Tree Shaker

[WIP] This is an experimental tree shaker for JS based on Oxc.

If this project goes well, I personally hope it can become part of the Oxc or the Rolldown project.

• Try it online: https://kermanx.github.io/tree-shaker/
• Test262 Result: Goto commits and view the latest comment

Goal

Tree shake the following code (this already works!):

export function f() {
  function g(a) {
    if (a)
      console.log('effect')
    else
      return 'str'
  }
  let { ["x"]: y = 1 } = { x: g('') ? undefined : g(1) }
  return y
}

To:

export function f() {
  return 1
}

Todo

• Performance!
• JS Builtins metadata
• Pure notation support
• Test against fixtures from other tree shakers like Rollup
• Implement built-in objects and properties
• Rollup-like try-scope optimization/de-optimization
• Reuse code with oxc_minifier for JS computation logics
• Type narrowing
• Multiple-module support

Approach

1. Parse the code via oxc_parser.
2. Build the semantic information via oxc_semantic.
3. Tree shake the code.
   • Emulate the runtime behavior of the code. (Control flow, Side effects, ...)
   • Analyze the possible runtime values of the variables.
   • Remove the dead code.
4. Minify the code via oxc_minifier. (Optional)

Concepts

• Entity: Represents the analyzed information of a JS value.
• Consumable: Entity or AST Nodes or some other things that the runtime value of Entity depends on.
• Scopes:
  • Call Scope: Function call scope.
  • Cf Scope: Control flow scope.
  • Variable Scope: Variable scope.
  • Try Scope: Try statement or function.