Please see http://eslint.org/docs/rules/no-unused-vars; note that this patch purposely uses the same rule options as in `mozilla-central`, such that it fixes part of issue 7957.
It wasn't, in my opinion, entirely straightforward to enable this rule compared to the already existing rules. In many cases a `var descriptiveName = ...` format was used (more or less) to document the code, and I choose to place the old variable name in a trailing comment to not lose that information.
I welcome feedback on these changes, since it wasn't always entirely easy to know what changes made the most sense in every situation.
*Please note that most of the necessary code adjustments were made in PR 7890.*
ESLint has a number of advantageous properties, compared to JSHint. Among those are:
- The ability to find subtle bugs, thanks to more rules (e.g. PR 7881).
- Much more customizable in general, and many rules allow fine-tuned behaviour rather than the just the on/off rules in JSHint.
- Many more rules that can help developers avoid bugs, and a lot of rules that can be used to enforce a consistent coding style. The latter should be particularily useful for new contributors (and reduce the amount of stylistic review comments necessary).
- The ability to easily specify exactly what rules to use/not to use, as opposed to JSHint which has a default set. *Note:* in future JSHint version some of the rules we depend on will be removed, according to warnings in http://jshint.com/docs/options/, so we wouldn't be able to update without losing lint coverage.
- More easily disable one, or more, rules temporarily. In JSHint this requires using a numeric code, which isn't very user friendly, whereas in ESLint the rule name is simply used instead.
By default there's no rules enabled in ESLint, but there are some default rule sets available. However, to prevent linting failures if we update ESLint in the future, it seemed easier to just explicitly specify what rules we want.
Obviously this makes the ESLint config file somewhat bigger than the old JSHint config file, but given how rarely that one has been updated over the years I don't think that matters too much.
I've tried, to the best of my ability, to ensure that we enable the same rules for ESLint that we had for JSHint. Furthermore, I've also enabled a number of rules that seemed to make sense, both to catch possible errors *and* various style guide violations.
Despite the ESLint README claiming that it's slower that JSHint, https://github.com/eslint/eslint#how-does-eslint-performance-compare-to-jshint, locally this patch actually reduces the runtime for `gulp` lint (by approximately 20-25%).
A couple of stylistic rules that would have been nice to enable, but where our code currently differs to much to make it feasible:
- `comma-dangle`, controls trailing commas in Objects and Arrays (among others).
- `object-curly-spacing`, controls spacing inside of Objects.
- `spaced-comment`, used to enforce spaces after `//` and `/*. (This is made difficult by the fact that there's still some usage of the old preprocessor left.)
Rules that I indend to look into possibly enabling in follow-ups, if it seems to make sense: `no-else-return`, `no-lonely-if`, `brace-style` with the `allowSingleLine` parameter removed.
Useful links:
- http://eslint.org/docs/user-guide/configuring
- http://eslint.org/docs/rules/
Currently `importl10n` fails, since mxr.mozilla.org has been down for a while. Based on discussions in #developers, it isn't clear to me if/when it'll be available again.
Furthermore, I'm not sure why we're even getting the l10n files through a code search tool, rather than just using the official Mozilla repository directly.
This is regression from PR 7063, causing `gulp importl10n` to fail:
```
$ gulp importl10n
[19:45:02] Using gulpfile c:\Users\Jonas\Git\pdfjs\gulpfile.js
[19:45:02] Starting 'importl10n'...
Downloading ach...
[19:45:02] 'importl10n' errored after 4.42 ms
[19:45:02] Error: EEXIST, file already exists 'c:\Users\Jonas\Git\pdfjs\l10n\ach
'
at Error (native)
at Object.fs.mkdirSync (fs.js:747:18)
at downloadLanguageFiles (c:\Users\Jonas\Git\pdfjs\external\importL10n\local
es.js:59:8)
at next (c:\Users\Jonas\Git\pdfjs\external\importL10n\locales.js:90:5)
at Object.downloadL10n (c:\Users\Jonas\Git\pdfjs\external\importL10n\locales
.js:91:5)
at Gulp.<anonymous> (c:\Users\Jonas\Git\pdfjs\gulpfile.js:92:11)
at module.exports (c:\Users\Jonas\Git\pdfjs\node_modules\gulp\node_modules\o
rchestrator\lib\runTask.js:34:7)
at Gulp.Orchestrator._runTask (c:\Users\Jonas\Git\pdfjs\node_modules\gulp\no
de_modules\orchestrator\index.js:273:3)
at Gulp.Orchestrator._runStep (c:\Users\Jonas\Git\pdfjs\node_modules\gulp\no
de_modules\orchestrator\index.js:214:10)
at Gulp.Orchestrator.start (c:\Users\Jonas\Git\pdfjs\node_modules\gulp\node_
modules\orchestrator\index.js:134:8)
```
