Add prefix output

README.md

@@ -855,6 +855,7 @@ The following environment variables affect the behavior of Wireit:
 | `CI`                    | Affects the default value of `WIREIT_CACHE`.<br><br>Automatically set to `true` by [GitHub Actions](https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables) and most other CI (continuous integration) services.<br><br>Must be exactly `true`. If unset or any other value, interpreted as `false`.                                                                                                                                                                                                                                                                                                                                                              |
 | `WIREIT_MAX_OPEN_FILES` | Limits the number of file descriptors Wireit will have open concurrently. Prevents resource exhaustion when checking large numbers of cached files. Set to a lower number if you hit file descriptor limits.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
 | `WIREIT_LOGGER`         | How to present progress and results on the command line.<br><br>Options:<br><ul><li>`quiet` (default): writes a single dynamically updating line summarizing progress. Only passes along stdout and stderr from commands if there's a failure, or if the command is a service. The planned new default, please try it out.</li><li>`simple` (default): A verbose logger that presents clear information about the work that Wireit is doing.</li><li>`metrics`: Like `simple`, but also presents a summary table of results once a command is finished.</li><li>`quiet-ci` (default when env.CI or !stdout.isTTY): like `quiet` but optimized for non-interactive environments, like GitHub Actions runners.</li></ul> |
+| `WIREIT_LOGGER_PREFIX` | When this env variable is present and not empty, Wireit will prefix each stdout and stderr line from the script with its name. |
 
 ### Glob patterns
 

src/logging/default-logger.ts

@@ -7,7 +7,7 @@
 import * as pathlib from 'path';
 import {unreachable} from '../util/unreachable.js';
 
-import type {Event} from '../event.js';
+import type {Event, Stderr, Stdout} from '../event.js';
 import type {Logger, Console} from './logger.js';
 import {type PackageReference, type ScriptReference} from '../config.js';
 import {DiagnosticPrinter} from '../error.js';
@@ -42,6 +42,8 @@ export class DefaultLogger implements Logger {
   readonly console: Console;
   readonly #diagnosticPrinter: DiagnosticPrinter;
 
+  private outputWrite: typeof DefaultLogger.prototype.outputWriteDebug;
+
   /**
    * @param rootPackage The npm package directory that the root script being
    * executed belongs to.
@@ -50,6 +52,15 @@ export class DefaultLogger implements Logger {
     this.#rootPackageDir = rootPackage;
     this.#diagnosticPrinter = new DiagnosticPrinter(this.#rootPackageDir);
     this.console = ourConsole;
+    this.outputWrite = process.env['WIREIT_LOGGER_PREFIX'] ? this.outputWriteDebug : this.outputWriteDefault;
+  }
+
+  private outputWriteDefault(this: void, stream: NodeJS.WritableStream, event: Stdout | Stderr) {
+    stream.write(event.data);
+  }
+
+  private outputWriteDebug(this: void, stream: NodeJS.WritableStream, event: Stdout | Stderr, label: string) {
+    stream.write(event.data.toString().split('\n').map(line => line.trim() ? `[${label}] ${line}` : line).join('\n'));
   }
 
   log(event: Event) {
@@ -222,11 +233,11 @@ export class DefaultLogger implements Logger {
           // TODO(aomarks) More advanced handling of output streams so that
           // output isn't simply interweaved.
           case 'stdout': {
-            this.console.stdout.write(event.data);
+            this.outputWrite(this.console.stdout, event, label);
             break;
           }
           case 'stderr': {
-            this.console.stderr.write(event.data);
+            this.outputWrite(this.console.stderr, event, label);
             break;
           }
         }

src/logging/quiet/run-tracker.ts

@@ -600,6 +600,13 @@ export class QuietRunLogger implements Disposable {
     return state.hasBufferedOutput;
   }
 
+  private outputWrite = process.env['WIREIT_LOGGER_PREFIX'] ? (stream: NodeJS.WritableStream, output: Output) => {
+    const label = labelForScript(this.#rootPackage, output.script);
+    stream.write(output.data.toString().split('\n').map(line => line.trim() ? `[${label}] ${line}` : line).join('\n'));
+  } : (stream: NodeJS.WritableStream, output: Output) => {
+    stream.write(output.data);
+  }
+
   #handleOutput(event: Output): StatusLineResult {
     const key = scriptReferenceToString(event.script);
     const state = this.#running.get(key);
@@ -618,9 +625,9 @@ export class QuietRunLogger implements Disposable {
       // eslint-disable-next-line @typescript-eslint/no-unused-vars
       using _pause = this.#statusLineWriter.clearUntilDisposed();
       if (event.stream === 'stdout') {
-        process.stdout.write(event.data);
+        this.outputWrite(process.stdout, event);
       } else {
-        process.stderr.write(event.data);
+        this.outputWrite(process.stderr, event);
       }
       return noChange;
     }