Unexpected duplicate items

[JVimes]

Issue Description

In the Dependency target below, OutFiles is what I expect. But its content is duplicated when accessed in the Primary target.

The issue goes away if I remove the Input and Output attributes.

Issue.targets:

<Project DefaultTargets="Primary">

    <ItemGroup>
        <InFiles Include="A.in;B.in" />
    </ItemGroup>

    <Target Name="Primary"
            DependsOnTargets="Dependency">
        <Message Text="In Primary target.    OutFiles: @(OutFiles)" Importance="high" />
    </Target>

    <Target Name="Dependency"
            Inputs="@(InFiles)"
            Outputs="@(InFiles->'%(filename).out')">
        <ItemGroup>
            <OutFiles Include="*.out" />
        </ItemGroup>
        <Message Text="In Dependency target. OutFiles: @(OutFiles)" Importance="high" />
    </Target>

</Project>

Output:

PS> dotnet build Issue.targets --nologo

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out;A.out;B.out

Steps to Reproduce

Here's a working example, since it may depend on file time stamps:
MSBuildIssue.zip

Unzip and run dotnet build Issue.targets.

Expected Behavior

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out

Actual Behavior

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out;A.out;B.out

Versions & Configurations

msbuild.exe

• Microsoft (R) Build Engine version 17.3.0-preview-22277-01+f1dae6ab6 for .NET Framework
  17.3.0.27701

dotnet.exe

• 6.0.400-preview.22301.10

[rainersigwald]

Team triage: this is a super weird bug with a great repro, thank you!

It looks like you can work around by specifying

Outputs="@(InFiles->'%(Directory)%(FileName).out')"

but we're not totally sure why yet.

We initially thought that something was erroneously causing MSBuild to interpret the item transform expression in your Outputs as a batch operation, so the entire target was running for each InFiles item. But that's not the case; the list is only ever doubled, even when there are more InFiles items, and we don't see the log message from inside Dependency more than once.

[Nirmal4G]

Try

<OutFiles Include="@(InFiles->'%(FileName).out')" />

We can rule out globbing if this also produces similar output!

~~Also, I only have v17.2.5 and this doesn't happen on that version so something must have changed in-between!~~

[rainersigwald]

Also, I only have v17.2.5 and this doesn't happen on that version so something must have changed in-between!

I repro on 17.2:

❯ msbuild .\Issue.targets -v:m
Microsoft (R) Build Engine version 17.2.1+52cd2da31 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out;A.out;B.out

And older:

❯ msbuild Issue.targets -v:m
Microsoft (R) Build Engine version 16.11.2+f32259642 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out;A.out;B.out

Edit: and even older:

> C:\Windows\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe Issue.targets -v:m
Microsoft (R) Build Engine version 4.8.4161.0
[Microsoft .NET Framework, version 4.0.30319.42000]
Copyright (C) Microsoft Corporation. All rights reserved.

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out;A.out;B.out

[Nirmal4G]

With <OutFiles Include="@(InFiles->'%(FileName).out')" />, it produces

❯ msbuild Issue.targets -v:m
Microsoft (R) Build Engine version 4.8.9032.0
[Microsoft .NET Framework, version 4.0.30319.42000]
Copyright (C) Microsoft Corporation. All rights reserved.

  In Dependency target. OutFiles: B.out
  In Primary target.    OutFiles: A.out;B.out

Is this expected output?

---

By directly specifying the file, it also duplicates the items:

❯ msbuild Issue.targets -v:m
Microsoft (R) Build Engine version 4.8.9032.0
[Microsoft .NET Framework, version 4.0.30319.42000]
Copyright (C) Microsoft Corporation. All rights reserved.

  In Dependency target. OutFiles: A.out;B.out
  In Primary target.    OutFiles: A.out;B.out;A.out;B.out

When I included the extra item, as expected with your repro, it also duplicates further.

❯ msbuild Issue.targets -v:m
Microsoft (R) Build Engine version 4.8.9032.0
[Microsoft .NET Framework, version 4.0.30319.42000]
Copyright (C) Microsoft Corporation. All rights reserved.

  In Dependency target. OutFiles: A.out;B.out;A.out
  In Primary target.    OutFiles: A.out;B.out;A.out;A.out;B.out;A.out

So, I think no globbing is involved!