Plugin Ordering (Part 2)

[hzoo]

First discussion issue: #5623
Current PR: #5735

James wrote a good article about the general problem: http://thejameskyle.com/babel-plugin-ordering.html
Babel is single pass traversal so top level ordering isn't a thing (unless you use passPerPreset which is why we are going to remove that), however the individual node visitors have an ordering.

const visitors = plugins.map(plugin => plugin.visitor);
const mergedVisitors = merge(visitors);
traverse(ast, mergedVisitors);

I believe most agree on:

• introduce a before/after key to specify which plugin ordering
• should error/warn if the same plugin/capability is specified twice
  • edge case would be if you are using a plugin in a "preset" that you want to still use but want to modify it by using a plugin option - either error and not use the preset anymore or the user specified plugin should override the one used in the preset itself
• should any of this be user-specified (mostly likely no: if it's possible to encode for plugin authors we don't need to expose that to users)

Questions

• what exactly should be specified in the before/after:
  • a specific plugin name (probably taken from npm package) babel-plugin-transform-es2015-arrow-function (I'm not in favor personally)
  • the more generic "capability" of many plugins (ex: "arrowFunction", "jsx", "flow", "asyncFunction")
• does minification/info gathering plugin require a different approach/multiple passes again? They don't depend on a specific node type to run before/after but rather always before/after "everything else"?
  • #5623 discusses allowing free form strings for before/after vs. specifically named passes.
• how does the native host environment fit into this? How can we encode their support via preset-env data. If a syntax is natively provided, then it provides the capability and another plugin can output that syntax without it being transformed.

[sarupbanskota]

for the name bit within the core plugin packages, I've been using the npm package name so far: fc7b17b.

[AprilArcus]

In order to use babel-plugin-angularjs-annotate with async shorthand function members of object literals, I need to ensure that "@babel/plugin-transform-async-to-generator" linearly precedes "@babel/plugin-transform-shorthand-properties" if both are specified by @babel/preset-env. c.f. schmod/babel-plugin-angularjs-annotate#20 (comment)

However, if only one or neither plugin is required by @babel/preset-env, I don't wish to run both just to ensure that they fire in the correct order.

What is the current best practice around this? Should I file a bug report against @babel/preset-env?