Allow git upgrade-git-for-windows

[dscho]

Back in the days, we realized that allowing git upgrade-git-for-windows in the Microsoft fork would break user setups pretty quickly because VFS for Git required a specific Git version, and upgrading that without upgrading VFS for Git would break that link.

Therefore, we disabled this command (by implementing a built-in that overrides the script).

However, we recently decoupled that link and want VFS for Git users to upgrade their Git independently. The only catch is that it still needs to be a version from microsoft/git because of the patches supporting VFS for Git (and those patches are pretty much certain never to make it into Git for Windows proper). Meaning: we need git update-git-for-windows to look for updates not in git-for-windows/git but in microsoft/git.

To that end, I modified the Azure Pipeline we're using to build microsoft/git's Git installers, by adding the "Retarget auto-update to microsoft/git" task just before building the installer. It is a PowerShell task, executing this scriptlet:

c:\git-sdk-64-ci\git-cmd.exe --command=usr\bin\sh.exe -lc @"
    sed -i -e 's|git-for-windows/git|microsoft/git|g' \
        -e 's|\\(latest_tag_url=\\).*|\1https://api.github.com/repos/microsoft/git/releases/latest|' \
        -e 's|\\(latest=\\).*|\1`${latest_tag#*\\\\\"tag_name\\\\\": \\\\\"}; \1`${latest%%\\\\\"*}|' \
        /mingw64/libexec/git-core/git-update-git-for-windows &&
    cp /mingw64/libexec/git-core/git-update-git-for-windows /mingw64/libexec/git-core/git-update-git-for-windows.bup &&
    sed -i -e 's|pacman -S --noconfirm git-extra|& \\&\\& cp /mingw64/libexec/git-core/git-update-git-for-windows.bup /mingw64/libexec/git-core/git-update-git-for-windows|' /usr/src/build-extra/please.sh &&
    git -C /usr/src/build-extra commit -m 'Retarget update-git-for-windows to microsoft/git' please.sh
"@

(Yes, I agree, this looks awful, mainly due to the need to quote, escape and re-escape, with backticks for dollar signs and backslashes for double quote characters. That's what you get when you call PowerShell to call Bash which in turn needs to call sed. But hey, at least it works.)

Essentially, it edits the git-update-git-for-windows script such that it looks at microsoft/git's releases instead of git-for-windows/git's.

Side note: it is slightly more involved than that because we're trying to be nice in Git for Windows by not hammering the GitHub API endpoint. Instead, we're looking for the static file https://gitforwindows.org/latest-tag.txt, which is auto-generated as part of each Git for Windows release. However, there are many less users of Microsoft's Git fork, so we're "hammering the GitHub API endpoint" for the microsoft/git releases instead. Also, as git-update-git-for-windows is part of the git-extra package, which for technical reasons is always force-reinstalled just before packaging the installer, we need to add a hack where the modified script is copied back just after that package was reinstalled.

With this hack in place, it is time to drop the patch that disables git update-git-for-windows.

This also obviates the need to fix the bug where git update-git-for-windows would say git (NULL) is not supported (because I forgot to pass PARSE_OPT_KEEP_ARGV0 to the parse_options() function).

A successful installer with this change can be found here: https://dev.azure.com/gvfs/ci/_build/results?buildId=19647 and I verified that it correctly identifies what version to download, and manages to install it as intended.

[derrickstolee]

Thanks for building an installer. I successfully "upgraded" to v2.31.1.vfs.0.0 using the command-line. I appreciate that it closed Git Bash for me 😄 .