fix(meta): memory leak when loading meta table

refs #106

src/config/config.ts

@@ -9,6 +9,7 @@ import { MetaCopyableProperty, MetaDataTable } from "../meta/element";
 import { Plugin } from "../plugin";
 import schema from "../schema/config.json";
 import { TransformContext, Transformer, TRANSFORMER_API } from "../transform";
+import { requireUncached } from "../utils";
 import { ConfigData, RuleOptions, TransformMap } from "./config-data";
 import defaultConfig from "./default";
 import { ConfigError } from "./error";
@@ -64,12 +65,8 @@ function mergeInternal(base: ConfigData, rhs: ConfigData): ConfigData {
 function loadFromFile(filename: string): ConfigData {
 	let json;
 	try {
-		/* remove cached copy so we always load a fresh copy, important for editors
-		 * which keep a long-running instance of [[HtmlValidate]] around. */
-		delete require.cache[require.resolve(filename)];
-
 		/* load using require as it can process both js and json */
-		json = require(filename); // eslint-disable-line import/no-dynamic-require
+		json = requireUncached(filename);
 	} catch (err) {
 		throw new ConfigError(`Failed to read configuration from "${filename}"`, err);
 	}

src/meta/table.ts

@@ -5,6 +5,7 @@ import jsonMergePatch from "json-merge-patch";
 import { HtmlElement } from "../dom";
 import { SchemaValidationError, UserError } from "../error";
 import { SchemaValidationPatch } from "../plugin";
+import { requireUncached } from "../utils";
 import schema from "../schema/elements.json";
 import {
 	ElementTable,
@@ -139,13 +140,8 @@ export class MetaTable {
 	 */
 	public loadFromFile(filename: string): void {
 		try {
-			/* remove cached copy so we always load a fresh copy, important for
-			 * editors which keep a long-running instance of [[HtmlValidate]]
-			 * around. */
-			delete require.cache[require.resolve(filename)];
-
 			/* load using require as it can process both js and json */
-			const data = require(filename); // eslint-disable-line import/no-dynamic-require
+			const data = requireUncached(filename);
 			this.loadFromObject(data, filename);
 		} catch (err) {
 			if (err instanceof SchemaValidationError) {

src/utils/index.ts

+export { requireUncached } from "./require-uncached";
 export { ruleExists } from "./rule-exists";

src/utils/require-uncached.ts

+/**
+ * Similar to `require(..)` but removes the cached copy first.
+ */
+export function requireUncached(moduleId: string): any {
+	const filename = require.resolve(moduleId);
+
+	/* remove references from the parent module to prevent memory leak */
+	const m = require.cache[filename];
+	if (m && m.parent) {
+		const { parent } = m;
+		for (let i = parent.children.length - 1; i >= 0; i--) {
+			if (parent.children[i].id === filename) {
+				parent.children.splice(i, 1);
+			}
+		}
+	}
+
+	/* remove old module from cache */
+	delete require.cache[filename];
+
+	// eslint-disable-next-line import/no-dynamic-require
+	return require(filename);
+}