refactor: Remove database/sql from Driver interface

Just realized that the core godfish library code doesn't even need to
use the database/sql.DB connection. Removing this dependency frees up
the library to work with other databases that may not implement the
database/sql/driver.Driver interface at all.

driver.go

@@ -1,21 +1,13 @@
 package godfish
 
-import "database/sql"
-
-// A Driver describes what a database driver (anything at
-// https://github.com/golang/go/wiki/SQLDrivers) should be able to do.
+// Driver adapts a database implementation to use godfish.
 type Driver interface {
 	// Name should return the name of the driver: ie: postgres, mysql, etc
 	Name() string
 
-	// Connect should open a connection (a *sql.DB) to the database and save an
-	// internal reference to that connection for later use. This library might
-	// call this method multiple times, so use the internal reference if it's
-	// present instead of reconnecting to the database.
-	Connect(dsn string) (*sql.DB, error)
-	// Close should check if there's an internal reference to a database
-	// connection (a *sql.DB) and if it's present, close it. Then reset the
-	// internal reference to that connection to nil.
+	// Connect should open a connection to the database.
+	Connect(dsn string) error
+	// Close should close the database connection.
 	Close() error
 
 	// AppliedVersions queries the schema migrations table for migration
@@ -47,5 +39,3 @@ type AppliedVersions interface {
 	Next() bool
 	Scan(dest ...interface{}) error
 }
-
-var _ AppliedVersions = (*sql.Rows)(nil)

drivers/mysql/mysql.go

@@ -19,12 +19,12 @@ type driver struct {
 }
 
 func (d *driver) Name() string { return "mysql" }
-func (d *driver) Connect(dsn string) (conn *sql.DB, err error) {
+func (d *driver) Connect(dsn string) (err error) {
 	if d.connection != nil {
-		conn = d.connection
 		return
 	}
-	if conn, err = sql.Open(d.Name(), dsn); err != nil {
+	conn, err := sql.Open(d.Name(), dsn)
+	if err != nil {
 		return
 	}
 	d.connection = conn

drivers/postgres/postgres.go

@@ -16,12 +16,12 @@ type driver struct {
 }
 
 func (d *driver) Name() string { return "postgres" }
-func (d *driver) Connect(dsn string) (conn *sql.DB, err error) {
+func (d *driver) Connect(dsn string) (err error) {
 	if d.connection != nil {
-		conn = d.connection
 		return
 	}
-	if conn, err = sql.Open(d.Name(), dsn); err != nil {
+	conn, err := sql.Open(d.Name(), dsn)
+	if err != nil {
 		return
 	}
 	d.connection = conn

godfish.go

@@ -21,7 +21,7 @@ func Migrate(driver Driver, directoryPath string, direction Direction, finishAtV
 	if dsn, err = getDSN(); err != nil {
 		return
 	}
-	if _, err = driver.Connect(dsn); err != nil {
+	if err = driver.Connect(dsn); err != nil {
 		return
 	}
 	defer driver.Close()
@@ -72,7 +72,7 @@ func ApplyMigration(driver Driver, directoryPath string, direction Direction, ve
 	if dsn, err = getDSN(); err != nil {
 		return
 	}
-	if _, err = driver.Connect(dsn); err != nil {
+	if err = driver.Connect(dsn); err != nil {
 		return
 	}
 	defer driver.Close()
@@ -201,7 +201,7 @@ func CreateSchemaMigrationsTable(driver Driver) (err error) {
 	if dsn, err = getDSN(); err != nil {
 		return
 	}
-	if _, err = driver.Connect(dsn); err != nil {
+	if err = driver.Connect(dsn); err != nil {
 		return err
 	}
 	defer driver.Close()
@@ -214,7 +214,7 @@ func Info(driver Driver, directoryPath string, direction Direction, finishAtVers
 	if dsn, err = getDSN(); err != nil {
 		return
 	}
-	if _, err = driver.Connect(dsn); err != nil {
+	if err = driver.Connect(dsn); err != nil {
 		return err
 	}
 	defer driver.Close()

godfish_test.go

@@ -1,6 +1,7 @@
 package godfish_test
 
 import (
+	"database/sql"
 	"encoding/json"
 	"os"
 	"testing"
@@ -67,3 +68,12 @@ func TestInit(t *testing.T) {
 		)
 	}
 }
+
+func TestAppliedVersions(t *testing.T) {
+	// Regression test on the API. It's supposed to wrap this type from the
+	// standard library for the most common cases.
+	var thing interface{} = new(sql.Rows)
+	if _, ok := thing.(godfish.AppliedVersions); !ok {
+		t.Fatalf("expected %T to implement godfish.AppliedVersions", thing)
+	}
+}

internal/stub/driver.go

@@ -2,25 +2,23 @@
 package stub
 
 import (
-	"database/sql"
 	"fmt"
 	"strings"
 
 	"github.com/rafaelespinoza/godfish"
 )
 
 type Driver struct {
-	connection      *sql.DB
 	appliedVersions godfish.AppliedVersions
 	err             error
 	errorOnExecute  error
 }
 
 var _ godfish.Driver = (*Driver)(nil)
 
-func (d *Driver) Name() string                        { return "stub" }
-func (d *Driver) Connect(dsn string) (*sql.DB, error) { return d.connection, d.err }
-func (d *Driver) Close() error                        { return d.err }
+func (d *Driver) Name() string             { return "stub" }
+func (d *Driver) Connect(dsn string) error { return d.err }
+func (d *Driver) Close() error             { return d.err }
 func (d *Driver) CreateSchemaMigrationsTable() error {
 	if d.appliedVersions == nil {
 		d.appliedVersions = MakeAppliedVersions()

internal/test.go

@@ -615,7 +615,7 @@ func setup(driver godfish.Driver, testName string, stubs []testDriverStub, migra
 // teardown clears state after running a test.
 func teardown(driver godfish.Driver, path string, tablesToDrop ...string) {
 	var err error
-	if _, err = driver.Connect(mustDSN()); err != nil {
+	if err = driver.Connect(mustDSN()); err != nil {
 		panic(err)
 	}
 
@@ -811,7 +811,7 @@ func generateMigrationFiles(pathToTestDir string, stubs []testDriverStub) error
 func collectAppliedVersions(driver godfish.Driver) (out []string, err error) {
 	// Collect output of AppliedVersions.
 	// Reconnect here because ApplyMigration closes the connection.
-	if _, err = driver.Connect(mustDSN()); err != nil {
+	if err = driver.Connect(mustDSN()); err != nil {
 		return
 	}
 	defer driver.Close()