Merge pull request #26 from unsplash/getInternallyTaggedCodec-decode-…

…preserve-tag

`getInternallyTaggedCodec`: preserve tag when decoding

.prettierignore

@@ -1,5 +1,5 @@
+.direnv/
 node_modules/
 dist/
 coverage/
 docs/
-

flake.nix

@@ -0,0 +1,28 @@
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/master";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    { self
+    , nixpkgs
+    , flake-utils
+    ,
+    }:
+    flake-utils.lib.eachDefaultSystem
+      (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          nativeBuildInputs = [
+            pkgs.nodejs
+            pkgs.yarn
+          ];
+        };
+      });
+}

src/index.ts

@@ -682,8 +682,7 @@ const getInternallyTaggedMemberCodec =
       (i, ctx) =>
         pipe(
           t.type({ [tagKey]: t.literal(tag) }).validate(i, ctx),
-          // eslint-disable-next-line @typescript-eslint/no-unused-vars
-          E.chain(({ [tagKey]: _, ...rest }) => vc.validate(rest, ctx)),
+          E.chain(x => vc.validate(x, ctx)),
           E.map(x =>
             Sum.deserialize(sum)([tag, x] as unknown as Sum.Serialized<A>),
           ),

test/unit/index.ts

@@ -595,6 +595,20 @@ describe("index", () => {
       )
     })
 
+    it("preserves tag after decode", () => {
+      type T = Sum.Member<"B", { readonly tag: "B" }>
+      const T = Sum.create<T>()
+      const {
+        mk: { B },
+      } = T
+
+      const c = getInternallyTaggedCodec("tag")(T)({
+        B: t.strict({ tag: t.literal("B") }),
+      })
+
+      expect(c.decode({ tag: "B" })).toEqual(E.right(B({ tag: "B" })))
+    })
+
     // This is partially for documentative purposes.
     it("handles different nullary encodings", () => {
       type T = Sum.Member<"A">