Fix nix build, and also avoid IFD rebuilds

There is no good reason to call `cabal2nix` on the entire source dir, it
should only be called on the cabal file itself.

Author: Ericson2314

overlay.nix

@@ -29,32 +29,59 @@ in
 
   hnix-store-core =
     lib.pipe
-      (hself.callCabal2nix "hnix-store-core" ./hnix-store-core {})
+      (hself.callCabal2nix "hnix-store-core" ./hnix-store-core/hnix-store-core.cabal {})
       [
+        (drv: drv.overrideAttrs (old: { src = ./hnix-store-core; }))
         haskellLib.compose.buildFromSdist
       ];
   hnix-store-db =
     lib.pipe
-      (hself.callCabal2nix "hnix-store-db" ./hnix-store-db {})
+      (hself.callCabal2nix "hnix-store-db" ./hnix-store-db/hnix-store-db.cabal {})
       [
+        (drv: drv.overrideAttrs (old: { src = ./hnix-store-db; }))
         haskellLib.compose.buildFromSdist
       ];
   hnix-store-json =
+    let
+      # Include the JSON test data files from upstream Nix that we need
+      # for testing.
+      src = lib.fileset.toSource {
+        root = ./.;
+        fileset = lib.fileset.unions [
+          ./hnix-store-json
+          (lib.fileset.fileFilter (file: file.hasExt "json") ./upstream-nix/src/libstore-tests/data/content-address)
+          (lib.fileset.fileFilter (file: file.hasExt "json") ./upstream-nix/src/libstore-tests/data/derived-path)
+          (lib.fileset.fileFilter (file: file.hasExt "json") ./upstream-nix/src/libstore-tests/data/outputs-spec)
+          (lib.fileset.fileFilter (file: file.hasExt "json") ./upstream-nix/src/libstore-tests/data/realisation)
+          (lib.fileset.fileFilter (file: file.hasExt "json") ./upstream-nix/src/libstore-tests/data/store-path)
+          (lib.fileset.fileFilter (file: file.hasExt "json") ./upstream-nix/src/libutil-tests/data/hash)
+        ];
+      };
+    in
     lib.pipe
-      (hself.callCabal2nix "hnix-store-json" ./hnix-store-json {})
+      (hself.callCabal2nix "hnix-store-json" ./hnix-store-json/hnix-store-json.cabal {})
       [
+        (drv: drv.overrideAttrs (old: {
+          inherit src;
+          # Set up symlinks to upstream data files
+          postUnpack = ''
+            sourceRoot+=/hnix-store-json
+          '';
+        }))
         haskellLib.compose.buildFromSdist
       ];
   hnix-store-nar =
     lib.pipe
-      (hself.callCabal2nix "hnix-store-nar" ./hnix-store-nar {})
+      (hself.callCabal2nix "hnix-store-nar" ./hnix-store-nar/hnix-store-nar.cabal {})
       [
+        (drv: drv.overrideAttrs (old: { src = ./hnix-store-nar; }))
         haskellLib.compose.buildFromSdist
       ];
   hnix-store-readonly =
     lib.pipe
-      (hself.callCabal2nix "hnix-store-readonly" ./hnix-store-readonly {})
+      (hself.callCabal2nix "hnix-store-readonly" ./hnix-store-readonly/hnix-store-readonly.cabal {})
       [
+        (drv: drv.overrideAttrs (old: { src = ./hnix-store-readonly; }))
         haskellLib.compose.buildFromSdist
       ];
   hnix-store-remote =
@@ -66,10 +93,11 @@ in
       # after cabal2nix step
       (
       if pkgs.stdenv.isDarwin
-      then hself.callCabal2nix "hnix-store-remote" ./hnix-store-remote {}
-      else hself.callCabal2nixWithOptions "hnix-store-remote" ./hnix-store-remote "-fio-testsuite" {}
+      then hself.callCabal2nix "hnix-store-remote" ./hnix-store-remote/hnix-store-remote.cabal {}
+      else hself.callCabal2nixWithOptions "hnix-store-remote" ./hnix-store-remote/hnix-store-remote.cabal "-fio-testsuite" {}
       )
       [
+        (drv: drv.overrideAttrs (old: { src = ./hnix-store-remote; }))
         haskellLib.compose.buildFromSdist
         (pkg: pkg.overrideAttrs (attrs: {
           buildInputs = attrs.buildInputs ++ [
@@ -79,8 +107,9 @@ in
       ];
   hnix-store-tests =
     lib.pipe
-      (hself.callCabal2nix "hnix-store-tests" ./hnix-store-tests {})
+      (hself.callCabal2nix "hnix-store-tests" ./hnix-store-tests/hnix-store-tests.cabal {})
       [
+        (drv: drv.overrideAttrs (old: { src = ./hnix-store-tests; }))
         haskellLib.compose.buildFromSdist
       ];
 }