From 45d1128447d1a540aa1193ae62e6909309736b07 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 28 Aug 2021 18:12:55 +1200
Subject: [PATCH 01/23] Proof of concept suggestion for unknown command

---
 lib/command.js  | 20 +++++++++++-
 lib/distance.js | 82 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+), 1 deletion(-)
 create mode 100644 lib/distance.js

diff --git a/lib/command.js b/lib/command.js
index 4b44f4568..4b227ce1a 100644
--- a/lib/command.js
+++ b/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 { findSimilar } = require('./distance');
 
 // @ts-check
 
@@ -1528,7 +1529,24 @@ Expecting one of '${allowedValues.join("', '")}'`);
    */
 
   unknownCommand() {
-    const message = `error: unknown command '${this.args[0]}'`;
+    const unknownName = this.args[0];
+
+    let suggestion = '';
+    // Prefer names to aliases.
+    const exactNames = [];
+    const aliasedNames = [];
+    this.commands.forEach((command) => {
+      if (command._name.length > 1) exactNames.push(command._name);
+      if (command._aliases) aliasedNames.push(...command._aliases);
+    });
+    if (this._hasImplicitHelpCommand()) exactNames.push(this._helpCommandName);
+    const candidateNames = exactNames.concat(aliasedNames);
+    const similarCommand = findSimilar(unknownName, candidateNames);
+    if (similarCommand) {
+      suggestion = `\n(Did you mean ${similarCommand}?)`;
+    }
+
+    const message = `error: unknown command '${unknownName}'${suggestion}`;
     this._displayError(1, 'commander.unknownCommand', message);
   };
 
diff --git a/lib/distance.js b/lib/distance.js
new file mode 100644
index 000000000..b8ec05193
--- /dev/null
+++ b/lib/distance.js
@@ -0,0 +1,82 @@
+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.
+  const maxDistance = 2;
+  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 best match from candidates. Take first of equal matches.
+ *
+ * @param {string} word
+ * @param {string[]} candidates
+ * @returns string | undefined
+ */
+
+function findSimilar(word, candidates) {
+  if (!word || !candidates || word.length === 1) return undefined;
+
+  let similar;
+  let bestSimilarity = 0;
+  // allow just 1 edit for short strings, 2 edits otherwise
+  let bestDistance = word.length <= 3 ? 1 : 2;
+  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 (distance < bestDistance) {
+      // better edits
+      bestDistance = distance;
+      bestSimilarity = similarity;
+      similar = candidate;
+    } else if (distance === bestDistance && similarity > bestSimilarity) {
+      // better similarity
+      bestSimilarity = similarity;
+      similar = candidate;
+    }
+  });
+
+  return similar;
+}
+
+exports.findSimilar = findSimilar;

From 764488153ace3827f1d610dfb5b8c3a591171571 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 28 Aug 2021 18:50:46 +1200
Subject: [PATCH 02/23] Leave length check to similarity test

---
 lib/command.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/command.js b/lib/command.js
index 4b227ce1a..6d49cb25f 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1536,7 +1536,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
     const exactNames = [];
     const aliasedNames = [];
     this.commands.forEach((command) => {
-      if (command._name.length > 1) exactNames.push(command._name);
+      exactNames.push(command._name);
       if (command._aliases) aliasedNames.push(...command._aliases);
     });
     if (this._hasImplicitHelpCommand()) exactNames.push(this._helpCommandName);

From 23848bcf6f690c3e97e6a100668654bf0c99f825 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 28 Aug 2021 18:50:57 +1200
Subject: [PATCH 03/23] Fix JSDoc

---
 lib/distance.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/distance.js b/lib/distance.js
index b8ec05193..fbb73c93a 100644
--- a/lib/distance.js
+++ b/lib/distance.js
@@ -48,7 +48,7 @@ function editDistance(a, b) {
  *
  * @param {string} word
  * @param {string[]} candidates
- * @returns string | undefined
+ * @returns {string | undefined}
  */
 
 function findSimilar(word, candidates) {

From eeaeae13cb53a1a2c326f372c30c2051238c3637 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 28 Aug 2021 22:28:28 +1200
Subject: [PATCH 04/23] Add tests

---
 lib/command.js                      |  2 +-
 lib/{distance.js => findSimilar.js} |  0
 tests/help.suggestion.test.js       | 64 +++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 1 deletion(-)
 rename lib/{distance.js => findSimilar.js} (100%)
 create mode 100644 tests/help.suggestion.test.js

diff --git a/lib/command.js b/lib/command.js
index 6d49cb25f..751c81ec3 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -7,7 +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 { findSimilar } = require('./distance');
+const { findSimilar } = require('./findSimilar');
 
 // @ts-check
 
diff --git a/lib/distance.js b/lib/findSimilar.js
similarity index 100%
rename from lib/distance.js
rename to lib/findSimilar.js
diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
new file mode 100644
index 000000000..c9c3c1c4c
--- /dev/null
+++ b/tests/help.suggestion.test.js
@@ -0,0 +1,64 @@
+const { Command } = require('../typings');
+
+function getSuggestion(program, arg) {
+  let message = '';
+  program.exitOverride();
+  program.configureOutput({
+    writeErr: (str) => { message = str; }
+  });
+  try {
+    program.parse([arg], { from: 'user' });
+  } catch (err) {
+  }
+
+  const match = message.match(/Did you mean (.*)\?/);
+  return match ? match[1] : null;
+};
+
+test.each([
+  ['yyy', ['zzz'], null, 'none similar'],
+  ['a', ['ab'], null, 'no suggestions for single char'],
+  ['ab', ['a'], null, 'no suggestions of single char'],
+  ['at', ['cat'], 'cat', '1 insertion'],
+  ['cat', ['at'], 'at', '1 deletion'],
+  ['bat', ['cat'], 'cat', '1 substitution'],
+  ['act', ['cat'], 'cat', '1 transposition'],
+  ['cxx', ['cat'], null, '2 edits away and short string'],
+  ['caxx', ['cart'], 'cart', '2 edits away and longer string'],
+  ['1234567xxx', ['1234567890'], null, '3 edits away is too far'],
+  ['xat', ['rat', 'cat', 'bat'], 'rat', 'first of similar possibles'],
+  ['cart', ['camb', 'cant', 'bard'], 'cant', 'closest of different edit distances'],
+  ['carte', ['crate', 'carted'], 'carted', 'most similar of same edit distances (longer)']
+])('when cli of %s and commands %j then suggest %s because %s', (arg, commandNames, expected) => {
+  const program = new Command();
+  commandNames.forEach(name => { program.command(name); });
+  const suggestion = getSuggestion(program, arg);
+  expect(suggestion).toBe(expected);
+});
+
+test('when similar single alias then suggest alias', () => {
+  const program = new Command();
+  program.command('xyz')
+    .alias('car');
+  const suggestion = getSuggestion(program, 'bar');
+  expect(suggestion).toBe('car');
+});
+
+test('when similar hidden alias then suggest alias', () => {
+  const program = new Command();
+  program.command('xyz')
+    .alias('visible')
+    .alias('silent');
+  const suggestion = getSuggestion(program, 'slent');
+  expect(suggestion).toBe('silent');
+});
+
+test('when similar command and alias then suggest command', () => {
+  const program = new Command();
+  program.command('aaaaa')
+    .alias('cat');
+  program.command('bat');
+  program.command('ccccc');
+  const suggestion = getSuggestion(program, 'mat');
+  expect(suggestion).toBe('bat');
+});

From ace325903f52244d3a4d0d949f5c29a2230ff7fc Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 28 Aug 2021 22:36:29 +1200
Subject: [PATCH 05/23] Fix import

---
 lib/findSimilar.js            | 8 ++++----
 tests/help.suggestion.test.js | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/lib/findSimilar.js b/lib/findSimilar.js
index fbb73c93a..fc57acefa 100644
--- a/lib/findSimilar.js
+++ b/lib/findSimilar.js
@@ -48,13 +48,13 @@ function editDistance(a, b) {
  *
  * @param {string} word
  * @param {string[]} candidates
- * @returns {string | undefined}
+ * @returns {string | null}
  */
 
 function findSimilar(word, candidates) {
-  if (!word || !candidates || word.length === 1) return undefined;
+  if (!word || !candidates || word.length <= 1) return null;
 
-  let similar;
+  let similar = null;
   let bestSimilarity = 0;
   // allow just 1 edit for short strings, 2 edits otherwise
   let bestDistance = word.length <= 3 ? 1 : 2;
@@ -65,7 +65,7 @@ function findSimilar(word, candidates) {
     const length = Math.max(word.length, candidate.length);
     const similarity = (length - distance) / length;
     if (distance < bestDistance) {
-      // better edits
+      // better edit distance
       bestDistance = distance;
       bestSimilarity = similarity;
       similar = candidate;
diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index c9c3c1c4c..ed04c267c 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -1,4 +1,4 @@
-const { Command } = require('../typings');
+const { Command } = require('../');
 
 function getSuggestion(program, arg) {
   let message = '';

From 28f66c739c294d18db54f22dd1902ce1bb6f3cb5 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sun, 29 Aug 2021 16:50:02 +1200
Subject: [PATCH 06/23] Offer multiple suggestions

---
 lib/command.js                | 22 ++++++++++----------
 lib/findSimilar.js            | 38 ++++++++++++++++++-----------------
 tests/help.suggestion.test.js | 27 +++++++++++++------------
 3 files changed, 45 insertions(+), 42 deletions(-)

diff --git a/lib/command.js b/lib/command.js
index 751c81ec3..99dff806a 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1530,20 +1530,20 @@ Expecting one of '${allowedValues.join("', '")}'`);
 
   unknownCommand() {
     const unknownName = this.args[0];
-
     let suggestion = '';
-    // Prefer names to aliases.
-    const exactNames = [];
-    const aliasedNames = [];
+
+    const candidateNames = [];
     this.commands.forEach((command) => {
-      exactNames.push(command._name);
-      if (command._aliases) aliasedNames.push(...command._aliases);
+      candidateNames.push(command._name);
+      const alias = command.alias(); // Just visible alias
+      if (alias) candidateNames.push(alias);
     });
-    if (this._hasImplicitHelpCommand()) exactNames.push(this._helpCommandName);
-    const candidateNames = exactNames.concat(aliasedNames);
-    const similarCommand = findSimilar(unknownName, candidateNames);
-    if (similarCommand) {
-      suggestion = `\n(Did you mean ${similarCommand}?)`;
+    if (this._hasImplicitHelpCommand()) candidateNames.push(this._helpCommandName);
+    const similarNames = findSimilar(unknownName, candidateNames);
+    if (similarNames.length > 1) {
+      suggestion = `\n(Did you mean one of ${similarNames.join(', ')}?)`;
+    } else if (similarNames.length === 1) {
+      suggestion = `\n(Did you mean ${similarNames[0]}?)`;
     }
 
     const message = `error: unknown command '${unknownName}'${suggestion}`;
diff --git a/lib/findSimilar.js b/lib/findSimilar.js
index fc57acefa..15988645f 100644
--- a/lib/findSimilar.js
+++ b/lib/findSimilar.js
@@ -1,10 +1,11 @@
+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.
-  const maxDistance = 2;
   if (Math.abs(a.length - b.length) > maxDistance) return Math.max(a.length, b.length);
 
   // distance between prefix substrings of a and b
@@ -44,38 +45,39 @@ function editDistance(a, b) {
 }
 
 /**
- * Find best match from candidates. Take first of equal matches.
+ * Find close matches, restricted to same number of edits.
  *
  * @param {string} word
  * @param {string[]} candidates
- * @returns {string | null}
+ * @returns {string[]}
  */
 
 function findSimilar(word, candidates) {
-  if (!word || !candidates || word.length <= 1) return null;
-
-  let similar = null;
-  let bestSimilarity = 0;
-  // allow just 1 edit for short strings, 2 edits otherwise
-  let bestDistance = word.length <= 3 ? 1 : 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 (distance < bestDistance) {
-      // better edit distance
-      bestDistance = distance;
-      bestSimilarity = similarity;
-      similar = candidate;
-    } else if (distance === bestDistance && similarity > bestSimilarity) {
-      // better similarity
-      bestSimilarity = similarity;
-      similar = candidate;
+    // console.error(distance, similarity, candidate);
+    if (similarity > minSimilarity) {
+      if (distance < bestDistance) {
+        // better edit distance, reset the standard
+        bestDistance = distance;
+        similar = [candidate];
+      } else if (distance === bestDistance) {
+        similar.push(candidate);
+      }
     }
   });
 
+  similar.sort((a, b) => {
+    return a.localeCompare(b);
+  });
+
   return similar;
 }
 
diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index ed04c267c..3b3f1320a 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -11,24 +11,25 @@ function getSuggestion(program, arg) {
   } catch (err) {
   }
 
-  const match = message.match(/Did you mean (.*)\?/);
-  return match ? match[1] : null;
+  const match = message.match(/Did you mean (one of )?(.*)\?/);
+  return match ? match[2] : null;
 };
 
 test.each([
   ['yyy', ['zzz'], null, 'none similar'],
-  ['a', ['ab'], null, 'no suggestions for single char'],
-  ['ab', ['a'], null, 'no suggestions of single char'],
+  ['a', ['b'], null, 'one edit away but not similar'],
+  ['a', ['ab'], 'ab', 'one edit away'],
+  ['ab', ['a'], null, 'one edit away'],
   ['at', ['cat'], 'cat', '1 insertion'],
   ['cat', ['at'], 'at', '1 deletion'],
   ['bat', ['cat'], 'cat', '1 substitution'],
   ['act', ['cat'], 'cat', '1 transposition'],
   ['cxx', ['cat'], null, '2 edits away and short string'],
   ['caxx', ['cart'], 'cart', '2 edits away and longer string'],
-  ['1234567xxx', ['1234567890'], null, '3 edits away is too far'],
-  ['xat', ['rat', 'cat', 'bat'], 'rat', 'first of similar possibles'],
-  ['cart', ['camb', 'cant', 'bard'], 'cant', 'closest of different edit distances'],
-  ['carte', ['crate', 'carted'], 'carted', 'most similar of same edit distances (longer)']
+  ['1234567', ['1234567890'], '1234567890', '3 edits away is similar for long string'],
+  ['123456', ['1234567890'], null, '4 edits is too far'],
+  ['xat', ['rat', 'cat', 'bat'], 'bat, cat, rat', 'sorted possibles'],
+  ['cart', ['camb', 'cant', 'bard'], 'cant', 'only closest of different edit distances']
 ])('when cli of %s and commands %j then suggest %s because %s', (arg, commandNames, expected) => {
   const program = new Command();
   commandNames.forEach(name => { program.command(name); });
@@ -36,7 +37,7 @@ test.each([
   expect(suggestion).toBe(expected);
 });
 
-test('when similar single alias then suggest alias', () => {
+test('when similar alias then suggest alias', () => {
   const program = new Command();
   program.command('xyz')
     .alias('car');
@@ -44,21 +45,21 @@ test('when similar single alias then suggest alias', () => {
   expect(suggestion).toBe('car');
 });
 
-test('when similar hidden alias then suggest alias', () => {
+test('when similar hidden alias then not suggested', () => {
   const program = new Command();
   program.command('xyz')
     .alias('visible')
     .alias('silent');
   const suggestion = getSuggestion(program, 'slent');
-  expect(suggestion).toBe('silent');
+  expect(suggestion).toBe(null);
 });
 
-test('when similar command and alias then suggest command', () => {
+test('when similar command and alias then suggest both', () => {
   const program = new Command();
   program.command('aaaaa')
     .alias('cat');
   program.command('bat');
   program.command('ccccc');
   const suggestion = getSuggestion(program, 'mat');
-  expect(suggestion).toBe('bat');
+  expect(suggestion).toBe('bat, cat');
 });

From 80c396605222b7bec38500c48210c79b6bcbbe6f Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sun, 29 Aug 2021 18:08:21 +1200
Subject: [PATCH 07/23] Add search for similar option

---
 lib/command.js                            | 23 +++++++++++++++-------
 lib/{findSimilar.js => suggestSimilar.js} | 24 +++++++++++++++++++----
 2 files changed, 36 insertions(+), 11 deletions(-)
 rename lib/{findSimilar.js => suggestSimilar.js} (79%)

diff --git a/lib/command.js b/lib/command.js
index 99dff806a..f667ae2e0 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -7,7 +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 { findSimilar } = require('./findSimilar');
+const { suggestSimilar } = require('./suggestSimilar');
 
 // @ts-check
 
@@ -1501,7 +1501,19 @@ Expecting one of '${allowedValues.join("', '")}'`);
 
   unknownOption(flag) {
     if (this._allowUnknownOption) return;
-    const message = `error: unknown option '${flag}'`;
+    let suggestion = '';
+
+    if (flag.startsWith('--')) {
+      const candidateFlags = this.options
+        .filter(option => option.long)
+        .map(option => option.long);
+      if (this._hasHelpOption && this._helpLongFlag) candidateFlags.push(this._helpLongFlag);
+      if (candidateFlags.length > 0) {
+        suggestion = suggestSimilar(flag, candidateFlags);
+      }
+    }
+
+    const message = `error: unknown option '${flag}'${suggestion}`;
     this._displayError(1, 'commander.unknownOption', message);
   };
 
@@ -1539,11 +1551,8 @@ Expecting one of '${allowedValues.join("', '")}'`);
       if (alias) candidateNames.push(alias);
     });
     if (this._hasImplicitHelpCommand()) candidateNames.push(this._helpCommandName);
-    const similarNames = findSimilar(unknownName, candidateNames);
-    if (similarNames.length > 1) {
-      suggestion = `\n(Did you mean one of ${similarNames.join(', ')}?)`;
-    } else if (similarNames.length === 1) {
-      suggestion = `\n(Did you mean ${similarNames[0]}?)`;
+    if (candidateNames.length > 0) {
+      suggestion = suggestSimilar(unknownName, candidateNames);
     }
 
     const message = `error: unknown command '${unknownName}'${suggestion}`;
diff --git a/lib/findSimilar.js b/lib/suggestSimilar.js
similarity index 79%
rename from lib/findSimilar.js
rename to lib/suggestSimilar.js
index 15988645f..9283bc1a0 100644
--- a/lib/findSimilar.js
+++ b/lib/suggestSimilar.js
@@ -49,10 +49,16 @@ function editDistance(a, b) {
  *
  * @param {string} word
  * @param {string[]} candidates
- * @returns {string[]}
+ * @returns {string}
  */
 
-function findSimilar(word, candidates) {
+function suggestSimilar(word, 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;
@@ -77,8 +83,18 @@ function findSimilar(word, candidates) {
   similar.sort((a, b) => {
     return 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 similar;
+  return '';
 }
 
-exports.findSimilar = findSimilar;
+exports.suggestSimilar = suggestSimilar;

From 84bde40de872e0b15d75cf387e5d01464e8a98c6 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Mon, 30 Aug 2021 20:04:28 +1200
Subject: [PATCH 08/23] Add global options to suggestions

---
 lib/command.js | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/lib/command.js b/lib/command.js
index f667ae2e0..dd8d6e360 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1504,13 +1504,18 @@ Expecting one of '${allowedValues.join("', '")}'`);
     let suggestion = '';
 
     if (flag.startsWith('--')) {
-      const candidateFlags = this.options
-        .filter(option => option.long)
-        .map(option => option.long);
-      if (this._hasHelpOption && this._helpLongFlag) candidateFlags.push(this._helpLongFlag);
-      if (candidateFlags.length > 0) {
-        suggestion = suggestSimilar(flag, candidateFlags);
-      }
+      // Looping to pick up the global options too
+      let command = this;
+      do {
+        const candidateFlags = command.options
+          .filter(option => option.long)
+          .map(option => option.long);
+        if (command._hasHelpOption && command._helpLongFlag) candidateFlags.push(command._helpLongFlag);
+        if (candidateFlags.length > 0) {
+          suggestion = suggestSimilar(flag, candidateFlags);
+        }
+        command = command.parent;
+      } while (command && !command._enablePositionalOptions);
     }
 
     const message = `error: unknown option '${flag}'${suggestion}`;

From e2524baa9163537fcb90a9abd15ed5fcb92d2fac Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Mon, 30 Aug 2021 20:06:41 +1200
Subject: [PATCH 09/23] Show unknown (global) option rather than help

---
 lib/command.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/command.js b/lib/command.js
index dd8d6e360..38de957be 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1214,6 +1214,7 @@ 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 {

From ad8874fc80b70e7332bf59ce2fa97c173e484663 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Mon, 30 Aug 2021 22:19:23 +1200
Subject: [PATCH 10/23] Add tests for help command and option suggestions

---
 tests/help.suggestion.test.js | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index 3b3f1320a..1f5515864 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -63,3 +63,38 @@ test('when similar command and alias then suggest both', () => {
   const suggestion = getSuggestion(program, 'mat');
   expect(suggestion).toBe('bat, cat');
 });
+
+test('when implicit help command then help is candidate for suggestion', () => {
+  const program = new Command();
+  program.command('sub');
+  const suggestion = getSuggestion(program, 'hepl');
+  expect(suggestion).toBe('help');
+});
+
+test('when help command disabled then not candidate for suggestion', () => {
+  const program = new Command();
+  program.addHelpCommand(false);
+  program.command('sub');
+  const suggestion = getSuggestion(program, 'hepl');
+  expect(suggestion).toBe(null);
+});
+
+test('when default help option then --help is candidate for suggestion', () => {
+  const program = new Command();
+  const suggestion = getSuggestion(program, '--hepl');
+  expect(suggestion).toBe('--help');
+});
+
+test('when custom help option then --custom-help is candidate for suggestion', () => {
+  const program = new Command();
+  program.helpOption('-H, --custom-help');
+  const suggestion = getSuggestion(program, '--custom-hepl');
+  expect(suggestion).toBe('--custom-help');
+});
+
+test('when help option disabled then not candidate for suggestion', () => {
+  const program = new Command();
+  program.helpOption(false);
+  const suggestion = getSuggestion(program, '--hepl');
+  expect(suggestion).toBe(null);
+});

From b139504327780f8627a40db2012c91bb43c656c8 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Mon, 30 Aug 2021 23:29:45 +1200
Subject: [PATCH 11/23] Fix option suggestions for subcommands, and first raft
 of tests for option suggestions

---
 lib/command.js                | 12 ++++--
 tests/help.suggestion.test.js | 79 ++++++++++++++++++++++++++++++++++-
 2 files changed, 86 insertions(+), 5 deletions(-)

diff --git a/lib/command.js b/lib/command.js
index 38de957be..ff6e190ab 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1506,17 +1506,21 @@ Expecting one of '${allowedValues.join("', '")}'`);
 
     if (flag.startsWith('--')) {
       // Looping to pick up the global options too
+      const candidateFlags = [];
+      if (this._hasHelpOption && this._helpLongFlag) candidateFlags.push(this._helpLongFlag);
       let command = this;
       do {
-        const candidateFlags = command.options
+        const moreFlags = command.options
           .filter(option => option.long)
           .map(option => option.long);
-        if (command._hasHelpOption && command._helpLongFlag) candidateFlags.push(command._helpLongFlag);
-        if (candidateFlags.length > 0) {
-          suggestion = suggestSimilar(flag, candidateFlags);
+        if (moreFlags.length > 0) {
+          candidateFlags.push(...moreFlags);
         }
         command = command.parent;
       } while (command && !command._enablePositionalOptions);
+      if (candidateFlags.length > 0) {
+        suggestion = suggestSimilar(flag, candidateFlags);
+      }
     }
 
     const message = `error: unknown option '${flag}'${suggestion}`;
diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index 1f5515864..fae0cbee7 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -7,7 +7,10 @@ function getSuggestion(program, arg) {
     writeErr: (str) => { message = str; }
   });
   try {
-    program.parse([arg], { from: 'user' });
+    // Passing in an array for a few of the tests.
+    const args = Array.isArray(arg) ? arg : [arg];
+    expect(Array.isArray(args)).toBeTruthy();
+    program.parse(args, { from: 'user' });
   } catch (err) {
   }
 
@@ -98,3 +101,77 @@ test('when help option disabled then not candidate for suggestion', () => {
   const suggestion = getSuggestion(program, '--hepl');
   expect(suggestion).toBe(null);
 });
+
+// Easy to just run same tests as for commands with cut and paste!
+// Note: length calculations disregard the leading --
+test.each([
+  ['--yyy', ['--zzz'], null, 'none similar'],
+  ['--a', ['--b'], null, 'one edit away but not similar'],
+  ['--a', ['--ab'], '--ab', 'one edit away'],
+  ['--ab', ['--a'], null, 'one edit away'],
+  ['--at', ['--cat'], '--cat', '1 insertion'],
+  ['--cat', ['--at'], '--at', '1 deletion'],
+  ['--bat', ['--cat'], '--cat', '1 substitution'],
+  ['--act', ['--cat'], '--cat', '1 transposition'],
+  ['--cxx', ['--cat'], null, '2 edits away and short string'],
+  ['--caxx', ['--cart'], '--cart', '2 edits away and longer string'],
+  ['--1234567', ['--1234567890'], '--1234567890', '3 edits away is similar for long string'],
+  ['--123456', ['--1234567890'], null, '4 edits is too far'],
+  ['--xat', ['--rat', '--cat', '--bat'], '--bat, --cat, --rat', 'sorted possibles'],
+  ['--cart', ['--camb', '--cant', '--bard'], '--cant', 'only closest of different edit distances']
+])('when cli of %s and options %j then suggest %s because %s', (arg, commandNames, expected) => {
+  const program = new Command();
+  commandNames.forEach(name => { program.option(name); });
+  const suggestion = getSuggestion(program, arg);
+  expect(suggestion).toBe(expected);
+});
+
+test('when no options then no suggestion', () => {
+  // Checking nothing blows up as much as no suggestion!
+  const program = new Command();
+  program
+    .exitOverride()
+    .helpOption(false);
+  const suggestion = getSuggestion(program, '--option');
+  expect(suggestion).toBe(null);
+});
+
+test('when subcommand option then candidate for subcommand option suggestion', () => {
+  const program = new Command();
+  program.exitOverride();
+  program.command('sub')
+    .option('-l,--local');
+  const suggestion = getSuggestion(program, ['sub', '--loca']);
+  expect(suggestion).toBe('--local');
+});
+
+test('when global option then candidate for subcommand option suggestion', () => {
+  const program = new Command();
+  program.exitOverride();
+  program.option('-g, --global');
+  program.command('sub');
+  const suggestion = getSuggestion(program, ['sub', '--globla']);
+  expect(suggestion).toBe('--global');
+});
+
+test('when global option but positionalOptions then not candidate for subcommand suggestion', () => {
+  const program = new Command();
+  program
+    .exitOverride()
+    .enablePositionalOptions();
+  program.option('-g, --global');
+  program.command('sub');
+  const suggestion = getSuggestion(program, ['sub', '--globla']);
+  expect(suggestion).toBe(null);
+});
+
+test('when global and local options then both candidates', () => {
+  const program = new Command();
+  program
+    .exitOverride();
+  program.option('--cat');
+  program.command('sub')
+    .option('--rat');
+  const suggestion = getSuggestion(program, ['sub', '--bat']);
+  expect(suggestion).toBe('--cat, --rat');
+});

From 388361ea5a7a8d7f5d7acd048a0c0728bf2714f7 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 17:27:34 +1200
Subject: [PATCH 12/23] Do not suggest hidden candidates. Remove duplicates.

---
 lib/command.js                | 22 +++++++---------------
 lib/suggestSimilar.js         | 11 ++++++-----
 tests/help.suggestion.test.js | 24 +++++++++++++++++++++++-
 3 files changed, 36 insertions(+), 21 deletions(-)

diff --git a/lib/command.js b/lib/command.js
index ff6e190ab..70e093d4f 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1506,21 +1506,16 @@ Expecting one of '${allowedValues.join("', '")}'`);
 
     if (flag.startsWith('--')) {
       // Looping to pick up the global options too
-      const candidateFlags = [];
-      if (this._hasHelpOption && this._helpLongFlag) candidateFlags.push(this._helpLongFlag);
+      let candidateFlags = [];
       let command = this;
       do {
-        const moreFlags = command.options
+        const moreFlags = command.createHelp().visibleOptions(command)
           .filter(option => option.long)
           .map(option => option.long);
-        if (moreFlags.length > 0) {
-          candidateFlags.push(...moreFlags);
-        }
+        candidateFlags = candidateFlags.concat(moreFlags);
         command = command.parent;
       } while (command && !command._enablePositionalOptions);
-      if (candidateFlags.length > 0) {
-        suggestion = suggestSimilar(flag, candidateFlags);
-      }
+      suggestion = suggestSimilar(flag, candidateFlags);
     }
 
     const message = `error: unknown option '${flag}'${suggestion}`;
@@ -1555,15 +1550,12 @@ Expecting one of '${allowedValues.join("', '")}'`);
     let suggestion = '';
 
     const candidateNames = [];
-    this.commands.forEach((command) => {
-      candidateNames.push(command._name);
+    this.createHelp().visibleCommands(this).forEach((command) => {
+      candidateNames.push(command.name());
       const alias = command.alias(); // Just visible alias
       if (alias) candidateNames.push(alias);
     });
-    if (this._hasImplicitHelpCommand()) candidateNames.push(this._helpCommandName);
-    if (candidateNames.length > 0) {
-      suggestion = suggestSimilar(unknownName, candidateNames);
-    }
+    suggestion = suggestSimilar(unknownName, candidateNames);
 
     const message = `error: unknown command '${unknownName}'${suggestion}`;
     this._displayError(1, 'commander.unknownCommand', message);
diff --git a/lib/suggestSimilar.js b/lib/suggestSimilar.js
index 9283bc1a0..f77aa4d30 100644
--- a/lib/suggestSimilar.js
+++ b/lib/suggestSimilar.js
@@ -53,6 +53,10 @@ function editDistance(a, b) {
  */
 
 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);
@@ -71,7 +75,7 @@ function suggestSimilar(word, candidates) {
     // console.error(distance, similarity, candidate);
     if (similarity > minSimilarity) {
       if (distance < bestDistance) {
-        // better edit distance, reset the standard
+        // better edit distance, throw away previous worse matches
         bestDistance = distance;
         similar = [candidate];
       } else if (distance === bestDistance) {
@@ -80,9 +84,7 @@ function suggestSimilar(word, candidates) {
     }
   });
 
-  similar.sort((a, b) => {
-    return a.localeCompare(b);
-  });
+  similar.sort((a, b) => a.localeCompare(b));
   if (searchingOptions) {
     similar = similar.map(candidate => `--${candidate}`);
   }
@@ -93,7 +95,6 @@ function suggestSimilar(word, candidates) {
   if (similar.length === 1) {
     return `\n(Did you mean ${similar[0]}?)`;
   }
-
   return '';
 }
 
diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index fae0cbee7..092cad5cf 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -1,4 +1,4 @@
-const { Command } = require('../');
+const { Command, Option } = require('../');
 
 function getSuggestion(program, arg) {
   let message = '';
@@ -175,3 +175,25 @@ test('when global and local options then both candidates', () => {
   const suggestion = getSuggestion(program, ['sub', '--bat']);
   expect(suggestion).toBe('--cat, --rat');
 });
+
+test('when command hidden then not suggested as candidate', () => {
+  const program = new Command();
+  program.command('secret', { hidden: true });
+  const suggestion = getSuggestion(program, 'secrt');
+  expect(suggestion).toBe(null);
+});
+
+test('when option hidden then not suggested as candidate', () => {
+  const program = new Command();
+  program.addOption(new Option('--secret').hideHelp());
+  const suggestion = getSuggestion(program, '--secrt');
+  expect(suggestion).toBe(null);
+});
+
+test('when may be duplicate identical candidates then only return one', () => {
+  const program = new Command();
+  program.exitOverride();
+  program.command('sub');
+  const suggestion = getSuggestion(program, ['sub', '--hepl']);
+  expect(suggestion).toBe('--help');
+});

From 511a33a78d7f3de0e39c5bae33e3ada90fd91f8d Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 17:28:22 +1200
Subject: [PATCH 13/23] Tiny comment change

---
 lib/suggestSimilar.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/suggestSimilar.js b/lib/suggestSimilar.js
index f77aa4d30..a565b6c5d 100644
--- a/lib/suggestSimilar.js
+++ b/lib/suggestSimilar.js
@@ -54,7 +54,7 @@ function editDistance(a, b) {
 
 function suggestSimilar(word, candidates) {
   if (!candidates || candidates.length === 0) return '';
-  // Remove possible duplicates
+  // remove possible duplicates
   candidates = Array.from(new Set(candidates));
 
   const searchingOptions = word.startsWith('--');

From 2cf094217604c52f480ea3dcb401f56b85bb7b40 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 17:51:33 +1200
Subject: [PATCH 14/23] Add test for fixed behaviour, unknown option before
 subcommand

---
 tests/command.unknownOption.test.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tests/command.unknownOption.test.js b/tests/command.unknownOption.test.js
index 7ab72237d..0bd4261c9 100644
--- a/tests/command.unknownOption.test.js
+++ b/tests/command.unknownOption.test.js
@@ -96,3 +96,18 @@ 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');
+});

From b3e75bdac574a19cd4eda6a50ba87489657b75be Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 18:01:52 +1200
Subject: [PATCH 15/23] Remove low value local variable

---
 lib/command.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/command.js b/lib/command.js
index 70e093d4f..91f7d9292 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -1552,8 +1552,8 @@ Expecting one of '${allowedValues.join("', '")}'`);
     const candidateNames = [];
     this.createHelp().visibleCommands(this).forEach((command) => {
       candidateNames.push(command.name());
-      const alias = command.alias(); // Just visible alias
-      if (alias) candidateNames.push(alias);
+      // just visible alias
+      if (command.alias()) candidateNames.push(command.alias());
     });
     suggestion = suggestSimilar(unknownName, candidateNames);
 

From d44669fef39e57b868e70ccead3b2ee44bb6a225 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 18:26:00 +1200
Subject: [PATCH 16/23] Suppress output from test

---
 tests/command.unknownOption.test.js | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/tests/command.unknownOption.test.js b/tests/command.unknownOption.test.js
index 0bd4261c9..608f3f148 100644
--- a/tests/command.unknownOption.test.js
+++ b/tests/command.unknownOption.test.js
@@ -95,19 +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');
+  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');
+  });
 });

From 2b0f899b7627b62bfe746909a4337ed293333ccd Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 19:19:58 +1200
Subject: [PATCH 17/23] Add showSuggestionAfterError

---
 lib/command.js                                | 31 +++++++++---
 tests/command.chain.test.js                   |  6 +++
 .../command.showSuggestionAfterError.test.js  | 50 +++++++++++++++++++
 tests/help.suggestion.test.js                 | 25 +++++-----
 typings/index.d.ts                            |  7 ++-
 typings/index.test-d.ts                       |  4 ++
 6 files changed, 102 insertions(+), 21 deletions(-)
 create mode 100644 tests/command.showSuggestionAfterError.test.js

diff --git a/lib/command.js b/lib/command.js
index 91f7d9292..47c3bfd3f 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -52,6 +52,7 @@ class Command extends EventEmitter {
     this._lifeCycleHooks = {}; // a hash of arrays
     /** @type {boolean | string} */
     this._showHelpAfterError = false;
+    this._showSuggestionAfterError = true;
 
     // see .configureOutput() for docs
     this._outputConfiguration = {
@@ -100,6 +101,7 @@ class Command extends EventEmitter {
     this._allowExcessArguments = sourceCommand._allowExcessArguments;
     this._enablePositionalOptions = sourceCommand._enablePositionalOptions;
     this._showHelpAfterError = sourceCommand._showHelpAfterError;
+    this._showSuggestionAfterError = sourceCommand._showSuggestionAfterError;
 
     return this;
   }
@@ -234,6 +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.
    *
@@ -1504,7 +1517,7 @@ Expecting one of '${allowedValues.join("', '")}'`);
     if (this._allowUnknownOption) return;
     let suggestion = '';
 
-    if (flag.startsWith('--')) {
+    if (flag.startsWith('--') && this._showSuggestionAfterError) {
       // Looping to pick up the global options too
       let candidateFlags = [];
       let command = this;
@@ -1549,13 +1562,15 @@ Expecting one of '${allowedValues.join("', '")}'`);
     const unknownName = this.args[0];
     let suggestion = '';
 
-    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);
+    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);
diff --git a/tests/command.chain.test.js b/tests/command.chain.test.js
index e80c2b292..09fc6e5a3 100644
--- a/tests/command.chain.test.js
+++ b/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();
diff --git a/tests/command.showSuggestionAfterError.test.js b/tests/command.showSuggestionAfterError.test.js
new file mode 100644
index 000000000..76f379355
--- /dev/null
+++ b/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);
+});
diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index 092cad5cf..7c9fdbd18 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -1,15 +1,23 @@
 const { Command, Option } = require('../');
 
+// Note: setting up shared command configuration in getSuggestion,
+// and looking for possible subcommand 'sub'.
+
 function getSuggestion(program, arg) {
   let message = '';
-  program.exitOverride();
-  program.configureOutput({
-    writeErr: (str) => { message = str; }
-  });
+  program
+    .showSuggestionAfterError() // make sure on
+    .exitOverride()
+    .configureOutput({
+      writeErr: (str) => { message = str; }
+    });
+  // Do the same setup for subcommand.
+  const sub = program._findCommand('sub');
+  if (sub) sub.copyInheritedSettings(program);
+
   try {
     // Passing in an array for a few of the tests.
     const args = Array.isArray(arg) ? arg : [arg];
-    expect(Array.isArray(args)).toBeTruthy();
     program.parse(args, { from: 'user' });
   } catch (err) {
   }
@@ -130,7 +138,6 @@ test('when no options then no suggestion', () => {
   // Checking nothing blows up as much as no suggestion!
   const program = new Command();
   program
-    .exitOverride()
     .helpOption(false);
   const suggestion = getSuggestion(program, '--option');
   expect(suggestion).toBe(null);
@@ -138,7 +145,6 @@ test('when no options then no suggestion', () => {
 
 test('when subcommand option then candidate for subcommand option suggestion', () => {
   const program = new Command();
-  program.exitOverride();
   program.command('sub')
     .option('-l,--local');
   const suggestion = getSuggestion(program, ['sub', '--loca']);
@@ -147,7 +153,6 @@ test('when subcommand option then candidate for subcommand option suggestion', (
 
 test('when global option then candidate for subcommand option suggestion', () => {
   const program = new Command();
-  program.exitOverride();
   program.option('-g, --global');
   program.command('sub');
   const suggestion = getSuggestion(program, ['sub', '--globla']);
@@ -157,7 +162,6 @@ test('when global option then candidate for subcommand option suggestion', () =>
 test('when global option but positionalOptions then not candidate for subcommand suggestion', () => {
   const program = new Command();
   program
-    .exitOverride()
     .enablePositionalOptions();
   program.option('-g, --global');
   program.command('sub');
@@ -167,8 +171,6 @@ test('when global option but positionalOptions then not candidate for subcommand
 
 test('when global and local options then both candidates', () => {
   const program = new Command();
-  program
-    .exitOverride();
   program.option('--cat');
   program.command('sub')
     .option('--rat');
@@ -192,7 +194,6 @@ test('when option hidden then not suggested as candidate', () => {
 
 test('when may be duplicate identical candidates then only return one', () => {
   const program = new Command();
-  program.exitOverride();
   program.command('sub');
   const suggestion = getSuggestion(program, ['sub', '--hepl']);
   expect(suggestion).toBe('--help');
diff --git a/typings/index.d.ts b/typings/index.d.ts
index 725764b6a..43eeae563 100644
--- a/typings/index.d.ts
+++ b/typings/index.d.ts
@@ -412,7 +412,7 @@ export class Command {
    *
    * (Used internally when adding a command using `.command()` so subcommands inherit parent settings.)
    */
-   copyInheritedSettings(sourceCommand: Command): this;
+  copyInheritedSettings(sourceCommand: Command): this;
 
   /**
    * Display the help or a custom message after an error occurs.
@@ -420,6 +420,11 @@ export class Command {
   showHelpAfterError(displayHelp?: boolean | string): this;
 
   /**
+   * Display suggestion of similar commands for unknown commands, or options for unknown options.
+   */
+  showSuggestionAfterError(displaySuggestion?: boolean): this;
+
+   /**
    * Register callback `fn` for the command.
    *
    * @example
diff --git a/typings/index.test-d.ts b/typings/index.test-d.ts
index d37a0e386..ba1051092 100644
--- a/typings/index.test-d.ts
+++ b/typings/index.test-d.ts
@@ -293,6 +293,10 @@ expectType<commander.Command>(program.showHelpAfterError());
 expectType<commander.Command>(program.showHelpAfterError(true));
 expectType<commander.Command>(program.showHelpAfterError('See --help'));
 
+// showSuggestionAfterError
+expectType<commander.Command>(program.showSuggestionAfterError());
+expectType<commander.Command>(program.showSuggestionAfterError(false));
+
 // configureOutput
 expectType<commander.Command>(program.configureOutput({ }));
 expectType<commander.OutputConfiguration>(program.configureOutput());

From cb931b001692cf67f4cc59d44b19fa5aa0f7fffd Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Tue, 31 Aug 2021 19:27:02 +1200
Subject: [PATCH 18/23] Fix arg for parse

---
 tests/command.showSuggestionAfterError.test.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/command.showSuggestionAfterError.test.js b/tests/command.showSuggestionAfterError.test.js
index 76f379355..2e596f408 100644
--- a/tests/command.showSuggestionAfterError.test.js
+++ b/tests/command.showSuggestionAfterError.test.js
@@ -9,7 +9,7 @@ function getSuggestion(program, arg) {
     });
 
   try {
-    program.parse(arg, { from: 'user' });
+    program.parse([arg], { from: 'user' });
   } catch (err) {
   }
 

From 30bd2d2eed061f09dc6ae1f39890e9a154dc9fd5 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 4 Sep 2021 10:14:42 +1200
Subject: [PATCH 19/23] Suggestions off by default for now

---
 lib/command.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/command.js b/lib/command.js
index 47c3bfd3f..184bc0b79 100644
--- a/lib/command.js
+++ b/lib/command.js
@@ -52,7 +52,7 @@ class Command extends EventEmitter {
     this._lifeCycleHooks = {}; // a hash of arrays
     /** @type {boolean | string} */
     this._showHelpAfterError = false;
-    this._showSuggestionAfterError = true;
+    this._showSuggestionAfterError = false;
 
     // see .configureOutput() for docs
     this._outputConfiguration = {

From 1b151eeb81c766562a9d1a6634e35d636c6b3c53 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 4 Sep 2021 10:15:07 +1200
Subject: [PATCH 20/23] Add to README

---
 Readme.md | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Readme.md b/Readme.md
index 6e84460ce..24a324be6 100644
--- a/Readme.md
+++ b/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 unrecognised 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.

From 858aadd6392c018c4b5cadd40ac92a6f8ae5ab08 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 4 Sep 2021 10:21:50 +1200
Subject: [PATCH 21/23] Remove development trace statement

---
 lib/suggestSimilar.js | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/suggestSimilar.js b/lib/suggestSimilar.js
index a565b6c5d..9a4066c71 100644
--- a/lib/suggestSimilar.js
+++ b/lib/suggestSimilar.js
@@ -72,7 +72,6 @@ function suggestSimilar(word, candidates) {
     const distance = editDistance(word, candidate);
     const length = Math.max(word.length, candidate.length);
     const similarity = (length - distance) / length;
-    // console.error(distance, similarity, candidate);
     if (similarity > minSimilarity) {
       if (distance < bestDistance) {
         // better edit distance, throw away previous worse matches

From 4529eb4bd92a302bb5135cc34a02da67686cc40c Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 4 Sep 2021 10:56:53 +1200
Subject: [PATCH 22/23] Describe scenario using same terms as error

---
 Readme.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Readme.md b/Readme.md
index 24a324be6..a43dfc058 100644
--- a/Readme.md
+++ b/Readme.md
@@ -692,7 +692,7 @@ error: unknown option '--unknown'
 (add --help for additional information)
 ```
 
-You can also show suggestions after an error for an unrecognised command or option.
+You can also show suggestions after an error for an unknown command or option.
 
 ```js
 program.showSuggestionAfterError();

From fbed16758dc9498e1a7a23280dcb9905ebaf0154 Mon Sep 17 00:00:00 2001
From: John Gee <john@ruru.gen.nz>
Date: Sat, 4 Sep 2021 14:34:30 +1200
Subject: [PATCH 23/23] Add test that command:* listener blocks command
 suggestion

---
 tests/help.suggestion.test.js | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tests/help.suggestion.test.js b/tests/help.suggestion.test.js
index 7c9fdbd18..711eb1411 100644
--- a/tests/help.suggestion.test.js
+++ b/tests/help.suggestion.test.js
@@ -110,6 +110,16 @@ test('when help option disabled then not candidate for suggestion', () => {
   expect(suggestion).toBe(null);
 });
 
+test('when command:* listener and unknown command then no suggestion', () => {
+  // Because one use for command:* was to handle unknown commands.
+  // Listener actually stops error being thrown, but we just care about affect on suggestion in this test.
+  const program = new Command();
+  program.on('command:*', () => {});
+  program.command('rat');
+  const suggestion = getSuggestion(program, 'cat');
+  expect(suggestion).toBe(null);
+});
+
 // Easy to just run same tests as for commands with cut and paste!
 // Note: length calculations disregard the leading --
 test.each([