add git sparse checkout

[mobileoverlord]

This is a start to adding sparse checkout to the GIT SCM.

Sparse checkout can be used for picking a dep from a repo which may contain many deps in sub folders

For example.

The git repository
https://github.com/nerves-project/toolchains
contains many toolchains including
nerves_toolchain_armv5tejl_unknown_linux_musleabi

To use git and single out that subfolder int he repo as the dependency destination we could use sparse

{:nerves_toolchain_armv5tejl_unknown_linux_musleabi, github: "nerves-project/toolchains", sparse: "nerves_toolchain_armv5tejl_unknown_linux_musleabi"}

[mobileoverlord]

Things to do yet

• Verify update / locks
• Verify git version minimum for sparse checkout (1.7.0)
• Add tests

[josevalim]

You can store the :dest option as :checkout or :git_dest so you don't need to use replace_suffix later on.

[josevalim]

One of the scenarios we will need to test is using the same checkout and moving from sparse to non-sparse and vice-versa (i.e. add and remove the sparse option, does it still work?)

[ericmj]

You cannot use sparse with the other options?

[mobileoverlord]

I agree @ericmj I misunderstood the intention. I have changed it to revert that test and I have also added the ability to define multiple sparse options as the sparse function allows this. I haven't figured out a reason you would need to do this to satisfy a dependency, but, I also don't know of a reason not to allow it.

As per testing turning it off and on and updating. I didn't see any active git tests in the suite. Should I just try these scenarios out, or do we want to use this time to make additional tests?

[mobileoverlord]

hum thats curious, those tests didn't fail for me

[josevalim]

I don't think we should allow multiple sparse because dest will point to only one of them.

[mobileoverlord]

I don't understand why I am getting different test results. I don;t get this failure when I run make test but I do get other failures

test uniq/1 (EnumTest.Range)
     test/elixir/enum_test.exs:1236
     ** (UndefinedFunctionError) function Stream.Reducers.uniq_by/1 is undefined or private. Did you mean one of:

           * uniq_by/1
           * uniq_by/2

     stacktrace:
       (elixir) Stream.Reducers.uniq_by(#Function<187.4743325/1 in Enum.uniq/1>)
       (elixir) lib/enum.ex:2489: Enum.uniq_by/2
       test/elixir/enum_test.exs:1237: (test)

[mobileoverlord]

I figured out the tests 😄

[mobileoverlord]

so I added a helper which chooses :git_dest if it exists and falls back to :dest. I talked with @ericmj and I am not sure which approach is better, this or always having :git_dest. We would have to fix a handful of tests to include the git_dest key.

[mobileoverlord]

Also, I've been using this sample for testing
https://github.com/mobileoverlord/sparse