backport: do not evaluate constants in asm.js, fix IIFE mode detection

lib/ConstPlugin.js

@@ -119,6 +119,7 @@ class ConstPlugin {
 
 				const handler = parser => {
 					parser.hooks.statementIf.tap("ConstPlugin", statement => {
+						if (parser.scope.isAsmJs) return;
 						const param = parser.evaluateExpression(statement.test);
 						const bool = param.asBool();
 						if (typeof bool === "boolean") {
@@ -189,6 +190,7 @@ class ConstPlugin {
 					parser.hooks.expressionConditionalOperator.tap(
 						"ConstPlugin",
 						expression => {
+							if (parser.scope.isAsmJs) return;
 							const param = parser.evaluateExpression(expression.test);
 							const bool = param.asBool();
 							if (typeof bool === "boolean") {
@@ -224,6 +226,7 @@ class ConstPlugin {
 					parser.hooks.expressionLogicalOperator.tap(
 						"ConstPlugin",
 						expression => {
+							if (parser.scope.isAsmJs) return;
 							if (
 								expression.operator === "&&" ||
 								expression.operator === "||"
@@ -309,6 +312,7 @@ class ConstPlugin {
 					parser.hooks.evaluateIdentifier
 						.for("__resourceQuery")
 						.tap("ConstPlugin", expr => {
+							if (parser.scope.isAsmJs) return;
 							if (!parser.state.module) return;
 							return ParserHelpers.evaluateToString(
 								getQuery(parser.state.module.resource)
@@ -317,6 +321,7 @@ class ConstPlugin {
 					parser.hooks.expression
 						.for("__resourceQuery")
 						.tap("ConstPlugin", () => {
+							if (parser.scope.isAsmJs) return;
 							if (!parser.state.module) return;
 							parser.state.current.addVariable(
 								"__resourceQuery",

lib/Parser.js

@@ -1229,7 +1229,7 @@ class Parser extends Tapable {
 				this.walkPattern(param);
 			}
 			if (statement.body.type === "BlockStatement") {
-				this.detectStrictMode(statement.body.body);
+				this.detectMode(statement.body.body);
 				this.prewalkStatement(statement.body);
 				this.walkStatement(statement.body);
 			} else {
@@ -1697,7 +1697,7 @@ class Parser extends Tapable {
 				this.walkPattern(param);
 			}
 			if (expression.body.type === "BlockStatement") {
-				this.detectStrictMode(expression.body.body);
+				this.detectMode(expression.body.body);
 				this.prewalkStatement(expression.body);
 				this.walkStatement(expression.body);
 			} else {
@@ -1713,7 +1713,7 @@ class Parser extends Tapable {
 				this.walkPattern(param);
 			}
 			if (expression.body.type === "BlockStatement") {
-				this.detectStrictMode(expression.body.body);
+				this.detectMode(expression.body.body);
 				this.prewalkStatement(expression.body);
 				this.walkStatement(expression.body);
 			} else {
@@ -1894,6 +1894,7 @@ class Parser extends Tapable {
 				this.scope.renames.set(params[i].name, param);
 			}
 			if (functionExpression.body.type === "BlockStatement") {
+				this.detectMode(functionExpression.body.body);
 				this.prewalkStatement(functionExpression.body);
 				this.walkStatement(functionExpression.body);
 			} else {
@@ -2001,6 +2002,7 @@ class Parser extends Tapable {
 			inTry: false,
 			inShorthand: false,
 			isStrict: oldScope.isStrict,
+			isAsmJs: oldScope.isAsmJs,
 			definitions: oldScope.definitions.createChild(),
 			renames: oldScope.renames.createChild()
 		};
@@ -2024,6 +2026,7 @@ class Parser extends Tapable {
 			inTry: false,
 			inShorthand: false,
 			isStrict: oldScope.isStrict,
+			isAsmJs: oldScope.isAsmJs,
 			definitions: oldScope.definitions.createChild(),
 			renames: oldScope.renames.createChild()
 		};
@@ -2049,6 +2052,7 @@ class Parser extends Tapable {
 			inTry: oldScope.inTry,
 			inShorthand: false,
 			isStrict: oldScope.isStrict,
+			isAsmJs: oldScope.isAsmJs,
 			definitions: oldScope.definitions.createChild(),
 			renames: oldScope.renames.createChild()
 		};
@@ -2058,15 +2062,23 @@ class Parser extends Tapable {
 		this.scope = oldScope;
 	}
 
+	// TODO webpack 5: remove this methods
+	// only for backward-compat
 	detectStrictMode(statements) {
-		const isStrict =
+		this.detectMode(statements);
+	}
+
+	detectMode(statements) {
+		const isLiteral =
 			statements.length >= 1 &&
 			statements[0].type === "ExpressionStatement" &&
-			statements[0].expression.type === "Literal" &&
-			statements[0].expression.value === "use strict";
-		if (isStrict) {
+			statements[0].expression.type === "Literal";
+		if (isLiteral && statements[0].expression.value === "use strict") {
 			this.scope.isStrict = true;
 		}
+		if (isLiteral && statements[0].expression.value === "use asm") {
+			this.scope.isAsmJs = true;
+		}
 	}
 
 	enterPatterns(patterns, onIdent) {
@@ -2272,13 +2284,14 @@ class Parser extends Tapable {
 			inTry: false,
 			inShorthand: false,
 			isStrict: false,
+			isAsmJs: false,
 			definitions: new StackedSetMap(),
 			renames: new StackedSetMap()
 		};
 		const state = (this.state = initialState || {});
 		this.comments = comments;
 		if (this.hooks.program.call(ast, comments) === undefined) {
-			this.detectStrictMode(ast.body);
+			this.detectMode(ast.body);
 			this.prewalkStatements(ast.body);
 			this.blockPrewalkStatements(ast.body);
 			this.walkStatements(ast.body);

test/Compiler.test.js

@@ -168,6 +168,26 @@ describe("Compiler", () => {
 			done();
 		});
 	});
+
+	it("should not evaluate constants in asm.js", done => {
+		compile("./asmjs", {}, (stats, files) => {
+			expect(Object.keys(files)).toEqual(["/main.js"]);
+			const bundle = files["/main.js"];
+			expect(bundle).toMatch('"use asm";');
+			expect(bundle).toMatch("101");
+			expect(bundle).toMatch("102");
+			expect(bundle).toMatch("103");
+			expect(bundle).toMatch("104");
+			expect(bundle).toMatch("105");
+			expect(bundle).not.toMatch("106");
+			expect(bundle).not.toMatch("107");
+			expect(bundle).not.toMatch("108");
+			expect(bundle).toMatch("109");
+			expect(bundle).toMatch("110");
+			done();
+		});
+	});
+
 	describe("methods", () => {
 		let compiler;
 		beforeEach(() => {

test/fixtures/asmjs.js

@@ -0,0 +1,22 @@
+module.exports = function a() {
+	function b() {
+		"use asm";
+		if (0 == 0) {
+			return 1 == 1 ? 101 : 102;
+		} else {
+			return 0 == 1 ? 103 : 104;
+		}
+	}
+	function c() {
+		if (0 == 0) {
+			return 1 == 1 ? 105 : 106;
+		} else {
+			return 0 == 1 ? 107 : 108;
+		}
+	}
+	var d = (function() {
+		"use asm";
+		return 1 == 1 ? 109 : 110;
+	})();
+	return b() + c() + d;
+};