cmd: Friendly error messages when plugin not found (#432)

* Update error message when upgrading plugin that isn't in the manifest

Also remove line from run-tests.sh for file that was deleted in e37ee1d#diff-d78b6f30225cdc811adfe8d4e7c9fd34

* Update messaging when installing non-existent plugin

* Skip installing plugins that are already installed

* Use os.IsNotExist

* Code review changes

emove check on installed plugin and use %q and errors.New

* Use errors.Errorf

cmd/krew/cmd/install.go

@@ -89,6 +89,9 @@ Remarks:
 			for _, name := range pluginNames {
 				plugin, err := indexscanner.LoadPluginFileFromFS(paths.IndexPluginsPath(), name)
 				if err != nil {
+					if os.IsNotExist(err) {
+						return errors.Errorf("plugin %q does not exist in the plugin index", name)
+					}
 					return errors.Wrapf(err, "failed to load plugin %q from the index", name)
 				}
 				install = append(install, plugin)

cmd/krew/cmd/upgrade.go

@@ -64,6 +64,9 @@ kubectl krew upgrade foo bar"`,
 			for _, name := range pluginNames {
 				plugin, err := indexscanner.LoadPluginFileFromFS(paths.IndexPluginsPath(), name)
 				if err != nil {
+					if os.IsNotExist(err) {
+						return errors.Errorf("plugin %q does not exist in the plugin index", name)
+					}
 					return errors.Wrapf(err, "failed to load the plugin manifest for plugin %s", name)
 				}
 

hack/run-tests.sh

@@ -40,9 +40,6 @@ trap print_status EXIT
 print_with_color "$color_blue" 'Checking boilerplate'
 "$SCRIPTDIR"/verify-boilerplate.sh
 
-print_with_color "$color_blue" 'Running gofmt'
-"$SCRIPTDIR"/verify-gofmt.sh
-
 print_with_color "$color_blue" 'Running tests'
 go test -short -race sigs.k8s.io/krew/...