Document the differences between normal and design-time builds

[KirillOsenkov]

I've glanced through this article:
https://github.com/dotnet/project-system/blob/master/docs/design-time-builds.md

But it doesn't seem to mention what the actual differences are between a design-time build and a regular command-line build. I'd like to be able to emulate a design-time build to an extent to be able to understand what is happening inside Visual Studio.

I can't remember the exact list, but I think there's a set of properties you need to set, such as:

DesignTimeBuild = true
BuildingInsideVisualStudio = true
BuildProjectReferences = false
SkipCompilerExecution = true
ProvideCommandLineArgs = true

Since the article above is the first place I'd go looking for this information it'd be nice to have it there. I'd send a PR but I'm not quite sure what is the exact set of properties and/or targets required.

It's OK if we can't fully emulate the design-time build, but it'd be nice to get to it as close as possible.

@davkean @panopticoncentral

[maxinfet]

This would be fantastic information, the most consistent way I trigger them currently is by switching the configuration of the project. Would be much better if I knew how to trigger these from the command line.

[KirillOsenkov]

@davkean @davidwengier @jmarolf @panopticoncentral @jjmew any chance we could have these properties documented soon?

It would be really helpful to have authoritative guidance on how to properly run design-time builds. This would greatly help VSMac.

[jjmew]

@davkean Is it even possible to emulate a DTB?

[panopticoncentral]

It's definitely possible, just a matter of replicating the properties set when the build is run. I tried at one point to work out the various properties set by CSProj and there were actually some variances between the various codepaths that run them. It would be helpful to bring everyone into agreement on what to set.