Plugins: Optimize creation of Golang errors and slices (#69448)

* tidy up

* fix tests

pkg/plugins/manager/loader/finder/local.go

@@ -44,8 +44,9 @@ func (l *Local) Find(ctx context.Context, src plugins.PluginSource) ([]*plugins.
 		return []*plugins.FoundBundle{}, nil
 	}
 
-	var pluginJSONPaths []string
-	for _, path := range src.PluginURIs(ctx) {
+	pluginURIs := src.PluginURIs(ctx)
+	pluginJSONPaths := make([]string, 0, len(pluginURIs))
+	for _, path := range pluginURIs {
 		exists, err := fs.Exists(path)
 		if err != nil {
 			l.log.Warn("Skipping finding plugins as an error occurred", "path", path, "err", err)
@@ -85,7 +86,7 @@ func (l *Local) Find(ctx context.Context, src plugins.PluginSource) ([]*plugins.
 		foundPlugins[filepath.Dir(pluginJSONAbsPath)] = plugin
 	}
 
-	var res = make(map[string]*plugins.FoundBundle)
+	res := make(map[string]*plugins.FoundBundle)
 	for pluginDir, data := range foundPlugins {
 		var pluginFs plugins.FS
 		pluginFs = plugins.NewLocalFS(pluginDir)
@@ -106,7 +107,7 @@ func (l *Local) Find(ctx context.Context, src plugins.PluginSource) ([]*plugins.
 		}
 	}
 
-	var result []*plugins.FoundBundle
+	result := make([]*plugins.FoundBundle, 0, len(foundPlugins))
 	for dir := range foundPlugins {
 		ancestors := strings.Split(dir, string(filepath.Separator))
 		ancestors = ancestors[0 : len(ancestors)-1]

pkg/plugins/manager/loader/finder/local_test.go

@@ -3,7 +3,6 @@ package finder
 import (
 	"context"
 	"errors"
-	"fmt"
 	"os"
 	"path/filepath"
 	"sort"
@@ -317,7 +316,7 @@ func TestFinder_getAbsPluginJSONPaths(t *testing.T) {
 	t.Run("When scanning a folder that returns a non-handled error should return that error", func(t *testing.T) {
 		origWalk := walk
 		walk = func(path string, followSymlinks, detectSymlinkInfiniteLoop bool, walkFn util.WalkFunc) error {
-			return walkFn(path, nil, fmt.Errorf("random error"))
+			return walkFn(path, nil, errors.New("random error"))
 		}
 		t.Cleanup(func() {
 			walk = origWalk

pkg/plugins/manager/loader/loader.go

@@ -81,7 +81,7 @@ func (l *Loader) Load(ctx context.Context, src plugins.PluginSource) ([]*plugins
 
 // nolint:gocyclo
 func (l *Loader) loadPlugins(ctx context.Context, src plugins.PluginSource, found []*plugins.FoundBundle) ([]*plugins.Plugin, error) {
-	var loadedPlugins []*plugins.Plugin
+	loadedPlugins := make([]*plugins.Plugin, 0, len(found))
 
 	for _, p := range found {
 		if _, exists := l.pluginRegistry.Plugin(ctx, p.Primary.JSONData.ID); exists {
@@ -129,7 +129,7 @@ func (l *Loader) loadPlugins(ctx context.Context, src plugins.PluginSource, foun
 	}
 
 	// validate signatures
-	verifiedPlugins := make([]*plugins.Plugin, 0)
+	verifiedPlugins := make([]*plugins.Plugin, 0, len(loadedPlugins))
 	for _, plugin := range loadedPlugins {
 		signingError := l.signatureValidator.Validate(plugin)
 		if signingError != nil {
@@ -180,7 +180,7 @@ func (l *Loader) loadPlugins(ctx context.Context, src plugins.PluginSource, foun
 	}
 
 	// initialize plugins
-	initializedPlugins := make([]*plugins.Plugin, 0)
+	initializedPlugins := make([]*plugins.Plugin, 0, len(verifiedPlugins))
 	for _, p := range verifiedPlugins {
 		// Detect angular for external plugins
 		if p.IsExternalPlugin() {
@@ -360,7 +360,7 @@ func defaultLogoPath(pluginType plugins.Type) string {
 }
 
 func (l *Loader) PluginErrors() []*plugins.Error {
-	errs := make([]*plugins.Error, 0)
+	errs := make([]*plugins.Error, 0, len(l.errs))
 	for _, err := range l.errs {
 		errs = append(errs, &plugins.Error{
 			PluginID:  err.PluginID,

pkg/plugins/manager/loader/loader_test.go

@@ -2,7 +2,7 @@ package loader
 
 import (
 	"context"
-	"fmt"
+	"errors"
 	"path/filepath"
 	"sort"
 	"testing"
@@ -1048,7 +1048,7 @@ func TestLoader_Load_SkipUninitializedPlugins(t *testing.T) {
 		procPrvdr.BackendFactoryFunc = func(ctx context.Context, p *plugins.Plugin) backendplugin.PluginFactoryFunc {
 			return func(pluginID string, _ log.Logger, _ []string) (backendplugin.Plugin, error) {
 				if pluginID == "test-datasource" {
-					return nil, fmt.Errorf("failed to initialize")
+					return nil, errors.New("failed to initialize")
 				}
 				return &fakes.FakePluginClient{}, nil
 			}