cabal.project Per GHC Version (Part 2)

In the cabal.project Per GHC Version blog entry, I mentioned that I changed the PhatSort Makefile so that a cabal.project file can be specified. Unlike Stack configuration, however, it was easy to use the wrong configuration and get a misleading error message. I updated the Makefile to resolve this issue.

The Makefile uses a CONFIG argument to select a stack.yaml configuration file when using Stack. In this case, the configuration file determines which version of GHC is used, so there cannot be a mismatch. I implemented a PROJECT_FILE argument to select a cabal.project file in a similar way, but the version of GHC used is determined by the PATH, not the configuration file. If I forget to specify the PROJECT_FILE when in an environment using GHC 9.2.1, for example, the default cabal.project file is used, resulting in failure.

I changed the Makefile to make it easier to use. If a PROJECT_FILE argument is passed, it is used. Otherwise, a cabal.project file for the version of GHC in the PATH is used if it exists.

ifneq ($(origin CABAL), undefined)
  MODE := cabal
  CABAL_ARGS :=
  ifneq ($(origin PROJECT_FILE), undefined)
    CABAL_ARGS += "--project-file=$(PROJECT_FILE)"
  else
    PROJECT_FILE := cabal-$(shell ghc --version | sed 's/.* //').project
    ifneq (,$(wildcard $(PROJECT_FILE)))
      CABAL_ARGS += "--project-file=$(PROJECT_FILE)"
    endif
  endif
endif

As usual, writing Makefile code was much more painful and time consuming than it should be. I had to refactor and test many times before finally arriving on the above code, which works but does not seem much different from other code that did not.