babel-plugin-debug-macros-2 v0.1.10

Babel Debug Macros And Feature Flags

This provides debug macros and feature flagging.

Setup

The plugin takes 5 types options: envFlags, features, debugTools, externalizeHelpers and svelte. The importSpecifier is used as a hint to this plugin as to where macros are being imported and completely configurable by the host. Like Babel you can supply your own helpers using the externalizeHelpers options.

{
  plugins: [
    ['babel-debug-macros', {
      // @required
      envFlags: {
        source: '@ember/env-flags',
        flags: { DEBUG: true }
      },
      // @required
      debugTools: {
        source: 'debug-tools',
        // @optional
        assertPredicateIndex: 0
      },
      // @optional
      features: {
        name: 'ember-source',
        source: '@ember/features',
        flags: { FEATURE_A: false, FEATURE_B: true, DEPRECATED_CONTROLLERS: "2.12.0" }
      },
      // @optional
      svelte: {
        'ember-source': "2.15.0"
      },
      // @optional
      externalizeHelpers: {
        module: true,
        // global: '__my_global_ns__'
      }
    }]
  ]
}

Flags and features are inlined into the consuming module so that something like UglifyJS will DCE them when they are unreachable.

Simple environment and fetaure flags

import { DEBUG } from '@ember/env-flags';
import { FEATURE_A, FEATURE_B } from '@ember/features';

if (DEBUG) {
  console.log('Hello from debug');
}

let woot;
if (FEATURE_A) {
  woot = () => 'woot';
} else if (FEATURE_B) {
  woot = () => 'toow';
}

woot();

Transforms to:

if (true) {
  console.log('Hello from debug');
}

let woot;
if (false) {
  woot = () => 'woot';
} else if (true) {
  woot = () => 'toow';
}

woot();

warn macro expansion

import { warn } from 'debug-tools';

warn('this is a warning');

Expands into:

(true && console.warn('this is a warning'));

assert macro expansion

The assert macro can expand in a more intelligent way with the correct configuration. When babel-plugin-debug-macros is provided with the assertPredicateIndex the predicate is injected in front of the assertion in order to avoid costly assertion message generation when not needed.

import { assert } from 'debug-tools';

assert((() => {
  return 1 === 1;
})(), 'You bad!');

With the debugTools: { assertPredicateIndex: 0 } configuration the following expansion is done:

(true && !((() => { return 1 === 1;})()) && console.assert(false, 'this is a warning'));

When assertPredicateIndex is not specified, the following expansion is done:

(true && console.assert((() => { return 1 === 1;})(), 'this is a warning'));

deprecate macro expansion

import { deprecate } from 'debug-tools';

let foo = 2;

deprecate('This is deprecated.', foo % 2);

Expands into:

let foo = 2;

(true && !(foo % 2) && console.warn('This is deprecated.'));

Externalized Helpers

When you externalize helpers you must provide runtime implementations for the above macros. An expansion will still occur, however we will emit references to those runtime helpers.

A global expansion looks like the following:

import { warn } from 'debug-tools';

warn('this is a warning');

Expands into:

(true && Ember.warn('this is a warning'));

While externalizing the helpers to a module looks like the following:

import { warn } from 'debug-tools';

warn('this is a warning');

Expands into:

(true && warn('this is a warning'));

Svelte

Svelte allows for consumers to opt into stripping deprecated code from your dependecies. By adding a package name and minimum version that contains no deprecations, that code will be compiled away.

For example, consider you are on ember-source@2.10.0 and you have no deprecations. All deprecated code in ember-source that is <=2.10.0 will be removed.

...
svelte: {
  "ember-source": "2.10.0"
}
...

Now if you bump to ember-source@2.11.0 you may encounter new deprecations. The workflow would then be to clear out all deprecations and then bump the version in the svelte options.

svelte: {
  "ember-source": "2.11.0"
}

Hygenic

As you may notice that we inject DEBUG into the code when we expand the macro. We guarantee that the binding is unique when injected and follow the local binding name if it is imported directly.

babel-plugin-debug-macros npm cdn at unpkg