prune-globals.js

// Usage: node prune-globals.js
// This script will document which `window.* = ...` assignments are used by other files in the src directory.
// Also its purpose is very specific; it only looks for global assignments following a "// Temporary globals" comment.

const fs = require("fs");
const path = require("path");
const espree = require("espree");

// Assuming all files are in the src directory and not subdirectories
const srcDir = "./src";

// Silly wrapper function to read a file and return its content
function readFile(filePath) {
	return fs.readFileSync(filePath, "utf8");
}

// Function to write content to a file
function writeFile(filePath, content) {
	console.log("Writing file", filePath);
	fs.writeFileSync(filePath, content, "utf8");
}

// function escapeRegExp(string) {
// 	return string.replace(/[.*+?^${}()|[\]\\]/g, "\\$&"); // $& means the whole matched string
// }

// Function to find non-ESM usages of an identifier
// Unstructured naive search
// function findDependencies(identifier, fileContent, excludeFiles = []) {
// 	// console.log("Finding dependencies for", identifier);
// 	const importRegex = new RegExp(`^\\s*import .*${escapeRegExp(identifier)}.* from`, "m");
// 	// Identifiers starting with $ will not work with \b because $ is not part of \w
// 	// const usageRegex = new RegExp(`\\b${escapeRegExp(identifier)}\\b`, "m");
// 	// So instead we use a negative lookbehind and a negative lookahead
// 	// This is not Unicode-friendly, but it should work for ASCII
// 	const usageRegex = new RegExp(`(?<![0-9A-Z_$])${escapeRegExp(identifier)}(?![0-9A-Z_$])`, "m");
// 	const dependencies = [];
// 	for (const [filePath, content] of Object.entries(fileContent)) {
// 		if (excludeFiles.includes(filePath)) {
// 			continue;
// 		}
// 		if (usageRegex.test(content)) {
// 			if (!importRegex.test(content)) {
// 				// console.log(`'${filePath}' includes '${identifier}' but doesn't match ${importRegex}`);
// 				// console.log("Usage:\n    ", content.match(new RegExp(`.*${escapeRegExp(identifier)}.*`, "m"))[0]);
// 				dependencies.push(filePath);
// 			}
// 		}
// 	}
// 	return dependencies;
// }

// Somewhat more structured search using tokens but not fully utilizing AST
// This will correctly ignore comments and strings, but will still give false positives for identifiers in local scopes and such.
function findDependencies(identifier, fileContentTree, excludeFiles = []) {
	const dependencies = [];
	for (const [filePath, tree] of Object.entries(fileContentTree)) {
		if (excludeFiles.includes(filePath)) {
			continue;
		}
		console.log("Checking", filePath, "for", identifier);
		// Look for imports of the identifier:
		let foundImport = false;
		for (const node of tree.body) {
			if (node.type === "ImportDeclaration") {
				for (const specifier of node.specifiers) {
					if (specifier.imported.name === identifier) {
						console.log("Found ESM (non-global) import of", identifier, "in", filePath);
						foundImport = true;
						break;
					}
				}
			}
		}
		if (foundImport) {
			continue;
		}

		// Look for other usages of the identifier:
		// console.log("Tokens:", tree.tokens);
		for (const token of tree.tokens) {
			if (token.type === "Identifier" && token.value === identifier) {
				// const parent = token.parent;
				dependencies.push(filePath);
				console.log("Found", identifier, "in", filePath);
				break;
			}
		}
	}
	return dependencies;
}

// Function to process each file in the src directory
function processFiles() {
	const fileUpperContent = {};
	const fileUpperContentTree = {};
	const fileLowerContent = {};
	fs.readdir(srcDir, (err, files) => {
		if (err) {
			console.error("Error reading directory:", err);
			return;
		}
		// First read all files into memory, since we'll need to look at each file
		// in reference to every other file, and there's not that many files.
		for (const file of files) {
			if (path.extname(file) === ".js") {
				const filePath = path.join(srcDir, file);
				const content = readFile(filePath);
				// Break the files into content above and below (and including) the "// Temporary globals" comment,
				// in order to avoid matching the identifier within the comments generated by this script.
				// The identifier matching is still naive, but this lets the script be idempotent.
				// By passing only upper content to findDependencies,
				// while the replacements are only made to the lower content,
				// we avoid changes to the content that would affect the ultimate behavior of the script.
				const startIndex = content.indexOf("// Temporary globals");
				if (startIndex !== -1) {
					fileUpperContent[filePath] = content.slice(0, startIndex);
					fileLowerContent[filePath] = content.slice(startIndex);
				} else {
					fileUpperContent[filePath] = content;
					fileLowerContent[filePath] = "";
				}
				try {
					fileUpperContentTree[filePath] = espree.parse(fileUpperContent[filePath], {
						ecmaVersion: 2020,
						sourceType: fileUpperContent[filePath].match(/import .* from/) ? "module" : "script",
						tokens: true,
					});
				} catch (e) {
					console.error(`Error parsing ${filePath}:`, e);
				}
			}
		}
		// Then process each file.
		for (const filePath of Object.keys(fileUpperContent)) {
			console.log("--------", filePath);
			const upper = fileUpperContent[filePath];
			const lower = fileLowerContent[filePath];
			// Match and replace in one fell swoop
			const updatedContent = upper + lower.replace(
				/(?:\/\/\s*)?(window\.(.*?) = .*;)(\s*\/\/.*)?/g,
				(_match, assignment, identifier, _comment) => {
					const dependencies = findDependencies(identifier, fileUpperContentTree, [filePath]);
					const formatPath = (filePath) => path.relative(srcDir, filePath).replace(/\\/g, "/");
					const formattedPaths = dependencies.map(formatPath).join(", ");
					console.log(`Dependencies for ${identifier}: ${formattedPaths || "(none found)"}`);
					if (dependencies.length) {
						return `${assignment} // may be used by ${formattedPaths}`;
					} else {
						return `// ${assignment} // unused`;
					}
				}
			);
			writeFile(filePath, updatedContent);
		}
	});
}

processFiles();