GH-50412: [CI][GLib][Ruby] Remove some unnecessary Ubuntu 20.04 cases

[raulcd]

Rationale for this change

We did drop support for Ubuntu 20.04 almost a year ago. We should remove cases that cater for it.

What changes are included in this PR?

Found a couple places where we still seem to be doing some minor fixes for Ubuntu 20.04. Clean those up.

Are these changes tested?

CI has been run

Are there any user-facing changes?

No

• GitHub Issue: [Other][Dev] Remove remnants for Ubuntu 20.04 #50412

[github-actions]

⚠️ GitHub issue #50412 has been automatically assigned in GitHub to PR creator.

[raulcd]

I added this just as a mark so I can comment. @kou is the Ubuntu 20.04 mention relevant? Should we be able to replace the version management with version.replace now then? I can try :)

[kou]

Yes! We can use version.replace() here. Could you try the following?

diff --git a/c_glib/doc/meson.build b/c_glib/doc/meson.build
index 82f300aa03..9c92465f1a 100644
--- a/c_glib/doc/meson.build
+++ b/c_glib/doc/meson.build
@@ -20,20 +20,7 @@ gi_docgen = find_program('gi-docgen')
 
 gi_docgen_toml_conf = configuration_data()
 gi_docgen_toml_conf.set('SOURCE_REFERENCE', source_reference)
-# We can't use "version.replace('-SNAPSHOT', '.dev')" here because
-# Ubuntu 20.04's Meson is < 0.58.0.
-if version_tag == ''
-    gi_docgen_version_tag = ''
-else
-    # GI-DocGen doesn't like MAJOR.MINOR.PATCH-SNAPSHOT format.
-    gi_docgen_version_tag = '.dev'
-endif
-gi_docgen_version = '@0@.@1@.@2@@3@'.format(
-    version_major,
-    version_minor,
-    version_micro,
-    gi_docgen_version_tag,
-)
+gi_docgen_version = version.replace('-SNAPSHOT', '.dev')
 gi_docgen_toml_conf.set('VERSION', gi_docgen_version)
 
 gir_top_build_dir = meson.current_build_dir() / '..'

[raulcd]

Seems to be good, @kou do I have to trigger any specific CI job for this or current CI already validates?

[Copilot]

Pull request overview

This PR cleans up remaining Ubuntu 20.04-specific workarounds in Arrow’s CI/build tooling and GLib/Ruby components, aligning the repo with the already-dropped Ubuntu 20.04 support policy (GH-50412).

Changes:

• Remove a Ruby extension build workaround that stripped -std=c++11 from $CXXFLAGS (previously noted as Ubuntu 20.04-specific).
• Remove a CI Emscripten build guard that explicitly rejected UBUNTU=20.04.
• Simplify GI-DocGen version string generation in Meson now that c_glib requires Meson >=0.61.2.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
ruby/red-arrow/ext/arrow/extconf.rb	Drops an Ubuntu 20.04-specific C++ flags workaround from the Ruby extension build.
ci/scripts/cpp_build.sh	Removes an Ubuntu 20.04 Emscripten build block, consistent with dropping 20.04 support.
c_glib/doc/meson.build	Simplifies version formatting using version.replace(...), relying on newer Meson versions already required by c_glib.