[subset] update hb_subset api with final changes before going stable.

[garretrieger]

Makes some changes to the hb-subset.h API before we stabilize it:

• Remove individual get/set methods for bool properties and instead use an enum of property names.
• hb_subset_input is now const on the hb_subset() call.
• Add hb_subset_or_fail ()
• Adds set/get user data methods that are standard on hb_objects.
• Adds passthrough tables and no subset tables to match fontTools table dropping and retention logic.

I've still got a couple things left to do before this is ready:

• Documentation on the properties enum.
• Documentation for all methods.
• Remove hb_subset() in favor of hb_subset_or_fail()
• Re-order get/set user data methods.

[behdad]

Thanks Garret!

CC @jfkthame @drott @bungeman @mapreri #3012

[drott]

Thanks, @garretrieger! API change generally LGTM but I am not too familiar with the API and its usage. third_party/skia/src/pdf/SkPDFSubsetFont.cpp owners are better suited to answer.

What's hb_subset_input_set_user_data used for?

IIUC this will need a migration off of hb_subset_input_set_retain_gids to hb_subset_set_flags in Skia & Chromium. Usually the way that's done is to define a compile flag in Skia, set this compile flag in Chromium's top level skia/BUILD.gn defines list when rolling HarfBuzz in Chromium. Are you up for handling that migration?

[behdad]

What's hb_subset_input_set_user_data used for?

That's generic part of HB object model; so you can attach arbitrary (say, SkFace) data to a HB object.

[behdad]

That's generic part of HB object model; so you can attach arbitrary (say, SkFace) data to a HB object.

Sometimes used by language bindings.

[garretrieger]

IIUC this will need a migration off of hb_subset_input_set_retain_gids to hb_subset_set_flags in Skia & Chromium. Usually the way that's done is to define a compile flag in Skia, set this compile flag in Chromium's top level skia/BUILD.gn defines list when rolling HarfBuzz in Chromium. Are you up for handling that migration?

Yes I can try and do that migration.

[khaledhosny]

I don't think subset documentation is currently generated, appropriate section need to be added to the files unders /docs.

[behdad]

Thanks. Garret, can you also add a SECTION:hb-subset comment to hb-subset.cc to provide some description for this section of the docs? See top of hb-shape.cc for example.

[garretrieger]

Thanks. Garret, can you also add a SECTION:hb-subset comment to hb-subset.cc to provide some description for this section of the docs? See top of hb-shape.cc for example.

Done.

[garretrieger]

I don't think subset documentation is currently generated, appropriate section need to be added to the files unders /docs.

Done.