[cache-processor] chore: Lint and modernize (#47347) (#47887)

In preparation for #46985.

I ran
```sh
go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./libbeat/processors/cache
golangci-lint run --fix ./libbeat/processors/cache
```

and fixed any errors.

(cherry picked from commit 050f433)

Co-authored-by: Orestis Floros <[email protected]>

Author: mergify[bot]

libbeat/processors/cache/cache.go

@@ -274,7 +274,7 @@ func (p *cache) getFor(event *beat.Event) (result *beat.Event, err error) {
 	if meta == nil {
 		return nil, fmt.Errorf("%w for '%s' in %s", ErrNoData, k, p.store)
 	}
-	if m, ok := meta.(map[string]interface{}); ok {
+	if m, ok := meta.(map[string]any); ok {
 		meta = mapstr.M(m)
 	}
 	// ... and write it into the event.

libbeat/processors/cache/cache_test.go

@@ -27,7 +27,6 @@ import (
 
 	"github.com/elastic/beats/v7/libbeat/beat"
 	conf "github.com/elastic/elastic-agent-libs/config"
-	"github.com/elastic/elastic-agent-libs/logp"
 	"github.com/elastic/elastic-agent-libs/logp/logptest"
 	"github.com/elastic/elastic-agent-libs/mapstr"
 	"github.com/elastic/elastic-agent-libs/paths"
@@ -645,7 +644,6 @@ type testConfig struct {
 }
 
 func TestCache(t *testing.T) {
-	logp.TestingSetup(logp.WithSelectors(name))
 	for _, test := range cacheTests {
 		t.Run(test.name, func(t *testing.T) {
 			var processors []beat.Processor
@@ -687,7 +685,6 @@ func TestCache(t *testing.T) {
 						t.Errorf("unexpected error from c.Close(): %v", err)
 					}
 				}()
-
 				processors = append(processors, p)
 			}
 

libbeat/processors/cache/file_store.go

@@ -191,9 +191,10 @@ func (c *fileStore) readState() {
 		var e CacheEntry
 		err = dec.Decode(&e)
 		if err != nil {
-			if err != io.EOF {
-				switch err := err.(type) {
-				case *json.SyntaxError:
+			if !errors.Is(err, io.EOF) {
+				var err *json.SyntaxError
+				switch {
+				case errors.As(err, &err):
 					c.log.Errorw("failed to read state element", "error", err, "path", c.path, "offset", err.Offset)
 				default:
 					c.log.Errorw("failed to read state element", "error", err, "path", c.path)

libbeat/processors/cache/file_store_test.go

@@ -513,7 +513,7 @@ func TestFileStore(t *testing.T) {
 				var e CacheEntry
 				err = dec.Decode(&e)
 				if err != nil {
-					if err != io.EOF {
+					if !errors.Is(err, io.EOF) {
 						t.Fatalf("unexpected error reading persisted cache data: %v", err)
 					}
 					break

libbeat/processors/cache/mem_store.go

@@ -237,7 +237,7 @@ var _ heap.Interface = (*expiryHeap)(nil)
 type expiryHeap []*CacheEntry
 
 func (h *expiryHeap) pop() *CacheEntry {
-	e := heap.Pop(h).(*CacheEntry)
+	e := heap.Pop(h).(*CacheEntry) //nolint:errcheck // Should never happen, panicing here is preferred
 	e.index = -1
 	return e
 }
@@ -254,7 +254,7 @@ func (h expiryHeap) Swap(i, j int) {
 	h[j].index = j
 }
 func (h *expiryHeap) Push(v any) {
-	e := v.(*CacheEntry)
+	e := v.(*CacheEntry) //nolint:errcheck // Should never happen, panicing here is preferred
 	e.index = len(*h)
 	*h = append(*h, e)
 }