Fixes #3585

src/TemplateContent.js

@@ -19,17 +19,14 @@ const { set: lodashSet } = lodash;
 const debug = debugUtil("Eleventy:TemplateContent");
 const debugDev = debugUtil("Dev:Eleventy:TemplateContent");
 
-class TemplateContentConfigError extends EleventyBaseError {}
 class TemplateContentFrontMatterError extends EleventyBaseError {}
 class TemplateContentCompileError extends EleventyBaseError {}
 class TemplateContentRenderError extends EleventyBaseError {}
 
 class TemplateContent {
 	constructor(inputPath, templateConfig) {
 		if (!templateConfig || templateConfig.constructor.name !== "TemplateConfig") {
-			throw new TemplateContentConfigError(
-				"Missing or invalid `templateConfig` argument to TemplateContent",
-			);
+			throw new Error("Missing or invalid `templateConfig` argument");
 		}
 		this.eleventyConfig = templateConfig;
 		this.inputPath = inputPath;
@@ -96,15 +93,15 @@ class TemplateContent {
 		if (this._config.constructor.name === "TemplateConfig") {
 			this._configOptions = this._config.getConfig();
 		} else {
-			throw new TemplateContentConfigError("Tried to get an TemplateConfig but none was found.");
+			throw new Error("Tried to get an TemplateConfig but none was found.");
 		}
 	}
 
 	get eleventyConfig() {
 		if (this._config.constructor.name === "TemplateConfig") {
 			return this._config;
 		}
-		throw new TemplateContentConfigError("Tried to get an TemplateConfig but none was found.");
+		throw new Error("Tried to get an TemplateConfig but none was found.");
 	}
 
 	get config() {

src/TemplateMap.js

@@ -1,7 +1,6 @@
 import { DepGraph as DependencyGraph } from "dependency-graph";
 import { isPlainObject, TemplatePath } from "@11ty/eleventy-utils";
 import debugUtil from "debug";
-import os from "node:os";
 import pMap from "p-map";
 
 import TemplateCollection from "./TemplateCollection.js";
@@ -26,8 +25,8 @@ const EXTENSIONLESS_URL_ALLOWLIST = [
 
 class TemplateMap {
 	constructor(eleventyConfig) {
-		if (!eleventyConfig) {
-			throw new Error("Missing config argument.");
+		if (!eleventyConfig || eleventyConfig.constructor.name !== "TemplateConfig") {
+			throw new Error("Missing or invalid `eleventyConfig` argument.");
 		}
 		this.eleventyConfig = eleventyConfig;
 		this.map = [];
@@ -569,7 +568,9 @@ class TemplateMap {
 				}
 				debugDev("Added this.map[...].templateContent, outputPath, et al for one map entry");
 			},
-			{ concurrency: os.availableParallelism() },
+			{
+				concurrency: this.userConfig.getConcurrency(),
+			},
 		);
 
 		for (let map of usedTemplateContentTooEarlyMap) {

src/UserConfig.js

@@ -1,3 +1,4 @@
+import os from "node:os";
 import chalk from "kleur";
 import { DateTime } from "luxon";
 import yaml from "js-yaml";
@@ -36,6 +37,8 @@ class UserConfig {
 	#dataDeepMergeModified = false;
 	/** @type {number|undefined} */
 	#uniqueId;
+	/** @type {number} */
+	#concurrency = os.availableParallelism();
 
 	constructor() {
 		// These are completely unnecessary lines to satisfy TypeScript
@@ -238,6 +241,8 @@ class UserConfig {
 		this.errorReporting = {};
 		/** @type {object} */
 		this.templateHandling = {};
+
+		this.#concurrency = os.availableParallelism();
 	}
 
 	// compatibleRange is optional in 2.0.0-beta.2
@@ -1223,6 +1228,18 @@ class UserConfig {
 		return augmentFunction(fn, options);
 	}
 
+	setConcurrency(number) {
+		if (typeof number !== "number") {
+			throw new UserConfigError("Argument passed to `setConcurrency` must be a number.");
+		}
+
+		this.#concurrency = number;
+	}
+
+	getConcurrency() {
+		return this.#concurrency;
+	}
+
 	getMergingConfigObject() {
 		let obj = {
 			// filters removed in 1.0 (use addTransform instead)