configure output (#1387)

* Add output configuration and use for version and errors * Tests passing using write/writeErr * Suppress test output on stderr using spyon * Accurately set help columns for stdout/stderr * Remove bogus file * Tidy comments * Only using single argument to write, simplify declaration to match * Add tests for configureOutput write and writeError * Add tests for configureOutput getColumns and getErrorColumns * Add error case too * Use configureOutput instead of jest.spyon for some tests * Add configureOutput to chain tests * Add set/get test for configureOutput * Rename routines with symmetrical out/err * Add outputError simple code * Add tests for outputError * Add JSDoc * Tweak wording * First cut at TypeScript * Add TypeScript sanity check for configureOutput * Add example for configureOutput * Add configureOutput to README * Make example in README a little clearer
tj · Nov 17, 2020 · ed7f13e · ed7f13e
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diff --git a/Readme.md b/Readme.md
@@ -41,7 +41,7 @@ Read this in other languages: English | [简体中文](./Readme_zh-CN.md)
     - [Import into ECMAScript Module](#import-into-ecmascript-module)
     - [Node options such as `--harmony`](#node-options-such-as---harmony)
     - [Debugging stand-alone executable subcommands](#debugging-stand-alone-executable-subcommands)
-    - [Override exit handling](#override-exit-handling)
+    - [Override exit and output handling](#override-exit-and-output-handling)
     - [Additional documentation](#additional-documentation)
   - [Examples](#examples)
   - [Support](#support)
@@ -772,7 +772,7 @@ the inspector port is incremented by 1 for the spawned subcommand.
 
 If you are using VSCode to debug executable subcommands you need to set the `"autoAttachChildProcesses": true` flag in your launch.json configuration.
 
-### Override exit handling
+### Override exit and output handling
 
 By default Commander calls `process.exit` when it detects errors, or after displaying the help or version. You can override
 this behaviour and optionally supply a callback. The default override throws a `CommanderError`.
@@ -790,6 +790,28 @@ try {
 }
 ```
 
+By default Commander is configured for a command-line application and writes to stdout and stderr.
+You can modify this behaviour for custom applications. In addition, you can modify the display of error messages.
+
+Example file: [configure-output.js](./examples/configure-output.js)
+
+
+```js
+function errorColor(str) {
+  // Add ANSI escape codes to display text in red.
+  return `\x1b[31m${str}\x1b[0m`;
+}
+
+program
+  .configureOutput({
+    // Visibly override write routines as example!
+    writeOut: (str) => process.stdout.write(`[OUT] ${str}`),
+    writeErr: (str) => process.stdout.write(`[ERR] ${str}`),
+    // Highlight errors in color.
+    outputError: (str, write) => write(errorColor(str))
+  });
+```
+
 ### Additional documentation
 
 There is more information available about:

diff --git a/examples/configure-output.js b/examples/configure-output.js
@@ -0,0 +1,31 @@
+// const commander = require('commander'); // (normal include)
+const commander = require('../'); // include commander in git clone of commander repo
+
+const program = new commander.Command();
+
+function errorColor(str) {
+  // Add ANSI escape codes to display text in red.
+  return `\x1b[31m${str}\x1b[0m`;
+}
+
+program
+  .configureOutput({
+    // Visibly override write routines as example!
+    writeOut: (str) => process.stdout.write(`[OUT] ${str}`),
+    writeErr: (str) => process.stdout.write(`[ERR] ${str}`),
+    // Output errors in red.
+    outputError: (str, write) => write(errorColor(str))
+  });
+
+program
+  .version('1.2.3')
+  .option('-c, --compress')
+  .command('sub-command');
+
+program.parse();
+
+// Try the following:
+//  node configure-output.js --version
+//  node configure-output.js --unknown
+//  node configure-output.js --help
+//  node configure-output.js
diff --git a/index.js b/index.js
@@ -12,7 +12,7 @@ const fs = require('fs');
 // Although this is a class, methods are static in style to allow override using subclass or just functions.
 class Help {
   constructor() {
-    this.columns = process.stdout.columns || 80;
+    this.columns = undefined;
     this.sortSubcommands = false;
     this.sortOptions = false;
   }
@@ -243,7 +243,7 @@ class Help {
 
   formatHelp(cmd, helper) {
     const termWidth = helper.padWidth(cmd, helper);
-    const columns = helper.columns;
+    const columns = helper.columns || 80;
     const itemIndentWidth = 2;
     const itemSeparatorWidth = 2;
     // itemIndent term itemSeparator description
@@ -543,6 +543,15 @@ class Command extends EventEmitter {
     this._description = '';
     this._argsDescription = undefined;
 
+    // see .configureOutput() for docs
+    this._outputConfiguration = {
+      writeOut: (str) => process.stdout.write(str),
+      writeErr: (str) => process.stderr.write(str),
+      getOutColumns: () => process.stdout.isTTY ? process.stdout.columns : undefined,
+      getErrColumns: () => process.stderr.isTTY ? process.stderr.columns : undefined,
+      outputError: (str, write) => write(str)
+    };
+
     this._hidden = false;
     this._hasHelpOption = true;
     this._helpFlags = '-h, --help';
@@ -663,6 +672,32 @@ class Command extends EventEmitter {
     return this;
   }
 
+  /**
+   * The default output goes to stdout and stderr. You can customise this for special
+   * applications. You can also customise the display of errors by overriding outputError.
+   *
+   * The configuration properties are all functions:
+   *
+   *    // functions to change where being written, stdout and stderr
+   *    writeOut(str)
+   *    writeErr(str)
+   *    // matching functions to specify columns for wrapping help
+   *    getOutColumns()
+   *    getErrColumns()
+   *    // functions based on what is being written out
+   *    outputError(str, write) // used for displaying errors, and not used for displaying help
+   *
+   * @param {Object} [configuration] - configuration options
+   * @return {Command|Object} `this` command for chaining, or stored configuration
+   */
+
+  configureOutput(configuration) {
+    if (configuration === undefined) return this._outputConfiguration;
+
+    Object.assign(this._outputConfiguration, configuration);
+    return this;
+  }
+
   /**
    * Add a prepared subcommand.
    *
@@ -968,8 +1003,7 @@ Read more on https://git.io/JJc0W`);
           val = option.parseArg(val, oldValue === undefined ? defaultValue : oldValue);
         } catch (err) {
           if (err.code === 'commander.optionArgumentRejected') {
-            console.error(err.message);
-            this._exit(err.exitCode, err.code, err.message);
+            this._displayError(err.exitCode, err.code, err.message);
           }
           throw err;
         }
@@ -1639,6 +1673,16 @@ Read more on https://git.io/JJc0W`);
     return this._optionValues;
   };
 
+  /**
+   * Internal bottleneck for handling of parsing errors.
+   *
+   * @api private
+   */
+  _displayError(exitCode, code, message) {
+    this._outputConfiguration.outputError(`${message}\n`, this._outputConfiguration.writeErr);
+    this._exit(exitCode, code, message);
+  }
+
   /**
    * Argument `name` is missing.
    *
@@ -1648,8 +1692,7 @@ Read more on https://git.io/JJc0W`);
 
   missingArgument(name) {
     const message = `error: missing required argument '${name}'`;
-    console.error(message);
-    this._exit(1, 'commander.missingArgument', message);
+    this._displayError(1, 'commander.missingArgument', message);
   };
 
   /**
@@ -1667,8 +1710,7 @@ Read more on https://git.io/JJc0W`);
     } else {
       message = `error: option '${option.flags}' argument missing`;
     }
-    console.error(message);
-    this._exit(1, 'commander.optionMissingArgument', message);
+    this._displayError(1, 'commander.optionMissingArgument', message);
   };
 
   /**
@@ -1680,8 +1722,7 @@ Read more on https://git.io/JJc0W`);
 
   missingMandatoryOptionValue(option) {
     const message = `error: required option '${option.flags}' not specified`;
-    console.error(message);
-    this._exit(1, 'commander.missingMandatoryOptionValue', message);
+    this._displayError(1, 'commander.missingMandatoryOptionValue', message);
   };
 
   /**
@@ -1694,8 +1735,7 @@ Read more on https://git.io/JJc0W`);
   unknownOption(flag) {
     if (this._allowUnknownOption) return;
     const message = `error: unknown option '${flag}'`;
-    console.error(message);
-    this._exit(1, 'commander.unknownOption', message);
+    this._displayError(1, 'commander.unknownOption', message);
   };
 
   /**
@@ -1712,8 +1752,7 @@ Read more on https://git.io/JJc0W`);
     const fullCommand = partCommands.join(' ');
     const message = `error: unknown command '${this.args[0]}'.` +
       (this._hasHelpOption ? ` See '${fullCommand} ${this._helpLongFlag}'.` : '');
-    console.error(message);
-    this._exit(1, 'commander.unknownCommand', message);
+    this._displayError(1, 'commander.unknownCommand', message);
   };
 
   /**
@@ -1739,7 +1778,7 @@ Read more on https://git.io/JJc0W`);
     this._versionOptionName = versionOption.attributeName();
     this.options.push(versionOption);
     this.on('option:' + versionOption.name(), () => {
-      process.stdout.write(str + '\n');
+      this._outputConfiguration.writeOut(`${str}\n`);
       this._exit(0, 'commander.version', str);
     });
     return this;
@@ -1841,11 +1880,15 @@ Read more on https://git.io/JJc0W`);
   /**
    * Return program help documentation.
    *
+   * @param {{ error: boolean }} [contextOptions] - pass {error:true} to wrap for stderr instead of stdout
    * @return {string}
    */
 
-  helpInformation() {
+  helpInformation(contextOptions) {
     const helper = this.createHelp();
+    if (helper.columns === undefined) {
+      helper.columns = (contextOptions && contextOptions.error) ? this._outputConfiguration.getErrColumns() : this._outputConfiguration.getOutColumns();
+    }
     return helper.formatHelp(this, helper);
   };
 
@@ -1858,9 +1901,9 @@ Read more on https://git.io/JJc0W`);
     const context = { error: !!contextOptions.error };
     let write;
     if (context.error) {
-      write = (arg, ...args) => process.stderr.write(arg, ...args);
+      write = (arg) => this._outputConfiguration.writeErr(arg);
     } else {
-      write = (arg, ...args) => process.stdout.write(arg, ...args);
+      write = (arg) => this._outputConfiguration.writeOut(arg);
     }
     context.write = contextOptions.write || write;
     context.command = this;
@@ -1893,7 +1936,7 @@ Read more on https://git.io/JJc0W`);
     groupListeners.slice().reverse().forEach(command => command.emit('beforeAllHelp', context));
     this.emit('beforeHelp', context);
 
-    let helpInformation = this.helpInformation();
+    let helpInformation = this.helpInformation(context);
     if (deprecatedCallback) {
       helpInformation = deprecatedCallback(helpInformation);
       if (typeof helpInformation !== 'string' && !Buffer.isBuffer(helpInformation)) {

diff --git a/tests/args.variadic.test.js b/tests/args.variadic.test.js
@@ -3,21 +3,6 @@ const commander = require('../');
 // Testing variadic arguments. Testing all the action arguments, but could test just variadicArg.
 
 describe('variadic argument', () => {
-  // Optional. Use internal knowledge to suppress output to keep test output clean.
-  let consoleErrorSpy;
-
-  beforeAll(() => {
-    consoleErrorSpy = jest.spyOn(console, 'error').mockImplementation(() => { });
-  });
-
-  afterEach(() => {
-    consoleErrorSpy.mockClear();
-  });
-
-  afterAll(() => {
-    consoleErrorSpy.mockRestore();
-  });
-
   test('when no extra arguments specified for program then variadic arg is empty array', () => {
     const actionMock = jest.fn();
     const program = new commander.Command();

diff --git a/tests/command.action.test.js b/tests/command.action.test.js
@@ -46,19 +46,17 @@ test('when .action on program with required argument and argument supplied then
 });
 
 test('when .action on program with required argument and argument not supplied then action not called', () => {
-  // Optional. Use internal knowledge to suppress output to keep test output clean.
-  const consoleErrorSpy = jest.spyOn(console, 'error').mockImplementation(() => { });
   const actionMock = jest.fn();
   const program = new commander.Command();
   program
     .exitOverride()
+    .configureOutput({ writeErr: () => {} })
     .arguments('<file>')
     .action(actionMock);
   expect(() => {
     program.parse(['node', 'test']);
   }).toThrow();
   expect(actionMock).not.toHaveBeenCalled();
-  consoleErrorSpy.mockRestore();
 });
 
 // Changes made in #729 to call program action handler

diff --git a/tests/command.allowUnknownOption.test.js b/tests/command.allowUnknownOption.test.js
@@ -4,18 +4,18 @@ const commander = require('../');
 
 describe('allowUnknownOption', () => {
   // Optional. Use internal knowledge to suppress output to keep test output clean.
-  let consoleErrorSpy;
+  let writeErrorSpy;
 
   beforeAll(() => {
-    consoleErrorSpy = jest.spyOn(console, 'error').mockImplementation(() => { });
+    writeErrorSpy = jest.spyOn(process.stderr, 'write').mockImplementation(() => { });
   });
 
   afterEach(() => {
-    consoleErrorSpy.mockClear();
+    writeErrorSpy.mockClear();
   });
 
   afterAll(() => {
-    consoleErrorSpy.mockRestore();
+    writeErrorSpy.mockRestore();
   });
 
   test('when specify unknown program option then error', () => {

diff --git a/tests/command.chain.test.js b/tests/command.chain.test.js
@@ -135,4 +135,10 @@ describe('Command methods that should return this for chaining', () => {
     const result = program.configureHelp({ });
     expect(result).toBe(program);
   });
+
+  test('when call .configureOutput() then returns this', () => {
+    const program = new Command();
+    const result = program.configureOutput({ });
+    expect(result).toBe(program);
+  });
 });