support cross targeting msbuild projects (multiple target framework)

[enricosada]

these with <TargetFrameworks> (plural)

from root, if crossgen, choose the first target (atm FSAC doesnt support pass a preference)
After that, redo the inspect with that target framework, and ask msbuild about what frameworks
the project references should use

fix #162

[enricosada]

as a note @Krzysztof-Cieslak @kjnilsson @rneatherway this doesnt had any new configuration, just fix for crossgen, using the first target framework of the list.

Fix also a common scenario:

• console (single fw, like netcoreapp) who reference a library (multi fw, like netstandard+net40). now works correctly

pratically traversing the project references, i ask to msbuild what target framework the project reference should use.

But now is easier to add because:

• if the starting suppoet multiple projects, i know what are (user can choose)
• is possible to pass it directly (now the function accept the target framework, if user know that already)

[enricosada]

Ah this repo https://github.com/enricosada/DotnetNewFsprojTestingSamples contains some examples ready to use with some scenario (if can help vim/emacs testing)

[rneatherway]

Is there much more to come along these lines? I think it'll be more efficient if I take a batch of updates over to emacs.

[enricosada]

@rneatherway Dont think so, maybe just a perfomance improvement for bigger solution ( https://github.com/fsharp/FsAutoComplete/blob/master/src/FsAutoComplete.Core/ProjectCoreCracker.fs#L93 and #161 ) but depends if i have time to do it (not in short term anyway, maybe next month).

Other changes require changes to public api, so need discussion before do it. Stuff like:

• passing the starting project
• support sln
• choose initial configuration (debug/release) and target framework
• update configuration (debug/release) and target framework later, and invalidate
• special errors for stuff like restore required, choose the target framework from avaliable..

support new sdk on mono will wait a bit, because sdk 2.0 is changing...

[rneatherway]

Ah sorry I caused a conflict here, would you mind updating?

[enricosada]

@rneatherway sure np, i'll always rebase as needed.
i also need to fix a bug found on sdk2.0 (test suite for sdk2.0 paid already 😄

[enricosada]

nice behaviour.
So on unix (dunno what configuration can enable it but happen in travis ubuntu), if i do Path.GetTempFileName() but delete the file (i just want a path), that can be reused by a later Path.GetTempFileName().
it's lovely to have test suites...