darcs equivalent for git's submodules? - git-submodules

Question

so yeah just wondering if darcs has anything equivalent to git's submodules.
i.e. lets say I have a repo (myapp) and I have a folder in it called mylibrary. mylibrary doesn't really have anything to do with myapp's development, it just has to be included. mylibrary's development happens in it's own repo, but when someone pulls myapp, it'll also pull an up-to-date version of mylibrary. any ideas?

Answer 1

My first thought: Since darcs is simpler than git (i.e., no branches and remotes--instead you just use directories and URLs, and it's your task to manage them), a darcs submodule would not give much more than what you can achieve with standard things like subdirectories or files inside you darcs repo.
If you needed a submodule in order to fix a certain state of the source of the used library, you could perhaps simply put a copy of the library's repo as a subdir and add it to your project's darcs. Compared to git, this would have the disadvantage of bloating the data transfer when someone gets your repo.
If you needed a submodule to tell those who get your repo where to get the updated source of the library (without bloating the size of your repo), you could simply put an URL and an instruction into a README file, or a script, or whatever. Compared to git, the disadvantage is that the state of the library's source as it was when you used it wouldn't be recorded in your commit, so people might get another version of the library, and the compilation wouldn't succeed, and it wouldn't be clear why.
So, the really interesting goal of a submodule could be not just to tell people where to get the library source from (as you write in the question), but to record the state of the subproject that you have actually used for compiling your project, and not to bloat your repo for those who don't want to get the source of the subproject.
Probably, this goal could also be achieved by storing more complex metadata about the state of the subproject, and a more complex hook to get exactly that state (or--by choice--another state) of the subproject. AFAIK from the docs, there is no built-in mechanism for such submodules.
Update (found on the darcs site):
http://darcs.net/Ideas/Subrepositories;
http://darcs.net/Ideas/NestedRepositories.
So, darcs will notice another darcs repo inside your working and it won't touch it. So the first way I've suggested above is shut (if you leave the darcs metadata there).
The second way is like something suggested in one of the section of the latter link. (They suggest an "uglu" script for something like this.)
Another (3rd) idea
Import the patches from the repo you intend to have as a submodule, but first move all files into a subdir. If it were possible just to apply such a moving special patch once and if it was effective for all the patches you import from the repo intended as submodule, but not to the patches you import from a "branch" of the main repo...
...well, it could be a special variant of the pull command (say, import) and of the push command (say, export) that would additionaly translate the paths accordingly.

Answer 2

I don't know of any submodule concept for darcs, which means the usual way to refer to another (shared) repo from a darcs repo would be through symlinks.
Since symlinks aren't supported with darcs, that means you needs to put in place a "posthook sh update-symlinks.sh" hook script to restore those links.
But you could also use add to this hook a check to see first what version of the lined repo is currently loaded, and update that version if needed (provided you have store in one way or another the exact version you need for that shared repo).
That last suggestion is actually close to the implementation of Git submodules or Mercurial subrepos.