$(RepoRoot) is missing trailing slash so local builds fail

[SteveSandersonMS]

Not sure if this is a known issue yet, but it seems not to work to run dotnet build in almost any of the project directories under src/Components. Most likely other projects will fail too.

For some reason, $(RepoRoot) evaluates to a location without a trailing slash, even though code in the top-level Directory.Build.props explicitly generates a value with a trailing slash. This makes many project references and <Import> declarations fail to resolve correctly, since they assume there would be a trailing slash after $(RepoRoot). Also for some reason, this doesn't affect build.cmd - perhaps it overrides the reporoot in some way.

As a workaround, you can do dotnet build /p:RepoRoot=C:\your\path\to\aspnetcore\.

Update

I tracked down the source of the bad value: it's the build.cmd scripts, as they set an environment variable called RepoRoot with the non-slash-ended value. Then the MSBuild logic only creates a value with a trailing slash if there isn't already a value, but there is already a value because of the env var.

So the remaining question is: how did this ever work in the past? I see that build.cmd hasn't changed recently. One possible clue is this comment from the top Directory.build.props:

<!-- $(RepoRoot) is normally set globally and Arcade overrides it to ensure a trailing slash. -->

Maybe Arcade no longer has this behavior of overriding it to ensure a trailing slash.

---

Older report

This seems to be a recent regression. Repro:

• cd src\Components
• git checkout main
• git reset --hard
• build.cmd
• cd Samples\BlazorServerApp
• dotnet build

Expected: builds the project
Actual: fails with errors like this:

C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\Microsoft.NET.Sdk.Razor.SourceGenerators\Microsoft.NET.Sdk.Razor.SourceGenerators.RazorSourceGenerator\BlazorServerApp.UnifiedAssembly.Info.g.cs(1,30): error CS0234: The type or namespace name 'AspNetCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?) [C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\BlazorServerApp.csproj]
C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\Microsoft.NET.Sdk.Razor.SourceGenerators\Microsoft.NET.Sdk.Razor.SourceGenerators.RazorSourceGenerator\_Pages__Host_cshtml.cs(4,30): error CS0234: The type or namespace name 'AspNetCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?) [C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\BlazorServerApp.csproj]
C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\Program.cs(6,17): error CS0234: The type or namespace name 'AspNetCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?) [C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\BlazorServerApp.csproj]
C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\Program.cs(7,17): error CS0234: The type or namespace name 'AspNetCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?) [C:\git\dotnet\aspnetcore\src\Components\Samples\BlazorServerApp\BlazorServerApp.csproj]

Something to do with source generators, it appears.

[captainsafia]

@SteveSandersonMS Can you share the binlogs for the failing dotnet build invocation?

At the expense of being That Person(tm), I couldn't get a repro of this in a fresh sandbox against commit bc5960e.

[SteveSandersonMS]

Sure, will email the binlog. One good way to see the problem in action is by evaluating the RepoRoot environment variable before and after running build.cmd:

• echo %RepoRoot% (no output)
• Inside src\Components, run build.cmd (millions of pages of output)
• echo %RepoRoot% => c:\your\path\to\aspnetcore\src\Components\..\..

Now the presence of this RepoRoot env var breaks other attempts to build:

• cd Samples\BlazorServerApp
• dotnet build (loads of errors, which are because $(RepoRoot) evaluates as the string from above with no trailing slash)

... and removing it fixes it:

• set RepoRoot=
• dotnet build (works)

This problem didn't occur until recently - not sure what's changed!

[captainsafia]

So, I tried two scenarios when validating this.

• Running dotnet build immediately in the Samples/BlazorServerApp

• Running the build.cmd script in src/Components then running dotnet build in Samples/BlazorServerApp

The RepoRoot environment variable defined in the build scripts was only intended to be used to resolve the location of the root build script.

Now, MSBuild does support referencing the value of an environment variable in the build. However, when both an environment variable and a build property share the same name, it is meant to favor the build property over the environment variable. Maybe the recent Arcade update brought in some differing behavior?

In any case, although I can't repro it myself, I think it's probably a good hygiene measure to unset the RepoRoot environment variable in the local build scripts to avoid any confusion between the two. Our build script shouldn't leave any variables behind.

[dougbu]

this doesn't affect build.cmd - perhaps it overrides the reporoot in some way.

See https://github.com/dotnet/arcade/blob/e7ede87875f41a9b3df898ae08da5ebc96e24f56/src/Microsoft.DotNet.Arcade.Sdk/tools/Build.proj#L37

Our build script shouldn't leave any variables behind.

We absolutely should not do anything w/ the Bash or Powershell RepoRoot settings. As @SteveSandersonMS said, "this doesn't affect build.cmd". And, if we stop setting RepoRoot, builds using the Arcade wrappers will fail. See https://github.com/dotnet/arcade/blob/e7ede87875f41a9b3df898ae08da5ebc96e24f56/src/Microsoft.DotNet.Arcade.Sdk/tools/Build.proj#L83

[dougbu]

/btw Build.proj hasn't changed since early January

[captainsafia]

The Build.proj only comes in to play if you are using the build.cmd script, correct?

When you build with dotnet it uses the properties defined in the Directory.Build.props file, but not the ones in the Arcade project. That's why the behavior is different between the two now.

And, if we stop setting RepoRoot, builds using the Arcade wrappers will fail. See https://github.com/dotnet/arcade/blob/e7ede87875f41a9b3df898ae08da5ebc96e24f56/src/Microsoft.DotNet.Arcade.Sdk/tools/Build.proj#L83

OK -- that makes sense to me.

[dougbu]

I'm starting to understand this:

• Reproduction of this bug requires use of the cmd command line. I can't see it because I always use bash and pwsh. @captainsafia is that true for you as well❔
• My change in the root Directory.Build.props relied on Arcade doing the right thing (which it still does) and no other messed-up RepoRoot settings.
• Unfortunately, our build.cmd scripts pollute the environment with a bad $(RepoRoot) value but (somehow) the root Directory.Build.props was previously able to fix that up.

Bottom line, my change in #32552 removed a fix for the "set but w/o a trailing slash" case and we're hitting that here. I don't get why %RepoRoot% is not handled as a global property (which should mean it can't be overridden) but have enough to go on.

@BrennanConroy this likely explains the SignalR failures as well as why I haven't seen that issue locally either.