avoid_throw_in_catch_block

v0.4.0 Warning Fix Control Flow

Warns when a throw expression is used inside a catch block. Throwing a new exception (or re-throwing the caught one with throw e) discards the original stack trace, making debugging significantly harder. Use rethrow or Error.throwWithStackTrace() instead.

Why use this rule

When you use throw inside a catch block, the original stack trace is lost. This means error reports and logs will point to the catch block instead of the actual source of the error. Using rethrow preserves the full stack trace, and Error.throwWithStackTrace() lets you throw a different exception while keeping the original stack trace attached.

See also: Exceptions | Dart lint: throw_in_finally | Dart lint: only_throw_errors

Don’t

void bad() {
  // throw loses original stack trace
  try {
    networkDataProvider();
  } on Object {
    throw RepositoryException();
  }

  // throw with caught exception still loses stack trace
  try {
    networkDataProvider();
  } catch (e) {
    throw e;
  }

  // throw with logic before it
  try {
    networkDataProvider();
  } catch (e) {
    print(e);
    throw RepositoryException('failed');
  }
}

Do

void good() {
  // Use Error.throwWithStackTrace to preserve the stack trace
  try {
    networkDataProvider();
  } catch (_, stack) {
    Error.throwWithStackTrace(RepositoryException(), stack);
  }

  // Use rethrow to re-throw the original exception
  try {
    networkDataProvider();
  } catch (e) {
    print(e);
    rethrow;
  }

  // Throw inside a closure is fine — it's not in the catch scope
  try {
    networkDataProvider();
  } catch (e) {
    final callback = () {
      throw RepositoryException();
    };
    callback();
  }
}

Configuration

This rule is in the recommended preset, so it is on with preset: recommended or preset: opinionated. Add it to preset: core with avoid_throw_in_catch_block: true.

To turn it off:

many_lints.yaml

rules:
  avoid_throw_in_catch_block: false

To keep the rule on but skip certain paths, use per-rule exclude.

Related rules

• avoid_empty_catch — Detect catch clauses that silently discard the failure.
• avoid_cascade_after_if_null — Detect cascades after if-null operators without parentheses.
• avoid_collapsible_if — Merge nested if statements with &&.
• avoid_constant_conditions — Detect comparisons where both sides are constants.