fix: allow diff to run with stopped db (#3829)

Author: sweatybridge

internal/db/diff/diff.go

@@ -31,14 +31,6 @@ import (
 type DiffFunc func(context.Context, string, string, []string) (string, error)
 
 func Run(ctx context.Context, schema []string, file string, config pgconn.Config, differ DiffFunc, fsys afero.Fs, options ...func(*pgx.ConnConfig)) (err error) {
-	// 1. Load all user defined schemas
-	if len(schema) == 0 {
-		schema, err = loadSchema(ctx, config, options...)
-		if err != nil {
-			return err
-		}
-	}
-	// 3. Run migra to diff schema
 	out, err := DiffDatabase(ctx, schema, config, os.Stderr, fsys, differ, options...)
 	if err != nil {
 		return err
@@ -185,6 +177,12 @@ func DiffDatabase(ctx context.Context, schema []string, config pgconn.Config, w
 			}
 		}
 	}
+	// Load all user defined schemas
+	if len(schema) == 0 {
+		if schema, err = loadSchema(ctx, config, options...); err != nil {
+			return "", err
+		}
+	}
 	fmt.Fprintln(w, "Diffing schemas:", strings.Join(schema, ","))
 	source := utils.ToPostgresURL(shadowConfig)
 	target := utils.ToPostgresURL(config)

internal/db/diff/diff_test.go

@@ -87,20 +87,6 @@ func TestRun(t *testing.T) {
 		assert.Equal(t, []byte(diff), contents)
 	})
 
-	t.Run("throws error on failure to load user schemas", func(t *testing.T) {
-		// Setup in-memory fs
-		fsys := afero.NewMemMapFs()
-		// Setup mock postgres
-		conn := pgtest.NewConn()
-		defer conn.Close(t)
-		conn.Query(migration.ListSchemas, migration.ManagedSchemas).
-			ReplyError(pgerrcode.DuplicateTable, `relation "test" already exists`)
-		// Run test
-		err := Run(context.Background(), []string{}, "", dbConfig, DiffSchemaMigra, fsys, conn.Intercept)
-		// Check error
-		assert.ErrorContains(t, err, `ERROR: relation "test" already exists (SQLSTATE 42P07)`)
-	})
-
 	t.Run("throws error on failure to diff target", func(t *testing.T) {
 		// Setup in-memory fs
 		fsys := afero.NewMemMapFs()