hackage2nix: add excluded-packages config option

Author: wolfgangwalther

cabal2nix/CHANGELOG.md

@@ -5,12 +5,16 @@
 * 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. These
+  packages will be set to `null` explicitly.
+
 ## 2.20.1
 
 * Add support for Cabal `== 3.14.*` in the test suite.
@@ -131,7 +135,7 @@ 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

@@ -170,8 +170,11 @@ main = do
 
           overrides :: Doc
           overrides = fcat $ punctuate space [ pPrint b <> semi | b <- Set.toList (view (dependencies . each) drv `Set.union` view extraFunctionArgs drv), not (isFromHackage b) ]
-      return $ render $ nest 2 $
-        hang (doubleQuotes (text  attr) <+> equals <+> text "callPackage") 2 (parens (pPrint drv)) <+> (braces overrides <> semi)
+
+          def :: Doc
+          def | Set.member name $ excludedPackages config = doubleQuotes (text  attr) <+> equals <+> text "null"
+              | otherwise = hang (doubleQuotes (text  attr) <+> equals <+> text "callPackage") 2 (parens (pPrint drv)) <+> (braces overrides)
+      return $ render $ nest 2 def <> semi
 
     return (intercalate "\n\n" defs)
 

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)