Vue Build Cache Optimization

This challenge focuses on improving the build performance of a Vue.js application by implementing a build cache. Caching frequently used build artifacts, such as compiled components and utility functions, can significantly reduce build times, especially in large projects or CI/CD pipelines. You will create a system that intelligently stores and retrieves these artifacts.

Problem Description

Your task is to design and implement a build cache mechanism for a hypothetical Vue.js build process. This cache should store compiled JavaScript modules and potentially other intermediate build results. The goal is to avoid redundant compilation or processing of modules that have not changed since their last build.

Key Requirements:

1. Cache Storage: Implement a mechanism to store build artifacts (e.g., compiled JavaScript code) keyed by a unique identifier derived from the source file and its dependencies.
2. Cache Invalidation: The cache must be invalidated effectively. If a source file or any of its direct or indirect dependencies change, the corresponding cached artifact should be considered stale and recompiled.
3. Cache Retrieval: When a module is requested, the system should first check if a valid cached artifact exists. If it does, the cached version should be returned; otherwise, the module should be compiled, and the result stored in the cache.
4. Dependency Tracking: For accurate cache invalidation, the system needs to track dependencies between modules. This means understanding which other modules a given module imports.
5. File Hashing: A robust hashing mechanism should be used to generate unique identifiers for cache keys. This hash should consider the content of the source file itself and the content of all its direct dependencies.

Expected Behavior:

• The first time a module is built, it should be compiled, and its compiled output should be stored in the cache.
• Subsequent builds of the same module, if its content or the content of its dependencies hasn't changed, should retrieve the artifact directly from the cache, skipping the compilation step.
• If a module or any of its dependencies change, the cache entry for that module should be invalidated, and it should be recompiled.

Edge Cases:

• Handling modules with no dependencies.
• Resolving circular dependencies (though a full implementation of this is out of scope, assume a mechanism exists to detect and handle them gracefully for cache key generation).
• Empty files or files with syntax errors (how should these be cached, if at all?).
• The initial state of the cache (empty).

Examples

Example 1:

Imagine a simple Vue component Button.vue that imports a utility function utils.js.

• Button.vue content:

  <template>
    <button @click="onClick">{{ message }}</button>
  </template>
  <script lang="ts">
  import { formatMessage } from './utils'; // Dependency
  export default {
    data() {
      return {
        message: formatMessage('Hello from Button!')
      }
    },
    methods: {
      onClick() {
        alert('Button clicked!');
      }
    }
  }
  </script>
  

• utils.js content:

  export function formatMessage(msg) {
    return `[${msg}]`;
  }
  

Scenario:

1. Initial Build: Button.vue and utils.js are compiled. The compiled JavaScript for Button.vue is generated. A cache entry is created for Button.vue, keyed by a hash that incorporates the content of Button.vue and utils.js.
2. No Changes: Button.vue and utils.js remain unchanged. The build process checks the cache. A valid entry is found, and the cached compiled JavaScript is used. Compilation is skipped.
3. utils.js Changes: The formatMessage function in utils.js is modified to export function formatMessage(msg) { return *** ${msg} ***; }.
   • The build process detects the change in utils.js.
   • The cache entry for Button.vue is invalidated because its dependency (utils.js) has changed.
   • Button.vue is recompiled using the new utils.js.
   • A new cache entry is created for Button.vue with an updated hash.

Example 2:

Consider a scenario with multiple modules and a shared dependency.

• App.vue: Imports Navbar.vue and Footer.vue.
• Navbar.vue: Imports config.js.
• Footer.vue: Imports config.js.
• config.js: Contains application-wide configuration settings.

Scenario:

1. Build 1: App.vue, Navbar.vue, Footer.vue, and config.js are compiled. Cache entries are created for all.
2. Change config.js: If config.js is modified, the cache entries for Navbar.vue and Footer.vue (and subsequently App.vue, as it depends on them) will be invalidated. Navbar.vue and Footer.vue will be recompiled. App.vue will then be recompiled using the updated versions of Navbar.vue and Footer.vue.
3. Change Navbar.vue only: Only the cache entry for Navbar.vue will be invalidated. Navbar.vue will be recompiled. App.vue will be recompiled using the new Navbar.vue and the cached Footer.vue (since Footer.vue and its dependencies didn't change).

Constraints

• You will be working with a simulated file system or a predefined set of file contents and their dependencies. Actual file system operations are not required.
• The hashing algorithm should be deterministic and sensitive to content changes. SHA-256 or a similar cryptographic hash is recommended.
• Dependency resolution can be simplified. Assume a function getDependencies(filePath: string): string[] is available, which returns an array of file paths that the given file depends on (directly).
• The maximum number of files to manage in the cache is 1000.
• The maximum file size is 1MB.
• The expected cache hit rate in an optimized scenario should be above 80% for repeated builds with minimal changes.

Notes

• Think about how to represent the "compiled artifact." For this challenge, a simple string representing the compiled JavaScript code will suffice.
• The core of this challenge lies in designing the cache invalidation strategy. The hash for a cache key must incorporate the content of the file itself and the content of all its dependencies. This can be achieved recursively.
• Consider how to efficiently calculate the hash of a file and its dependencies without recalculating everything every time.
• You'll need to simulate a "build" operation. This can be a simple function that takes the file content and returns a dummy "compiled" string.
• This challenge is about the caching logic, not the intricacies of Vue compilation or complex module bundler internals. Focus on the cache data structure and the update/retrieval logic.