narrow: fix flaky behavior described in issue6150 This has been plaguing the CI for a good while, and it doesn't appear to have an easy fix proposed yet. The solution in this change is to always do an unambiguous (but expensive) lookup in case of comparison. This should always be correct, albeit suboptimal. Differential Revision: https://phab.mercurial-scm.org/D10034

patch: make diff --git to differentiate b/w file is empty or doesn't exists Before this patch, as we didn't differentiate the two cases of a file in a context: 1. File doesn't exists 2. File is empty which causes the blob id to be same for both the cases. Now we use `nullhex` for a file which doesn't exists in a context (aligning it with the git diff format) Changes in test file reflect the fixed behavior. Differential Revision: https://phab.mercurial-scm.org/D10001

tests: add a test to demonstrate a bug in `hg diff --git` (issue6486) Issue url: https://bz.mercurial-scm.org/show_bug.cgi?id=6486 This will be fixed in next patch. Differential Revision: https://phab.mercurial-scm.org/D10000