Saturday, February 06, 2010

F# October '09 & February '10 CTP and VS 2008 - output window glitch

I first noticed this when adding a simple post-build step through the project properties for running unit tests as part of the build inside Visual Studio -- the May '09 CTP echoed the data going to stdout just like with any other language; in October everything went black; and it remains that way at the February '10 CTP.

Subsequently I find that this also applies to other MSbuild targets. For example, take a completely new F# library project, and edit the .fsproj file to have the following AfterBuild target:

<Target Name="AfterBuild">
    <Error Text="Hello world" />
  </Target>

Reloading and rebuilding gives

------ Build started: Project: Library4, Configuration: Debug Any CPU ------
        C:\Program Files\FSharp-1.9.7.8\\bin\fsc.exe -o:obj\Debug\Library4.dll -g --debug:full --noframework --define:DEBUG --define:TRACE --optimize- --tailcalls- -r:"C:\Program Files\FSharp-1.9.7.8\\bin\FSharp.Core.dll" -r:C:\Windows\Microsoft.NET\Framework\v2.0.50727\mscorlib.dll -r:"C:\Program Files\Reference Assemblies\Microsoft\Framework\v3.5\System.Core.dll" -r:C:\Windows\Microsoft.NET\Framework\v2.0.50727\System.dll --target:library --warn:3 --warnaserror:76 --vserrors --utf8output --fullpaths --flaterrors Module1.fs
========== Build: 0 succeeded or up-to-date, 1 failed, 0 skipped ==========

Using msbuild at a console, the output is shown

Project "C:\Users\Steve\Documents\Visual Studio 2008\Projects\Library4\Library4.fsproj" on node 0 (default targets).
  Processing 0 EDMX files.
  Finished processing 0 EDMX files.
CopyFilesToOutputDirectory:
  Copying file from "obj\Debug\Library4.dll" to "bin\Debug\Library4.dll".
  Library4 -> C:\Users\Steve\Documents\Visual Studio 2008\Projects\Library4\bin\Debug\Library4.dll
  Copying file from "obj\Debug\Library4.pdb" to "bin\Debug\Library4.pdb".
C:\Users\Steve\Documents\Visual Studio 2008\Projects\Library4\Library4.fsproj(51,5): error : Hello world
Done Building Project "C:\Users\Steve\Documents\Visual Studio 2008\Projects\Library4\Library4.fsproj" (default targets)
 -- FAILED.


Build FAILED.

On the up side -- messages emitted by the Error or Warning tasks (but not the Message task) do appear in the Error List tab; so you can get some feedback inside Visual Studio as to why your build failed, even if not all the realtime tracing you might be used to with other languages.

I suspect this may be as simple as a linker flag change to the VS plugin (all the plausibly relevant F# assemblies I've looked at in 1.9.7.8 are marked as GUI sub-system, and IIRC, VS plug-ins need to be Console -- i.e. to have a useful stdout).

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