feat: add download configuration option to support pre-installed binaries

Add optional `download` config to allow using a pre-installed binary
instead of downloading on each run.

When `download: false`, uses monorepo-diff-buildkite-plugin from PATH.
Benefits: reduced build time, improved security, supports policies
against runtime downloads.

Defaults to `download: true` for backward compatibility.

Author: rajatvig

README.md

@@ -281,6 +281,30 @@ steps:
                 trigger: "deploy-foo-service"
 ```
 
+### `download` (optional)
+
+Default: `true`
+
+By setting `download` to `false`, the plugin will use a pre-installed binary instead of downloading it on each run. The binary `monorepo-diff-buildkite-plugin` must be available in your PATH (typically `/usr/bin`).
+
+This option is useful for:
+- Reducing build time by avoiding repeated downloads
+- Improving security by using pre-vetted binaries
+- Organizations with policies against runtime binary downloads
+
+```yaml
+steps:
+  - label: "Triggering pipelines"
+    plugins:
+      - monorepo-diff#v1.5.1:
+          download: false
+          diff: "git diff --name-only HEAD~1"
+          watch:
+            - path: "foo-service/"
+              config:
+                trigger: "deploy-foo-service"
+```
+
 ### `hooks` (optional)
 
 Currently supports a list of `commands` you wish to execute after the `watched` pipelines have been triggered

hooks/command

@@ -106,8 +106,25 @@ download_binary_and_run() {
 
   # todo: move it to a more secure place
   chmod +x ${_executable}
-  
+
   ./${_executable}
 }
 
-download_binary_and_run "$@" || exit 1
+run_preinstalled_binary() {
+  local _executable="monorepo-diff-buildkite-plugin"
+
+  if ! check_cmd "$_executable"; then
+    err "Binary '$_executable' not found in PATH. Please install it or set download: true"
+  fi
+
+  ${_executable} "$@"
+}
+
+# Check if download option is disabled (default is true for backward compatibility)
+download_enabled="${BUILDKITE_PLUGIN_MONOREPO_DIFF_DOWNLOAD:-true}"
+
+if [[ "$download_enabled" == "false" ]]; then
+  run_preinstalled_binary "$@" || exit 1
+else
+  download_binary_and_run "$@" || exit 1
+fi

plugin.yml

@@ -7,6 +7,8 @@ configuration:
   properties:
     diff:
       type: string
+    download:
+      type: boolean
     log_level:
       type: string
     interpolation: