fix postgres migration issue with 0.24

Fixes juanfont#2351

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/db/db.go

@@ -478,6 +478,38 @@ func NewHeadscaleDatabase(
 				// populate the user with more interesting information.
 				ID: "202407191627",
 				Migrate: func(tx *gorm.DB) error {
+					// Fix an issue where the automigration in GORM expected a constraint to
+					// exists that didnt, and add the one it wanted.
+					// Fixes https://github.com/juanfont/headscale/issues/2351
+					if cfg.Type == types.DatabasePostgres {
+						err := tx.Exec(`
+BEGIN;
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint
+        WHERE conname = 'uni_users_name'
+    ) THEN
+        ALTER TABLE users ADD CONSTRAINT uni_users_name UNIQUE (name);
+    END IF;
+END $$;
+
+DO $$
+BEGIN
+    IF EXISTS (
+        SELECT 1 FROM pg_constraint
+        WHERE conname = 'users_name_key'
+    ) THEN
+        ALTER TABLE users DROP CONSTRAINT users_name_key;
+    END IF;
+END $$;
+COMMIT;
+`).Error
+						if err != nil {
+							return fmt.Errorf("failed to rename constraint: %w", err)
+						}
+					}
+
 					err := tx.AutoMigrate(&types.User{})
 					if err != nil {
 						return err