Drop snapshot download-from-remote codepath

The new one from parsing elm.json should be sufficient.

Also, add the ability to customise the paths for elm.json and
registry.dat. Inspired by me trying to test using `cabal run`, and not
knowing how to do that outside the repo working directory (where my
elm.json is).

README.md

@@ -9,7 +9,7 @@ Convert an [Elm](http://elm-lang.org/) project into
 It consists of multiple commands:
 - `elm2nix convert`: Given `elm.json` in current directory, all dependencies are
   parsed and their sha256sum calculated
-- `elm2nix snapshot`: Downloads snapshot of https://package.elm-lang.org/all-packages json and converts into binary `registry.dat` used by [elm-compiler](https://github.com/elm/compiler/blob/047d5026fe6547c842db65f7196fed3f0b4743ee/builder/src/Stuff.hs#L147) as a cache
+- `elm2nix snapshot`: Reads packages from `elm.json` and writes them to binary cache file `registry.dat` used by [elm-compiler](https://github.com/elm/compiler/blob/047d5026fe6547c842db65f7196fed3f0b4743ee/builder/src/Stuff.hs#L147).
 - `elm2nix init`: Generates `default.nix` that glues everything together
 
 ## Assumptions

elm2nix.cabal

@@ -35,13 +35,8 @@ library
     , bytestring
     , binary
     , containers
-    , data-default
-    , directory
-    , filepath
     , here
-    , mtl
     , process
-    , req
     , text
     , transformers
     , unordered-containers
@@ -68,7 +63,6 @@ executable elm2nix
   build-depends:
       base >= 4.7 && < 5
     , elm2nix
-    , directory
     , optparse-applicative
     , here
     , ansi-wl-pprint

elm2nix/Main.hs

@@ -16,7 +16,7 @@ import qualified Text.PrettyPrint.ANSI.Leijen as PP
 data Command
   = Init
   | Convert
-  | Snapshot { fromElmJson :: Bool }
+  | Snapshot { elmJson :: FilePath, writeTo :: FilePath }
 
 main :: IO ()
 main = do
@@ -26,7 +26,7 @@ main = do
   case cmd of
     Convert -> Elm2Nix.convert
     Init -> Elm2Nix.initialize
-    Snapshot { fromElmJson } -> Elm2Nix.snapshot fromElmJson
+    Snapshot { elmJson, writeTo } -> Elm2Nix.snapshot elmJson writeTo
 
 getOpts :: IO Command
 getOpts = customExecParser p (infoH opts rest)
@@ -45,14 +45,20 @@ getOpts = customExecParser p (infoH opts rest)
 
       $ elm2nix init > default.nix
       $ elm2nix convert > elm-srcs.nix
-      $ elm2nix snapshot --from-elm-json
+      $ elm2nix snapshot
       $ nix-build
 
       Note: You have to run elm2nix from top-level directory of an Elm project.
     |]
 
     snapshotOpts :: Parser Command
-    snapshotOpts = Snapshot <$> switch (long "from-elm-json")
+    snapshotOpts =
+      Snapshot
+      <$> (arg "elm-json" <|> pure "elm.json")
+      <*> (arg "write-to" <|> pure "registry.dat")
+      where
+        arg name = strOption $
+          long name <> metavar "FILENAME" <> completer (bashCompleter "file")
 
     opts :: Parser Command
     opts = subparser

src/Elm2Nix.hs

@@ -1,7 +1,6 @@
 {-# LANGUAGE QuasiQuotes #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE CPP #-}
 
 module Elm2Nix
     ( convert
@@ -20,7 +19,7 @@ import System.IO (hPutStrLn, stderr)
 
 import qualified Data.Text as Text
 
-import Elm2Nix.ElmJson (Dep, Elm2NixError(..), readElmJson, toErrorMessage)
+import Elm2Nix.ElmJson (Elm2NixError(..), readElmJson, toErrorMessage)
 import Elm2Nix.FixedOutput (FixedDerivation(..), prefetch)
 import Elm2Nix.PackagesSnapshot (snapshot)
 
@@ -40,7 +39,7 @@ convert :: IO ()
 convert = runCLI $ do
   liftIO (hPutStrLn stderr "Resolving elm.json dependencies into Nix ...")
 
-  deps <- either throwErr return =<< liftIO readElmJson
+  deps <- either throwErr return =<< liftIO (readElmJson "elm.json")
   liftIO (hPutStrLn stderr "Prefetching tarballs and computing sha256 hashes ...")
 
   sources <- liftIO (mapConcurrently (uncurry prefetch) deps)

src/Elm2Nix/ElmJson.hs

@@ -38,9 +38,9 @@ toErrorMessage err =
     ElmJsonReadError s -> "Error reading json: " ++ s
     KeyNotFound key -> "Key not found in json: " ++ Text.unpack key
 
-readElmJson :: IO (Either Elm2NixError [Dep])
-readElmJson = do
-  res <- Json.eitherDecode <$> LBS.readFile "elm.json"
+readElmJson :: FilePath -> IO (Either Elm2NixError [Dep])
+readElmJson path = do
+  res <- Json.eitherDecode <$> LBS.readFile path
   pure $
     either
       (Left . ElmJsonReadError)

src/Elm2Nix/PackagesSnapshot.hs

@@ -1,36 +1,26 @@
-{- Downloads binary serialized https://package.elm-lang.org/all-packages
-   as Elm compiler expects it to parse.
+{- Writes a binary serialized package registry for the Elm compiler to consume.
 
   Takes Elm upstream code from:
-  - https://github.com/elm/compiler/blob/master/builder/src/Deps/Cache.hs
-  - https://github.com/elm/compiler/blob/master/builder/src/Deps/Website.hs
+  - https://github.com/elm/compiler/blob/master/builder/src/Deps/Registry.hs
   - https://github.com/elm/compiler/blob/master/compiler/src/Elm/Package.hs
-
 -}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE BangPatterns #-}
 module Elm2Nix.PackagesSnapshot
   ( snapshot
   ) where
 
 import Control.Monad (liftM2, liftM3)
-import qualified Data.Aeson as Aeson
 import qualified Data.Binary as Binary
 import Data.Binary (Binary, put, get, putWord8, getWord8)
 import Data.Binary.Put (putBuilder)
 import Data.Binary.Get.Internal (readN)
 import qualified Data.Map as Map
-#if MIN_VERSION_req(2,0,0)
-#else
-import Data.Default (def)
-#endif
 import Data.Map (Map)
 import Data.Text (Text)
 import qualified Data.Text as Text
 import qualified Data.Text.Encoding as Text
 import Data.Word (Word16)
-import qualified Network.HTTP.Req as Req
 import qualified Data.List as List
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Builder as BS
@@ -147,48 +137,23 @@ instance Binary Registry where
   get = liftM2 Registry get get
   put (Registry a b) = put a >> put b
 
-#if MIN_VERSION_req(2,0,0)
-defHttpConfig = Req.defaultHttpConfig
-#else
-defHttpConfig = def
-#endif
-
-getFromElmJson :: IO Packages
-getFromElmJson = do
-  deps <- either (error . toErrorMessage) id <$> readElmJson
+snapshot :: FilePath -> FilePath -> IO ()
+snapshot elmJson writeTo = do
+  deps <- either (error . toErrorMessage) id <$> readElmJson elmJson
   let
     parseDep (k, v) = do
       name <- parseName (Text.pack k)
       version <- parseVersion (Text.pack v)
-      pure (name, KnownVersions version [])
-  Packages . Map.fromList <$> mapM parseDep deps
-
-getFromPackageServer :: IO Packages
-getFromPackageServer = do
-  r <- Req.runReq defHttpConfig $
-    Req.req
-    Req.POST
-    (Req.https "package.elm-lang.org" Req./: "all-packages")
-    Req.NoReqBody
-    Req.jsonResponse
-    mempty
-  case Aeson.fromJSON (Req.responseBody r) of
-    Aeson.Error s -> error s
-    Aeson.Success val -> pure val
-
-snapshot :: Bool -> IO ()
-snapshot fromElmJson = do
-  packages <- unwrap <$> if fromElmJson then getFromElmJson else getFromPackageServer
+      pure (name, [version])
+  packages <- toKnownVersions . Map.fromListWith (<>) <$> mapM parseDep deps
   let size = Map.foldr' addEntry 0 packages
       registry = Registry size packages
 
       addEntry :: KnownVersions -> Int -> Int
       addEntry (KnownVersions _ vs) count =
         count + 1 + length vs
 
-  Binary.encodeFile "registry.dat" registry
-
-newtype Packages = Packages { unwrap :: Map.Map Name KnownVersions }
+  Binary.encodeFile writeTo registry
 
 toKnownVersions ::  Map.Map Name [Version] -> Map.Map Name KnownVersions
 toKnownVersions  =
@@ -197,18 +162,3 @@ toKnownVersions  =
             v:vs -> KnownVersions v vs
             [] -> undefined
        )
-
-instance Aeson.FromJSON Packages where
-  parseJSON v = Packages <$> fmap toKnownVersions (Aeson.parseJSON v)
-
-
-instance Aeson.FromJSON Version where
-  parseJSON = Aeson.withText "string" parseVersion
-
-
-instance Aeson.FromJSON Name where
-  parseJSON = Aeson.withText "string" parseName
-
-
-instance Aeson.FromJSONKey Name where
-  fromJSONKey = Aeson.FromJSONKeyTextParser parseName