Missing prettier config silently ignored

[duncanbeevers]

Currently, when specifying --prettier-config <FILE>, no complaint is made if <FILE> doesn't exist.
Instead, a fallback prettier config is silently used.

I came across this behavior while refining specs for #890
Many of these specs specific a --prettier-config but end up using this fallback behavior.

I began work on enforcing the existence of this config file, if specified, but since it breaks so many existing specs I figured I'd put on the brakes and ask whether this is intentional behavior, and to see what you'd like to do about it.

Enforcement

diff --git a/src/index.ts b/src/index.ts
index 5d67142..3f45ffc 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,5 +1,6 @@
 import type { GlobalContext, OpenAPI2, OpenAPI3, SchemaObject, SwaggerToTSOptions } from "./types.js";
 import path from "path";
+import fs from "fs";
 import prettier from "prettier";
 import parserTypescript from "prettier/parser-typescript.js";
 import { Readable } from "stream";
@@ -115,7 +116,9 @@ async function openapiTS(
   };
   if (options && options.prettierConfig) {
     try {
-      const userOptions = await prettier.resolveConfig(path.resolve(process.cwd(), options.prettierConfig));
+      const prettierConfigFile = path.resolve(process.cwd(), options.prettierConfig);
+      await fs.promises.access(prettierConfigFile, fs.constants.F_OK);
+      const userOptions = await prettier.resolveConfig(prettierConfigFile);
       prettierOptions = {
         ...(userOptions || {}),
         ...prettierOptions,