dx: warn about long paths disabled

[earloc]

Summary of the changes

• refactored Directory.Targets.props to centralize import of common targets
• introducing check for enabled long path support on windows
• added docs to guide contributors on how to enable long path support

Now, when building with build.cmd, the following Warningis generated:

{{PATH-TO-REPOSITORY}}\eng\targets\CheckLongPathSupport.targets(26,5): error LongPathsDisabled: Long paths support is required for this project. See 'docs/contributing/LongPaths.md' on how to overcome this. 

Opening VS will show the warning as well, with clickable link to docs/contributing/LongPaths.md :

fixes #11139

[earloc]

@davidwengier, @ryzngard
Took me some time to recover some long forgotten msbuild wizardry, but finally got a proposal to integrate the check for long path support when working with this repo on a windows machine together.

As the original errors already happen during project load-time (f.e.: in VS, the affected project refuses to load), this was a bit tricky to achieve, but I feel this is unobtrusive enough to ease up the overall first-time experience when working with this repo.

Only "donwside" of the current approach is, that this check might be carried out for every project within the solution - which might put some additional time on top of overall build-time. This may be somehow refactored in a way, that the imported target only gets imported once, but I didn`t manage to achieve this so far.

Curious about your thoughts on this...

[davidwengier]

No issues from me.

[DustinCampbell]

I'd be very interested in @jaredpar taking a look to make sure we're following the best practices. I know that dotnet/roslyn does something specific for long paths.

[earloc]

@DustinCampbell fyi: this change basically adopts what roslyn does, but integrates it in a slightly different way. Mostly due to the fact that those nasty path-too-long-errors might pop up very early (at load-time). This is why I decided to utilize InitialTargets in favor of BeforeTargets="BeforeBuild" , as the error(s) prevented the build from reaching this target at all.

[DustinCampbell]

@DustinCampbell fyi: this change basically adopts what roslyn does, but integrates it in a slightly different way. Mostly due to the fact that those nasty path-too-long-errors might pop up very early (at load-time). This is why I decided to utilize InitialTargets in favor of BeforeTargets="BeforeBuild" , as the error(s) prevented the build from reaching this target at all.

I totally understand @earloc! That's why I was hoping @jaredpar would take a look, since he manages so much of the infrastructure in Roslyn and Razor. 😄

[earloc]

@jaredpar you probably have a ton of other things on your plate. Would appreciate any feedback on this here if you find the time 👌.

Also, I'm wondering if this might be packaged into a standalone nuget, which projects would be able to just pull in 🤔.

[ryzngard]

Thanks for the contribution @earloc !