hackage2nix: add excluded-packages config option

Author: wolfgangwalther

cabal2nix/CHANGELOG.md

@@ -5,12 +5,15 @@
 * In expressions generated by `cabal2nix --shell`, use the `inNixShell`
   function argument instead of `pkgs.lib.inNixShell`. Note that this
   requires [Nix 2.4 or later](https://github.com/NixOS/nix/pull/3168).
-  
+
   Note that this only works correctly if the generated expression is
   the top level expression. If you want to use a wrapper expression,
   make sure it has an `inNixShell` argument and pass that through
   to the generated one.
 
+* `hackage2nix` now supports an `excluded-packages` config option to
+  prevent creating expressions for specific packages entirely.
+
 ## 2.20.1
 
 * Add support for Cabal `== 3.14.*` in the test suite.
@@ -131,7 +134,7 @@ see [#506](https://github.com/NixOS/cabal2nix/pull/506).
 * Argument parsing logic in `cabal2nix` has been refactored
   in [#544](https://github.com/NixOS/cabal2nix/pull/544).
   **API breaking change** for the following modules:
-  
+
   * `Cabal2nix`
   * `Distribution.Nixpkgs.Fetch`
   * `Distribution.Nixpkgs.Haskell.Derivation` (removed instance)

cabal2nix/hackage2nix/Main.hs

@@ -80,13 +80,15 @@ main = do
   config <- sconcat <$> mapM (\file -> readConfiguration (nixpkgsRepository </> file)) configFiles
   nixpkgs <- readNixpkgPackageMap nixpkgsRepository (Just "{ config = { allowAliases = false; }; }")
   preferredVersions <- readPreferredVersions (fromMaybe (hackageRepository </> "preferred-versions") preferredVersionsFile)
-  let fixup = Map.delete "acme-everything"      -- TODO: https://github.com/NixOS/cabal2nix/issues/164
-            . Map.delete "type"                 -- TODO: https://github.com/NixOS/cabal2nix/issues/163
-            . Map.delete "control-invariants"   -- TODO: depends on "assert"
-            . Map.delete "ConcurrentUtils"      -- TODO: depends on "assert"
-            . Map.delete "with"                 -- TODO: https://github.com/NixOS/cabal2nix/issues/164
-            . over (at "hermes") (fmap (set (contains "1.3.4.3") False))  -- TODO: https://github.com/haskell/hackage-server/issues/436
-  hackage <- fixup <$> readHackage hackageRepository
+  let excluded = excludedPackages config `Set.union` Set.fromList
+        [ "acme-everything"      -- TODO: https://github.com/NixOS/cabal2nix/issues/164
+        , "type"                 -- TODO: https://github.com/NixOS/cabal2nix/issues/163
+        , "control-invariants"   -- TODO: depends on "assert"
+        , "ConcurrentUtils"      -- TODO: depends on "assert"
+        , "with"                 -- TODO: https://github.com/NixOS/cabal2nix/issues/164
+        , "hermes"               -- TODO: https://github.com/haskell/hackage-server/issues/436
+        ]
+  hackage <- flip Map.withoutKeys excluded <$> readHackage hackageRepository
   let
       hackagePackagesFile :: FilePath
       hackagePackagesFile = nixpkgsRepository </> "pkgs/development/haskell-modules/hackage-packages.nix"

cabal2nix/src/Distribution/Nixpkgs/Haskell/FromCabal.hs

@@ -157,6 +157,9 @@ fromPackageDescription haskellResolver nixpkgsResolver missingDeps flags Package
 
     resolveInHackage :: Identifier -> Binding
     resolveInHackage i | (i^.ident) `elem` [ unPackageName n | (Dependency n _ _) <- missingDeps ] = bindNull i
+                       -- Excluded dependencies might not be listed as missing, if they're behind a flag, thus
+                       -- double check whether the package exists at all.
+                       | not $ haskellResolver (PackageVersionConstraint (mkPackageName (i^.ident)) anyVersion) = bindNull i
                        | otherwise = binding # (i, path # ["self",i])   -- TODO: "self" shouldn't be hardcoded.
 
     -- TODO: This is all very confusing. Haskell packages refer to the Nixpkgs

cabal2nix/src/Distribution/Nixpkgs/Haskell/FromCabal/Configuration.hs

@@ -64,6 +64,11 @@ data Configuration = Configuration
   -- also disable their meta.hydraPlatforms attribute to avoid cluttering our
   -- Hydra job with lots of failure messages.
   , brokenPackages :: [Constraint]
+
+  -- |These packages have likely been broken for a long time and are unmaintained
+  -- upstream. To reduce the size of hackage-packages.nix, we don't even create
+  -- expressions for them.
+  , excludedPackages :: Set PackageName
   }
   deriving (Show, Generic)
 
@@ -79,6 +84,7 @@ instance Semigroup Configuration where
                          , unsupportedPlatforms = unsupportedPlatforms l <> unsupportedPlatforms r
                          , dontDistributePackages = dontDistributePackages l <> dontDistributePackages r
                          , brokenPackages = brokenPackages l <> brokenPackages r
+                         , excludedPackages = excludedPackages l <> excludedPackages r
                          }
 
 instance FromJSON Configuration where
@@ -92,6 +98,7 @@ instance FromJSON Configuration where
         <*> o .:? "unsupported-platforms" .!= mempty
         <*> o .:? "dont-distribute-packages" .!= mempty
         <*> o .:? "broken-packages" .!= mempty
+        <*> o .:? "excluded-packages" .!= mempty
   parseJSON _ = error "invalid Configuration"
 
 instance FromJSON Identifier where
@@ -114,7 +121,11 @@ assertConsistency :: MonadFail m => Configuration -> m Configuration
 assertConsistency cfg@Configuration {..} = do
   let report msg = fail ("*** configuration error: " ++ msg)
       maintainedPackages = Set.unions (Map.elems packageMaintainers)
-      disabledPackages = dontDistributePackages `Set.union` Set.fromList (constraintPkgName <$> brokenPackages)
+      disabledPackages = Set.unions
+        [ dontDistributePackages
+        , Set.fromList (constraintPkgName <$> brokenPackages)
+        , excludedPackages
+        ]
       disabledMaintainedPackages = maintainedPackages `Set.intersection` disabledPackages
   unless (Set.null disabledMaintainedPackages) $
     report ("disabled packages that have a maintainer: " ++ show disabledMaintainedPackages)