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MergeDuplicateChunksPlugin.js
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Thu, Feb 13, 13:32

MergeDuplicateChunksPlugin.js
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/*
MIT License http://www.opensource.org/licenses/mit-license.php
Author Tobias Koppers @sokra
*/
"use strict";
const { STAGE_BASIC } = require("../OptimizationStages");
const { runtimeEqual } = require("../util/runtime");
/** @typedef {import("../Compiler")} Compiler */
class MergeDuplicateChunksPlugin {
/**
* @param {Compiler} compiler the compiler
* @returns {void}
*/
apply(compiler) {
compiler.hooks.compilation.tap(
"MergeDuplicateChunksPlugin",
compilation => {
compilation.hooks.optimizeChunks.tap(
{
name: "MergeDuplicateChunksPlugin",
stage: STAGE_BASIC
},
chunks => {
const { chunkGraph, moduleGraph } = compilation;
// remember already tested chunks for performance
const notDuplicates = new Set();
// for each chunk
for (const chunk of chunks) {
// track a Set of all chunk that could be duplicates
let possibleDuplicates;
for (const module of chunkGraph.getChunkModulesIterable(chunk)) {
if (possibleDuplicates === undefined) {
// when possibleDuplicates is not yet set,
// create a new Set from chunks of the current module
// including only chunks with the same number of modules
for (const dup of chunkGraph.getModuleChunksIterable(
module
)) {
if (
dup !== chunk &&
chunkGraph.getNumberOfChunkModules(chunk) ===
chunkGraph.getNumberOfChunkModules(dup) &&
!notDuplicates.has(dup)
) {
// delay allocating the new Set until here, reduce memory pressure
if (possibleDuplicates === undefined) {
possibleDuplicates = new Set();
}
possibleDuplicates.add(dup);
}
}
// when no chunk is possible we can break here
if (possibleDuplicates === undefined) break;
} else {
// validate existing possible duplicates
for (const dup of possibleDuplicates) {
// remove possible duplicate when module is not contained
if (!chunkGraph.isModuleInChunk(module, dup)) {
possibleDuplicates.delete(dup);
}
}
// when all chunks has been removed we can break here
if (possibleDuplicates.size === 0) break;
}
}
// when we found duplicates
if (
possibleDuplicates !== undefined &&
possibleDuplicates.size > 0
) {
outer: for (const otherChunk of possibleDuplicates) {
if (otherChunk.hasRuntime() !== chunk.hasRuntime()) continue;
if (chunkGraph.getNumberOfEntryModules(chunk) > 0) continue;
if (chunkGraph.getNumberOfEntryModules(otherChunk) > 0)
continue;
if (!runtimeEqual(chunk.runtime, otherChunk.runtime)) {
for (const module of chunkGraph.getChunkModulesIterable(
chunk
)) {
const exportsInfo = moduleGraph.getExportsInfo(module);
if (
!exportsInfo.isEquallyUsed(
chunk.runtime,
otherChunk.runtime
)
) {
continue outer;
}
}
}
// merge them
if (chunkGraph.canChunksBeIntegrated(chunk, otherChunk)) {
chunkGraph.integrateChunks(chunk, otherChunk);
compilation.chunks.delete(otherChunk);
}
}
}
// don't check already processed chunks twice
notDuplicates.add(chunk);
}
}
);
}
);
}
}
module.exports = MergeDuplicateChunksPlugin;

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