Forge-hosted projects packaging automation

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Accepted proposal
This proposal has been accepted and is now part of Packaging Guidelines, section Referencing Source

Projects published on a “forge” can be packaged using the forgemeta macro.

This proposal is a requisite for the More Go packaging draft.

What is a “forge”?
Any software publishing website, permitting the download of source code archives on normalized URLs, that can be deduced from version, commit, tag, scm, extension values and a project root URL on the website, is a “forge” that can be supported by forgemeta.

Links

• Accepted guidelines
• FPC ticket
• redhat-rpm-macros RFE with the macro file → DONE
• fedora-release RFE to make dist munging safe
• packaging@lists.fedoraproject.org discussion
• pagure.io RFE to make pagure.io compatible with forgemeta
• GitLab CE RFE to remove GitLab quirks
• More Go packaging draft that depends on this proposal.

Benefits and limitations

• Benefits:

1. Fedora packagers no longer need to know about the URL structure of well-known forges.
2. Spec files are simpler, less error-prone, easier to maintain and audit.
3. Forge URLs can be defined and fixed in a single place, without waiting for guidelines to percolate.
4. The macros are mostly written in Lua, making them more verbose but easier to adjust and extend.
5. The macros are written in Lua and can perform error handling.
6. It is very easy to switch from commit to tag to version (or any combination of those).
7. spectool just works©.
8. scm snapshot date is exact and does not rely on a variable which may or may not have been updated.
9. Almost all the computations are done in optional rpm variables that can be ignored by the packager if he does not need or does not like the result.
10. Fedora forge know-how can be capitalized over time.
11. The macro normalizes common spec constructs such as archivename.

• Limitations:

1. The macro is not intended to be used in spec files that package multiple forge archives (it could probably be extended, is the added flexibility worth the complexity?).
2. The macro needs to be updated when a forge changes its structure (but better changing one place than lots of spec files).
3. New forges need to be added to the macro before it can be used with them.
4. dist munging can not be easily reverted once forgemeta has been called. The solution would be to change fedora-release to define dist as %{?distprefix}.fcxx
5. dist commit date computation relies on source files with the correct modification time (incorrect source file modification time → incorrect dist date).
6. The macro highlights some historical rpm design mistakes: bad separation of upstream and package metadata, special magic variables. This is why version declaration occurs in an unusual (for rpm) order and requires a specific syntax.

Usage

A. The packager declares upstream-dependent metadata :

• forgeurl: the project URL on the target software hosting service
• version: the project release to package, if non nil (as Version: xxx)
• commit: the commit hash to package, if any
• tag: the project tag to package, if any

B. The packager calls %forgemeta. This macro will attempt to compute and set the following variables if they are not already set by the packager:

• forgesource: an URL that can be used as SourceX: value
• forgesetupargs: the correct arguments to pass to %setup for this source; used by %forgesetup and %forgeautosetup
• archivename: the source archive filename, without extentions
• archiveext: the source archive filename extensions, without leading dot
• archiveurl: the url that can be used to download the source archive, without renaming
• scm: the scm type, when packaging code snapshots (commits or tags)

If the macro is unable to parse the %{forgeurl} value the packager should set at least %{archivename} and %{archiveurl} before calling it.

The macro also accepts the following optional parameters:

• -u <url>: ignore %{forgeurl} even if it exists and use <url> instead; note that the macro will still end up setting <url> as %{forgeurl} if it manages to parse it
• -s: silently ignore problems in %{forgeurl}, use it if it can be parsed, ignore it otherwise
• -p : restore problem handling, override -s
• -v : be verbose and print every variable the macro sets
• -i: Print some info about the state of variables the macro may use or set at the end of the processing

C. The packager uses the computed metadata as needed.

%{dist} modification for code snapshots

Most of the macro behavior is optional and safe. You can override the computed rpm variables values before or after the %forgemeta call, or ignore those variables altogether and don't use them in the rest of the spec file. There is one exception:

The macro will change the value of %{dist} in a non-reversible way, when packaging a code snapshot (commit or tag). Redefine %{dist} manually after the %forgemeta call if you don't like the result. Alternatively, don't use %forgemeta.

The root cause is that Fedora does not provide currently provide a placeholder prefix macro inside %{dist} that could be adjusted without redefining %{dist} as a whole.

Extending the macro

If the project you're packaging is published on a software publishing service forgemeta has no knowledge of, don't be sad, that's pretty easy to fix.

• note down the archive URLs you want to generate for versions, tags and commits
• locate the latest version of the forgemeta macro (it should be installed in /usr/lib/rpm/macros.d/macros.forge-srpm by fedora-rpm-macros)
• copy the definition block closest to your needs after the other definition blocks. It should look like :

 if (forge == "vvv") then
 […]
 end

or

 if (string.match(forge, "vvv")) then
 […]
 end

• change the "vvv" value

Don't be afraid of Lua patterns!
While the Lua pattern syntax is a bit unusual, it is quite simple. You can launch an interactive interpreter to experiment in with the lua command. Most of the times the existing forgemeta macro will already contain something similar to what you need to accomplish.

• adapt the initial normalization rule

    forgeurl = string.match(forgeurl, "www")

• adapt the initial error message

     rpm.expand("%{error:"xxx URLs must match yyy!\\n}")

• set the hosting service defaults

   safeset("archiveext",     "tar.bz2")
   safeset("forgesetupargs", "-n %%{archivename}")
   if (commit ~= "") or (tag ~= "") then
     safeset("scm", "git")
   end

• scrap the variables you need from forgeurl using:

      local myvariable = string.match(forgeurl, "zzz")

• use your variables to define archivename and archiveurl in the following if tag/commit/version block
• install the result in /usr/lib/rpm/macros.d/macros.forge-srpm
• test with forgemeta -i or forgemeta -v and rpmbuild -bs myspecfile.spec
• submit the enhancement for inclusion in redhat-rpm-macros once it works satisfactorily.