nixpkgs/elvish: fix carapace build

.config/nixpkgs/elvish/flake.nix

@@ -3,33 +3,40 @@
 
   outputs = { self, nixpkgs }:
     {
-      packages.x86_64-linux.default =
+      packages.x86_64-linux.carapace-bin =
         with import nixpkgs {
           system = "x86_64-linux";
         };
-        let
-          carapace-bin = buildGoModule rec {
-            pname = "carapace-bin";
-            version = "0.15.0";
+        buildGoModule rec {
+          pname = "carapace-bin";
+          version = "0.15.0";
+
+          src = fetchFromGitHub {
+            owner = "rsteube";
+            repo = "carapace-bin";
+            rev = "v${version}";
+            sha256 = "0lnsrma6f6s25j21gyn56bsh3yfagb50xsw10sgsw6iczc8ri5fx";
+          };
 
-            src = fetchFromGitHub {
-              owner = "rsteube";
-              repo = "carapace-bin";
-              rev = "v${version}";
-              sha256 = "0lnsrma6f6s25j21gyn56bsh3yfagb50xsw10sgsw6iczc8ri5fx";
-            };
+          ldflags = [ "-s" "-w" ];
 
-            ldflags = [ "-s" "-w" ];
+          tags = [ "release" ];
 
-            tags = [ "release" ];
+          subPackages = [ "cmd/carapace" ];
 
-            preBuild = ''
-              cd cmd/carapace
-              go generate ./...
-            '';
+          preBuild = ''
+            go generate ./...
+          '';
 
-            vendorSha256 = "sha256-OrbVqCgsVX5b5knN6IdlJBWeGfg2fh09a2xe5+2EGEs=";
-          };
+          vendorSha256 = "sha256-OrbVqCgsVX5b5knN6IdlJBWeGfg2fh09a2xe5+2EGEs=";
+        };
+
+      packages.x86_64-linux.default =
+        with import nixpkgs {
+          system = "x86_64-linux";
+        };
+        let
+          carapace-bin = self.packages.x86_64-linux.carapace-bin;
           config = runCommand "elvish-config" {
             nativeBuildInputs = [ makeWrapper ];
           } ''