WIP: Per-source minification (DO NOT MERGE)

[guybedford]

Here's a proof of concept towards caching for minification in #46.

Because minification is done per-source, the output currently looks like:

module.exports =
/******/ (function(modules) { // webpackBootstrap
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/ ETC
/************************************************************************/
/******/ ([
/* 0 */
/***/ (function(module, exports, __webpack_require__) {
// minified line:
var bind=__webpack_require__(4),isBuffer=__webpack_require__(5),toString=Object.prototype.toString;
/***/ }),
/* 2 */
/***/ (function(module, exports, __webpack_require__) {

// another minified line:
var utils=__webpack_require__(0),normalizeHeaderName=__webpack_require__(26),DEFAULT_CONTENT_TYPE={"Content-Type":"application/x-www-form-urlencoded"}
// ETC
/***/ })
/******/ ]);
//# sourceMappingURL=index.js.map

It could be possible to hack the various webpack outputs to reduce the gaps here, but it definitely would be quite a hack.

The benefit at the end of the day would be per-source minification caching which would significantly speed up builds with minification.

Let me know if this seems like a worthwhile direction to continue along.

[codecov-io]

Codecov Report

Merging #115 into master will increase coverage by 0.34%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #115      +/-   ##
==========================================
+ Coverage   77.29%   77.64%   +0.34%     
==========================================
  Files          11       12       +1     
  Lines         511      519       +8     
==========================================
+ Hits          395      403       +8     
  Misses        116      116

Impacted Files	Coverage Δ
src/index.js	93.47% <ø> (ø)	⬆️
src/loaders/terser-loader.js	100% <100%> (ø)

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[timneutkens]

Yeah so hacking those outputs would be very breaking when trying to upgrade webpack. However it's not like webpack's current output is the biggest part of minification work, so it makes sense to not minify those parts.

[sokra]

This might be an interesting source if you looking for performance vs size tradeoffs too: https://github.com/terser-js/terser#terser-fast-minify-mode

[guybedford]

@sokra good point, added in #161. Am I right in thinking Webpack already does the simple optimizations which would explain why we're seeing absolutely no difference?