fix: only merge and emit when i18n files changed (#14)

lib/plugins/I18nPlugin.js

@@ -1,6 +1,9 @@
 const { utils: { XML } } = require('alloy-utils');
 const globby = require('globby');
 const path = require('path');
+const { RawSource } = require('webpack-sources');
+
+const i18nFilePattern = /app[/\\]i18n[/\\].*\.xml$/;
 
 /**
  * @typedef I18nSource
@@ -29,31 +32,79 @@ class I18nPlugin {
 	}
 
 	apply(compiler) {
-		let i18nSources = this.getI18nSourceLocations();
+		const i18nSources = this.getI18nSourceLocations();
+		const currentAssets = new Map();
 		let fileDependencies = [];
-		compiler.hooks.emit.tap('AlloyLoaderPlugin', compilation => {
-			const { files, content, errors, warnings } = this.mergeI18n(i18nSources);
-			fileDependencies = files;
-			if (errors.length > 0) {
-				compilation.errors.push(...errors);
-				return;
-			}
-			if (warnings.length > 0) {
-				compilation.warnings.push(...warnings);
+		let firstCompilation = true;
+		let i18nFileChanged = false;
+
+		compiler.hooks.watchRun.tap('AlloyI18nPlugin', () => {
+			compiler.removedFiles.forEach(filePathAndName => {
+				if (i18nFilePattern.test(filePathAndName)) {
+					currentAssets.delete(filePathAndName);
+				}
+			});
+		});
+		compiler.hooks.invalid.tap('AlloyI18nPlugin', filePathAndName => {
+			firstCompilation = false;
+			if (i18nFilePattern.test(filePathAndName)) {
+				i18nFileChanged = true;
 			}
-			content.forEach((xmlContent, identifier) => {
-				const targetPath = path.join('..', 'i18n', identifier);
-				compilation.assets[targetPath] = {
-					size() {
-						return xmlContent.length;
-					},
-					source() {
-						return xmlContent;
+		});
+		compiler.hooks.compilation.tap('AlloyI18nPlugin', compilation => {
+			const outputPath = compilation.getPath(compiler.outputPath);
+			compilation.hooks.additionalAssets.tap('AlloyI18nPlugin', () => {
+				const emitAsset = (targetFile, content) => {
+					const targetPath = compiler.outputFileSystem.join(
+						outputPath,
+						targetFile
+					);
+					const source = new RawSource(content);
+					if (currentAssets.get(targetPath) === content) {
+						// set `existsAt` so Webpack 4 will skip emitting this asset
+						source.existsAt = targetPath;
+					}
+					if (typeof compilation.emitAsset === 'function') {
+						compilation.emitAsset(targetFile, source);
+					} else {
+						compilation.assets[targetFile] = source;
 					}
 				};
+
+				if (!firstCompilation && !i18nFileChanged) {
+					// if no i18n files where changed in a subsequent watch compilation,
+					// just add back the current assets
+					currentAssets.forEach(
+						(content, filePathAndName) => emitAsset(
+							path.relative(outputPath, filePathAndName), content
+						)
+					);
+					return;
+				}
+
+				currentAssets.clear();
+				const { files, content, errors, warnings } = this.mergeI18n(i18nSources);
+				fileDependencies = files;
+				if (errors.length > 0) {
+					compilation.errors.push(...errors);
+					return;
+				}
+				if (warnings.length > 0) {
+					compilation.warnings.push(...warnings);
+				}
+				content.forEach((xmlContent, identifier) => {
+					const targetFile = path.join('..', 'i18n', identifier);
+					const targetPath = compiler.outputFileSystem.join(
+						outputPath,
+						targetFile
+					);
+					emitAsset(targetFile, xmlContent);
+					currentAssets.set(targetPath, content);
+				});
 			});
 		});
-		compiler.hooks.afterEmit.tap('AlloyLoaderPlugin', compilation => {
+
+		compiler.hooks.afterEmit.tap('AlloyI18nPlugin', compilation => {
 			const addDependencies = (target, deps) => {
 				if ('addAll' in target) {
 					target.addAll(deps);
@@ -68,6 +119,10 @@ class I18nPlugin {
 			// watch existing files for changes
 			addDependencies(compilation.fileDependencies, fileDependencies);
 		});
+
+		compiler.hooks.done.tap('AlloyI18nPlugin', () => {
+			i18nFileChanged = false;
+		});
 	}
 
 	getI18nSourceLocations() {

package.json

@@ -27,7 +27,8 @@
     "globby": "^11.0.0",
     "loader-utils": "^2.0.0",
     "neo-async": "^2.6.1",
-    "source-map": "^0.7.3"
+    "source-map": "^0.7.3",
+    "webpack-sources": "^1.4.3"
   },
   "devDependencies": {
     "eslint": "^6.6.0",