What version are you running?
3.0 Final
What's the URL of the page containing the problem?
http://localhost:8080/r/9/diff/1#index_header
What steps will reproduce the problem?

Add a Mercurial repo to RB
Create a simple patch file to an existing file in repo
Got to localhost:8080/r/new/ and upload patch file (from previous hg diff or something like that)
Publish review request
Click on "diff"
RB shows an exception for that part of diff


What is the expected output? What do you see instead?
First: Show the diff correctly
Second: Show the part of that patch file as RB 3.0 says it "Improved display for patch errors." in release notes. But I still cannot see anything useful.
What operating system are you using? What browser?
Linux, Firefox 57
Please provide any additional information below.
There was an error displaying this diff.


The file 'AUTHORS' (rUNKNOWN) could not be found in the repository



This may be a bug in the software, a temporary outage, or an issue

   with the format of your diff.




Please try again, and if you still have trouble,

   contact support.







Details



Traceback (most recent call last):

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/views.py", line 330, in get

    response = renderer.render_to_response(request)

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/renderers.py", line 58, in render_to_response

    return HttpResponse(self.render_to_string(request))

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/renderers.py", line 76, in render_to_string

    large_data=True)

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 298, in cache_memoize

    compress_large_data))

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 252, in cache_memoize_iter

    items = items_or_callable()

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 295, in <lambda>

    lambda: [lookup_callable()],

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/renderers.py", line 75, in <lambda>

    lambda: self.render_to_string_uncached(request),

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/renderers.py", line 89, in render_to_string_uncached

    request=request)

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/diffutils.py", line 698, in populate_diff_chunks

    chunks = list(generator.get_chunks())

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/chunk_generator.py", line 786, in get_chunks

    for chunk in super(DiffChunkGenerator, self).get_chunks(cache_key):

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/chunk_generator.py", line 107, in get_chunks

    large_data=True)

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 298, in cache_memoize

    compress_large_data))

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 252, in cache_memoize_iter

    items = items_or_callable()

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 295, in <lambda>

    lambda: [lookup_callable()],

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/chunk_generator.py", line 106, in <lambda>

    lambda: list(self.get_chunks_uncached()),

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/chunk_generator.py", line 792, in get_chunks_uncached

    self.encoding_list)

  File "/home/andre/git/reviewboard/reviewboard/diffviewer/diffutils.py", line 227, in get_original_file

    request=request)

  File "/home/andre/git/reviewboard/reviewboard/scmtools/models.py", line 404, in get_file

    large_data=True)[0]

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 298, in cache_memoize

    compress_large_data))

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 252, in cache_memoize_iter

    items = items_or_callable()

  File "/home/andre/tmp/rb/lib/python2.7/site-packages/djblets/cache/backend.py", line 295, in <lambda>

    lambda: [lookup_callable()],

  File "/home/andre/git/reviewboard/reviewboard/scmtools/models.py", line 403, in <lambda>

    request)],

  File "/home/andre/git/reviewboard/reviewboard/scmtools/models.py", line 597, in _get_file_uncached

    base_commit_id=base_commit_id)

  File "/home/andre/git/reviewboard/reviewboard/scmtools/hg.py", line 51, in get_file

    base_commit_id=base_commit_id)

  File "/home/andre/git/reviewboard/reviewboard/scmtools/hg.py", line 465, in cat_file

    raise FileNotFoundError(path, rev)

FileNotFoundError: The file 'AUTHORS' (rUNKNOWN) could not be found in the repository