Refactor how source type is handled by the parser

lib/JavascriptModulesPlugin.js

@@ -11,13 +11,15 @@ class JavascriptModulesPlugin {
 		compiler.hooks.compilation.tap("JavascriptModulesPlugin", (compilation, {
 			normalModuleFactory
 		}) => {
-			const createParser = () => {
-				return new Parser();
-			};
-
-			normalModuleFactory.hooks.createParser.for("javascript/auto").tap("JavascriptModulesPlugin", createParser);
-			normalModuleFactory.hooks.createParser.for("javascript/dynamic").tap("JavascriptModulesPlugin", createParser);
-			normalModuleFactory.hooks.createParser.for("javascript/esm").tap("JavascriptModulesPlugin", createParser);
+			normalModuleFactory.hooks.createParser.for("javascript/auto").tap("JavascriptModulesPlugin", options => {
+				return new Parser(options, "auto");
+			});
+			normalModuleFactory.hooks.createParser.for("javascript/dynamic").tap("JavascriptModulesPlugin", options => {
+				return new Parser(options, "script");
+			});
+			normalModuleFactory.hooks.createParser.for("javascript/esm").tap("JavascriptModulesPlugin", options => {
+				return new Parser(options, "module");
+			});
 		});
 	}
 }

lib/NormalModuleFactory.js

@@ -88,7 +88,7 @@ class NormalModuleFactory extends Tapable {
 		this.ruleSet = new RuleSet(options.defaultRules.concat(options.rules));
 		this.cachePredicate = typeof options.unsafeCache === "function" ? options.unsafeCache : Boolean.bind(null, options.unsafeCache);
 		this.context = context || "";
-		this.parserCache = {};
+		this.parserCache = Object.create(null);
 		this.hooks.factory.tap("NormalModuleFactory", () => (result, callback) => {
 			let resolver = this.hooks.resolver.call(null);
 
@@ -332,14 +332,13 @@ class NormalModuleFactory extends Tapable {
 			else
 				ident = JSON.stringify([type, parserOptions]);
 		}
-		const parser = this.parserCache[ident];
-		if(parser)
-			return parser;
+		if(ident in this.parserCache) {
+			return this.parserCache[ident];
+		}
 		return this.parserCache[ident] = this.createParser(type, parserOptions);
 	}
 
-	createParser(type, parserOptions) {
-		parserOptions = parserOptions || {};
+	createParser(type, parserOptions = {}) {
 		const parser = this.hooks.createParser.for(type).call(parserOptions);
 		if(!parser) {
 			throw new Error(`No parser registered for ${type}`);

lib/Parser.js

@@ -21,28 +21,19 @@ const joinRanges = (startRange, endRange) => {
 	return [startRange[0], endRange[1]];
 };
 
-const ECMA_VERSION = 2017;
-
-const POSSIBLE_AST_OPTIONS = [{
+const defaultParserOptions = {
 	ranges: true,
 	locations: true,
-	ecmaVersion: ECMA_VERSION,
+	ecmaVersion: 2017,
 	sourceType: "module",
+	onComment: null,
 	plugins: {
 		dynamicImport: true
 	}
-}, {
-	ranges: true,
-	locations: true,
-	ecmaVersion: ECMA_VERSION,
-	sourceType: "script",
-	plugins: {
-		dynamicImport: true
-	}
-}];
+};
 
 class Parser extends Tapable {
-	constructor(options) {
+	constructor(options, sourceType = "auto") {
 		super();
 		this.hooks = {
 			evaluateTypeof: new HookMap(() => new SyncBailHook(["expression"])),
@@ -116,6 +107,7 @@ class Parser extends Tapable {
 			}
 		});
 		this.options = options;
+		this.sourceType = sourceType;
 		this.scope = undefined;
 		this.state = undefined;
 		this.comments = undefined;
@@ -1761,37 +1753,18 @@ class Parser extends Tapable {
 
 	parse(source, initialState) {
 		let ast;
-		let comments = [];
+		let comments;
 		if(typeof source === "object" && source !== null) {
 			ast = source;
 			comments = source.comments;
-		}
-		for(let i = 0, len = POSSIBLE_AST_OPTIONS.length; i < len; i++) {
-			if(!ast) {
-				try {
-					comments.length = 0;
-					POSSIBLE_AST_OPTIONS[i].onComment = comments;
-					ast = acorn.parse(source, POSSIBLE_AST_OPTIONS[i]);
-				} catch(e) {
-					// ignore the error
-				}
-			}
-		}
-		if(!ast) {
-			// for the error
-			ast = acorn.parse(source, {
-				ranges: true,
-				locations: true,
-				ecmaVersion: ECMA_VERSION,
-				sourceType: "module",
-				plugins: {
-					dynamicImport: true
-				},
+		} else {
+			comments = [];
+			ast = Parser.parse(source, {
+				sourceType: this.sourceType,
 				onComment: comments
 			});
 		}
-		if(!ast || typeof ast !== "object")
-			throw new Error("Source couldn't be parsed");
+
 		const oldScope = this.scope;
 		const oldState = this.state;
 		const oldComments = this.comments;
@@ -1817,17 +1790,10 @@ class Parser extends Tapable {
 	}
 
 	evaluate(source) {
-		const ast = acorn.parse("(" + source + ")", {
-			ranges: true,
-			locations: true,
-			ecmaVersion: ECMA_VERSION,
-			sourceType: "module",
-			plugins: {
-				dynamicImport: true
-			}
+		const ast = Parser.parse("(" + source + ")", {
+			sourceType: this.sourceType,
+			locations: false,
 		});
-		if(!ast || typeof ast !== "object" || ast.type !== "Program")
-			throw new Error("evaluate: Source couldn't be parsed");
 		if(ast.body.length !== 1 || ast.body[0].type !== "ExpressionStatement")
 			throw new Error("evaluate: Source is not a expression");
 		return this.evaluateExpression(ast.body[0].expression);
@@ -1885,8 +1851,41 @@ class Parser extends Tapable {
 		};
 	}
 
+	static parse(code, options) {
+		const type = options.sourceType;
+		const parserOptions = Object.assign(Object.create(null), defaultParserOptions, options);
+
+		if(type === "auto") {
+			parserOptions.sourceType = "module";
+		}
+
+		let ast;
+		let error;
+		let threw = false;
+		try {
+			ast = acorn.parse(code, parserOptions);
+		} catch(e) {
+			error = e;
+			threw = true;
+		}
+
+		if(threw && type === "auto") {
+			parserOptions.sourceType = "script";
+			if(Array.isArray(parserOptions.onComment)) {
+				parserOptions.onComment.length = 0;
+			}
+			try {
+				ast = acorn.parse(code, parserOptions);
+				threw = false;
+			} catch(e) {}
+		}
+
+		if(threw) {
+			throw error;
+		}
+
+		return ast;
+	}
 }
 
-Parser.ECMA_VERSION = ECMA_VERSION;
-
 module.exports = Parser;

lib/optimize/ConcatenatedModule.js

@@ -7,7 +7,6 @@
 const Module = require("../Module");
 const Template = require("../Template");
 const Parser = require("../Parser");
-const acorn = require("acorn");
 const eslintScope = require("eslint-scope");
 const ReplaceSource = require("webpack-sources").ReplaceSource;
 const ConcatSource = require("webpack-sources").ConcatSource;
@@ -483,11 +482,8 @@ class ConcatenatedModule extends Module {
 				const code = source.source();
 				let ast;
 				try {
-					ast = acorn.parse(code, {
-						ranges: true,
-						locations: true,
-						ecmaVersion: Parser.ECMA_VERSION,
-						sourceType: "module"
+					ast = Parser.parse(code, {
+						sourceType: "module",
 					});
 				} catch(err) {
 					if(err.loc && typeof err.loc === "object" && typeof err.loc.line === "number") {