Lazy load autoprefixer module

[ybiquitous]

This change is based on my patch on #4971 (comment).
This mainly lazy-loads the autoprefixer module in lib/utils/isAutoprefixable.js.

Which issue, if any, is this issue related to?

Maybe fix #4971

Is there anything in the PR that needs further explanation?

I don't know how to get an effective benchmark for this change. Could you lease help if you have any good ideas?

[ybiquitous]

[note] Fixed duplication of prefixes.remove[prop.toLowerCase()].

[jeddy3]

I don't know how to get an effective benchmark for this change. Could you lease help if you have any good ideas?

I don't know either, I'm afraid.

Code looks good, though.

[hudochenkov]

isAutoprefixable.js is only used in -no-vendor-prefix rules. We lazy load all rules, and load only rules, which are in the config. Is this change is needed? Autoprefixer will be loaded anyway if it's needed. And it won't be loaded if not needed (no affected rule is enabled).

[ybiquitous]

@hudochenkov Thanks for your comment. Surely, I also think we should avoid the hack on this PR if possible (to make the code simple).

But, when I examine whether lazy-loading autoprefixer works on the master branch, I find it does not. Please check it out below:

1. Output the log when autoprefixer is loaded as follows:

--- a/lib/utils/isAutoprefixable.js
+++ b/lib/utils/isAutoprefixable.js
@@ -1,6 +1,7 @@
 'use strict';
 
 const autoprefixer = require('autoprefixer');
+console.log("autoprefixer loaded!!!")
 const Browsers = require('autoprefixer/lib/browsers');
 const Prefixes = require('autoprefixer/lib/prefixes');
 

2. Prepare a tested CSS file and .stylelintrc.json as follows:

/* a.css */
@-webkit-keyframes { 0% { top: 0; } }

{
  "rules": {
    "at-rule-no-vendor-prefix": null
  }
}

3. Run stylelint:

$ bin/stylelint.js a.css --no-cache
autoprefixer loaded!!!

4. Remove at-rule-no-vendor-prefix from .stylelintrc.json:

{
  "rules": {
  }
}

5. Run stylelint again:

$ bin/stylelint.js a.css --no-cache

Perhaps, may this be another kind of bug?

[hudochenkov]

Do you think we can find why it is loaded, when it shouldn't and try to fix that?

[ybiquitous]

I'm not sure the following patch is correct, but it can prevent loading a rule module that has null:

--- a/lib/normalizeAllRuleSettings.js
+++ b/lib/normalizeAllRuleSettings.js
@@ -20,6 +20,10 @@ function normalizeAllRuleSettings(config) {
 	Object.keys(config.rules).forEach((ruleName) => {
 		const rawRuleSettings = _.get(config, ['rules', ruleName]);
 
+		if (rawRuleSettings === null) {
+			return;
+		}
+
 		const rule = rules[ruleName] || _.get(config, ['pluginFunctions', ruleName]);
 
 		if (!rule) {

stylelint/lib/normalizeAllRuleSettings.js

Line 21 in 5a84657

const rawRuleSettings = _.get(config, ['rules', ruleName]);