amber-lang: generate bash completion

pkgs/by-name/am/amber-lang/package.nix

@@ -5,6 +5,8 @@
   bc,
   util-linux,
   makeWrapper,
+  installShellFiles,
+  stdenv,
   runCommand,
   amber-lang,
   nix-update-script,
@@ -29,7 +31,10 @@ rustPlatform.buildRustPackage rec {
       --replace-fail 'Command::new("/usr/bin/env")' 'Command::new("env")'
   '';
 
-  nativeBuildInputs = [ makeWrapper ];
+  nativeBuildInputs = [
+    makeWrapper
+    installShellFiles
+  ];
 
   nativeCheckInputs = [
     bc
@@ -43,9 +48,14 @@ rustPlatform.buildRustPackage rec {
     "--skip=tests::formatter::all_exist"
   ];
 
-  postInstall = ''
-    wrapProgram "$out/bin/amber" --prefix PATH : "${lib.makeBinPath [ bc ]}"
-  '';
+  postInstall =
+    ''
+      wrapProgram "$out/bin/amber" --prefix PATH : "${lib.makeBinPath [ bc ]}"
+    ''
+    + lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
+      installShellCompletion --cmd amber \
+        --bash <($out/bin/amber completion)
+    '';
 
   passthru = {
     updateScript = nix-update-script { };