ProjectDepsFilePath broken when output path is changed.

[NickCraver]

Repro steps

1. Grab the MiniProfiler repo here: https://github.com/MiniProfiler/dotnet/tree/09c96865f550f0d75b27119837853fc4b613bfe4
2. Open in VS 2017 build 26116.0
3. Build solution

If you already have the repo, git clean away the samples\Samples.Mvc5\bin\net462 directory (it should not exist)

Open building, you'll get an error:

Error:MSB4018
Details:
The "GenerateDepsFile" task failed unexpectedly.
System.IO.DirectoryNotFoundException: Could not find a part of the path 'C:\git\MiniProfiler\dotnet\samples\Samples.Mvc5\bin\net462\Samples.Mvc5.deps.json'.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize)
at Microsoft.NET.Build.Tasks.GenerateDepsFile.ExecuteCore()
at Microsoft.NET.Build.Tasks.TaskBase.Execute()
at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute()
at Microsoft.Build.BackEnd.TaskBuilder.d__26.MoveNext()
Project: Samples.Mvc5
File: C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\Sdks\Microsoft.NET.Sdk\build\Microsoft.NET.Sdk.targets
Line: 76

Context

To work around the always appending the TFM to the output path (see #550), there's currently a Directory.build.targets in place:

<Project>
    <!-- Working around https://github.com/dotnet/sdk/issues/550 -->
    <PropertyGroup>
        <OutputPath>bin/</OutputPath>
        <OutDir>bin/</OutDir>
    </PropertyGroup>
</Project>

However, the GenerateBuildDependencyFile target doesn't seem to be respecting this. It still creates the $(project).deps.json at:
samples\Samples.Mvc5\bin\net462\Samples.Mvc5.deps.json. It doesn't automatically create the net462 folder, so this causes the build failure above. I'm not saying it should automatically create the directory, instead it should put it in the bin\ folder beneath, like all other output.

[mattwar]

GenerateBuildDependencyFile depends on/writes to ProjectDepsFilePath which is based on TargetPath which is based on your project directory and OutDir.

Modifying OutDir in the directory.build.targets only changes the state of OutDir after the other variables are computed, so it won't change where ProjectDepsFilePath goes, or any other variable that is relative to TargetPath.

However, when the build is executed (after variable evaluation) the output directory is created from OutDir, which has now been changed by directory.build.targets. Which unfortunately leaves any task writing to files based on TargetPath potentially writing to a non-existent directory.. Which is what causes the exception during build.

You might be able to succeed by also modifying ProjectDepsFilePath in your directory.build.targets, but I doubt it is a good idea to do this unless you are absolutely aware of and okay with all the ramifications of changing a variable like this late in the evaluation stage of msbuild.

[nguerrera]

Using the new opt-out from appending the target framework to the output path should make this just work for you without mucking with a Directory.build.targets: #550 (comment)