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node_modules/webpack/lib/optimize/MergeDuplicateChunksPlugin.js

@@ -5,24 +5,74 @@
 "use strict";
 
 class MergeDuplicateChunksPlugin {
-
 	apply(compiler) {
-		compiler.plugin("compilation", (compilation) => {
-			compilation.plugin("optimize-chunks-basic", (chunks) => {
-				const map = Object.create(null);
-				chunks.slice().forEach((chunk) => {
-					if(chunk.hasRuntime() || chunk.hasEntryModule()) return;
-					const ident = chunk.getModulesIdent();
-					const otherChunk = map[ident];
-					if(otherChunk) {
-						if(otherChunk.integrate(chunk, "duplicate"))
-							chunks.splice(chunks.indexOf(chunk), 1);
-						return;
+		compiler.hooks.compilation.tap(
+			"MergeDuplicateChunksPlugin",
+			compilation => {
+				compilation.hooks.optimizeChunksBasic.tap(
+					"MergeDuplicateChunksPlugin",
+					chunks => {
+						// 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 chunk.modulesIterable) {
+								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 module.chunksIterable) {
+										if (
+											dup !== chunk &&
+											chunk.getNumberOfModules() === dup.getNumberOfModules() &&
+											!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 (!dup.containsModule(module)) {
+											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
+							) {
+								for (const otherChunk of possibleDuplicates) {
+									if (otherChunk.hasRuntime() !== chunk.hasRuntime()) continue;
+									// merge them
+									if (chunk.integrate(otherChunk, "duplicate")) {
+										chunks.splice(chunks.indexOf(otherChunk), 1);
+									}
+								}
+							}
+
+							// don't check already processed chunks twice
+							notDuplicates.add(chunk);
+						}
 					}
-					map[ident] = chunk;
-				});
-			});
-		});
+				);
+			}
+		);
 	}
 }
 module.exports = MergeDuplicateChunksPlugin;