loader: Set default 'pretty' option properly

Set the default `options.pretty` value based on stderr rather than
stdout, as this is where errors are printed.

The loader thread does not get a process.stderr.isTTY set, because its
"stderr" is actually a pipe. If `options.pretty` is not set explicitly,
the GlobalPreload's `context.port` is used to send a message from the
main thread indicating the state of stderr.isTTY.

Adds `Service.setPrettyErrors` method to enable setting this value when
needed.

Author: isaacs

src/esm.ts

@@ -4,6 +4,7 @@ import { extname, resolve as pathResolve } from 'path';
 import * as assert from 'assert';
 import { normalizeSlashes, versionGteLt } from './util';
 import { createRequire } from 'module';
+import type { MessagePort } from 'worker_threads';
 
 // Note: On Windows, URLs look like this: file:///D:/dev/@TypeStrong/ts-node-examples/foo.ts
 
@@ -75,7 +76,7 @@ export namespace NodeLoaderHooksAPI2 {
   export interface NodeImportAssertions {
     type?: 'json';
   }
-  export type GlobalPreloadHook = () => string;
+  export type GlobalPreloadHook = (context?: { port: MessagePort }) => string;
 }
 
 export type NodeLoaderHooksFormat = 'builtin' | 'commonjs' | 'dynamic' | 'json' | 'module' | 'wasm';
@@ -123,10 +124,29 @@ export function createEsmHooks(tsNodeService: Service) {
     globalPreload: useLoaderThread ? globalPreload : undefined,
   });
 
-  function globalPreload() {
+  function globalPreload({ port }: { port?: MessagePort } = {}) {
+    // The loader thread doesn't get process.stderr.isTTY properly,
+    // so this signal lets us infer it based on the state of the main
+    // thread, but only relevant if options.pretty is unset.
+    let stderrTTYSignal: string;
+    if (tsNodeService.options.pretty === undefined) {
+      port?.on('message', (data) => {
+        if (data?.stderrIsTTY) {
+          tsNodeService.setPrettyErrors(true);
+        }
+      });
+      stderrTTYSignal = `
+        port.postMessage({
+          stderrIsTTY: !!process.stderr.isTTY
+        });
+      `;
+    } else {
+      stderrTTYSignal = '';
+    }
     return `
       const { createRequire } = getBuiltin('module');
       const require = createRequire(${JSON.stringify(__filename)});
+      ${stderrTTYSignal}
       require('./index').register();
     `;
   }

src/index.ts

@@ -480,6 +480,7 @@ export interface Service {
   ignored(fileName: string): boolean;
   compile(code: string, fileName: string, lineOffset?: number): string;
   getTypeInfo(code: string, fileName: string, position: number): TypeInfo;
+  setPrettyErrors(pretty: boolean): void;
   /** @internal */
   configFilePath: string | undefined;
   /** @internal */
@@ -719,11 +720,16 @@ export function createFromPreloadedConfig(foundConfigResult: ReturnType<typeof f
     });
   }
 
-  const shouldHavePrettyErrors = options.pretty === undefined ? process.stdout.isTTY : options.pretty;
+  let shouldHavePrettyErrors!: boolean;
+  let formatDiagnostics: (diagnostics: readonly _ts.Diagnostic[], host: _ts.FormatDiagnosticsHost) => string;
 
-  const formatDiagnostics = shouldHavePrettyErrors
-    ? ts.formatDiagnosticsWithColorAndContext || ts.formatDiagnostics
-    : ts.formatDiagnostics;
+  function setPrettyErrors(pretty: boolean) {
+    shouldHavePrettyErrors = pretty;
+    formatDiagnostics = shouldHavePrettyErrors
+      ? ts.formatDiagnosticsWithColorAndContext || ts.formatDiagnostics
+      : ts.formatDiagnostics;
+  }
+  setPrettyErrors(options.pretty !== undefined ? options.pretty : !!process.stderr.isTTY);
 
   function createTSError(diagnostics: ReadonlyArray<_ts.Diagnostic>) {
     const diagnosticText = formatDiagnostics(diagnostics, diagnosticHost);
@@ -1282,6 +1288,7 @@ export function createFromPreloadedConfig(foundConfigResult: ReturnType<typeof f
     getNodeEsmGetFormat,
     getNodeCjsLoader,
     extensions,
+    setPrettyErrors,
   };
 }