Add Jansson dependency

[manuq]

Emacs 27.1 uses this library if available.

Fixes #35

[flathubbot]

Started test build 36802

[flathubbot]

Build 36802 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/35430/org.gnu.emacs.flatpakref

[muep]

@manuq thank you for the PR.

Are there other effects from this, apart from JSON operations becoming faster? If the changes are limited to performance, which use cases in particular suffer from the elisp-based JSON support?

I am mainly asking to balance the benefit against the added work of keeping the bundled libjansson up to date and the risk that would result from neglecting that maintenance.

[muep]

One thing that bothers me about this PR is that it does not seem to build correctly with flatpak-builder 1.0.5 as shipped in Debian. It does get though the automatic test, which makes me suspect that this is related to the exact version of flatpak-builder.

build.log

[hfiguiere]

It did build with flatpak-builder 1.0.5 on Debian Buster (Raspberry Pi, 64-bits). Not sure what happened on your system.

[muep]

Looks like my initial attempt at logging the build was missing its stderr. Here is a build log that actually has the error visible.
build.log

[muep]

So now after some more studying, it seems to me that flatpak in Debian stable does not do anything to activate content from /app/lib during the build. It does get used when the build results are run, though /etc/ld.so.conf.

On a Fedora 33 VM that I set up as a comparison, LD_LIBRARY_PATH is set up to refer the dynamic linker to /app/lib:

LD_LIBRARY_PATH=/app/lib:/usr/lib/x86_64-linux-gnu/GL/default/lib:/usr/lib/x86_64-linux-gnu/openh264/extra

This seems to depend more on the version of flatpak rather than flatpak-builder.

[muep]

The problems I saw seem to be a recently introduced problem in the Debian package. I filed it as https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=980323

@manuq , now that I understand what this confusing problem resulted from, I would like to ask a small addition to this change. Namely, the files not needed from Jansson at runtime should be removed. There seems to be an example of what to specify at https://github.com/flathub/com.github.paolostivanin.OTPClient/blob/fe78de8dc086a6b80ac6f4080182584b93f8b880/com.github.paolostivanin.OTPClient.yaml#L31

[flathubbot]

Started test build 37080

[manuq]

@manuq , now that I understand what this confusing problem resulted from, I would like to ask a small addition to this change. Namely, the files not needed from Jansson at runtime should be removed. There seems to be an example of what to specify at https://github.com/flathub/com.github.paolostivanin.OTPClient/blob/fe78de8dc086a6b80ac6f4080182584b93f8b880/com.github.paolostivanin.OTPClient.yaml#L31

Ah thanks for the reference, I couldn't find any. PR updated.

Are there other effects from this, apart from JSON operations becoming faster? If the changes are limited to performance, which use cases in particular suffer from the elisp-based JSON support?

All I know is from the NEWS file and my personal experience. I sometimes have buffers with giant JSON data, and I can perceive a noticeable performance boost in JSON operations. Without this Emacs UI freezes in those buffers. Other than that, I don't see any other effects, and there's nothing mentioned in the NEWS file as well.

I am mainly asking to balance the benefit against the added work of keeping the bundled libjansson up to date and the risk that would result from neglecting that maintenance.

Yes I will understand and happily accept your decision, if you think this shouldn't be merged because of the costs of maintenance.

[flathubbot]

Build 37080 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/35700/org.gnu.emacs.flatpakref

[muep]

Hi @manuq - there is still still one file that I would like to be absent. The /app/lib/libjansson.a file should be unnecessary at runtime.

Otherwise, I think the change looks good.

[flathubbot]

Started test build 37083

[manuq]

Hi @manuq - there is still still one file that I would like to be absent. The /app/lib/libjansson.a file should be unnecessary at runtime.

Sounds good. Fixup added.

[muep]

This probably should be just /lib/libjansson.a - similar to how you remove the other bits.

[manuq]

Ouch, yes, sorry.

[flathubbot]

Build 37083 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/35703/org.gnu.emacs.flatpakref

[flathubbot]

Started test build 37085

[flathubbot]

Build 37085 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/35705/org.gnu.emacs.flatpakref

[muep]

Thanks you @manuq for the PR and your patience 😄