Test ls_tree() with subfolder.

[jdblischak]

I was testing out the function ls_tree() and observed some strange behavior. I noticed that the tests in tests/tree.R did not cover the use cases described in man/ls_tree.Rd. Specifically, the presence of a subfolder gives ls_tree() problems.

This PR converts the examples from ?ls_tree into a test file. It also adds additional tests corresponding to the results of git ls-tree.

To compare, below is the output of git ls-tree -lr HEAD. There are 3 lines corresponding to the 3 files in the repository.

$ git ls-tree -lr HEAD
100644 blob 4c5fd919d52e3c1b08f7924cfa05d6de100912fd      11    example-1.txt
100644 blob f89598da398eb016c504a5e272cb3eb1a31e2687      11    example-3.txt
100644 blob 20d5b672a347112783818b3fc8cc7cd66ade3008      12    subfolder/example-2.txt

In contrast, ls_tree() returns 4 lines. It includes the tree subfolder as its own line, and then the final line does not include the file inside the subfolder.

ls_tree(repo = repo)
    mode type                                      sha path          name   len
1 100644 blob 4c5fd919d52e3c1b08f7924cfa05d6de100912fd      example-1.txt    11
2 100644 blob f89598da398eb016c504a5e272cb3eb1a31e2687      example-3.txt    11
3 040000 tree 10cf266f7fd804e61b37419841a45699bc6fe74b          subfolder    NA
4                                                                         21899

Lastly, I found it strange that the argument tree accepts the characters "HEAD:subfolder" and "HEAD:", but not "HEAD".

> ls_tree(tree = "HEAD:", repo = repo)
    mode type                                      sha path          name   len
1 100644 blob 4c5fd919d52e3c1b08f7924cfa05d6de100912fd      example-1.txt    11
2 100644 blob f89598da398eb016c504a5e272cb3eb1a31e2687      example-3.txt    11
3 040000 tree 10cf266f7fd804e61b37419841a45699bc6fe74b          subfolder    NA
4                                                                         21899
> ls_tree(tree = "HEAD", repo = repo)
Error in data.frame(.Call(git2r_tree_walk, tree, recursive), stringsAsFactors = FALSE) : 
  Error in 'git2r_tree_walk': 'tree' must be an S3 class git_tree

[stewid]

I have finally come around to fix the problems you identified in 'ls_tree' - apologies for the delay.
Thanks.

[jdblischak]

Thanks! I tested and confirmed that ls_tree() now gives results similar to git ls-tree -lr.