Suggestion for unknown command and unknown option

Readme.md

@@ -692,6 +692,18 @@ error: unknown option '--unknown'
 (add --help for additional information)
 ```
 
+You can also show suggestions after an error for an unknown command or option.
+
+```js
+program.showSuggestionAfterError();
+```
+
+```sh
+$ pizza --hepl
+error: unknown option '--hepl'
+(Did you mean --help?)
+```
+
 ### Display help from code
 
 `.help()`: display help information and exit immediately. You can optionally pass `{ error: true }` to display on stderr and exit with an error status.

lib/command.js

@@ -7,6 +7,7 @@ const { Argument, humanReadableArgName } = require('./argument.js');
 const { CommanderError } = require('./error.js');
 const { Help } = require('./help.js');
 const { Option, splitOptionFlags } = require('./option.js');
+const { suggestSimilar } = require('./suggestSimilar');
 
 // @ts-check
 
@@ -51,6 +52,7 @@ class Command extends EventEmitter {
     this._lifeCycleHooks = {}; // a hash of arrays
     /** @type {boolean | string} */
     this._showHelpAfterError = false;
+    this._showSuggestionAfterError = false;
 
     // see .configureOutput() for docs
     this._outputConfiguration = {
@@ -99,6 +101,7 @@ class Command extends EventEmitter {
     this._allowExcessArguments = sourceCommand._allowExcessArguments;
     this._enablePositionalOptions = sourceCommand._enablePositionalOptions;
     this._showHelpAfterError = sourceCommand._showHelpAfterError;
+    this._showSuggestionAfterError = sourceCommand._showSuggestionAfterError;
 
     return this;
   }
@@ -233,6 +236,17 @@ class Command extends EventEmitter {
     return this;
   }
 
+  /**
+   * Display suggestion of similar commands for unknown commands, or options for unknown options.
+   *
+   * @param {boolean} [displaySuggestion]
+   * @return {Command} `this` command for chaining
+   */
+  showSuggestionAfterError(displaySuggestion = true) {
+    this._showSuggestionAfterError = !!displaySuggestion;
+    return this;
+  }
+
   /**
    * Add a prepared subcommand.
    *
@@ -1213,6 +1227,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
         this._processArguments();
       }
     } else if (this.commands.length) {
+      checkForUnknownOptions();
       // This command has subcommands and nothing hooked up at this level, so display help (and exit).
       this.help({ error: true });
     } else {
@@ -1500,7 +1515,23 @@ Expecting one of '${allowedValues.join("', '")}'`);
 
   unknownOption(flag) {
     if (this._allowUnknownOption) return;
-    const message = `error: unknown option '${flag}'`;
+    let suggestion = '';
+
+    if (flag.startsWith('--') && this._showSuggestionAfterError) {
+      // Looping to pick up the global options too
+      let candidateFlags = [];
+      let command = this;
+      do {
+        const moreFlags = command.createHelp().visibleOptions(command)
+          .filter(option => option.long)
+          .map(option => option.long);
+        candidateFlags = candidateFlags.concat(moreFlags);
+        command = command.parent;
+      } while (command && !command._enablePositionalOptions);
+      suggestion = suggestSimilar(flag, candidateFlags);
+    }
+
+    const message = `error: unknown option '${flag}'${suggestion}`;
     this._displayError(1, 'commander.unknownOption', message);
   };
 
@@ -1528,7 +1559,20 @@ Expecting one of '${allowedValues.join("', '")}'`);
    */
 
   unknownCommand() {
-    const message = `error: unknown command '${this.args[0]}'`;
+    const unknownName = this.args[0];
+    let suggestion = '';
+
+    if (this._showSuggestionAfterError) {
+      const candidateNames = [];
+      this.createHelp().visibleCommands(this).forEach((command) => {
+        candidateNames.push(command.name());
+        // just visible alias
+        if (command.alias()) candidateNames.push(command.alias());
+      });
+      suggestion = suggestSimilar(unknownName, candidateNames);
+    }
+
+    const message = `error: unknown command '${unknownName}'${suggestion}`;
     this._displayError(1, 'commander.unknownCommand', message);
   };
 

lib/suggestSimilar.js

@@ -0,0 +1,100 @@
+const maxDistance = 3;
+
+function editDistance(a, b) {
+  // https://en.wikipedia.org/wiki/Damerau–Levenshtein_distance
+  // Calculating optimal string alignment distance, no substring is edited more than once.
+  // (Simple implementation.)
+
+  // Quick early exit, return worst case.
+  if (Math.abs(a.length - b.length) > maxDistance) return Math.max(a.length, b.length);
+
+  // distance between prefix substrings of a and b
+  const d = [];
+
+  // pure deletions turn a into empty string
+  for (let i = 0; i <= a.length; i++) {
+    d[i] = [i];
+  }
+  // pure insertions turn empty string into b
+  for (let j = 0; j <= b.length; j++) {
+    d[0][j] = j;
+  }
+
+  // fill matrix
+  for (let j = 1; j <= b.length; j++) {
+    for (let i = 1; i <= a.length; i++) {
+      let cost = 1;
+      if (a[i - 1] === b[j - 1]) {
+        cost = 0;
+      } else {
+        cost = 1;
+      }
+      d[i][j] = Math.min(
+        d[i - 1][j] + 1, // deletion
+        d[i][j - 1] + 1, // insertion
+        d[i - 1][j - 1] + cost // substitution
+      );
+      // transposition
+      if (i > 1 && j > 1 && a[i - 1] === b[j - 2] && a[i - 2] === b[j - 1]) {
+        d[i][j] = Math.min(d[i][j], d[i - 2][j - 2] + 1);
+      }
+    }
+  }
+
+  return d[a.length][b.length];
+}
+
+/**
+ * Find close matches, restricted to same number of edits.
+ *
+ * @param {string} word
+ * @param {string[]} candidates
+ * @returns {string}
+ */
+
+function suggestSimilar(word, candidates) {
+  if (!candidates || candidates.length === 0) return '';
+  // remove possible duplicates
+  candidates = Array.from(new Set(candidates));
+
+  const searchingOptions = word.startsWith('--');
+  if (searchingOptions) {
+    word = word.slice(2);
+    candidates = candidates.map(candidate => candidate.slice(2));
+  }
+
+  let similar = [];
+  let bestDistance = maxDistance;
+  const minSimilarity = 0.4;
+  candidates.forEach((candidate) => {
+    if (candidate.length <= 1) return; // no one character guesses
+
+    const distance = editDistance(word, candidate);
+    const length = Math.max(word.length, candidate.length);
+    const similarity = (length - distance) / length;
+    if (similarity > minSimilarity) {
+      if (distance < bestDistance) {
+        // better edit distance, throw away previous worse matches
+        bestDistance = distance;
+        similar = [candidate];
+      } else if (distance === bestDistance) {
+        similar.push(candidate);
+      }
+    }
+  });
+
+  similar.sort((a, b) => a.localeCompare(b));
+  if (searchingOptions) {
+    similar = similar.map(candidate => `--${candidate}`);
+  }
+
+  if (similar.length > 1) {
+    return `\n(Did you mean one of ${similar.join(', ')}?)`;
+  }
+  if (similar.length === 1) {
+    return `\n(Did you mean ${similar[0]}?)`;
+  }
+  return '';
+}
+
+exports.suggestSimilar = suggestSimilar;

tests/command.chain.test.js

@@ -184,6 +184,12 @@ describe('Command methods that should return this for chaining', () => {
     expect(result).toBe(program);
   });
 
+  test('when call .showSuggestionAfterError() then returns this', () => {
+    const program = new Command();
+    const result = program.showSuggestionAfterError();
+    expect(result).toBe(program);
+  });
+
   test('when call .copyInheritedSettings() then returns this', () => {
     const program = new Command();
     const cmd = new Command();

tests/command.showSuggestionAfterError.test.js

@@ -0,0 +1,50 @@
+const { Command } = require('../');
+
+function getSuggestion(program, arg) {
+  let message = '';
+  program
+    .exitOverride()
+    .configureOutput({
+      writeErr: (str) => { message = str; }
+    });
+
+  try {
+    program.parse([arg], { from: 'user' });
+  } catch (err) {
+  }
+
+  const match = message.match(/Did you mean (one of )?(.*)\?/);
+  return match ? match[2] : null;
+};
+
+test('when unknown command and showSuggestionAfterError() then show suggestion', () => {
+  const program = new Command();
+  program.showSuggestionAfterError();
+  program.command('example');
+  const suggestion = getSuggestion(program, 'exampel');
+  expect(suggestion).toBe('example');
+});
+
+test('when unknown command and showSuggestionAfterError(false) then do not show suggestion', () => {
+  const program = new Command();
+  program.showSuggestionAfterError(false);
+  program.command('example');
+  const suggestion = getSuggestion(program, 'exampel');
+  expect(suggestion).toBe(null);
+});
+
+test('when unknown option and showSuggestionAfterError() then show suggestion', () => {
+  const program = new Command();
+  program.showSuggestionAfterError();
+  program.option('--example');
+  const suggestion = getSuggestion(program, '--exampel');
+  expect(suggestion).toBe('--example');
+});
+
+test('when unknown option and showSuggestionAfterError(false) then do not show suggestion', () => {
+  const program = new Command();
+  program.showSuggestionAfterError(false);
+  program.option('--example');
+  const suggestion = getSuggestion(program, '--exampel');
+  expect(suggestion).toBe(null);
+});

tests/command.unknownOption.test.js

@@ -95,4 +95,19 @@ describe('unknownOption', () => {
     }
     expect(caughtErr.code).toBe('commander.unknownOption');
   });
+
+  test('when specify unknown global option before subcommand then error', () => {
+    const program = new commander.Command();
+    program
+      .exitOverride();
+    program.command('sub');
+
+    let caughtErr;
+    try {
+      program.parse(['--NONSENSE', 'sub'], { from: 'user' });
+    } catch (err) {
+      caughtErr = err;
+    }
+    expect(caughtErr.code).toBe('commander.unknownOption');
+  });
 });