Stack: Stack fails to rebuild output executable if deleted

[ndmitchell]

Using Stack 1.4.0 on Windows:

• Checkout HLint, git clone https://github.com/ndmitchell/hlint.git && cd hlint
• Create a stack.yaml, stack init
• Build it, stack build
• Find the exe, stack exec where hlint - says something like c:\Neil\hlint\.stack-work\install\60f100ec\bin\hlint.exe
• Delete the exe, del c:\Neil\hlint\.stack-work\install\60f100ec\bin\hlint.exe
• Rebuild it, stack build - nothing happens, but it should detect that the output file is missing and rebuild it.

I suggest that if the output file no longer exists then stack rebuilds the inputs. Note that Shake takes this approach for build rules, rebuilding if either the inputs _or the outputs_ have changed.

[Blaisorblade]

I can reproduce this on OS X, on stack itself, with rm .stack-work/install/x86_64-osx/lts-6.25/7.10.3/bin/stack. I thought that's because this is, for Cabal, an installation step.

What I find worse, though, is that rm .stack-work/dist/x86_64-osx/Cabal-1.22.5.0/build/Stack/stack also does not trigger a rebuild.

Maybe because Cabal doesn't track binaries? Also rm .stack-work/dist/x86_64-osx/Cabal-1.22.5.0/build/libHSstack-1.4.1-JAZEAA7MgYMKhDOQquMlls* doesn't help.

@ndmitchell Any chance this is a bug with the Cabal library itself?

[ndmitchell]

I have no idea which of cabal/stack is at fault - but often stack will work around cabal bugs anyway so raising to stack is my first step.

[mgsloan]

Not sure if Cabal will detect the missing file and cause a rebuild. Certainly to handle this, stack's dirtiness checker would need to be amended.

Not sure if I'd consider it a bug, particularly for the exe at the install location. However, I can certainly understand the expectation that output removal would cause recompilation. PRs appreciated!

[ndmitchell]

For context, if the copy fails (e.g. out of disk space, file locked) then you get the same behaviour of not rebuilding, which I'd say was a bug. However, reproducing that condition is super difficult.

[LispyAriaro]

It seems that when doing a build, Stack finds out if any source files were changed before proceeding. I've found that when I add a space or empty newline to say src/Main.hs that does nothing, stack build then works and generates the executable.

[mgsloan]

An example of this being a problem: https://stackoverflow.com/questions/47638079/reinstalling-intero-using-stack . Using @Blaisorblade 's example of rm .stack-work/install/x86_64-osx/lts-6.25/7.10.3/bin/stack, the workaround is to also do rm .stack-work/install/x86_64-osx/lts-6.25/7.10.3/installed-packages/stack-* (or use the specific version instead of *

Makes sense to check for the output exe and rebuild if it doesn't exist.

[unhammer]

I don't understand @mgsloan 's workaround – the only other file I find in installed-packages is happy – will stack finally reinstall profiteur for me if I delete happy? I'm a bit afraid to try now that I can't even get profiteur installed (I'd rather not have to rm -rf ~/.stack and wait half a day to be productive again). stack obviously tracks that profiteur was installed, since it's not rebuilding it, so where does it track that?

EDIT: It seems rm -rf .stack in the project folder worked :-)