Fix only one middle dot being recognized in hashtags (#11345)

Fix #10934

app/models/tag.rb

@@ -17,7 +17,7 @@ class Tag < ApplicationRecord
   has_many :featured_tags, dependent: :destroy, inverse_of: :tag
   has_one :account_tag_stat, dependent: :destroy
 
-  HASHTAG_NAME_RE = '[[:word:]_]*[[:alpha:]_·][[:word:]_]*'
+  HASHTAG_NAME_RE = '[[:word:]_][[:word:]_]*[[:alpha:]_·]*[[:word:]_·]*[[:word:]_]'
   HASHTAG_RE = /(?:^|[^\/\)\w])#(#{HASHTAG_NAME_RE})/i
 
   validates :name, presence: true, uniqueness: true, format: { with: /\A#{HASHTAG_NAME_RE}\z/i }

spec/models/tag_spec.rb

@@ -31,7 +31,43 @@ RSpec.describe Tag, type: :model do
     end
 
     it 'matches #ａｅｓｔｈｅｔｉｃ' do
-      expect(subject.match('this is #ａｅｓｔｈｅｔｉｃ')).to_not be_nil
+      expect(subject.match('this is #ａｅｓｔｈｅｔｉｃ').to_s).to eq ' #ａｅｓｔｈｅｔｉｃ'
+    end
+
+    it 'matches digits at the start' do
+      expect(subject.match('hello #3d').to_s).to eq ' #3d'
+    end
+
+    it 'matches digits in the middle' do
+      expect(subject.match('hello #l33ts35k').to_s).to eq ' #l33ts35k'
+    end
+
+    it 'matches digits at the end' do
+      expect(subject.match('hello #world2016').to_s).to eq ' #world2016'
+    end
+
+    it 'matches underscores at the beginning' do
+      expect(subject.match('hello #_test').to_s).to eq ' #_test'
+    end
+
+    it 'matches underscores at the end' do
+      expect(subject.match('hello #test_').to_s).to eq ' #test_'
+    end
+
+    it 'matches underscores in the middle' do
+      expect(subject.match('hello #one_two_three').to_s).to eq ' #one_two_three'
+    end
+
+    it 'matches middle dots' do
+      expect(subject.match('hello #one·two·three').to_s).to eq ' #one·two·three'
+    end
+
+    it 'does not match middle dots at the start' do
+      expect(subject.match('hello #·one·two·three')).to be_nil
+    end
+
+    it 'does not match middle dots at the end' do
+      expect(subject.match('hello #one·two·three·').to_s).to eq ' #one·two·three'
     end
   end