Convert StorePathMetadata into Metadata a

Also derive bunch of common instances.

Closes #147

Author: sorki

hnix-store-core/CHANGELOG.md

@@ -1,6 +1,7 @@
 # Next
 
 * Changes:
+   * `StorePathMetadata` converted to `Metadata a` [#231](https://github.com/haskell-nix/hnix-store/pull/231)
    * Constructors of `StorePathName` and `StorePathHashPart` are no longer
      exported. Use respective `mkStorePath..` functions. [#230](https://github.com/haskell-nix/hnix-store/pull/230)
    * `StorePathSet` type alias is no more, use `HashSet StorePath` [#230](https://github.com/haskell-nix/hnix-store/pull/230)

hnix-store-core/src/System/Nix/StorePathMetadata.hs

@@ -1,27 +1,29 @@
 {-|
 Description : Metadata about Nix store paths.
 -}
-module System.Nix.StorePathMetadata where
+module System.Nix.StorePathMetadata
+  ( Metadata(..)
+  , StorePathTrust(..)
+  ) where
 
-import           System.Nix.StorePath           ( StorePath
-                                                , ContentAddressableAddress
-                                                )
-import           System.Nix.Hash                ( SomeNamedDigest )
-import           Data.Time                      ( UTCTime )
-import           System.Nix.Signature           ( NarSignature )
+import Data.Time (UTCTime)
 
--- | Metadata about a 'StorePath'
-data StorePathMetadata = StorePathMetadata
+import System.Nix.Hash (SomeNamedDigest)
+import System.Nix.Signature (NarSignature)
+import System.Nix.StorePath (ContentAddressableAddress)
+
+-- | Metadata (typically about a 'StorePath')
+data Metadata a = Metadata
   { -- | The path this metadata is about
-    path :: !StorePath
+    path :: !a
   , -- | The path to the derivation file that built this path, if any
     -- and known.
-    deriverPath :: !(Maybe StorePath)
+    deriverPath :: !(Maybe a)
   , -- TODO should this be optional?
     -- | The hash of the nar serialization of the path.
     narHash :: !SomeNamedDigest
   , -- | The paths that this path directly references
-    references :: !(HashSet StorePath)
+    references :: !(HashSet a)
   , -- | When was this path registered valid in the store?
     registrationTime :: !UTCTime
   , -- | The size of the nar serialization of the path, in bytes.
@@ -38,7 +40,7 @@ data StorePathMetadata = StorePathMetadata
     -- There is no guarantee from this type alone that this address
     -- is actually correct for this store path.
     contentAddressableAddress :: !(Maybe ContentAddressableAddress)
-  }
+  } deriving (Eq, Generic, Ord, Show)
 
 -- | How much do we trust the path, based on its provenance?
 data StorePathTrust
@@ -47,4 +49,4 @@ data StorePathTrust
   | -- | It was built elsewhere (and substituted or similar) and so
     -- is less trusted
     BuiltElsewhere
-  deriving (Show, Eq, Ord)
+  deriving (Eq, Enum, Generic, Ord, Show)

hnix-store-remote/src/System/Nix/Store/Remote.hs

@@ -58,7 +58,7 @@ import           System.Nix.StorePath           ( StorePath
                                                 , StorePathHashPart
                                                 , InvalidPathError
                                                 )
-import           System.Nix.StorePathMetadata   ( StorePathMetadata(..)
+import           System.Nix.StorePathMetadata   ( Metadata(..)
                                                 , StorePathTrust(..)
                                                 )
 import           System.Nix.Internal.Base       ( encodeWith )
@@ -225,7 +225,7 @@ querySubstitutablePaths ps = do
   runOpArgs QuerySubstitutablePaths $ putPaths storeDir ps
   sockGetPaths
 
-queryPathInfoUncached :: StorePath -> MonadStore StorePathMetadata
+queryPathInfoUncached :: StorePath -> MonadStore (Metadata StorePath)
 queryPathInfoUncached path = do
   storeDir <- getStoreDir
   runOpArgs QueryPathInfo $ do
@@ -266,7 +266,7 @@ queryPathInfoUncached path = do
 
       trust = if ultimate then BuiltLocally else BuiltElsewhere
 
-  pure $ StorePathMetadata{..}
+  pure $ Metadata{..}
 
 queryReferrers :: StorePath -> MonadStore (HashSet StorePath)
 queryReferrers p = do