Pull Request inline comment appears on GitHub.com but not in extension

[jcansdale]

• GitHub Extension for Visual Studio version: 2.4.1
• Visual Studio version: All

What happened (with steps, logs and screenshots, if possible)

1. Added inline comment using GitHub Extension: Ensure that the GitHubPaneViewModel is initalized. #1426 (review)
2. Comment appears on PR page (possibly the line above where I added it, not sure)
3. Open IPullRequestSessionManager.cs from PR details view
4. Inline comment doesn't appear on diff view or PR file tree

Diagnosis

It appears the issue caused a dependency in the use of the git diff --indent-heuristic option. GitHub.com uses this but command line and libgit2 doesn't use it by default.

You can see the difference in the output from the following commands (on the github/VisualStudio repo):

git diff a39d0bb8..87058c77
git diff a39d0bb8..87058c77 --indent-heuristic

See here for when it was introduced:
https://github.com/github/experience-engineering-code/issues/483

Fix

The --indent-heuristic option is available in libgit:
https://github.com/libgit2/libgit2/blob/da8138b01217824cf211fa491608a7b067cf8e43/include/git2/diff.h#L134

But isn't currently available in libgit2sharp.

https://github.com/libgit2/libgit2sharp/blob/master/LibGit2Sharp/Core/GitDiff.cs#L191
Needs to learn about the new flag.

https://github.com/libgit2/libgit2sharp/blob/3f9b415fa1edfc31ce1ec2b4b3d18441c34adfff/LibGit2Sharp/Diff.cs#L21
Needs to know to set it.

We would need a DiffModifiers.IndentHeuristic bool

If you have a GitDiffOptions then you can turn on bit (1 << 31) of the Flags (which unfortunately we don't have access to). See libgit2/libgit2@7e3faf5

@ethomson said he might have a chance to tackle this on on a long flight tomorrow. It would be very much appreciated if he was able to! 😃

Update: it looks like this has changed to GIT_DIFF_INDENT_HEURISTIC = (1u << 18) in recent versions.
libgit2/libgit2@2d9d246

[jcansdale]

Here's a hacked version of LibGit2Sharp that should turn this on by default:
LibGit2Sharp.zip

The selected lined below have been added.

Even with this patched version I can't add a comment on that line. 😭

I'll double check the fix and see if I'm missing something. 😕

• It looks like Libgit2Sharp 0.23.1 is using LibGit2 0.25.1, which is before the version that includes the GIT_DIFF_INDENT_HEURISTIC option. 😭
• Libgit2Sharp 0.24.1 is using LibGit2 0.26.2 (which also doesn't contain the option).
• Targeting .NET 4.6.0 was removed here Remove the net40 target and other misc cleanup libgit2/libgit2sharp#1511
• Recent versions of LibGit2Sharp target .NET 4.6.1 (Provide .NET 4.6.1 framework target libgit2/libgit2sharp#1606) which isn't compatible with Visual Studio

You can see the difference by doing:

git diff 8887a8..a39d0b --indent-heuristic -- src/GitHub.Exports.Reactive/Services/IPullRequestSessionManager.cs

git diff 8887a8..a39d0b --no-indent-heuristic -- src/GitHub.Exports.Reactive/Services/IPullRequestSessionManager.cs

[jcansdale]

A proof of concept fix for this works! 🎈