Enum array changes should work (#2121)

We never realized the temporary enum as an array, if the original column
was one, causing drift and weird migration errors.

migration-engine/connectors/sql-migration-connector/src/sql_renderer/postgres_renderer.rs

@@ -140,13 +140,16 @@ impl SqlRenderer for PostgresFlavour {
             let affected_columns = walk_columns(schemas.next()).filter(|column| matches!(&column.column_type().family, ColumnTypeFamily::Enum(name) if name.as_str() == enums.next().name()));
 
             for column in affected_columns {
+                let array = if column.arity().is_list() { "[]" } else { "" };
+
                 let sql = format!(
                     "ALTER TABLE {table_name} \
-                            ALTER COLUMN {column_name} TYPE {tmp_name} \
-                                USING ({column_name}::text::{tmp_name})",
+                            ALTER COLUMN {column_name} TYPE {tmp_name}{array} \
+                                USING ({column_name}::text::{tmp_name}{array})",
                     table_name = Quoted::postgres_ident(column.table().name()),
                     column_name = Quoted::postgres_ident(column.name()),
                     tmp_name = Quoted::postgres_ident(&tmp_name),
+                    array = array,
                 );
 
                 stmts.push(sql);

migration-engine/migration-engine-tests/tests/migrations/enums.rs

@@ -504,3 +504,62 @@ fn existing_enums_are_picked_up(api: TestApi) {
         .assert_green_bang()
         .assert_no_steps();
 }
+
+// Bug: https://github.com/prisma/prisma/issues/8137
+#[test_connector(tags(Postgres))]
+fn enum_array_modification_should_work(api: TestApi) {
+    let migrations_directory = api.create_migrations_directory();
+
+    let dm = r#"
+        datasource test {
+            provider = "postgres"
+            url = "postgres://meowmeowmeow"
+        }
+
+        enum Position {
+            First
+            Second
+            Last
+        }
+
+        model Test {
+            id        String     @id @default(uuid())
+            positions Position[]
+        }
+    "#;
+
+    api.create_migration("01init", &dm, &migrations_directory).send_sync();
+
+    api.apply_migrations(&migrations_directory)
+        .send_sync()
+        .assert_applied_migrations(&["01init"]);
+
+    let dm = r#"
+        datasource test {
+            provider = "postgres"
+            url = "postgres://meowmeowmeow"
+        }
+
+        enum Position {
+            First
+            Second
+        }
+
+        model Test {
+            id        String     @id @default(uuid())
+            positions Position[]
+        }
+    "#;
+
+    api.create_migration("02remove", &dm, &migrations_directory).send_sync();
+
+    api.apply_migrations(&migrations_directory)
+        .send_sync()
+        .assert_applied_migrations(&["02remove"]);
+
+    api.create_migration("03empty", &dm, &migrations_directory).send_sync();
+
+    api.apply_migrations(&migrations_directory)
+        .send_sync()
+        .assert_applied_migrations(&[]);
+}