vcs-browser URL type in metadata.xml

[kfjahnke]

freedesktop.org specifies the content of metadata.xml in this document. In the url/ part, the specification lists a URL type 'vcs-browser':

`vcs-browser

URLs of this type should point to a webpage on which the user can browse the sourcecode. `

I tried to include this file in my metadata.xml, but it failed the validation. Maybe it's a new addition to the list of URL types, and the validation code is not yet ready to accept it? Including it actually fails the validation, so maybe code is needed to ignore it, if it's unwanted.

[probonopd]

Maybe it's a new addition to the list of URL types, and the validation code is not yet ready to accept it?

Most likely... these specs seems to be a moving target so that it's almost impossible to keep up. Can you find out in which version it was added to appstreamcli?

[kfjahnke]

this post mentioned a 'recent' addition of the vcs-browser URL type 'a year ago'. And this one also complains about it - also 'a year ago'. So the new URL type seems to have been around for a while. I can't figure out the precise version when it was added, but it should have been more than a year ago, if that is any help to you.

[probonopd]

Since the appstreamcli versions that came out a year ago won't run on the oldest still-supported LTS releases of distritbutions at this time, we can't use such new additions to the spec yet. Maybe revisit in ~3 years...

[kfjahnke]

Re. ubpm: here we have a project also using this URL type. I think people handing in AppImages for inclusion in the catalog will rather follow the specification than figuring out that using this URL type makes the outdated appstreamcli version you use fail. What to do? Since the input is XML, one might filter it to throw out the offending element, which should not be too hard - probably easier than trying to mess with appstreamcli and build a version which ignores the element.

[kfjahnke]

Filtering the XML: to specifically remove the url with type=vcs-browser, one might use xmlstarlet:
xmlstarlet ed -L -d "component/url[@type='vcs-browser']" some.xml (working in-place)
cat some.xml | xmlstarlet ed -d "component/url[@type='vcs-browser']" > filtered.xml (not working in-place)

[probonopd]

Sooner or later we may drop support for AppStream due to it being a moving target.

[kfjahnke]

Do you mean to drop appstreamcli to process/validate the metadata, or to use a different system of providing the metadata altogether? While it's used, prefiltering the XML is a viable option, and I've seen xmlstarlet used in your project, so it wouldn't add another dependency. For vcs-browser, it would avoid the pitfall that the exit code is the same for runs with errors as for runs with warnings (namely, 3), which is unfortunate and makes it more difficult to handle recent additions.

[probonopd]

I mean that the AppStream format is not ideal for AppImage because it keeps changing over time. We need a format that will not change over time (only additions like new fields should be allowed, not changes in the existing fields). Ideally something in YAML that can be easily created from existing AppStream. But right now I don't have the time currently to think about this.

[1Maxnet1]

We need a format that will not change over time (only additions like new fields should be allowed, not changes in the existing fields).

In the meantime appstream reached version 1.0 and since then has a stable format that does follow semantic versioning (aka only adds fields instead of removing old ones). So this would allow to continue using appstream format.