Font Dependencies 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 multiple varied fonts providing coverage for languages and so an arbitrary fonts of unknown quality would get selected, so the mechanism is not unreliable.

This change uses instead the default fonts selected 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
Email: tagoh@redhat.com
Release notes owner:

Current status

Targeted release: Fedora 32
Last updated: 2019-12-27
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 terribly 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 gurantee of quality or expected style. This random dependency 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 Changes proposal aims to improve the user experience around font dependencies by moving the meta-provides the langpacks package instead. Langpacks contains various dependencies to use for certain languages, including dependencies for default fonts. so it will resolve the above issues.

Specifically speaking, currently font dependency is generated like this:

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

and at the build time, it is transformed to:

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

After this proposal, 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 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

Check dependencies in langpacks-core-*. They must have corresponding Provides: font(:lang=...) line when asking with rpm -q --provides.
Check dependencies in fonts packages. They must contain no Provides: font(:lang=...) lines
Check that langpacks-core-* pulls in default expected font for the language.

User Experience

Users should see better fonts chosen for 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 of fonts packages to add back the provides.

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

Documentation

N/A

Release Notes

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Changes/FontLangProvidesToLangpacks

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