Added new Couchbase Driver

Makefile

@@ -1,5 +1,5 @@
 SOURCE ?= file go_bindata github github_ee bitbucket aws_s3 google_cloud_storage godoc_vfs gitlab
-DATABASE ?= postgres mysql redshift cassandra spanner cockroachdb yugabytedb clickhouse mongodb sqlserver firebird neo4j pgx pgx5 rqlite
+DATABASE ?= postgres mysql redshift cassandra spanner cockroachdb yugabytedb clickhouse mongodb sqlserver firebird neo4j pgx pgx5 rqlite couchbase
 DATABASE_TEST ?= $(DATABASE) sqlite sqlite3 sqlcipher
 VERSION ?= $(shell git describe --tags 2>/dev/null | cut -c 2-)
 TEST_FLAGS ?=

database/couchbase/README.md

@@ -0,0 +1,103 @@
+# couchbase
+
+`couchbase://user:password@host:port/bucket?query` (`couchbases://` for TLS)
+
+Migrations are JSON files containing arrays of N1QL statements:
+
+```json
+[
+  {"query": "CREATE PRIMARY INDEX IF NOT EXISTS ON `mybucket`.`_default`.`_default`"},
+  {"query": "UPSERT INTO `mybucket` (KEY, VALUE) VALUES ($1, $2)", "params": ["doc::1", {"name": "Alice"}]}
+]
+```
+
+| URL Query  | WithInstance Config | Description |
+|------------|---------------------|-------------|
+| `x-scope` | `ScopeName` | Couchbase scope for migration metadata (default: `_default`) |
+| `x-migrations-collection` | `MigrationsCollection` | Collection to store migration version (default: `migrations`) |
+| `x-advisory-locking` | `Locking.Enabled` | Enable advisory locking (default: `true`) |
+| `x-advisory-lock-collection` | `Locking.CollectionName` | Collection for lock document (default: `migrate_advisory_lock`) |
+| `x-advisory-lock-timeout` | `Locking.Timeout` | Seconds to wait for lock acquisition (default: `15`) |
+| `x-advisory-lock-timeout-interval` | `Locking.Interval` | Max backoff interval in seconds between lock retries (default: `10`) |
+
+## Usage
+
+### CLI
+
+```bash
+# Apply all up migrations
+migrate -source file://migrations -database "couchbase://Administrator:password@localhost:11210/mybucket?x-scope=_default" up
+
+# Roll back one migration
+migrate -source file://migrations -database "couchbase://Administrator:password@localhost:11210/mybucket" down 1
+
+# Force a specific version (useful for fixing dirty state)
+migrate -source file://migrations -database "couchbase://Administrator:password@localhost:11210/mybucket" force 3
+
+# TLS connection
+migrate -source file://migrations -database "couchbases://Administrator:password@localhost:11207/mybucket" up
+```
+
+### Go
+
+```go
+import (
+    "github.com/couchbase/gocb/v2"
+    "github.com/golang-migrate/migrate/v4"
+    "github.com/golang-migrate/migrate/v4/database/couchbase"
+    _ "github.com/golang-migrate/migrate/v4/source/file"
+)
+
+// Using a URL
+m, err := migrate.New("file://migrations", "couchbase://user:pass@localhost:11210/mybucket")
+
+// Using an existing cluster instance
+cluster, _ := gocb.Connect("couchbase://localhost", gocb.ClusterOptions{
+    Authenticator: gocb.PasswordAuthenticator{
+        Username: "Administrator",
+        Password: "password",
+    },
+})
+
+driver, err := couchbase.WithInstance(cluster, &couchbase.Config{
+    BucketName: "mybucket",
+    ScopeName:  "_default",
+    Locking: couchbase.Locking{
+        Enabled: true,
+        Timeout: 15,
+    },
+})
+
+m, err := migrate.NewWithDatabaseInstance("file://migrations", "mybucket", driver)
+m.Up()
+```
+
+## Migration file format
+
+Each migration file is a JSON array of objects. Each object has a `query` field (required) and an optional `params` field for positional parameters:
+
+```json
+[
+  {"query": "CREATE COLLECTION `mybucket`.`myscope`.`users` IF NOT EXISTS"},
+  {"query": "CREATE INDEX idx_email IF NOT EXISTS ON `mybucket`.`myscope`.`users`(email)"},
+  {"query": "UPSERT INTO `mybucket` (KEY, VALUE) VALUES ($1, $2)", "params": ["key1", {"field": "value"}]}
+]
+```
+
+See the [examples/migrations](examples/migrations) directory for a complete set of migrations covering collections, indexes, and data operations.
+
+## Advisory locking
+
+Advisory locking is enabled by default and uses a document-based lock in a dedicated collection. This prevents concurrent migration runs from corrupting state. The lock uses exponential backoff when waiting for acquisition.
+
+To disable locking (e.g., for single-instance deployments):
+
+```
+couchbase://user:pass@host/bucket?x-advisory-locking=false
+```
+
+## Couchbase version support
+
+Tested against:
+- Couchbase Community Edition 7.6.2
+- Couchbase Community Edition 8.0.0