Building metadata projects outside vscmd results in failure to find cl.exe

[riverar]

Just creating an official issue to track fixing a long time annoyance. dotnet build in a vanilla Terminal session results in midl.exe/cl.exe failures due to tooling paths not getting wired up correctly.

[ChrisDenton]

Should be possible to use vswhere to find the exes for us?

[riverar]

The Microsoft.Windows.WinmdGenerator SDK already pulls in Microsoft.Windows.SDK.CPP, i.e.:

win32metadata/sources/GeneratorSdk/sdk/sdk.props

Lines 48 to 51 in 9d6d88a

	<ItemGroup>
	<PackageReference Include="Microsoft.Windows.SDK.CPP" Version="10.0.19041.5" GeneratePathProperty="true"/>
	<PackageReference Include="Microsoft.Windows.SDK.Win32Metadata" Version="10.0.19041.202-preview" GeneratePathProperty="true"/>
	</ItemGroup>

Which sets a bunch of properties, some of which we rely upon (e.g. WindowsSDKVersionedBinRoot to find midl.exe):

win32metadata/sources/GeneratorSdk/sdk/sdk.targets

Lines 124 to 133 in 9d6d88a

	<CompileIdls
	Idls="@(Idls)"
	ObjDir="$(ObjDir)"
	CompiledHeadersDir="$(CompiledHeadersDir)"
	ScriptsDir="$(ScriptsDir)"
	SdkIncRoot="$(SdkIncRoot)"
	SdkBinDir="$(WindowsSDKVersionedBinRoot)"
	AdditionalIncludes="$(AdditionalIncludes)"
	MidlSwitches="$(MidlSwitches)"
	MSBuildProjectDirectory="$(MSBuildProjectDirectory)"/>

But then we also have these properties to contend with:

win32metadata/sources/GeneratorSdk/sdk/sdk.props

Lines 24 to 31 in 9d6d88a

	<Win32MetadataSdkRoot>$([System.IO.Path]::GetFullPath('$(MSBuildThisFileDirectory)..'))</Win32MetadataSdkRoot>
	<TaskBinDir Condition="'$(TaskBinDir)' == ''">$(Win32MetadataSdkRoot)\tools\net8.0</TaskBinDir>
	<ToolsBinDir Condition="'$(ToolsBinDir)' == ''">$(Win32MetadataSdkRoot)\tools\net8.0</ToolsBinDir>
	<LibToolsBinDir Condition="'$(LibToolsBinDir)' == ''">$(Win32MetadataSdkRoot)\tools</LibToolsBinDir>
	<ScriptsDir Condition="'$(ScriptsDir)' == ''">$(Win32MetadataSdkRoot)\scripts</ScriptsDir>
	<ObjDir Condition="'$(ObjDir)' == ''">$(MSBuildProjectDirectory)\obj</ObjDir>
	<CompiledHeadersDir Condition="'$(CompiledHeadersDir)' == ''">$(ObjDir)\CompiledHeaders</CompiledHeadersDir>
	<SdkIncRoot>$(TargetPlatformSdkRootOverride)\include\$(TargetPlatformVersion)</SdkIncRoot>

And... that's as far as I've gotten at the moment. We just need to spend a bit more time following all the wires around, see what we've got, determine what *.SDK.CPP offers, and hopefully clean things up a bit so that we're working with a properly hydrated build environment.