Cannot view asset dif if it is in Git LFS and not already downloaded to local LFS storage

[DJm00n]

Seems like UE Git plugin runs git cat-file --filters to produce temp file to compare with but its binary content is prepended with Downloading $filename ($size) text sometimes.
Source of issue that git cat-file --filters calls smudge filter hook and git-lfs.exe under the hood and outputs text to stderr if file is not already in local FLS storage (.git/lfs/objects):
https://github.com/git-lfs/git-lfs/blob/d2341b5c06cb70cc660f0e2cb9c2012855998566/lfs/gitfilter_smudge.go#L87

I think you need find a way to ignore stderr output here:
https://github.com/SRombauts/UE4GitPlugin/blob/46d94ff40f7b6bcc73639f9473eb03d63649747f/Source/GitSourceControl/Private/GitSourceControlUtils.cpp#L1014

I just added new param void * PipeErrorChild to FGenericPlatformProcess and implemented it on each platform:

-       static FProcHandle CreateProc( const TCHAR* URL, const TCHAR* Parms, bool bLaunchDetached, bool bLaunchHidden, bool bLaunchReallyHidden, uint32* OutProcessID, int32 PriorityModifier, const TCHAR* OptionalWorkingDirectory, void* PipeWriteChild, void * PipeReadChild = nullptr);
+       static FProcHandle CreateProc( const TCHAR* URL, const TCHAR* Parms, bool bLaunchDetached, bool bLaunchHidden, bool bLaunchReallyHidden, uint32* OutProcessID, int32 PriorityModifier, const TCHAR* OptionalWorkingDirectory, void* PipeWriteChild, void * PipeReadChild = nullptr, void * PipeErrorChild = nullptr);

Current implementation just maps stderr to PipeWriteChild on Windows and Mac but ignores it at all on Linux.
Maybe you can find a better way to fix this obvious bug.

[SRombauts]

ha, yes, I've already encounter this, it's even possible I have already consider quite the same fix, but I try to avoid modifying the engine low level APIs since it's hard to get these change accepted upstream

[geordiemhall]

Not sure if a different workaround was ever found for this, but it looks like UE5 will finally have a way to separate stdout and stderr we could use to properly fix this LFS issue
https://github.com/EpicGames/UnrealEngine/commit/06f3ad8098ab3c87f91dc5b0a1fe40a78502b646