:in `compact': Compaction isn't available on this platform (NotImplementedError)
	from (irb):2:in `<main>'
	from /usr/lib/ruby/gems/3.0.0/gems/irb-1.3.5/exe/irb:11:in `<top (required)>'
	from /usr/bin/irb:23:in `load'
	from /usr/bin/irb:23:in `<main>'

I'd prefer a PR that did the appropriate checks in initialize_nokogiri_test_gc_level than wrapped these calls in rescue blocks, if that's possible.

For that, you would need to actuall call GC.compact at the beginning. I just sent an updated patch, let me know what you think.

[stevecheckoway]

For that, you would need to actuall call GC.compact at the beginning. I just sent an updated patch, let me know what you think.

This seems like a reasonable approach.

[flavorjones]

I agree, this looks good! I've just kicked off CI.

I'm wondering if it would be worth running CI on ppc64le (using qemu like we do for native gem installations) ...

[stevecheckoway]

Little endian PowerPC seems like a pretty esoteric platform. Maybe something that runs periodically but not on every commit?

[flavorjones]

I'm curious if there's a way I can easily reproduce what you're seeing? I'm trying the platform=linux/ppc64le docker container for ruby:3.0 (and multiarch/qemu-user-static to emulate that hardware), but it seems to be working OK (using current main at 199434c):

warnings: []
nokogiri:
  version: 1.14.0.dev
  cppflags:
  - "-I/root/nokogiri/ext/nokogiri"
  ldflags: []
ruby:
  version: 3.0.4
  platform: powerpc64le-linux
  gem_platform: powerpc64le-linux
  description: ruby 3.0.4p208 (2022-04-12 revision 3fa771dded) [powerpc64le-linux]
  engine: ruby
libxml:
  source: system
  memory_management: ruby
  iconv_enabled: true
  compiled: 2.9.10
  loaded: 2.9.10
libxslt:
  source: system
  datetime_enabled: true
  compiled: 1.1.34
  loaded: 1.1.34
other_libraries:
  libgumbo: 1.0.0-nokogiri

# Running tests with run options --seed 63270:

/root/nokogiri/test/helper.rb:157: NOKOGIRI_TEST_GC_LEVEL: compact
........................................................................................................................................................................................................................................S....................................S........................................S....................................................................................................................................................................................S.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................S.................................................SSS.................................................................................................................................S..........................................................S.......S.....S....S................................S.....................S......S.........S........S.......S.............................................................................................................................................................................................................................................................................................................^Z

[flavorjones]

Ah, never mind, I compiled a custom version of ruby with GC_COMPACTION_SUPPORTED set to 0 and I'm testing it that way.

[flavorjones]

@terceiro Thanks for this! Merging.

[flavorjones]

Note for posterity, this was reported upstream in https://bugs.ruby-lang.org/issues/18779