Add support for different LFS url to vcpkg_from_git

[DDoS]

Add an optional argument to the LFS keyword in vcpkg_from_git, so a different URL can be used. Update the documentation and tests.

Fixes #28593

[DDoS]

The tests are failing on Windows because the agent image has an old version of Git LFS: 2.13.3 which is almost two years out of date. The test script needs the --force flag on prune, which is a feature that came in the next release (3.0.0). I also noticed that the macOS and Linux images don't have LFS installed.

I'm not sure how to fix this other than updating the VM images, which I don't know how to do.

[JonLiu1993]

The tests are failing on Windows because the agent image has an old version of Git LFS: 2.13.3 which is almost two years out of date. The test script needs the --force flag on prune, which is a feature that came in the next release (3.0.0). I also noticed that the macOS and Linux images don't have LFS installed.

I'm not sure how to fix this other than updating the VM images, which I don't know how to do.

@vicroms, could you please take a look?

[vicroms]

@BillyONeal would it be possible to update Git LFS on our VMs?

[BillyONeal]

@BillyONeal would it be possible to update Git LFS on our VMs?

We are deploying the copy that comes with Visual Studio. If the user needs a copy more recent than that I have serious concerns about being able to accept that in a port.

[DDoS]

@BillyONeal This is just for testing. The scripts don't need anything more recent normally, but I can't implement a proper test without some newer LFS features. I could just disable that part of the test if the LFS version is too old, but then it's not automatically tested...

[BillyONeal]

@BillyONeal This is just for testing. The scripts don't need anything more recent normally, but I can't implement a proper test without some newer LFS features. I could just disable that part of the test if the LFS version is too old, but then it's not automatically tested...

We don't have a means of restricting such a machine-wide configuration change to your test.

[DDoS]

@BillyONeal I'm surprised that the vcpkg VM images are even using a two year old Git LFS version... The default Azure hosted agent images are up-to-date.
Does anything else in vcpkg even depends on LFS? I was under the impression that there was no support for it until it was added to vcpk_from_git.
But anyway if updating LFS is not an option, I can disable the test for older versions, or just abandon this PR.

[BillyONeal]

I'm surprised that the vcpkg VM images are even using a two year old Git LFS version...

That's what comes with Visual Studio 2022.

The default Azure hosted agent images are up-to-date.

The default Azure hosted images contain everything under the sun because they are trying to maximize the likelihood of your build working. vcpkg's lab contains only what a developer is likely to have installed for themselves because we don't want ports silently depending on one of those external dependencies like one might find on the default Azure hosted images.

Does anything else in vcpkg even depends on LFS?

Intentionally? Probably not. But we invoke arbitrary user build scripts which could.

But anyway if updating LFS is not an option, I can disable the test for older versions, or just abandon this PR.

Or we could just wait until a version which does what you need has enough market penetration that we can confidently assume its presence.

[DDoS]

@BillyONeal How does vcpkg even handle testing ports that require specific tooling if it can't be installed? I know that vcpkg acquires some programs automatically, but looking at the code it just asks you to install it yourself in many cases.

Maybe the oldest viable LFS version (3.0.0 from March 2021) can be installed instead of the latest one? But if you insist on waiting for LFS to be updated externally, then feel free to close this PR. I don't personally need this change, I just did it because someone asked for it and I thought it would be a quick and easy. I don't want to spend that much more time working on it.

[BillyONeal]

How does vcpkg even handle testing ports that require specific tooling if it can't be installed?

It depends. But usually these days we probably wouldn't accept adding stuff like that to the curated registry. Ports are on the hook for being broadly installable with a "typical developer workstation". Seeing that we have something only for it to explode in your face is a bad experience.

The one big notable exception I'm aware of right now is CUDA, but pretty much every port that wants CUDA has that controlled by an optional feature. (And there, it isn't that we wouldn't solve the problem of getting what's necessary, it's that we are legally unable to under NVIDIA's license terms)

But if you insist on waiting for LFS to be updated externally, then feel free to close this PR.

I will confirm with other maintainers before going there. (Should know by ~Thursday)

[BillyONeal]

@vicroms @dan-shaw @ras0219-msft @AugP @JavierMatosD and I discussed this today and came up with the following outcomes:

1. Because this feature doesn't break people who don't use it, we are happy to accept the new feature.
2. We do not want to modify our VMs to install unlikely-to-be-what-users-use copies of git.
3. We would accept the feature even if we can't test it right now; please include the test in a disabled form with a comment like "when (component) is available turn this test on"

Does that sound reasonable @DDoS ?

[DDoS]

@BillyONeal Sounds good. I'm away for a week, so I'll make this change next Thursday or Friday.

[vicroms]

As discussed, disable test until we are ready to enable it in our VMs.

@DDoS
Ping me when done to merge this PR! 😄

[DDoS]

@horenmar Can you test if these changes fix your issue (#28593)?

@vicroms I added a version check to the test. That way it should enable automatically when a suitable LFS version is available.

[BillyONeal]

I will merge this closer to the end of the day. (Just don't want to push a merge conflict with the world while still processing today's changes)

[BillyONeal]

Thank you!