different behavior of VS 2019 build and dotnet msbuild

[codingdave]

Description

From what I understand dotnet msbuild shall behave identical to building with Visual Studio (I have not read that anywhere and such my premises might be wrong).

My expectation is the behavior of Visual Studio: That the PostBuildEvent is not called if the output is not updated.

When I compile my sample from Visual Studio 2019 16.8.4 this is the output

Build started...
1>------ Build started: Project: testLibrary, Configuration: Debug Any CPU ------
1>testLibrary -> D:\Projects\msbuildTest\testLibrary\bin\Debug\net5.0\testLibrary.dll
1>"**************************** Post-build testLibrary ****************************"
2>------ Build started: Project: testConsoleApplication, Configuration: Debug Any CPU ------
2>testConsoleApplication -> D:\Projects\msbuildTest\testConsoleApplication\bin\Debug\net5.0\testConsoleApplication.dll
2>"**************************** Post-build testConsoleApplication ****************************"
========== Build: 2 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

The second run then yields:

Build started...
========== Build: 0 succeeded, 0 failed, 2 up-to-date, 0 skipped ==========

When I compile it using dotnet build

PS D:\Projects\msbuildTest> dotnet build

Microsoft (R) Build Engine version 16.8.3+39993bd9d for .NET
Copyright (C) Microsoft Corporation. All rights reserved.   

  Determining projects to restore...
  Restored D:\Projects\msbuildTest\testConsoleApplication\testConsoleApplication.csproj (in 77 ms).
  Restored D:\Projects\msbuildTest\testLibrary\testLibrary.csproj (in 76 ms).
  testLibrary -> D:\Projects\msbuildTest\testLibrary\bin\Debug\net5.0\testLibrary.dll
  "**************************** Post-build testLibrary ****************************"
  testConsoleApplication -> D:\Projects\msbuildTest\testConsoleApplication\bin\Debug\net5.0\testConsoleApplication.dll
  "**************************** Post-build testConsoleApplication ****************************"

Build succeeded.        
    0 Warning(s)        
    0 Error(s)

Time Elapsed 00:00:07.38

The second run then yields:

PS D:\Projects\msbuildTest> dotnet build

Microsoft (R) Build Engine version 16.8.3+39993bd9d for .NET
Copyright (C) Microsoft Corporation. All rights reserved.   

  Determining projects to restore...
  All projects are up-to-date for restore.
  testLibrary -> D:\Projects\msbuildTest\testLibrary\bin\Debug\net5.0\testLibrary.dll
  "**************************** Post-build testLibrary ****************************"
  testConsoleApplication -> D:\Projects\msbuildTest\testConsoleApplication\bin\Debug\net5.0\testConsoleApplication.dll
  "**************************** Post-build testConsoleApplication ****************************"

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:01.34

When I compile it using dotnet msbuild

PS D:\Projects\msbuildTest> dotnet msbuild

Microsoft (R) Build Engine version 16.8.3+39993bd9d for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  testLibrary -> D:\Projects\msbuildTest\testLibrary\bin\Debug\net5.0\testLibrary.dll
  "**************************** Post-build testLibrary ****************************"
  testConsoleApplication -> D:\Projects\msbuildTest\testConsoleApplication\bin\Debug\net5.0\testConsoleApplication.dll
  "**************************** Post-build testConsoleApplication ****************************"

The second run then yields:

PS D:\Projects\msbuildTest> dotnet msbuild

Microsoft (R) Build Engine version 16.8.3+39993bd9d for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  testLibrary -> D:\Projects\msbuildTest\testLibrary\bin\Debug\net5.0\testLibrary.dll
  "**************************** Post-build testLibrary ****************************"
  testConsoleApplication -> D:\Projects\msbuildTest\testConsoleApplication\bin\Debug\net5.0\testConsoleApplication.dll
  "**************************** Post-build testConsoleApplication ****************************"

So what we can observe here is that dotnet build and dotnet msbuild both call the PostBuildEvent even when the output was not updated but Visual Studio does that only when the output was updated.

Configuration

• dotnet: 5.0.102
• Visual Studio 2019 16.8.4

Additional Information

I have added the minimal sample msbuildTest.zip I have been using for the results given above.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[dotnet-issue-labeler]

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[sfoslund]

VS build and dotnet msbuild behavior will not always match exactly, so it sounds like this is expected. It looks like VS detects that no files have been changed and does not run the build the second time (meaning it skips the post build event too). Since that logic does not exist on the command line, when you run 'dotnet msbuild' or 'dotnet build' the build and the post build event are both rerun the second time.

Is there a specific difference here that you think might be a bug or are we okay to close this?

[codingdave]

Hi @sfoslund, thanks for your reply.

It looks like dotnet cannot deal with incremental builds. I am using the postbuild event in this example only to showcase that the incremental build does not seem to work.

I am migrating a bigger non-sdk style project that was built with VS 2019 to the net sdk-style projects and dotnet. I expect that I can end up with a build flow similar to my old (VS 2019) feature wise.

One important aspect of a build system for me is incremental building and being able to hook into build events. Imagine I want to recompile an assembly every time the git revision has changed (using e.g. gitversion) or I want to generate a set of files every time a dependent project has changed (executing "$(TargetPath)" in the post-build event). It does not make sense to execute these tasks when the dependencies did not change.

This does work fine with VS 2019, thats why I assumed it should also work with dotnet.