Better version duplicate check

goose.go

@@ -3,9 +3,33 @@ package goose
 import (
 	"database/sql"
 	"fmt"
+	"sync"
 )
 
+var (
+	duplicateCheckOnce sync.Once
+	minVersion         = int64(0)
+	maxVersion         = int64((1 << 63) - 1)
+)
+
+func checkVersionDuplicates(dir string) error {
+	migrations, err := CollectMigrations(dir, minVersion, maxVersion)
+	if err != nil {
+		return err
+	}
+
+	// Try sorting all migrations, so we get panic on any duplicates.
+	ms := migrationSorter(migrations)
+	ms.Sort(true)
+	ms.Sort(false)
+	return nil
+}
+
 func Run(command string, db *sql.DB, dir string, args ...string) error {
+	if err := checkVersionDuplicates(dir); err != nil {
+		return err
+	}
+
 	switch command {
 	case "up":
 		if err := Up(db, dir); err != nil {

migrate.go

@@ -43,7 +43,7 @@ func (ms migrationSorter) Len() int      { return len(ms) }
 func (ms migrationSorter) Swap(i, j int) { ms[i], ms[j] = ms[j], ms[i] }
 func (ms migrationSorter) Less(i, j int) bool {
 	if ms[i].Version == ms[j].Version {
-		panic(fmt.Sprintf("goose: duplicate version %v detected:\n%v\n%v", ms[i].Version, ms[i].Source, ms[j].Source))
+		log.Fatalf("goose: duplicate version %v detected:\n%v\n%v", ms[i].Version, ms[i].Source, ms[j].Source)
 	}
 	return ms[i].Version < ms[j].Version
 }
@@ -259,7 +259,7 @@ func EnsureDBVersion(db *sql.DB) (int64, error) {
 		toSkip = append(toSkip, row.VersionId)
 	}
 
-	panic("failure in EnsureDBVersion()")
+	panic("unreachable")
 }
 
 // Create the goose_db_version table

status.go

@@ -10,9 +10,7 @@ import (
 
 func Status(db *sql.DB, dir string) error {
 	// collect all migrations
-	min := int64(0)
-	max := int64((1 << 63) - 1)
-	migrations, err := CollectMigrations(dir, min, max)
+	migrations, err := CollectMigrations(dir, minVersion, maxVersion)
 	if err != nil {
 		return err
 	}