cli-plugins: add build-time system plugin directory

Signed-off-by: Conlan Cesar <conlan.cesar@datadoghq.com>

Author: HeroCC

cli-plugins/manager/manager.go

@@ -32,6 +32,12 @@ func (e errPluginNotFound) Error() string {
 	return "Error: No such CLI plugin: " + string(e)
 }
 
+// additionalSystemPluginDir is an optional system plugin directory that can be
+// set at build time using -ldflags -X.
+//
+// For example: -X github.com/docker/cli/cli-plugins/manager.additionalSystemPluginDir=/path/to/cli-plugins
+var additionalSystemPluginDir string
+
 // getPluginDirs returns the platform-specific locations to search for plugins
 // in order of preference.
 //
@@ -50,6 +56,9 @@ func getPluginDirs(cfg *configfile.ConfigFile) []string {
 	}
 	pluginDir := filepath.Join(config.Dir(), "cli-plugins")
 	pluginDirs = append(pluginDirs, pluginDir)
+	if additionalSystemPluginDir != "" {
+		pluginDirs = append(pluginDirs, additionalSystemPluginDir)
+	}
 	pluginDirs = append(pluginDirs, defaultSystemPluginDirs...)
 	return pluginDirs
 }

cli-plugins/manager/manager_test.go

@@ -172,6 +172,12 @@ func TestGetPluginDirs(t *testing.T) {
 	cli := test.NewFakeCli(nil)
 
 	pluginDir := filepath.Join(config.Dir(), "cli-plugins")
+	originalAdditionalSystemPluginDir := additionalSystemPluginDir
+	additionalSystemPluginDir = ""
+	t.Cleanup(func() {
+		additionalSystemPluginDir = originalAdditionalSystemPluginDir
+	})
+
 	expected := append([]string{pluginDir}, defaultSystemPluginDirs...)
 
 	pluginDirs := getPluginDirs(cli.ConfigFile())
@@ -185,4 +191,10 @@ func TestGetPluginDirs(t *testing.T) {
 	})
 	pluginDirs = getPluginDirs(cli.ConfigFile())
 	assert.DeepEqual(t, expected, pluginDirs)
+
+	additionalSystemPluginDir = "qux"
+	expected = append(extras, pluginDir, additionalSystemPluginDir)
+	expected = append(expected, defaultSystemPluginDirs...)
+	pluginDirs = getPluginDirs(cli.ConfigFile())
+	assert.DeepEqual(t, expected, pluginDirs)
 }