Flow Error Try Catch Removal

Remove Try-Catch Antipattern from Step Calls

Overview

This skill helps identify and remove the try-catch antipattern that's common in Flow SDK code but incorrect in Output SDK. In Output SDK, step calls should NOT be wrapped in try-catch blocks - errors should propagate up the chain.

When to Use This Skill

During Migration:

• Converting Flow SDK workflows that use try-catch around activity calls
• Reviewing migrated workflow code for error handling patterns

Code Patterns to Fix:

• Try-catch blocks wrapping step calls
• Re-throwing errors as FatalError after catching
• Generic error handling around workflow execution

Why Try-Catch is Wrong for Step Calls

In Output SDK, the workflow execution engine handles errors automatically:

1. Automatic Retry Logic: Steps have built-in retry mechanisms that try-catch interferes with
2. Error Propagation: Errors need to bubble up for proper workflow state management
3. Observability: Caught and re-thrown errors lose stack trace and context
4. Workflow Recovery: The engine can only recover workflows properly when it sees the original error

Error Patterns

Flow SDK Pattern (Common but Wrong for Output SDK)

// WRONG: Wrapping step calls in try-catch
export default workflow( {
  name: 'someWorkflow',
  description: 'a workflow description',
  inputSchema: WorkflowInputSchema,
  outputSchema: WorkflowOutputSchema,
  fn: async input => {
    try {
      // Step 1: Get User data
      const userData = await getUserData( { userId: input.userId } );

      // Step 2: Get role configuration
      const roleConfig = await getRoleConfig( { role: userData.role } );

      // Step 3: Ensure something
      await ensureSomething( { config: roleConfig } );

      return { success: true };
    } catch ( error ) {
      throw new FatalError( error instanceof Error ? error.message : 'Unknown workflow error' );
    }
  }
} );

Output SDK Pattern (Correct)

// CORRECT: Let errors propagate naturally
export default workflow( {
  name: 'someWorkflow',
  description: 'a workflow description',
  inputSchema: WorkflowInputSchema,
  outputSchema: WorkflowOutputSchema,
  fn: async input => {
    // Step 1: Get User data
    const userData = await getUserData( { userId: input.userId } );

    // Step 2: Get role configuration
    const roleConfig = await getRoleConfig( { role: userData.role } );

    // Step 3: Ensure something
    await ensureSomething( { config: roleConfig } );

    return { success: true };
  }
} );

Solution

Step 1: Find Try-Catch Blocks in Workflows

Search for try-catch patterns in workflow files:

grep -r "try {" src/workflows/*/workflow.ts
grep -r "} catch" src/workflows/*/workflow.ts

Step 2: Analyze the Try-Catch Purpose

Before removing, understand what the try-catch was doing:

1. Generic error wrapping → Remove entirely
2. Specific error transformation → Consider if really needed
3. Cleanup logic → May need different approach

Step 3: Remove Try-Catch, Keep Logic

Remove the try-catch wrapper but keep the step calls:

// Before
fn: async input => {
  try {
    const result = await someStep( input );
    return result;
  } catch ( error ) {
    throw new FatalError( error.message );
  }
}

// After
fn: async input => {
  const result = await someStep( input );
  return result;
}

When Try-Catch IS Appropriate

Try-catch is still appropriate in specific cases:

1. Inside Steps (Not Workflows)

Steps can use try-catch for internal logic:

export const fetchExternalData = step( {
  name: 'fetchExternalData',
  inputSchema: z.object( { url: z.string() } ),
  fn: async ( input ) => {
    try {
      const response = await fetch( input.url );
      return response.json();
    } catch ( error ) {
      // Transform to ValidationError for expected failures
      throw new ValidationError( `Failed to fetch: ${input.url}` );
    }
  }
} );

2. For Specific Error Types

When you need to handle a specific error type differently:

fn: async input => {
  const userData = await getUserData( { userId: input.userId } );

  try {
    await sendNotification( { userId: userData.id } );
  } catch ( error ) {
    // Only catch specific expected errors
    if ( error instanceof NotificationDisabledError ) {
      // User has notifications disabled - continue without notification
      console.log( 'Notifications disabled for user' );
    } else {
      throw error; // Re-throw unexpected errors
    }
  }

  return { success: true };
}

3. For Optional Operations

When a failure shouldn't stop the workflow:

fn: async input => {
  const result = await processData( input );

  // Optional: try to cache result, but don't fail if caching fails
  try {
    await cacheResult( { key: input.id, value: result } );
  } catch {
    // Caching failed - log but continue
    console.warn( 'Failed to cache result' );
  }

  return result;
}

Complete Migration Example

Before (Flow SDK with Try-Catch)

import { FatalError } from '@flow/sdk';
import { getUserData, processUser, saveResults } from './activities';

export default class UserProcessingWorkflow {
  async execute(input: WorkflowInput): Promise<WorkflowOutput> {
    try {
      const user = await getUserData(input.userId);
      const processed = await processUser(user);
      await saveResults(processed);
      return { success: true, userId: user.id };
    } catch (error) {
      throw new FatalError(`Workflow failed: ${error.message}`);
    }
  }
}

After (Output SDK without Try-Catch)

import { workflow, z } from '@output.ai/core';
import { getUserData, processUser, saveResults } from './steps.js';
import { WorkflowInputSchema, WorkflowOutputSchema } from './types.js';

export default workflow( {
  name: 'userProcessing',
  description: 'Process user data',
  inputSchema: WorkflowInputSchema,
  outputSchema: WorkflowOutputSchema,
  fn: async input => {
    const user = await getUserData( { userId: input.userId } );
    const processed = await processUser( { user } );
    await saveResults( { data: processed } );
    return { success: true, userId: user.id };
  }
} );

Verification Steps

1. Search for remaining try-catch in workflows

# Should return minimal results (only appropriate uses)
grep -A5 "try {" src/workflows/*/workflow.ts

2. Run the workflow

npx output workflow run <workflowName> --input '{}'

3. Test error scenarios

Intentionally trigger an error to verify it propagates correctly.

Related Skills

• flow-convert-workflow-definition - Full workflow conversion
• flow-convert-activities-to-steps - Step conversion patterns
• flow-validation-checklist - Complete migration validation