Support object based dependencies (#139)

* support obscure format for specifying dependencies using an object with a "version" key

* add test in circle

* add a comment

.circleci/config.yml

@@ -74,3 +74,11 @@ jobs:
             cd $(mktemp -d)
             nixfromnpm -o output -p '[email protected]'
             nix-build output -A nodePackages.sane_2-5-0 --max-jobs 2
+
+      - run:
+          name: Build package which uses an undocumented format for specifying dependencies
+          command: |
+            PATH=$(readlink result)/bin:$PATH
+            cd $(mktemp -d)
+            nixfromnpm -o output -p deep-diff
+            nix-build output -A nodePackages.deep-diff --max-jobs 2

src/NixFromNpm/Npm/Version.hs

@@ -5,6 +5,7 @@
 module NixFromNpm.Npm.Version where
 
 import qualified Data.Text as T
+import qualified Data.HashMap.Strict as H
 
 import Data.SemVer
 import Data.Aeson
@@ -85,6 +86,18 @@ instance FromJSON NpmVersionRange where
     String s -> case parseNpmVersionRange s of
       Nothing -> return $ InvalidVersion s
       Just range -> return range
+    -- NOTE: I couldn't find a mention of this format for specifying
+    -- versions in the official package.json documentation. However,
+    -- this was encountered in the wild:
+    --
+    --   https://github.com/adnelson/nixfromnpm/issues/138
+    --
+    -- Making a special case for it here seems pretty harmless,
+    -- especially if it was at one point supported. Alternatively, we
+    -- could allow parsing dev dependencies and such-like to fail.
+    Object m -> case H.lookup "version" m of
+      Just v -> parseJSON v
+      Nothing -> fail "no 'version' key found in dependency object"
     _ -> Aeson.typeMismatch "string" v
 
 -- | A package name can be passed in directly, or a version range can be