Make external diff command work again (fixes #163)

[hartwork]

.. by fixing SHA1 inspection in method copyFileToDiffIfNeeded where any SHA1 matched regex pattern "0*".

That led the external diff feature to always compare the working directory state of a file against itself rather than comparing the version from a given commit against the version from the commit' parent.

Regression from commit 1cb9acf

---

Fixes #163

@elBoberido @tibirna does this fix the issue for you?

[elBoberido]

@hartwork I need to find some time to build qgit from source. Quite busy with other stuff at the moment. By when would you like to know if the patch fixes the bug?

[hartwork]

@hartwork I need to find some time to build qgit from source.

@elBoberido are you on Windows, macOS, or Linux? For Linux it would be:

cd "$(mktemp -d)"
git clone --branch fix-external-diff-regression https://github.com/hartwork/qgit
cd qgit
cmake -S . -B build
make -C build
./build/qgit  # .. on its own Git history

Quite busy with other stuff at the moment. By when would you like to know if the patch fixes the bug?

I'm not sure how to answer that but thanks for the report and the quick reply!

[elBoberido]

@hartwork thanks for the instructions. It seems all dev dependencies where installed, so it was indeed a piece of cake :)

I can confirm that the bug is fixed on your branch and also cross checked that it is present on current master.

Thanks very much for taking care of this.

[tibirna]

I confirm the patch fixes #163 . Looking at what broke it, I see that I had to replace a QRegExp::exactMatch, which does not anymore exist in QRegularExpression, with whatever behaviour the latter introduced. I'm still not sure the latest fix is equivalent with the original code (which seemed to have been matching any SHA containing a string of zeros, not only the ZERO_SHA string). It might be that some obscure StGIT functionality might still not work as expected. I guess not many people are still using StGIT though...

[elBoberido]

Oh, I don't know if it is related to this patch, but now the search and filter is broken

[hartwork]

@tibirna would you prefer ^0*$?

@elBoberido with this commit merged but not the parent commit? Sounds like #165 somehow which was reported fixed on master. Which commit is this broken for?

[tibirna]

@elBoberido thanks a lot for testing. From @hartwork 's instructions you have got a version of the source that doesn't contain my fix for the filtering. It will be fixed in the next release.

[hartwork]

Makes sense, my fix was sitting right on top of qgit-2.12 rather than master 👍

[hartwork]

It will be fixed in the next release.

@tibirna thanks for 2.13 🙏 The new release allowed me to cleanly fix this for everyone using Gentoo: gentoo/gentoo@762624c .