trivy: add shell completions

pkgs/tools/admin/trivy/default.nix

@@ -1,6 +1,9 @@
 { lib
+, stdenv
+, buildPackages
 , buildGoModule
 , fetchFromGitHub
+, installShellFiles
 , testers
 , trivy
 }:
@@ -29,9 +32,22 @@ buildGoModule rec {
     "-X=github.com/aquasecurity/trivy/pkg/version.ver=v${version}"
   ];
 
+  nativeBuildInputs = [ installShellFiles ];
+
   # Tests require network access
   doCheck = false;
 
+  postInstall =
+    let
+      trivy = if stdenv.buildPlatform.canExecute stdenv.hostPlatform then placeholder "out" else buildPackages.trivy;
+    in
+    ''
+      installShellCompletion --cmd trivy \
+        --bash <(${trivy}/bin/trivy completion bash) \
+        --fish <(${trivy}/bin/trivy completion fish) \
+        --zsh <(${trivy}/bin/trivy completion zsh)
+    '';
+
   doInstallCheck = true;
 
   passthru.tests.version = testers.testVersion {