Check if all required dependencies are present and show an error if this is not the case

src/compatibility.js

@@ -34,3 +34,20 @@ export function measureDistances(segments, token, shape, gridSpaces=true, option
 	}
 }
 
+export function checkDependencies() {
+	if (!game.modules.get("socketlib")?.active) {
+		console.error("Drag Ruler | The `socketlib` module isn't enabled, but it's required for Drag Ruler to operate properly.");
+		if (game.user.isGM) {
+			new Dialog({
+				title: game.i18n.localize("drag-ruler.dependencies.socketlib.title"),
+				content: `<h2>${game.i18n.localize("drag-ruler.dependencies.socketlib.title")}</h2><p>${game.i18n.localize("drag-ruler.dependencies.socketlib.text")}</p>`,
+				buttons: {
+					ok: {
+						icon: '<i class="fas fa-check"></i>',
+						label: game.i18n.localize("drag-ruler.dependencies.ok")
+					}
+				},
+			}).render(true);
+		}
+	}
+}

src/main.js

@@ -1,7 +1,7 @@
 "use strict"
 
 import {currentSpeedProvider, getMovedDistanceFromToken, getRangesFromSpeedProvider, getUnreachableColorFromSpeedProvider, initApi, registerModule, registerSystem} from "./api.js"
-import {getHexSizeSupportTokenGridCenter} from "./compatibility.js"
+import {checkDependencies, getHexSizeSupportTokenGridCenter} from "./compatibility.js";
 import {moveTokens, onMouseMove} from "./foundry_imports.js"
 import {performMigrations} from "./migration.js"
 import {DragRulerRuler} from "./ruler.js";
@@ -27,6 +27,7 @@ Hooks.once("init", () => {
 
 Hooks.once("ready", () => {
 	performMigrations()
+	checkDependencies();
 	Hooks.callAll("dragRuler.ready", SpeedProvider)
 })