Changes/FontLangProvidesToLangpacks

Move fonts language Provides to Langpacks

Summary

Move Provides: font(:lang=...) from fonts packages into the langpacks package, giving predictable default fonts for language scripts.

Motivation

Currently fonts packages has auto-generated font(:lang=...) provides, which can be used as a dependency identifier to satisfy font coverage required for a certain language requirement. This is used by GTK application to install missing fonts via PackageKit for example. However in practice it has not been very useful since usually there are assorted multiple fonts that provide the language coverage and so an arbitrary fonts of unknown quality would get selected, so the mechanism is not reliable.

This change uses instead the default fonts chosen in langpacks for each language, to give reliable predictable default fonts for each language and improve the user application experience around fonts.

Owner

• Name: Akira TAGOH, Parag Nemade
• Email: tagoh@redhat.com, pnemade@redhat.com
• Release notes owner:

Current status

• Targeted release: Fedora 32
• Last updated: 2020-01-13
• Tracker bug: <will be assigned by the Wrangler>

Detailed Description

The language based metadata for fonts packages was introduced in Fedora 11. The idea being to provide a mechanism to find and install a font for missing glyphs through PackageKit and was useful for minority languages which might be missing default installed fonts packages. But the user experience was generally not very good.

Users cannot predict which fonts will be installed. This often leads to poor fonts choices installed, particularly for languages with too many available fonts such as English, since the first font found lexically will be arbitrarily chosen with guarantee of quality or expected style. This random dependency resolution sometimes introduces highly unexpected results too - for example a font from an external repository may get chosen by chance. This would be particularly problematic when composing ISOs, eg when including EPEL.

So this Change proposal aims to improve the user experience around font dependencies by moving the Provides: tag into the langpacks package instead. Langpacks contains various dependencies to help to use that langpacks language. Langpacks have langpacks-core-* subpackages which installs default font and input-method. Once Provides: tag added to these subpackages, whenever missing glyph font installation is requested, only langpacks-core-<lang> package will get installed which will be anyway already having default font set using Requires: tag.

Currently font provides are auto-generated using fc-query by rpm like this:

$ fc-query -f %{=pkgkit}  /usr/share/fonts/dejavu/DejaVuSans.ttf
font(dejavusans)
font(:lang=aa)
font(:lang=ab)
...

and at the font package build time, it is transformed to:

Provides: font(dejavusans)
Provides: font(:lang=aa)
Provides: font(:lang=ab)
...

After this proposal will be implemented, the above result will be:

Provides: font(dejavusans)

and then add Provides: font(:lang=...) line to corresponding sub-packages langpacks-core-*.

So asking for a font for a certain language through PackageKit will be achieved by langpacks-core-* instead of a random font package.

Benefit to Fedora

This proposal will provide reliable, predictable, and consistent font dependencies.

Scope

• Proposal owners:
  • Update fontconfig to drop generating font(:lang=...) from the alias of the formatter for %{=pkgkit}
  • Add a line of Provides: font(:lang=...) to each langpacks-core-.... For instance, Provides: font(:lang=hi) needs to be added to langpacks-core-hi.

• Other developers: Release Engineers needs to rebuild all fonts packages with the updated fontconfig package.

• Release engineering: #9132
  • List of deliverables: None

• Policies and guidelines: None

• Trademark approval: None

Upgrade/compatibility impact

Some packages may be installed after upgrading if corresponding langpacks-core-* packages isn't yet installed.

How To Test

1. Use https://copr.fedorainfracloud.org/coprs/pnemade/FontLangProvidesToLangpacks/ repo for F31+ releases
2. Check that langpacks-core-* provide corresponding font(:lang=...) using rpm -q --provides.
3. Check that fonts packages no longer provide font(:lang=...).
4. Check that langpacks-core-* pulls in the default expected font for the language.

User Experience

Users should see better quality fonts for the chosen languages when they install a font to cover a certain language script through PackageKit or through font meta dependencies of other packages.

Dependencies

All fonts packages

Contingency Plan

• Contingency mechanism: proposal owners will revert all the changes and rebuild all fonts packages to add back the provides.

• Contingency deadline: the beta freeze
• Blocks release? No
• Blocks product? N/A

Documentation

N/A