Design-time builds in CPS are doing too much work because BuildingProject is set to true

[davkean]

To reduce build times, CPS groups build targets for a project together. This has the unintended side-effect of turning $(BuildingProject) on during lots of CPS design-time builds.

Lots of behavior in common targets is driven by $(BuildingProject), it's basically the legacy equivalent of $(DesignTimeBuild) != 'true'":

186>------ Build started: Project: Microsoft.VisualStudio.ProjectSystem.Managed, Targets: CollectResolvedSDKReferencesDesignTime, DebugSymbolsProjectOutputGroup, CollectPackageReferences, ResolveComReferencesDesignTime, ContentFilesProjectOutputGroup, DocumentationProjectOutputGroupDependencies, SGenFilesOutputGroup, ResolveProjectReferencesDesignTime, SourceFilesProjectOutputGroup, DebugSymbolsProjectOutputGroupDependencies, SatelliteDllsProjectOutputGroup, BuiltProjectOutputGroup, SGenFilesOutputGroupDependencies, ResolveAssemblyReferencesDesignTime, CollectAnalyzersDesignTime, CollectSDKReferencesDesignTime, DocumentationProjectOutputGroup, PriFilesOutputGroup, BuiltProjectOutputGroupDependencies, ResolvePackageDependenciesDesignTime, SatelliteDllsProjectOutputGroupDependencies, SDKRedistOutputGroup, CompileDesignTime, CollectResolvedCompilationReferencesDesignTime ------

...

186>Target "BuildOnlySettings" in file "C:\Program Files (x86)\Microsoft Visual Studio\Preview\Enterprise\MSBuild\15.0\Bin\Microsoft.Common.CurrentVersion.targets":
186>  Set Property: BuildingProject=true

BuildOnlySettings is basically a dependency of most of the output groups targets.

Things that I'm seeing we're doing:

• ResolveAssemblyReferences; FindDependencies, FindSatellites, FindSerializationAssemblies, FindRelatedFiles is all true.
• ResolveAssemblyReferences; Silent is false - undecided if this is good or bad.

This would explain why ResolveAssemblyReferences is showing up on traces, FindDependencies is very slow.

[davkean]

This is also blocking XAML: dotnet/project-system#2488.

[rainersigwald]

The output groups have been like this for a looooooooong time. It went in with this commit:

Change 1159138 by ███████ on 2005/05/30 22:19:17

	   MSBuild RTM bugs
	
	   Fixes for the following bugs:
	   493328	"unable to copy file ... because it is being used by
	   another process" after building twice in a row, old resx format
	   494837	.RESTEXT files are not given the right manifest resource
	   name.
	   494963	Default value for metadata <InProject> should be "false"
	   when item is coming from a .TARGETS file.
	   494967	There's no way for the author of a custom build process
	   to add entries into the BuildAction dropdown in the IDE.
	   494968	Tasks that have ContinueOnError=true should not log
	   errors.
	   495734	Visual Studio holds/leaks reference to build target
	   DLLs, preventing builds.
	   495747	MSBUILD: Usage of "Target" metadata in AL.exe /link
	   option does not work
	   496301	We should kill the "AssignTargetPaths" target if
	   possible.
	   498702	ToolTask needs a way to allow the task author to parse
	   stdout/stderror themselves.
	   456966	Saving a vb code file to a different location causes
	   information to be lost over VB->C# project reference.

None of those bugs looks particularly related to me.

I'd be willing to try dropping the dependency and seeing what happens.