Understand relationship between `stack repl` and Cabal (the library) `repl`

commercialhaskell / stack

The Haskell Tool Stack

BSD 3-Clause "New" or "Revised" License

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Motivation:

@sheaf's observations here: https://github.com/haskellfoundation/tech-proposals/pull/60#issuecomment-2034340587 ...
... here: https://github.com/commercialhaskell/stack/issues/6542#issuecomment-2034348791 ...
... here: https://github.com/haskell/cabal/issues/9857#issuecomment-2034465886 ...
... and here: https://github.com/haskell/cabal/issues/9856#issuecomment-2034370726.

Is there a reason that Stack avoids the use of Cabal (the library) repl (from Cabal >= 2.2)?

Context: Stack.Build.ExecutePackage.realConfigAndBuild (extracts):

        case ( ee.buildOptsCLI.onlyConfigure
             , ee.buildOptsCLI.initialBuildSteps && taskIsTarget task
             ) of
          ...
          (_, True) | null ac.downstream || installedMapHasThisPkg -> do
            initialBuildSteps cabal announce
...
 where
  ...
  initialBuildSteps cabal announce = do
    announce ("initial-build-steps" <> display annSuffix)
    cabal KeepTHLoading ["repl", "stack-initial-build-steps"]

Stack.GhciCmd.ghciCmd (extracts):

ghciCmd ghciOpts =
  let boptsCLI = defaultBuildOptsCLI
        { ...
        , initialBuildSteps = True
        ...
        }
  in  withConfig YesReexec $ withEnvConfig AllowNoTargets boptsCLI $ do
        bopts <- view buildOptsL
        -- override env so running of tests and benchmarks is disabled
        let boptsLocal = bopts
              { testOpts = bopts.testOpts { TestOpts.disableRun = True }
              , benchmarkOpts =
                  bopts.benchmarkOpts { BenchmarkOpts.disableRun = True }
              }
        local (set buildOptsL boptsLocal) (ghci ghciOpts)

Stack.GhciCmd.ghci (extracts):

-- | Launch a GHCi session for the given project package targets with the given
-- options and configure it with the load paths and extensions of those targets.
ghci :: HasEnvConfig env => GhciOpts -> RIO env ()
ghci opts = do
  ...  
  -- Build required dependencies and setup project packages.
  buildDepsAndInitialSteps opts $
    concatMap (\(pn, (_, t)) -> pkgTargets pn t) localTargets
  ...
  -- Finally, do the invocation of ghci
  runGhci
    opts
    localTargets
    mainFile
    pkgs
    (maybe [] snd mfileTargets)
    (nonLocalTargets ++ addPkgs)
    relevantDependencies

History:

May 2015: https://github.com/commercialhaskell/stack/issues/130 (at that time, there were aspects of Cabal's repl that the Stack project did not want to emulate)

> stack --snapshot lts-12.0 runghc -- Setup.hs repl --help Open an interpreter session for the given component. Usage: Setup.hs repl [COMPONENT] [FLAGS] If the current directory contains no package, ignores COMPONENT parameters and opens an interactive interpreter session; if a sandbox is present, its package database will be used. Otherwise, (re)configures with the given or default flags, and loads the interpreter with the relevant modules. For executables, tests and benchmarks, loads the main module (and its dependencies); for libraries all exposed/other modules. The default component is the library itself, or the executable if that is the only component. Support for loading specific modules is planned but not implemented yet. For certain scenarios, `Setup.hs exec -- ghci :l Foo` may be used instead. Note that `exec` will not (re)configure and you will have to specify the location of other modules, if required. Flags for repl: -h --help Show this help text -v --verbose[=n] Control verbosity (n is 0--3, default verbosity level is 1) --builddir=DIR The directory where Cabal puts generated build files (default dist) --with-PROG=PATH give the path to PROG --PROG-option=OPT give an extra option to PROG (no need to quote options containing spaces) --PROG-options=OPTS give extra options to PROG Examples: Setup.hs repl The first component in the package Setup.hs repl foo A named component (i.e. lib, exe, test suite) Setup.hs repl --ghc-options="-lstdc++" Specifying flags for interpreter

commercialhaskell / stack

Understand relationship between `stack repl` and Cabal (the library) `repl` #6548