check-case-conflict doesn't notice directory name conflicts

[andyjack]

$ git status
On branch master

Initial commit

Changes to be committed:
  (use "git rm --cached <file>..." to unstage)

    new file:   TEST/foo
    new file:   test/bar

$ git commit -m "Test"
Check for case conflicts...................................................................................Passed
[master (root-commit) 6931ba5] Test
 2 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 TEST/foo
 create mode 100644 test/bar

$ cat .pre-commit-config.yaml
- repo: git://github.com/pre-commit/pre-commit-hooks
  sha: '0d88124ef6343fbbc6c9d2872853f73546c98a3f'
  hooks:
      - id: check-case-conflict

A conflict such as Test/foo and test/foo is caught though.

[guykisel]

Whoops, I think this is my fault. This is a use case I didn't think of.

To fix this I'm thinking that when we generate the set of relevant files to check for conflicts, we should also add to the set all of the parent directories/paths of those relevant files. This has the potential to get messy/inefficient though.

[dizel3d]

[asottile]