Angular Incremental Compilation

Modern web development demands fast build times, especially in large Angular applications. Manual compilation can become a bottleneck as projects grow. This challenge focuses on understanding and implementing a core aspect of Angular's build optimization: incremental compilation. You will simulate and demonstrate how Angular can recompile only the necessary parts of your application when changes are made, leading to significantly faster build cycles.

Problem Description

Your task is to simulate the behavior of Angular's incremental compilation. You will create a simplified model that tracks dependencies between Angular modules and components. When a "change" is introduced to a specific file, your model should identify and report all other files that would need to be recompiled as a direct or indirect consequence of that change.

What needs to be achieved:

• Model a simplified Angular project structure with modules, components, and their dependencies.
• Implement a mechanism to simulate a file change.
• Develop a logic to determine which files are affected by a change and thus need recompilation.

Key requirements:

1. Dependency Graph: Represent the relationships between Angular entities (modules, components, services, etc.). For this challenge, we can simplify this to:
   • Components depend on Services.
   • Modules depend on Components.
   • A module might import other modules.
2. Change Simulation: Define a function that simulates a change to a specific file (e.g., a component file, a service file, or a module file).
3. Impact Analysis: Given a changed file, identify all other files that are directly or indirectly dependent on it and would therefore need to be recompiled.
4. Output Reporting: The output should clearly list all files that need recompilation.

Expected Behavior:

When a file is "changed", the system should:

1. Identify the immediate dependents of the changed file.
2. Recursively identify dependents of those dependents, and so on.
3. Compile a complete list of all affected files.

Important Edge Cases:

• Circular Dependencies: While less common in well-structured Angular apps, consider how your model might handle them (though for this simulation, we can assume no direct circular dependencies for simplicity, but indirect ones could arise).
• Unused Files: Changes to files not currently imported or used by any other part of the application should not trigger recompilation of other parts.
• Root Module: Changes to the root module might have a cascading effect on almost everything.

Examples

Example 1:

Project Structure (Simplified):

• app.module.ts (imports HomeComponent, UserService)
• home.component.ts (uses UserService)
• user.service.ts

Dependencies:

• home.component.ts -> user.service.ts
• app.module.ts -> home.component.ts
• app.module.ts -> user.service.ts

Input: changeFile('user.service.ts')

Output:

Files to recompile:
- user.service.ts
- home.component.ts
- app.module.ts

Explanation: Changing user.service.ts directly affects home.component.ts (as it uses the service) and app.module.ts (as it imports the service). home.component.ts needs recompilation because its dependency changed. app.module.ts needs recompilation because it directly imports the service and indirectly depends on it via home.component.ts.

Example 2:

Project Structure (Simplified):

• app.module.ts (imports DashboardComponent, SettingsModule)
• dashboard.component.ts (uses DataService)
• settings.module.ts (imports UserListComponent)
• user.list.component.ts (uses UserService)
• data.service.ts
• user.service.ts

Dependencies:

• dashboard.component.ts -> data.service.ts
• user.list.component.ts -> user.service.ts
• settings.module.ts -> user.list.component.ts
• app.module.ts -> dashboard.component.ts
• app.module.ts -> settings.module.ts
• app.module.ts -> data.service.ts (implicitly through dashboard)
• app.module.ts -> user.service.ts (implicitly through user list in settings)

Input: changeFile('user.service.ts')

Output:

Files to recompile:
- user.service.ts
- user.list.component.ts
- settings.module.ts
- app.module.ts

Explanation: Changing user.service.ts directly affects user.list.component.ts. user.list.component.ts is imported by settings.module.ts. settings.module.ts is imported by app.module.ts. Therefore, all three are impacted.

Example 3: (Edge Case - Unused File)

Project Structure (Simplified):

• app.module.ts (imports HomeComponent)
• home.component.ts
• unused.service.ts

Dependencies:

• app.module.ts -> home.component.ts

Input: changeFile('unused.service.ts')

Output:

Files to recompile:
- unused.service.ts

Explanation: The unused.service.ts file has no declared dependencies from any other part of the application that is currently being tracked. Therefore, a change to it only affects itself.

Constraints

• The simulation should focus on TypeScript files (.ts).
• Assume a maximum of 100 files in the simulated project for performance considerations in your simulation logic.
• The dependency graph can be represented using simple data structures (e.g., maps, sets).
• Your solution should be implemented in TypeScript.

Notes

• Think about how Angular's compiler actually resolves dependencies. It scans files, looks for imports, decorators (@Component, @Injectable, @NgModule), and class definitions.
• For this simulation, you don't need to parse actual TypeScript code. You can pre-define the dependencies between your mock files.
• Consider using a recursive function or a breadth-first/depth-first search approach to traverse the dependency graph.
• The core idea is to model the "ripple effect" of a change.