[Feature]: Support for Task Nesting and Conditional Execution in YAML Scripts

[754334879]

midscene.js provides a powerful YAML-based automation script format that allows defining test scenarios in a declarative way. However, when building complex test suites, we encountered scenarios where the current YAML syntax falls short.

Feature 1: Task Nesting / Task Reuse

Problem:
Currently, there's no way to call one task from another. This leads to code duplication when the same sequence of actions needs to be performed in multiple tasks.

Example use case:
A "Login" task needs to be called before many other tasks. Without task nesting, the login steps must be duplicated in every task that requires authentication.

Proposed syntax:

tasks:
  - name: Login
    flow:
      - aiTap: username input field
      - aiInput:
          value: testuser
      - aiTap: password input field
      - aiInput:
          value: password123
      - aiTap: login button

  - name: Search Train
    flow:
      - callTask: Login        # nested call to Login task
      - aiTap: search button
      # ... other steps

  - name: Book Train
    flow:
      - callTask: Login        # reuse Login task
      - aiTap: book button
      # ... other steps

Alternative syntax options:

# Option A: callTask (recommended - concise and explicit)
- callTask: Login

# Option B: include (familiar to template engine users)
- include: Login

Feature 2: Conditional Execution

Problem:
There's no way to conditionally execute steps based on runtime conditions (e.g., page state, assertion results, variable values).

Example use case:

• If a popup appears, dismiss it
• If already logged in, skip the login flow
• Handle different app states based on what's visible

Proposed syntax:

tasks:
  - name: Handle Login State
    flow:
      # Conditional: if-else based on assertion
      - if:
          condition:
            aiAssert: login button is visible on current page
          then:
            - aiTap: login button
            # ... login flow
          else:
            - aiAction: already logged in, continue with operations

      # Conditional: if-only (skip if condition not met)
      - if:
          condition:
            aiAssert: popup ad is visible
          then:
            - aiTap: close ad button

      # Conditional: based on variable
      - if:
          condition: ${isLoggedIn} == false
          then:
            - callTask: Login

Benefits

1. Code Reusability - Define common flows once, reuse across tasks
2. Maintainability - Update login logic in one place, all tasks benefit
3. Expressiveness - Handle complex real-world scenarios gracefully
4. Non-developer Friendly - Clear, readable syntax for QA/PM

Current Workaround

Users can:

1. Duplicate steps across tasks (maintenance burden)
2. Use JavaScript for logic (less accessible for non-developers)
3. Build custom orchestration layer outside midscene (adds complexity)

[312654929]

we need it