Provide a better error message when format-resource doesn’t exists

Fixes #2291

news/changelog-1.2.md

@@ -16,6 +16,7 @@
 - HTML dependencies may now include `serviceworkers`, which are copied into the output directory.
 - New `quarto.doc.attachToDependency` function to attach files to html dependencies (copies files into the lib dir for a named HTML dependency).
 - Ensure that `quarto.utils.dump` works with pandoc's builtin global variables (#2254)
+- Provide a better error message for non-existent format resources (#2291)
 
 ## HTML Format
 

src/command/render/pandoc-dependencies-resources.ts

@@ -14,6 +14,7 @@ import {
   appendDependencies,
   FormatResourceDependency,
 } from "./pandoc-dependencies.ts";
+import { existsSync } from "https://deno.land/[email protected]/fs/exists.ts";
 
 export interface FormatResource {
   file: string;
@@ -32,9 +33,15 @@ export function writeFormatResources(
       : [formatResources];
 
     const dependencies: FormatResourceDependency[] = files.map((file) => {
+      const absPath = join(inputDir, file);
+      if (!existsSync(absPath)) {
+        throw new Error(
+          `The referenced format resource '${file}' does not exist.`,
+        );
+      }
       return {
         type: kFormatResources,
-        content: { file: join(inputDir, file) },
+        content: { file: absPath },
       };
     });
     appendDependencies(dependenciesFile, dependencies);