README.md

Bazel Runfiles

This is a small utility to enable discovery of the Bazel runfiles location. This is useful in tests for example.

module Main (main) where

import qualified Bazel.Runfiles as Runfiles
import Control.Monad (when)
import System.Process (callProcess)

main :: IO ()
main = do
    r <- Runfiles.create
    foo <- readFile (Runfiles.rlocation r "rules_haskell/tools/runfiles/test-data.txt")
    when (lines foo /= ["foo"]) -- ignore trailing newline
        $ error $ "Incorrect contents: got: " ++ show foo
    callProcess (Runfiles.rlocation r "rules_haskell/tools/runfiles/bin") []

haskell_runfiles

To resolve repository mappings with bzlmod, the runfiles library must know the name of the bazel module calling it (see the design document).

This is achieved by passing the __FILE__ constant to the createFromCurrentFile function of the library.

Since enabling the preprocessor can be inconvenient in some cases, the haskell_runfiles helper rule is provided in @rules_haskell//haskell:defs.bzl, which generates a small wrapper around the main runfiles library.

Note: using the haskell_runfiles rule is only required when the library accessing runfiles is used from another bazel module (which uses a different repository mapping). If the binary is defined in the same module, the default behavior which recovers the current module from the path of the binary is correct.