From cf210adfd3553a4f784e85950293f6129c82a2a4 Mon Sep 17 00:00:00 2001
From: youdie006 <xncb135@korea.ac.kr>
Date: Tue, 18 Aug 2026 14:33:18 +0900
Subject: [PATCH] fix: singularize/pluralize regular -s nouns like gas/lens

singularize() applies its rules first-match, front-to-back. For the small
class of regular nouns whose singular already ends in -s and whose plural
adds -es (gas/gases, lens/lenses), no -es rule matches, so the word falls
through to the generic tail rule /s$/ -> '' and gets over-stripped
(gases -> gase, lenses -> lense). The same generic rule also mangles the
already-singular form (gas -> ga), breaking the singularize(pluralize(x))
=== x round-trip.

Add start-anchored, bidirectional rules for the safe -s -> -ses class
gas|lens|bias|atlas|iris, following the existing summonses/nucleuses
convention already in the file. Anchoring ^...$ keeps the bare protect
rule from wrongly protecting words that merely end in the stem
(sagas/omegas/cameras) and keeps houses -> house / buses -> bus working.

Fixes #123.
---
 src/inflection.ts       |  6 ++++++
 test/inflection.test.ts | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/inflection.ts b/src/inflection.ts
index 0cd03c9..86528a8 100644
--- a/src/inflection.ts
+++ b/src/inflection.ts
@@ -378,6 +378,7 @@ const regex = {
     genera: new RegExp('^genera$', 'gi'),
     nuclei: new RegExp('^(nucle)i$', 'gi'),
     nucleuses: new RegExp('^(nucle)uses$', 'gi'),
+    gases: new RegExp('^(gas|lens|bias|atlas|iris)es$', 'gi'),
     ss: new RegExp('ss$', 'gi'),
     s: new RegExp('s$', 'gi'),
   },
@@ -412,6 +413,7 @@ const regex = {
     criterion: new RegExp('^(criteri)on$', 'gi'),
     genus: new RegExp('^genus$', 'gi'),
     nucleus: new RegExp('^(nucle)us$', 'gi'),
+    gas: new RegExp('^(gas|lens|bias|atlas|iris)$', 'gi'),
     s: new RegExp('s$', 'gi'),
     common: new RegExp('$', 'gi'),
   },
@@ -453,6 +455,7 @@ const pluralRules: [RegExp, string?][] = [
   [regex.plural.genera],
   [regex.plural.nuclei],
   [regex.plural.nucleuses],
+  [regex.plural.gases],
 
   // original rule
   [regex.singular.man, '$1en'],
@@ -484,6 +487,7 @@ const pluralRules: [RegExp, string?][] = [
   [regex.singular.criterion, '$1a'],
   [regex.singular.genus, 'genera'],
   [regex.singular.nucleus, '$1i'],
+  [regex.singular.gas, '$1es'],
 
   [regex.singular.s, 's'],
   [regex.singular.common, 's'],
@@ -522,6 +526,7 @@ const singularRules: [RegExp, string?][] = [
   [regex.singular.criterion],
   [regex.singular.genus],
   [regex.singular.nucleus],
+  [regex.singular.gas],
 
   // original rule
   [regex.plural.men, '$1an'],
@@ -560,6 +565,7 @@ const singularRules: [RegExp, string?][] = [
   [regex.plural.geese, 'goose'],
   [regex.plural.quizzes, '$1'],
   [regex.plural.whereases, '$1'],
+  [regex.plural.gases, '$1'],
 
   [regex.plural.ss, 'ss'],
   [regex.plural.s, ''],
diff --git a/test/inflection.test.ts b/test/inflection.test.ts
index 2e0a16c..7c1031e 100644
--- a/test/inflection.test.ts
+++ b/test/inflection.test.ts
@@ -54,6 +54,10 @@ describe('test .pluralize', function () {
     expect(inflection.pluralize('nucleus')).toEqual('nuclei');
     expect(inflection.pluralize('nuclei')).toEqual('nuclei');
     expect(inflection.pluralize('nucleuses')).toEqual('nucleuses');
+    expect(inflection.pluralize('gas')).toEqual('gases');
+    expect(inflection.pluralize('gases')).toEqual('gases');
+    expect(inflection.pluralize('lens')).toEqual('lenses');
+    expect(inflection.pluralize('lenses')).toEqual('lenses');
   });
 });
 
@@ -114,6 +118,21 @@ describe('test .singularize', function () {
     expect(inflection.singularize('analyses')).toEqual('analysis');
     expect(inflection.singularize('bases')).toEqual('basis');
     expect(inflection.singularize('diagnoses')).toEqual('diagnosis');
+    // regular -s nouns whose plural ends in -ses (issue #123)
+    expect(inflection.singularize('gases')).toEqual('gas');
+    expect(inflection.singularize('lenses')).toEqual('lens');
+    expect(inflection.singularize('gas')).toEqual('gas');
+    expect(inflection.singularize('lens')).toEqual('lens');
+    // singularize(pluralize(x)) === x round-trip
+    expect(inflection.singularize(inflection.pluralize('gas'))).toEqual('gas');
+    expect(inflection.singularize(inflection.pluralize('lens'))).toEqual('lens');
+    // must not regress: -ses plurals that are not the anchored class
+    expect(inflection.singularize('houses')).toEqual('house');
+    expect(inflection.singularize('buses')).toEqual('bus');
+    // must not over-protect: bare -gas/-s words that merely end in the stem
+    expect(inflection.singularize('sagas')).toEqual('saga');
+    expect(inflection.singularize('omegas')).toEqual('omega');
+    expect(inflection.singularize('cameras')).toEqual('camera');
   });
 });