`ceylon src` should support checking sources from source repo

[FroMage]

We should add the following annotation to the language module:

shared annotation class SourceRepository(shared String url, 
  shared String branch = "master", 
  shared String repositoryType = "git"){}

So we can annotate modules to point to the source repository. Then, ceylon src ceylon.openshift/1.3.0 will prompt:

$ ceylon src ceylon.openshift/1.3.0
ceylon.openshift is available from git at https://github.com/ceylon.openshift (master), 
do you want to check it out from git or just fetch the source files for that release?
Fetch from git [Y/Enter], or just source files [N]: Y
git clone https://github.com/ceylon.openshift
cd ceylon.openshift
git checkout master

Pros:

• That's a lot more useful than just the source files, as it includes the build scripts and config files, possibly overrides
• We can also use the same info from Maven modules
• That info can easily be stuffed into a Herd API for consumption

Cons:

• Requires changing the branch parameter on release (perhaps ceylon version --set should prompt to include this change?)
• Needs to be duplicated on each module of a project (like SDK)

[quintesse]

I would wholeheartedly agree with a ceylon src that would take GitHub URLs, but adding those URLs to the code... personally I don't really like the idea.

[FroMage]

Why not? Maven does that. It's useful, it also points the users to where the entire source code is, and which tag/branch to use in the module documentation.

[quintesse]

Where How does maven do that? I've never seen Java code with URLs to their source code repos.

[FroMage]

Well, in the pom.xml of course, that's where Maven defines modules.

[quintesse]

But that's indeed a Maven-only project-level artifact. That's not something we have. But on the other hand it's the only logical place we have. Ah well.

[tombentley]

For me the problem is maintaining those annotations. If I do a git branch I have to remember to update the annotations, and there must exist at least one commit in which the annotations are wrong.

Maven has the release plugin which tries to atomically keep version control and poms in sync when you release version x and start on version y. I tried to use it once and it was not an experience I'd wish to repeat or inflict on users.

Another problem is that you cannot guarantee that the binary you're running was actually compiled from the source code you've obtained.

So I don't really have a problem with the url and repositoryType attributes, it's the branch which just looks flaky, because it's so hard to maintain right. What might work better was a way to insert a git hash automatically at compile time. We'd need plugins for each RCS, but maybe we'd only need to support git initially.