happy can't be installed from a sandbox

[sol]

Steps to reproduce:

$ cabal unpack happy && cd happy-* && cabal sandbox init && cabal install --prefix ~/.bin
Unpacking to happy-1.19.5/
Writing a default package environment file to
/home/sol/sandbox/haskell/happy-1.19.5/cabal.sandbox.config
Creating a new sandbox at
/home/sol/sandbox/haskell/happy-1.19.5/.cabal-sandbox
Resolving dependencies...
Notice: installing into a sandbox located at
/home/sol/sandbox/haskell/happy-1.19.5/.cabal-sandbox
Configuring mtl-2.2.1...
Building mtl-2.2.1...
Installed mtl-2.2.1
Configuring happy-1.19.5...
Building happy-1.19.5...
Failed to install happy-1.19.5
Build log ( /home/sol/sandbox/haskell/happy-1.19.5/.cabal-sandbox/logs/happy-1.19.5.log ):
cabal: Entering directory '.'
[1 of 1] Compiling Main             ( dist/dist-sandbox-8adab01b/setup/setup.hs, dist/dist-sandbox-8adab01b/setup/Main.o )
Linking ./dist/dist-sandbox-8adab01b/setup/setup ...
Configuring happy-1.19.5...
Building happy-1.19.5...
Preprocessing executable 'happy' for happy-1.19.5...
setup: The program 'happy' is required but it could not be found
cabal: Leaving directory '.'
cabal: Error: some packages failed to install:
happy-1.19.5 failed during the building phase. The exception was:
ExitFailure 1

[23Skidoo]

Looks like a duplicate of #4574.

[sol]

@23Skidoo I guess kind of. #4574 has a different error message (specifically, I assume the data files for happy are missing). In my case, I don't have happy at all. Anyhow, the bug boils down to:

• Cabal tries to generate AttrGrammarParser.hs and Parser.hs, even though they are already present in dist/.

I think in general this even makes sense, and with that sentiment you could call this a "bug" in happy.

The surprising/buggy thing is that Cabal behaves different within/outside of a sandbox.

[p-alik]

I think in general this even makes sense, and with that sentiment you could call this a "bug" in happy.

see https://mail.haskell.org/pipermail/haskell-cafe/2017-June/127358.html for the happy-1.19.5 topic

[23Skidoo]

@p-alik I think that's an unrelated issue.

[hvr]

This sounds related to the conceptual problem with happy I described in haskell/happy#88 (comment) - the circular build-tool dependency on itself; I've shortly talked to @simonmar whether at some point we could get rid of it by changing the way the packaging works - to be continued

[simonmar]

I object somewhat to this being described as a "conceptual problem with Happy"! The way this was supposed to work was that cabal sdist would include the generated source files in the package, and cabal install would use them. Happy deliberately doesn't declare a dependency on itself in the .cabal file, because it is supposed to build without needing itself installed. This sort of worked with cabal install, but broke with sandboxes and new-build. I've opened issues around the flakiness of this in the past, e.g.: #2940

However, it's been broken for quite a while and in the interests of making stuff work for people I've gone ahead and checked in the generated source files: haskell/happy@ea3c22d

[hvr]

@simonmar Alright, the main problem is that the sdist tarball contains the generated Parser.hs file in a folder that isn't mentioned in the respective component's hs-source-dirs. How would you specify Cabal shall behave here?

[phadej]

sandbox functionality is removed.