fix -masen verbs being deinflected as negative potential polite (#1046)

* test

* fix

* positive test

2 files changed, 38 insertions, 19 deletions

diff --git a/ext/js/language/ja/japanese-transforms.js b/ext/js/language/ja/japanese-transforms.js
index c8f9f671..8e7ba243 100644
--- a/ext/js/language/ja/japanese-transforms.js
+++ b/ext/js/language/ja/japanese-transforms.js
@@ -72,6 +72,21 @@ export const japaneseTransforms = {
                 },
             ],
             isDictionaryForm: true,
+            subConditions: ['v5d', 'v5m'],
+        },
+        'v5d': {
+            name: 'Godan verb, dictionary form',
+            i18n: [
+                {
+                    language: 'ja',
+                    name: '五段動詞、辞書形',
+                },
+            ],
+            isDictionaryForm: false,
+        },
+        'v5m': {
+            name: 'Godan verb, polite (masu) form',
+            isDictionaryForm: false,
         },
         'vk': {
             name: 'Kuru verb',
@@ -789,15 +804,15 @@ export const japaneseTransforms = {
             name: 'polite',
             rules: [
                 suffixInflection('ます', 'る', ['v1'], ['v1']),
-                suffixInflection('います', 'う', ['v5'], ['v5']),
-                suffixInflection('きます', 'く', ['v5'], ['v5']),
-                suffixInflection('ぎます', 'ぐ', ['v5'], ['v5']),
-                suffixInflection('します', 'す', ['v5'], ['v5']),
-                suffixInflection('ちます', 'つ', ['v5'], ['v5']),
-                suffixInflection('にます', 'ぬ', ['v5'], ['v5']),
-                suffixInflection('びます', 'ぶ', ['v5'], ['v5']),
-                suffixInflection('みます', 'む', ['v5'], ['v5']),
-                suffixInflection('ります', 'る', ['v5'], ['v5']),
+                suffixInflection('います', 'う', ['v5m'], ['v5d']),
+                suffixInflection('きます', 'く', ['v5m'], ['v5d']),
+                suffixInflection('ぎます', 'ぐ', ['v5m'], ['v5d']),
+                suffixInflection('します', 'す', ['v5m'], ['v5d']),
+                suffixInflection('ちます', 'つ', ['v5m'], ['v5d']),
+                suffixInflection('にます', 'ぬ', ['v5m'], ['v5d']),
+                suffixInflection('びます', 'ぶ', ['v5m'], ['v5d']),
+                suffixInflection('みます', 'む', ['v5m'], ['v5d']),
+                suffixInflection('ります', 'る', ['v5m'], ['v5d']),
                 suffixInflection('じます', 'ずる', ['vz'], ['vz']),
                 suffixInflection('します', 'する', ['vs'], ['vs']),
                 suffixInflection('為ます', '為る', ['vs'], ['vs']),
@@ -810,15 +825,15 @@ export const japaneseTransforms = {
         'potential': {
             name: 'potential',
             rules: [
-                suffixInflection('れる', 'る', ['v1'], ['v1', 'v5']),
-                suffixInflection('える', 'う', ['v1'], ['v5']),
-                suffixInflection('ける', 'く', ['v1'], ['v5']),
-                suffixInflection('げる', 'ぐ', ['v1'], ['v5']),
-                suffixInflection('せる', 'す', ['v1'], ['v5']),
-                suffixInflection('てる', 'つ', ['v1'], ['v5']),
-                suffixInflection('ねる', 'ぬ', ['v1'], ['v5']),
-                suffixInflection('べる', 'ぶ', ['v1'], ['v5']),
-                suffixInflection('める', 'む', ['v1'], ['v5']),
+                suffixInflection('れる', 'る', ['v1'], ['v1', 'v5d']),
+                suffixInflection('える', 'う', ['v1'], ['v5d']),
+                suffixInflection('ける', 'く', ['v1'], ['v5d']),
+                suffixInflection('げる', 'ぐ', ['v1'], ['v5d']),
+                suffixInflection('せる', 'す', ['v1'], ['v5d']),
+                suffixInflection('てる', 'つ', ['v1'], ['v5d']),
+                suffixInflection('ねる', 'ぬ', ['v1'], ['v5d']),
+                suffixInflection('べる', 'ぶ', ['v1'], ['v5d']),
+                suffixInflection('める', 'む', ['v1'], ['v5d']),
                 suffixInflection('できる', 'する', ['v1'], ['vs']),
                 suffixInflection('出来る', 'する', ['v1'], ['vs']),
                 suffixInflection('これる', 'くる', ['v1'], ['vk']),
diff --git a/test/language/japanese-transforms.test.js b/test/language/japanese-transforms.test.js
index d0ff131e..f62eef0f 100644
--- a/test/language/japanese-transforms.test.js
+++ b/test/language/japanese-transforms.test.js
@@ -316,6 +316,8 @@ const tests = [
             {term: '話す', source: '話してる',         rule: 'v5', reasons: ['-te', 'progressive or perfect']},
             {term: '話す', source: '話しとる',         rule: 'v5', reasons: ['-te', 'progressive or perfect']},
             {term: '話す', source: '話してしまう',     rule: 'v5', reasons: ['-te', '-shimau']},
+
+            {term: '増す', source: '増せん',             rule: 'v5', reasons: ['potential', '-n']},
         ],
     },
     {
@@ -1097,10 +1099,12 @@ const tests = [
         ],
     },
     {
-        category: 'incorrect -te rule chain',
+        category: 'incorrect chains',
         valid: false,
         tests: [
             {term: '食べる', source: '食べて', rule: null, reasons: ['-te', 'progressive or perfect', 'masu stem']},
+
+            {term: 'なる', source: 'なりません', rule: null, reasons: ['polite', 'potential', '-n']},
         ],
     },
     // Kansai-ben