pandoc: remove GHC from the runtime closure (2.4GB -> 180MB)

pkgs/development/tools/pandoc/default.nix

@@ -0,0 +1,29 @@
+{ haskellPackages, haskell, removeReferencesTo }:
+
+let
+  static = haskell.lib.justStaticExecutables haskellPackages.pandoc;
+
+in
+  (haskell.lib.overrideCabal static (drv: {
+    configureFlags = drv.configureFlags or [] ++ ["-fembed_data_files"];
+    buildDepends = drv.buildDepends or [] ++ [haskellPackages.file-embed];
+    buildTools = (drv.buildTools or []) ++ [ removeReferencesTo ];
+  })).overrideAttrs (drv: {
+
+    # These libraries are still referenced, because pandoc references
+    # their `Paths_*` module for figuring out their version.
+    # The `Paths_*` module is generated by Cabal, and contains the
+    # version, but also paths to e.g. the data directories, which
+    # lead to a transitive runtime dependency on the whole GHC distribution.
+    # This should ideally be fixed in haskellPackages (or even Cabal),
+    # but a minimal pandoc is important enough to patch it manually.
+    disallowedReferences = [ haskellPackages.pandoc-types haskellPackages.HTTP ];
+    postInstall = ''
+      remove-references-to \
+        -t ${haskellPackages.pandoc-types} \
+        $out/bin/pandoc
+      remove-references-to \
+        -t ${haskellPackages.HTTP} \
+        $out/bin/pandoc
+    '';
+  })

pkgs/top-level/all-packages.nix

@@ -5752,10 +5752,7 @@ in
 
   pal = callPackage ../tools/misc/pal { };
 
-  pandoc = haskell.lib.overrideCabal (haskell.lib.justStaticExecutables haskellPackages.pandoc) (drv: {
-    configureFlags = drv.configureFlags or [] ++ ["-fembed_data_files"];
-    buildDepends = drv.buildDepends or [] ++ [haskellPackages.file-embed];
-  });
+  pandoc = callPackage ../development/tools/pandoc { };
 
   pamtester = callPackage ../tools/security/pamtester { };