webpack/lib/ConstPlugin.js

Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.

/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
*/

"use strict";

const CachedConstDependency = require("./dependencies/CachedConstDependency");
const ConstDependency = require("./dependencies/ConstDependency");
const { evaluateToString } = require("./javascript/JavascriptParserHelpers");
const { parseResource } = require("./util/identifier");

/** @typedef {import("estree").Expression} ExpressionNode */
/** @typedef {import("estree").Super} SuperNode */
/** @typedef {import("./Compiler")} Compiler */

const collectDeclaration = (declarations, pattern) => {
	const stack = [pattern];
	while (stack.length > 0) {
		const node = stack.pop();
		switch (node.type) {
			case "Identifier":
				declarations.add(node.name);
				break;
			case "ArrayPattern":
				for (const element of node.elements) {
					if (element) {
						stack.push(element);
					}
				}
				break;
			case "AssignmentPattern":
				stack.push(node.left);
				break;
			case "ObjectPattern":
				for (const property of node.properties) {
					stack.push(property.value);
				}
				break;
			case "RestElement":
				stack.push(node.argument);
				break;
		}
	}
};

const getHoistedDeclarations = (branch, includeFunctionDeclarations) => {
	const declarations = new Set();
	const stack = [branch];
	while (stack.length > 0) {
		const node = stack.pop();
		// Some node could be `null` or `undefined`.
		if (!node) continue;
		switch (node.type) {
			// Walk through control statements to look for hoisted declarations.
			// Some branches are skipped since they do not allow declarations.
			case "BlockStatement":
				for (const stmt of node.body) {
					stack.push(stmt);
				}
				break;
			case "IfStatement":
				stack.push(node.consequent);
				stack.push(node.alternate);
				break;
			case "ForStatement":
				stack.push(node.init);
				stack.push(node.body);
				break;
			case "ForInStatement":
			case "ForOfStatement":
				stack.push(node.left);
				stack.push(node.body);
				break;
			case "DoWhileStatement":
			case "WhileStatement":
			case "LabeledStatement":
				stack.push(node.body);
				break;
			case "SwitchStatement":
				for (const cs of node.cases) {
					for (const consequent of cs.consequent) {
						stack.push(consequent);
					}
				}
				break;
			case "TryStatement":
				stack.push(node.block);
				if (node.handler) {
					stack.push(node.handler.body);
				}
				stack.push(node.finalizer);
				break;
			case "FunctionDeclaration":
				if (includeFunctionDeclarations) {
					collectDeclaration(declarations, node.id);
				}
				break;
			case "VariableDeclaration":
				if (node.kind === "var") {
					for (const decl of node.declarations) {
						collectDeclaration(declarations, decl.id);
					}
				}
				break;
		}
	}
	return Array.from(declarations);
};

class ConstPlugin {
	/**
	 * Apply the plugin
	 * @param {Compiler} compiler the compiler instance
	 * @returns {void}
	 */
	apply(compiler) {
		const cachedParseResource = parseResource.bindCache(compiler.root);
		compiler.hooks.compilation.tap(
			"ConstPlugin",
			(compilation, { normalModuleFactory }) => {
				compilation.dependencyTemplates.set(
					ConstDependency,
					new ConstDependency.Template()
				);

				compilation.dependencyTemplates.set(
					CachedConstDependency,
					new CachedConstDependency.Template()
				);

				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") {
							if (!param.couldHaveSideEffects()) {
								const dep = new ConstDependency(`${bool}`, param.range);
								dep.loc = statement.loc;
								parser.state.module.addPresentationalDependency(dep);
							} else {
								parser.walkExpression(statement.test);
							}
							const branchToRemove = bool
								? statement.alternate
								: statement.consequent;
							if (branchToRemove) {
								// Before removing the dead branch, the hoisted declarations
								// must be collected.
								//
								// Given the following code:
								//
								//     if (true) f() else g()
								//     if (false) {
								//       function f() {}
								//       const g = function g() {}
								//       if (someTest) {
								//         let a = 1
								//         var x, {y, z} = obj
								//       }
								//     } else {
								//       …
								//     }
								//
								// the generated code is:
								//
								//     if (true) f() else {}
								//     if (false) {
								//       var f, x, y, z;   (in loose mode)
								//       var x, y, z;      (in strict mode)
								//     } else {
								//       …
								//     }
								//
								// NOTE: When code runs in strict mode, `var` declarations
								// are hoisted but `function` declarations don't.
								//
								let declarations;
								if (parser.scope.isStrict) {
									// If the code runs in strict mode, variable declarations
									// using `var` must be hoisted.
									declarations = getHoistedDeclarations(branchToRemove, false);
								} else {
									// Otherwise, collect all hoisted declaration.
									declarations = getHoistedDeclarations(branchToRemove, true);
								}
								let replacement;
								if (declarations.length > 0) {
									replacement = `{ var ${declarations.join(", ")}; }`;
								} else {
									replacement = "{}";
								}
								const dep = new ConstDependency(
									replacement,
									branchToRemove.range
								);
								dep.loc = branchToRemove.loc;
								parser.state.module.addPresentationalDependency(dep);
							}
							return bool;
						}
					});
					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") {
								if (!param.couldHaveSideEffects()) {
									const dep = new ConstDependency(` ${bool}`, param.range);
									dep.loc = expression.loc;
									parser.state.module.addPresentationalDependency(dep);
								} else {
									parser.walkExpression(expression.test);
								}
								// Expressions do not hoist.
								// It is safe to remove the dead branch.
								//
								// Given the following code:
								//
								//   false ? someExpression() : otherExpression();
								//
								// the generated code is:
								//
								//   false ? 0 : otherExpression();
								//
								const branchToRemove = bool
									? expression.alternate
									: expression.consequent;
								const dep = new ConstDependency("0", branchToRemove.range);
								dep.loc = branchToRemove.loc;
								parser.state.module.addPresentationalDependency(dep);
								return bool;
							}
						}
					);
					parser.hooks.expressionLogicalOperator.tap(
						"ConstPlugin",
						expression => {
							if (parser.scope.isAsmJs) return;
							if (
								expression.operator === "&&" ||
								expression.operator === "||"
							) {
								const param = parser.evaluateExpression(expression.left);
								const bool = param.asBool();
								if (typeof bool === "boolean") {
									// Expressions do not hoist.
									// It is safe to remove the dead branch.
									//
									// ------------------------------------------
									//
									// Given the following code:
									//
									//   falsyExpression() && someExpression();
									//
									// the generated code is:
									//
									//   falsyExpression() && false;
									//
									// ------------------------------------------
									//
									// Given the following code:
									//
									//   truthyExpression() && someExpression();
									//
									// the generated code is:
									//
									//   true && someExpression();
									//
									// ------------------------------------------
									//
									// Given the following code:
									//
									//   truthyExpression() || someExpression();
									//
									// the generated code is:
									//
									//   truthyExpression() || false;
									//
									// ------------------------------------------
									//
									// Given the following code:
									//
									//   falsyExpression() || someExpression();
									//
									// the generated code is:
									//
									//   false && someExpression();
									//
									const keepRight =
										(expression.operator === "&&" && bool) ||
										(expression.operator === "||" && !bool);

									if (
										!param.couldHaveSideEffects() &&
										(param.isBoolean() || keepRight)
									) {
										// for case like
										//
										//   return'development'===process.env.NODE_ENV&&'foo'
										//
										// we need a space before the bool to prevent result like
										//
										//   returnfalse&&'foo'
										//
										const dep = new ConstDependency(` ${bool}`, param.range);
										dep.loc = expression.loc;
										parser.state.module.addPresentationalDependency(dep);
									} else {
										parser.walkExpression(expression.left);
									}
									if (!keepRight) {
										const dep = new ConstDependency(
											"0",
											expression.right.range
										);
										dep.loc = expression.loc;
										parser.state.module.addPresentationalDependency(dep);
									}
									return keepRight;
								}
							} else if (expression.operator === "??") {
								const param = parser.evaluateExpression(expression.left);
								const keepRight = param && param.asNullish();
								if (typeof keepRight === "boolean") {
									// ------------------------------------------
									//
									// Given the following code:
									//
									//   nonNullish ?? someExpression();
									//
									// the generated code is:
									//
									//   nonNullish ?? 0;
									//
									// ------------------------------------------
									//
									// Given the following code:
									//
									//   nullish ?? someExpression();
									//
									// the generated code is:
									//
									//   null ?? someExpression();
									//
									if (!param.couldHaveSideEffects() && keepRight) {
										// cspell:word returnnull
										// for case like
										//
										//   return('development'===process.env.NODE_ENV&&null)??'foo'
										//
										// we need a space before the bool to prevent result like
										//
										//   returnnull??'foo'
										//
										const dep = new ConstDependency(" null", param.range);
										dep.loc = expression.loc;
										parser.state.module.addPresentationalDependency(dep);
									} else {
										const dep = new ConstDependency(
											"0",
											expression.right.range
										);
										dep.loc = expression.loc;
										parser.state.module.addPresentationalDependency(dep);
										parser.walkExpression(expression.left);
									}

									return keepRight;
								}
							}
						}
					);
					parser.hooks.optionalChaining.tap("ConstPlugin", expr => {
						/** @type {ExpressionNode[]} */
						const optionalExpressionsStack = [];
						/** @type {ExpressionNode|SuperNode} */
						let next = expr.expression;

						while (
							next.type === "MemberExpression" ||
							next.type === "CallExpression"
						) {
							if (next.type === "MemberExpression") {
								if (next.optional) {
									// SuperNode can not be optional
									optionalExpressionsStack.push(
										/** @type {ExpressionNode} */ (next.object)
									);
								}
								next = next.object;
							} else {
								if (next.optional) {
									// SuperNode can not be optional
									optionalExpressionsStack.push(
										/** @type {ExpressionNode} */ (next.callee)
									);
								}
								next = next.callee;
							}
						}

						while (optionalExpressionsStack.length) {
							const expression = optionalExpressionsStack.pop();
							const evaluated = parser.evaluateExpression(expression);

							if (evaluated && evaluated.asNullish()) {
								// ------------------------------------------
								//
								// Given the following code:
								//
								//   nullishMemberChain?.a.b();
								//
								// the generated code is:
								//
								//   undefined;
								//
								// ------------------------------------------
								//
								const dep = new ConstDependency(" undefined", expr.range);
								dep.loc = expr.loc;
								parser.state.module.addPresentationalDependency(dep);
								return true;
							}
						}
					});
					parser.hooks.evaluateIdentifier
						.for("__resourceQuery")
						.tap("ConstPlugin", expr => {
							if (parser.scope.isAsmJs) return;
							if (!parser.state.module) return;
							return evaluateToString(
								cachedParseResource(parser.state.module.resource).query
							)(expr);
						});
					parser.hooks.expression
						.for("__resourceQuery")
						.tap("ConstPlugin", expr => {
							if (parser.scope.isAsmJs) return;
							if (!parser.state.module) return;
							const dep = new CachedConstDependency(
								JSON.stringify(
									cachedParseResource(parser.state.module.resource).query
								),
								expr.range,
								"__resourceQuery"
							);
							dep.loc = expr.loc;
							parser.state.module.addPresentationalDependency(dep);
							return true;
						});

					parser.hooks.evaluateIdentifier
						.for("__resourceFragment")
						.tap("ConstPlugin", expr => {
							if (parser.scope.isAsmJs) return;
							if (!parser.state.module) return;
							return evaluateToString(
								cachedParseResource(parser.state.module.resource).fragment
							)(expr);
						});
					parser.hooks.expression
						.for("__resourceFragment")
						.tap("ConstPlugin", expr => {
							if (parser.scope.isAsmJs) return;
							if (!parser.state.module) return;
							const dep = new CachedConstDependency(
								JSON.stringify(
									cachedParseResource(parser.state.module.resource).fragment
								),
								expr.range,
								"__resourceFragment"
							);
							dep.loc = expr.loc;
							parser.state.module.addPresentationalDependency(dep);
							return true;
						});
				};

				normalModuleFactory.hooks.parser
					.for("javascript/auto")
					.tap("ConstPlugin", handler);
				normalModuleFactory.hooks.parser
					.for("javascript/dynamic")
					.tap("ConstPlugin", handler);
				normalModuleFactory.hooks.parser
					.for("javascript/esm")
					.tap("ConstPlugin", handler);
			}
		);
	}
}

module.exports = ConstPlugin;