fix(migrators/goose): read from filesytem if no FS (#26)

This CR should allow to read migrations folder from parent directory
like `../migrations`.

I have a `migrations` directory in the root of the project, so to make
migrations work, I need to provide `FS` with root directory:

```go
root, err := filepath.Abs("../../../..")
if err != nil {
  t.Fatal("get abs path", err)
}

migrator := goosemigrator.New("migrations", goosemigrator.WithFS(os.DirFS(root)))
```

This CR should allow to do just:
```go
migrator := goosemigrator.New("../../../../migrations")
```

Also, `golangmigrator` does not have `fs.FS` by default too.

Author: dmksnnk

migrators/goosemigrator/goose.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"io/fs"
 	"os"
+	"path/filepath"
 
 	"github.com/pressly/goose/v3"
 	"github.com/pressly/goose/v3/database"
@@ -44,7 +45,8 @@ func WithTableName(tableName string) Option {
 
 // WithFS specifies a `fs.FS` from which to read the migration files.
 //
-// Default: `os.DirFS(".")` (reads from the real filesystem in the current working directory)
+// Default: The base directory of migrationsDir, `os.DirFS(".")` for a local directory,
+// or `os.DirFS(filepath.Dir(migrationsDir))` for a relative path (e.g., "../../..").
 //
 // https://github.com/pressly/goose#embedded-sql-migrations
 func WithFS(dir fs.FS) Option {
@@ -66,10 +68,16 @@ func WithFS(dir fs.FS) Option {
 //   - [WithTableName] is the same as -table
 func New(migrationsDir string, opts ...Option) *GooseMigrator {
 	gm := &GooseMigrator{
-		MigrationsDir: migrationsDir,
+		MigrationsDir: filepath.Clean(migrationsDir),
 		TableName:     DefaultTableName,
 		FS:            os.DirFS("."),
 	}
+
+	if !filepath.IsLocal(gm.MigrationsDir) {
+		gm.FS = os.DirFS(filepath.Dir(gm.MigrationsDir))
+		gm.MigrationsDir = filepath.Base(gm.MigrationsDir)
+	}
+
 	for _, opt := range opts {
 		opt(gm)
 	}

migrators/goosemigrator/goose_test.go

@@ -13,11 +13,49 @@ import (
 	"github.com/peterldowns/pgtestdb/migrators/goosemigrator"
 )
 
-func TestGooseMigratorFromDisk(t *testing.T) {
+func TestGooseMigratorFromDiskWithSubdirectory(t *testing.T) {
 	t.Parallel()
 	ctx := context.Background()
 
-	m := goosemigrator.New("migrations")
+	m := goosemigrator.New("./migrations")
+	db := pgtestdb.New(t, pgtestdb.Config{
+		DriverName: "pgx",
+		Host:       "localhost",
+		User:       "postgres",
+		Password:   "password",
+		Port:       "5433",
+		Options:    "sslmode=disable",
+	}, m)
+	assert.NotEqual(t, nil, db)
+
+	assert.NoFailures(t, func() {
+		var lastAppliedMigration int
+		err := db.QueryRowContext(ctx, "select max(version_id) from goose_db_version").Scan(&lastAppliedMigration)
+		assert.Nil(t, err)
+		check.Equal(t, 2, lastAppliedMigration)
+	})
+
+	var numUsers int
+	err := db.QueryRowContext(ctx, "select count(*) from users").Scan(&numUsers)
+	assert.Nil(t, err)
+	check.Equal(t, 0, numUsers)
+
+	var numCats int
+	err = db.QueryRowContext(ctx, "select count(*) from cats").Scan(&numCats)
+	assert.Nil(t, err)
+	check.Equal(t, 0, numCats)
+
+	var numBlogPosts int
+	err = db.QueryRowContext(ctx, "select count(*) from blog_posts").Scan(&numBlogPosts)
+	assert.Nil(t, err)
+	check.Equal(t, 0, numBlogPosts)
+}
+
+func TestGooseMigratorFromDiskWithParentDirectoryRelativePath(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+
+	m := goosemigrator.New("../../migrators/goosemigrator/migrations")
 	db := pgtestdb.New(t, pgtestdb.Config{
 		DriverName: "pgx",
 		Host:       "localhost",
@@ -54,7 +92,7 @@ func TestGooseMigratorFromDisk(t *testing.T) {
 //go:embed migrations/*.sql
 var exampleFS embed.FS
 
-func TestGooseMigratorFromFS(t *testing.T) {
+func TestGooseMigratorFromEmbedFS(t *testing.T) {
 	t.Parallel()
 	ctx := context.Background()