Support for dbmate migrations (#511)

* Support for dbmate migrations

* Add dbmate to migration docs

Author: PeachIceTea

docs/migrations.md

@@ -65,8 +65,8 @@ DROP TABLE comment;
 package db
 
 type Comment struct {
-	ID     int32 
-	Text   string 
+	ID     int32
+	Text   string
 }
 ```
 
@@ -84,6 +84,7 @@ CREATE TABLE post (
 ```
 
 In `20060102.down.sql`:
+
 ```sql
 DROP TABLE post;
 ```
@@ -97,3 +98,21 @@ type Post struct {
 	Body  sql.NullString
 }
 ```
+
+## dbmate
+
+```sql
+-- migrate:up
+CREATE TABLE foo (bar INT NOT NULL);
+
+-- migrate:down
+DROP TABLE foo;
+```
+
+```go
+package db
+
+type Foo struct {
+	Bar int32
+}
+```

internal/migrations/migrations.go

@@ -9,7 +9,8 @@ import (
 //
 // goose:       -- +goose Down
 // sql-migrate: -- +migrate Down
-// tern: ---- create above / drop below ----
+// tern:        ---- create above / drop below ----
+// dbmate:      -- migrate:down
 func RemoveRollbackStatements(contents string) string {
 	s := bufio.NewScanner(strings.NewReader(contents))
 	var lines []string
@@ -23,6 +24,9 @@ func RemoveRollbackStatements(contents string) string {
 		if strings.HasPrefix(s.Text(), "---- create above / drop below ----") {
 			break
 		}
+		if strings.HasPrefix(s.Text(), "-- migrate:down") {
+			break
+		}
 		lines = append(lines, s.Text())
 	}
 	return strings.Join(lines, "\n")

internal/migrations/migrations_test.go

@@ -46,6 +46,16 @@ const outputTern = `
 -- Write your migrate up statements here
 ALTER TABLE todo RENAME COLUMN done TO is_done;`
 
+const inputDbmate = `
+-- migrate:up
+CREATE TABLE foo (bar int);
+-- migrate:down
+DROP TABLE foo;`
+
+const outputDbmate = `
+-- migrate:up
+CREATE TABLE foo (bar int);`
+
 func TestRemoveRollback(t *testing.T) {
 	if diff := cmp.Diff(outputGoose, RemoveRollbackStatements(inputGoose)); diff != "" {
 		t.Errorf("goose migration mismatch:\n%s", diff)
@@ -56,6 +66,9 @@ func TestRemoveRollback(t *testing.T) {
 	if diff := cmp.Diff(outputTern, RemoveRollbackStatements(inputTern)); diff != "" {
 		t.Errorf("tern migration mismatch:\n%s", diff)
 	}
+	if diff := cmp.Diff(outputDbmate, RemoveRollbackStatements(inputDbmate)); diff != "" {
+		t.Errorf("dbmate migration mismatch:\n%s", diff)
+	}
 }
 
 func TestRemoveGolangMigrateRollback(t *testing.T) {