Document "magic" file names picked up by MSBuild: Directory.build.props, *.sln.targets, etc

[KirillOsenkov]

There should be documentation on all file names recognized by MSBuild that are auto-included if present on disk, but never explicitly mentioned.

Examples that I know of:

• Directory.Build.props
• Directory.Build.targets
• .sln.targets
• Before..sln.targets (??)

[gfoidl]

Directory.Build.[props|targets] is documented in Customize your build - Visual Studio | Microsoft Docs

On the same page the others could be documented as well.

[dasMulli]

E.g. Directory.Build.rsp which is new and no one really knows about..

[jaredpar]

File names and file locations. Guessing it's not well known that MSBuild will also import these files from user locations. This is all the known ways that we have found they are imported

https://github.com/dotnet/roslyn/blob/master/src/Workspaces/CoreTestUtilities/Resources/Directory.Build.props

[rainersigwald]

Should definitely crosslink https://docs.microsoft.com/en-us/visualstudio/msbuild/msbuild-response-files#directorybuildrsp from the customize-your-build page too.

[rainersigwald]

Pulling this into 15.7 since it's doc-only and not too late.

[jaredpar]

There are target files you can apply to SLN files? What does that do?

[aL3891]

Those targets run once before/after all the projects in the solution, very useful but hidden feature.

[rainersigwald]

Feedback on MicrosoftDocs/visualstudio-docs#816 would be great: anything I missed? Got more questions about these mechanisms?

[jaredpar]

@rainersigwald overall looked good. Added some feedback.

One set of items I didn't see documented there was essentially all of the stuff listed in this file.

https://github.com/dotnet/roslyn/blob/master/src/Workspaces/CoreTestUtilities/Resources/Directory.Build.props

I actually don't even know if these are valid extension points or if I'm disabling the properly. IIRC I essentially did a /pp on a build, looked for every Import.*Before/After and added a disable.

[aL3891]

Looks good, just added some nit comments