Paths don't round trip on Unix

[lewing]

While testing out path problems in other parts of the system I ran into this case on unix

pwd
/Users/lewing/Source/Test#our codedir/File%20Test
xamlewing-good:File%20Test lewing$ dotnet build
Microsoft (R) Build Engine version 16.5.0+d4cbfca49 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.
  Restore completed in 50.91 ms for /Users/lewing/Source/Test#our codedir/File%20Test/File%20Test.csproj.
/usr/local/share/dotnet/sdk/3.1.201/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(234,5): error NETSDK1004: Assets file '/Users/lewing/Source/Test#our codedir/File Test/obj/project.assets.json' not found. Run a NuGet package restore to generate this file. [/Users/lewing/Source/Test#our codedir/File%20Test/File%20Test.csproj]
Build FAILED.
/usr/local/share/dotnet/sdk/3.1.201/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(234,5): error NETSDK1004: Assets file '/Users/lewing/Source/Test#our codedir/File Test/obj/project.assets.json' not found. Run a NuGet package restore to generate this file. [/Users/lewing/Source/Test#our codedir/File%20Test/File%20Test.csproj]
    0 Warning(s)
    1 Error(s)
Time Elapsed 00:00:00.88

The %20 in the actual path /Users/lewing/Source/Test#our codedir/File%20Test is being unescaped incorrectly leading to a build failure.

[lewing]

mkdir "Happy%20day"
cd "Happy%20day"
dotnet build

Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
/Users/lewing/Source/runtime/.dotnet/sdk/5.0.100-preview.8.20362.3/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(241,5): error NETSDK1004: Assets file '/Users/lewing/Source/Happy day/obj/project.assets.json' not found. Run a NuGet package restore to generate this file. [/Users/lewing/Source/Happy%20day/Happy%20day.csproj]

Build FAILED.

/Users/lewing/Source/runtime/.dotnet/sdk/5.0.100-preview.8.20362.3/Sdks/Microsoft.NET.Sdk/targets/Microsoft.PackageDependencyResolution.targets(241,5): error NETSDK1004: Assets file '/Users/lewing/Source/Happy day/obj/project.assets.json' not found. Run a NuGet package restore to generate this file. [/Users/lewing/Source/Happy%20day/Happy%20day.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.54

[lewing]

cc @rainersigwald

[lewing]

lewing@MacBook-Pro ~ % mkdir "Happy?day=no"
lewing@MacBook-Pro ~ % cd Happy\?day=no 
lewing@MacBook-Pro Happy?day=no % dotnet new console
The template "Console Application" was created successfully.

Processing post-creation actions...
Running 'dotnet restore' on /Users/lewing/Happy?day=no/Happy?day=no.csproj...
  Determining projects to restore...
  Restored /Users/lewing/Happy?day=no/Happy?day=no.csproj (in 56 ms).
Restore succeeded.

lewing@MacBook-Pro Happy?day=no % dotnet build
Microsoft (R) Build Engine version 16.7.0-preview-20360-03+188921e2f for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
/Users/lewing/Source/runtime/.dotnet/sdk/5.0.100-preview.8.20362.3/Current/Microsoft.Common.props(62,3): error MSB4019: The imported project "/Users/lewing/Happy?day=no/obj/Happy?day=no.csproj.*.props" was not found. Confirm that the expression in the Import declaration "/Users/lewing/Happy%3fday=no/obj/Happy%3fday=no.csproj.*.props" is correct, and that the file exists on disk. [/Users/lewing/Happy?day=no/Happy?day=no.csproj]

Build FAILED.

/Users/lewing/Source/runtime/.dotnet/sdk/5.0.100-preview.8.20362.3/Current/Microsoft.Common.props(62,3): error MSB4019: The imported project "/Users/lewing/Happy?day=no/obj/Happy?day=no.csproj.*.props" was not found. Confirm that the expression in the Import declaration "/Users/lewing/Happy%3fday=no/obj/Happy%3fday=no.csproj.*.props" is correct, and that the file exists on disk. [/Users/lewing/Happy?day=no/Happy?day=no.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.47

[lewing]

Round tripping is related to dotnet/runtime#1061

[rainersigwald]

Tracked by dotnet/msbuild#2178. Unfortunately, I don't think there's an easy way to resolve this because the MSBuild engine's internal escaping code is a typeless mess.