Msbuild: How to run MSBuild target only once before build?

[djanosik]

I have a multi targeting project with custom MSBuild target.

<Target Name="MyTarget" BeforeTargets="BeforeCompile">

The target is executed multiple times during build. Once for each target framework. Is there any way to make sure it will run only once?

[BalassaMarton]

I have the same issue with a custom MSBuild task that shuld run only once per build cycle, but instead runs for every target framework. Is there maybe another target for this purpose?

[kunalspathak]

Any update on this? My use-case is that I am building a custom non-MS project once per build (unrelated to target frameworks) and then I just want the output of the project to get copied in to bin\Debug\<target_framework_specific_dir>. Currently there is no way to do that. I will have to either add a Condition in Target saying to build just once and then not sure how i can copy it to other target framework's out directory.

[BalassaMarton]

I came up with a workaround, have a look at my .targets and .props files here:
https://github.com/BalassaMarton/MSBump/tree/master/MSBump
This solution uses a lock file to prevent the target from running when inside a multi-targeting build.

[dasMulli]

Easiest way is to change the BeforeTargets to hook to the specific targets:

  <PropertyGroup>
    <TargetFrameworks>netstandard1.3;netstandard2.0</TargetFrameworks>
  </PropertyGroup>

  <Target Name="CustomOnOuterBuild" BeforeTargets="DispatchToInnerBuilds">
    <Message Importance="high" Text="I'm running in the outer build (before). TFs: $(TargetFrameworks), TF: $(TargetFramework)" />
  </Target>

  <Target Name="CustomOnInnerBuild" BeforeTargets="BeforeBuild">
    <Message Importance="high" Text="I'm running in the inner build (before). TFs: $(TargetFrameworks), TF: $(TargetFramework)" />
  </Target>

  <Target Name="CustomOnAfterBuild" AfterTargets="Build">
    <Message Importance="high" Text="I'm running in the outer build (after).  TFs: $(TargetFrameworks), TF: $(TargetFramework)" Condition=" '$(IsCrossTargetingBuild)' == 'true' " />
    <Message Importance="high" Text="I'm running in the innter build (after). TFs: $(TargetFrameworks), TF: $(TargetFramework)" Condition=" '$(IsCrossTargetingBuild)' != 'true' " />
  </Target>

Should print

$ dotnet build
Microsoft (R) Build Engine version 15.4.8.50001 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  I'm running in the outer build (before). TFs: netstandard1.3;netstandard2.0, TF:
  I'm running in the inner build (before). TFs: netstandard1.3;netstandard2.0, TF: netstandard1.3
  I'm running in the inner build (before). TFs: netstandard1.3;netstandard2.0, TF: netstandard2.0
  testlib -> /Users/martin.ullrich/tmp/testlib/bin/Debug/netstandard1.3/testlib.dll
  I'm running in the innter build (after). TFs: netstandard1.3;netstandard2.0, TF: netstandard1.3
  testlib -> /Users/martin.ullrich/tmp/testlib/bin/Debug/netstandard2.0/testlib.dll
  I'm running in the innter build (after). TFs: netstandard1.3;netstandard2.0, TF: netstandard2.0
  I'm running in the outer build (after).  TFs: netstandard1.3;netstandard2.0, TF:

While you could also use BeforeTargets="Build" on the outer build target, this will run after the build since the multi-targeting Build target depends on the inner builds.

@djanosik the compile targets (BeforeCompile and friends) are only executed in the inner builds so you'd need to hook on a different target as well.

[JVimes]

@dasMulli The "outer build (after)" message does not appear when the target is defined in a targets file in my NuGet package. Any idea how to detect "after outer" in that case? The other messages work, so I'm suspicious that IsCrossTargetingBuild isn't working in this case.

[dasMulli]

NuGet targets only contribute to the inner builds since NuGet only resolves assets (including msbuild targets) per target framework involved. You can see the generated import statements in the obj*.g.nuget.props|targets files.

[dasMulli]

If you want to contribute to project logic in general without actually needing a target framework, maybe MSBuild SDKs are what you are looking for.
These can basically be NuGet packages with ´Sdk\Sdk.propsandSdk\Sdk.targets` files that will be imported by MSBuild itself and doesn't interfere with the nuget package graph of the project (that way it also works for packages.config projects ^^)

[rainersigwald]

NuGet targets only contribute to the inner builds since NuGet only resolves assets (including msbuild targets) per target framework involved. You can see the generated import statements in the obj*.g.nuget.props|targets files.

This is true for normal props/targets in the build/ folder, but you can have a buildMultitargeting/ folder in the package that is imported only for the "outer" no-TargetFramework build.

I don't think using an SDK helps here.

[JVimes]

@rainersigwald buildMultitargeting/ makes nearly all the common macros empty, including anything that would imply which project the package is in or where "bin/release" is actually located. Any ideas?

Edit: Also, buildMultitargeting does not support non-SDK-style projects. Using both causes my target to run multiple times. And I found no way to differentiate between non-SDK-style project build and inner builds in my NuGet task. I gave up hope.

[SimonCropp]

Condition="'$(TargetFrameworks)' == '' OR $(TargetFrameworks.EndsWith($(TargetFramework)))"