RFC: an improved ki18n_install

[Albert Astals Cid]

El dilluns, 6 de març de 2023, a les 20:31:01 (CET), Milian Wolff va escriure:
> Hey all,
> 
> for context please see [1] and [2].
> 
> [1]: https://bugs.kde.org/show_bug.cgi?id=460245
> [2]:
> https://discourse.cmake.org/t/feature-request-add-custom-command-all/7609
> 
> The gist is that me and Igor are annoyed by `ki18n_install` abusing
> `add_custom_target`, which makes the build always dirty. I.e. every time we
> run `ninja` we will, at the very least, run the two mo & ts generation
> targets. For kdevelop, these do non-trivial amounts of work that takes time
> even on a beefy laptop:
> 
> ```
> $ ninja && time ninja
> [2/2] Generating mo...
> [2/2] Generating mo...
> 
> real    0m1,780s
> user    0m5,742s
> sys     0m2,327s
> ```
> 
> I would like to fix this, but first want to get feedback from the KDE
> developers at large.
> 
> First of all: Are all projects using ki18n_install in the way we do? Why is
> no-one else complaining about this so far? Are your po files so small that
> this doesn't take a significant amount of time? Or are there potentially
> just so few of them in your project? KDevelop is heavily plugin based which
> means we have tons of po files. 2464 *.po files to be exact...
> 
> Secondly: does anyone know how to best approach a solution to this issue?
> The problem is that I don't see an easy way to solve it: While Kyle Edwards
> was nice enough to show me a way to tell CMake to not make the custom
> target always-dirty, `k18n_install` suffers from another design deficiency:
> It uses globbing internally and has an undefined amount of inputs and
> outputs, which basically makes it impossible for us to leverage
> `add_custom_command(OUTPUT` here, or?
> 
> As such, it seems like one would need a different approach to this problem
> anyways. Globbing is a known-evil in cmake land, and I would personally
> prefer to have the inputs explicitly listed, just like we do for source
> files etc. Because we have many languages though, listing all possible *.po
> or *.ts files is cumbersome. Instead, what about we maintain the list of
> known languages in the ki18n framework? Then we could have something like
> 
> ```
> ki18n_target(
>     # the target for which we are handling messages
>     TARGET KF5I18n
>     # the translation domain, added as compile_options and to find files
>     TRANSLATION_DOMAIN ki18n5
>     # the root po folder location, to look for the .po/.js files
>     PO_FOLDER ${KI18n_SOURCE_DIR}/po
> )
> ```
> 
> Internally, this would do what is currently done manually:
> 
> ```
> target_compile_options(KF5I18n PRIVATE -DTRANSLATION_DOMAIN=\"ki18n5\")
> ```
> 
> Then it would iterate over the list of known languages and try to find the
> .po or .js file. For every match, we would add_custom_target to generate
> the corresponding .mo/.ts file and add the reverse dependency.
> 
> What do others say to this approach?

How is globbing (checking what is in the filesystem) different from the checking 
against a known list that will check against the filesystem if a file exists?

Seems the same thing but with extra steps to me.

Cheers,
  Albert

> 
> Thanks