Changes for source-repository-package handling (input-output-hk#107)

Changes needed to support improved handling of `source-repository-package` in `cabal.project`.  Currently the `haskell.nix` 
`cabalProject` functions replace these with regular `packages:` pointing at the downloaded source and these are not treated the same by `cabal`.  We are planning to change it so:

* `haskell.nix` will use `git` to create local repos and a replacement `source-repoository-package`.
* Once the `plan.json` is generated and `plan-to-nix ` has replace these the `/nix/store` paths (so that materialization can work).
*  Have the src mapped to `fetchgit` in haskell.nix.

For this to work we need to be able to identify the `source-repository-packages`.  This change added `url`, `rev` and `sha256` attributes to the `src` for `source-repository-packages`.

It also fixes an issue where the `source-repository-package` is expected to be in `hackage` and allows fixes a problem with the cache if a `source-repository-package` did not have a sha256 provided (not needed if it is coming from `/nix/store`).

Used by input-output-hk#1166

Author: hamishmack

.buildkite/build.sh

@@ -17,7 +17,7 @@ cabal new-configure
 
 echo
 echo "+++ Run stable version of plan-to-nix"
-nix build '(let haskellNix = import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz") {}; in (import haskellNix.sources.nixpkgs haskellNix.nixpkgsArgs).haskell-nix.nix-tools.ghc883)' -o nt
+nix build '(let haskellNix = import (builtins.fetchTarball "https://github.com/input-output-hk/haskell.nix/archive/hkm/use-source-repo.tar.gz") {}; in (import haskellNix.sources.nixpkgs haskellNix.nixpkgsArgs).haskell-nix.nix-tools.ghc8105)' -o nt
 ./nt/bin/plan-to-nix --output .buildkite/nix1 --plan-json dist-newstyle/cache/plan.json
 
 # Replace currently broken plan-to-nix output

default.nix

@@ -1,4 +1,4 @@
-{ compiler-nix-name ? "ghc8104"
+{ compiler-nix-name ? "ghc8105"
 }:
 let
   sources = import ./nix/sources.nix {};

lib/Cabal2Nix.hs

@@ -235,7 +235,13 @@ srcToNix _ (Git url rev mbSha256 mbPath)
       , "sha256" $= case mbSha256 of
                       Just sha256 -> mkStr (fromString sha256)
                       Nothing     -> mkNull
-      ])
+      ]) $// mkNonRecSet
+      [ "url"    $= mkStr (fromString url)
+      , "rev"    $= mkStr (fromString rev)
+      , "sha256" $= case mbSha256 of
+                      Just sha256 -> mkStr (fromString sha256)
+                      Nothing     -> mkNull
+      ]
     ] <>
     [ "postUnpack"
       $= mkStr (fromString $ "sourceRoot+=/" <> root <> "; echo source root reset to $sourceRoot")

nix/sources.json

@@ -5,10 +5,10 @@
         "homepage": "https://input-output-hk.github.io/haskell.nix",
         "owner": "input-output-hk",
         "repo": "haskell.nix",
-        "rev": "958e9d3e9ec53fbce72ac720b10a6418f3b477f0",
-        "sha256": "0j9p3xyck636gv87rwd6yl7w9ssv3jwrfqyxvhpchszkj097qwi6",
+        "rev": "920ac43ee13d95f56d7539bece1f5ee41b10c8a9",
+        "sha256": "0px60yvag24ayj9zl82cbnpixm41slj2wqw4p2vgbwnbz125hgsx",
         "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/958e9d3e9ec53fbce72ac720b10a6418f3b477f0.tar.gz",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/920ac43ee13d95f56d7539bece1f5ee41b10c8a9.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "niv": {

plan2nix/Plan2Nix.hs

@@ -180,6 +180,10 @@ value2plan plan = Plan { packages, extras, compilerVersion, compilerPackages }
  where
   packages = fmap Just $ filterInstallPlan $ \pkg -> case ( pkg ^. key "type" . _String
                                               , pkg ^. key "style" . _String) of
+    -- source-repo packages will be included in `extras`.  We do not need them
+    -- in `packages` as well (this could lead to attribute not found errors looking
+    -- for them in hackage).
+    (_, _) | pkg ^. key "pkg-src" . key "type" . _String == "source-repo" -> Nothing
     (_, "global") -> Just $ Package
       { packageVersion  = pkg ^. key "pkg-version" . _String
       , packageRevision = Nothing

plan2nix/Plan2Nix/Cache.hs

@@ -17,11 +17,13 @@ readCache :: FilePath
                  )]
 readCache f = fmap (toTuple . words) . lines <$> readFile f
   where toTuple [ url, rev, subdir, sha256, pkgname, exprPath ]
-          = ( url, rev, subdir, sha256, pkgname, exprPath )
+          = ( url, rev, subdir, if sha256 == "NOHASH" then "" else sha256, pkgname, exprPath )
 
+-- When we do not need a hash (when the files are local) we store "NOHASH" instead of ""
+-- in the file so that the use of `words` function in `readCache` still works.
 appendCache :: FilePath -> String -> String -> String -> String -> String -> String -> IO ()
 appendCache f url rev subdir sha256 pkgname exprPath = do
-  appendFile f $ unwords [ url, rev, subdir, sha256, pkgname, exprPath ]
+  appendFile f $ unwords [ url, rev, subdir, if null sha256 then "NOHASH" else sha256, pkgname, exprPath ]
   appendFile f "\n"
 
 cacheHits :: FilePath -> String -> String -> String -> IO [ (String, String) ]

shell.nix

@@ -1,3 +1,3 @@
-{ compiler-nix-name ? "ghc8104" }:
+{ compiler-nix-name ? "ghc8105" }:
 (import ./. { inherit compiler-nix-name; }).shell