feat(third_party/bazel): Check in rules_haskell from Tweag

third_party/bazel/rules_haskell/tools/runfiles/src/Bazel/Runfiles.hs

@@ -0,0 +1,62 @@
+-- | This module enables finding data dependencies ("runfiles") of Haskell
+-- binaries at runtime.
+--
+-- For more information, see: https://github.com/bazelbuild/bazel/issues/4460
+--
+-- Note: this does not currently support the RUNFILES_MANIFEST environmental
+-- variable.  However, that's only necessary on Windows, which rules_haskell
+-- doesn't support yet.
+--
+-- Additionally, this is not yet supported by the REPL.
+module Bazel.Runfiles
+    ( Runfiles
+    , create
+    , rlocation
+    , env
+    ) where
+
+import System.Directory (doesDirectoryExist)
+import System.Environment (getExecutablePath, lookupEnv)
+import System.FilePath (FilePath, (</>), (<.>))
+
+-- | A path to a directory tree containing runfiles for the given
+newtype Runfiles = Runfiles FilePath
+    deriving Show
+
+-- | Construct a path to a data dependency within the given runfiles.
+--
+-- For example: @rlocation \"myworkspace/mypackage/myfile.txt\"@
+rlocation :: Runfiles -> FilePath -> FilePath
+rlocation (Runfiles f) g = f </> g
+
+-- | Set environmental variables for locating the given runfiles directory.
+--
+-- Note that Bazel will set these automatically when it runs tests
+-- (@bazel test@).  However, it will not automatically set them
+-- during "bazel run"; thus, non-test binaries should set the
+-- environment manually for processes that they call.
+env :: Runfiles -> [(String, String)]
+env (Runfiles f) = [(runfilesDirEnv, f)]
+
+runfilesDirEnv :: String
+runfilesDirEnv = "RUNFILES_DIR"
+
+-- | Locate the runfiles directory for the current binary.
+--
+-- This behaves according to the specification in:
+-- https://docs.google.com/document/d/e/2PACX-1vSDIrFnFvEYhKsCMdGdD40wZRBX3m3aZ5HhVj4CtHPmiXKDCxioTUbYsDydjKtFDAzER5eg7OjJWs3V/pub
+--
+-- Note: it does not currently support the @RUNFILES_MANIFEST@ environmental
+-- variable.  However, that's only necessary on Windows, which rules_haskell
+-- doesn't support yet anyway.
+create :: IO Runfiles
+create = do
+    exeRunfilesPath <- fmap (<.> "runfiles") getExecutablePath
+    exeRunfilesExists <- doesDirectoryExist exeRunfilesPath
+    if exeRunfilesExists
+      then return $ Runfiles exeRunfilesPath
+      else do
+        envDir <- lookupEnv runfilesDirEnv
+        case envDir of
+            Just f -> return $ Runfiles f
+            Nothing -> error "Unable to locate runfiles directory"