JarCastingBabel Debug Macros And Feature Flags
This provides debug macros and feature flagging.
Setup
The plugin takes 4 types options: flags, svelte, debugTools, and externalizeHelpers. 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', {
// @optional
debugTools: {
isDebug: true,
source: 'debug-tools',
// @optional
assertPredicateIndex: 0
},
flags: [
{ source: '@ember/env-flags', flags: { DEBUG: true } },
{
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 feature 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 /* DEBUG */) {
console.log('Hello from debug');
}
let woot;
if (false /* FEATURE_A */) {
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 [email protected] 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 [email protected] 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"
}
