[BUG] Changesets that create empty files produce bogus patches

[John A Meinel]

Aaron Bentley wrote:
> I've been working on an exact-patching function for bzr.  It seems very
> easy.  One problem I've found is that bogus patches are used by
> note_patch.  This happens when an empty file is added to the tree:
>
> *** added file sub/sub/emptyfile.txt //
> file-id:emptyfile.txt-20050727055518-be8239eb8f9d79ca //
> text-id:emptyfile.txt-20050727055518-9810517032907c49
> *** added file sub/sub/nonempty.txt ...

Well, if you do:
touch a
diff -u /dev/null a

You get no output.

>
> No patch.  A patch to add an empty file might look like:
> --- /dev/null
> +++ mod/sub/sub/emptyfile.txt
> @@ -0,0 +1,1 @@
> +
> \ No newline at end of file

I don't know that the above is a genuine statement. I would say that we
could easily just realize that an "add" with no content means we should
create an empty file.

I think the above patch looks pretty ugly, and doesn't really make it
clear that it is an empty file. (It could have whitespace)
John
=:->

>
> But we don't get anything like that in note_patch; we get an empty
> string.  I think we should only feed valid patches to note_patch.
>
> Here is a patch that will let you reproduce the problem:
>
> --- read_changeset.py
> +++ read_changeset.py
> @@ -690,6 +690,7 @@
>
>      def note_patch(self, new_path, patch):
>          """There is a patch for a given filename."""
> +        assert len(patch) > 0, "invalid patch for %s" % new_path
>          self.patches[new_path] = patch
>
>      def note_deletion(self, old_path):
>
> Aaron
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