feat: require metadata backend and add constructor logging

cachew.hcl

@@ -57,3 +57,5 @@ cache disk {
   limit-mb = 250000
   max-ttl = "8h"
 }
+
+metadata memory {}

internal/config/config.go

@@ -179,16 +179,16 @@ func Load(
 		return nil, nil, errors.Errorf("%s: expected at least one cache backend", ast.Pos)
 	}
 
-	var metadata metadatadb.Backend
-	if classified.metadata != nil {
-		name, inner, err := unwrapBlock(classified.metadata)
-		if err != nil {
-			return nil, nil, err
-		}
-		metadata, err = mr.Create(ctx, name, inner, vars)
-		if err != nil {
-			return nil, nil, errors.Errorf("%s: %w", classified.metadata.Pos, err)
-		}
+	if classified.metadata == nil {
+		return nil, nil, errors.Errorf("%s: expected a metadata backend", ast.Pos)
+	}
+	metaName, metaInner, err := unwrapBlock(classified.metadata)
+	if err != nil {
+		return nil, nil, err
+	}
+	metadata, err := mr.Create(ctx, metaName, metaInner, vars)
+	if err != nil {
+		return nil, nil, errors.Errorf("%s: %w", classified.metadata.Pos, err)
 	}
 
 	cache := cache.MaybeNewTiered(ctx, caches)

internal/config/config_test.go

@@ -1,11 +1,19 @@
 package config //nolint:testpackage
 
 import (
+	"context"
+	"log/slog"
+	"net/http"
 	"strings"
 	"testing"
 
 	"github.com/alecthomas/assert/v2"
 	"github.com/alecthomas/hcl/v2"
+
+	"github.com/block/cachew/internal/cache"
+	"github.com/block/cachew/internal/logging"
+	"github.com/block/cachew/internal/metadatadb"
+	"github.com/block/cachew/internal/strategy"
 )
 
 func TestUnwrapBlock(t *testing.T) {
@@ -175,3 +183,19 @@ git-clone {
 		})
 	}
 }
+
+func TestLoadRequiresMetadataBackend(t *testing.T) {
+	cr := cache.NewRegistry()
+	cache.RegisterMemory(cr)
+	mr := metadatadb.NewRegistry()
+	metadatadb.RegisterMemory(mr)
+	sr := strategy.NewRegistry()
+
+	ast, err := hcl.Parse(strings.NewReader(`cache memory {}`))
+	assert.NoError(t, err)
+
+	ctx := logging.ContextWithLogger(context.Background(), slog.Default())
+	_, _, err = Load(ctx, cr, mr, sr, ast, http.NewServeMux(), nil)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "expected a metadata backend")
+}

internal/metadatadb/memory.go

@@ -6,12 +6,15 @@ import (
 	"sync"
 
 	"github.com/alecthomas/errors"
+
+	"github.com/block/cachew/internal/logging"
 )
 
 // RegisterMemory registers the in-memory metadata backend.
 func RegisterMemory(r *Registry) {
 	Register(r, "memory", "In-memory metadata store for testing and single-instance deployments",
-		func(_ context.Context, _ MemoryConfig) (*MemoryBackend, error) {
+		func(ctx context.Context, _ MemoryConfig) (*MemoryBackend, error) {
+			logging.FromContext(ctx).InfoContext(ctx, "Constructing in-memory metadata backend")
 			return NewMemoryBackend(), nil
 		},
 	)

internal/metadatadb/s3.go

@@ -71,6 +71,9 @@ func NewS3Backend(ctx context.Context, clientProvider s3client.ClientProvider, c
 		return nil, errors.Errorf("bucket %s does not exist", config.Bucket)
 	}
 
+	logging.FromContext(ctx).InfoContext(ctx, "Constructing S3 metadata backend",
+		"bucket", config.Bucket, "prefix", config.Prefix, "lock-ttl", config.LockTTL, "sync-interval", config.SyncInterval)
+
 	ctx, cancel := context.WithCancel(ctx)
 	return &S3Backend{
 		client:       client,