Ignore min_chars_for_partial_matching unles trigrm

If we're not using a trigram index, then ignore the
min_chars_for_partial_matching setting

app/finders/issuable_finder.rb

@@ -429,7 +429,7 @@ class IssuableFinder
       items = klass.with(cte.to_arel).from(klass.table_name)
     end
 
-    items.full_search(search, matched_columns: params[:in])
+    items.full_search(search, matched_columns: params[:in], use_minimum_char_limit: !use_cte_for_search?)
   end
   # rubocop: enable CodeReuse/ActiveRecord
 

app/models/concerns/issuable.rb

@@ -168,7 +168,7 @@ module Issuable
     # matched_columns - Modify the scope of the query. 'title', 'description' or joining them with a comma.
     #
     # Returns an ActiveRecord::Relation.
-    def full_search(query, matched_columns: 'title,description')
+    def full_search(query, matched_columns: 'title,description', use_minimum_char_limit: true)
       allowed_columns = [:title, :description]
       matched_columns = matched_columns.to_s.split(',').map(&:to_sym)
       matched_columns &= allowed_columns
@@ -176,7 +176,7 @@ module Issuable
       # Matching title or description if the matched_columns did not contain any allowed columns.
       matched_columns = [:title, :description] if matched_columns.empty?
 
-      fuzzy_search(query, matched_columns)
+      fuzzy_search(query, matched_columns, use_minimum_char_limit: use_minimum_char_limit)
     end
 
     def simple_sorts

changelogs/unreleased/40379-CJK-search-min-chars.yml

@@ -0,0 +1,5 @@
+---
+title: Remove minimum character limits for fuzzy searches when using a CTE
+merge_request: 29810
+author:
+type: fixed

lib/gitlab/sql/pattern.rb

@@ -9,14 +9,16 @@ module Gitlab
       REGEX_QUOTED_WORD = /(?<=\A| )"[^"]+"(?= |\z)/.freeze
 
       class_methods do
-        def fuzzy_search(query, columns)
-          matches = columns.map { |col| fuzzy_arel_match(col, query) }.compact.reduce(:or)
+        def fuzzy_search(query, columns, use_minimum_char_limit: true)
+          matches = columns.map do |col|
+            fuzzy_arel_match(col, query, use_minimum_char_limit: use_minimum_char_limit)
+          end.compact.reduce(:or)
 
           where(matches)
         end
 
-        def to_pattern(query)
-          if partial_matching?(query)
+        def to_pattern(query, use_minimum_char_limit: true)
+          if partial_matching?(query, use_minimum_char_limit: use_minimum_char_limit)
             "%#{sanitize_sql_like(query)}%"
           else
             sanitize_sql_like(query)
@@ -27,7 +29,9 @@ module Gitlab
           MIN_CHARS_FOR_PARTIAL_MATCHING
         end
 
-        def partial_matching?(query)
+        def partial_matching?(query, use_minimum_char_limit: true)
+          return true unless use_minimum_char_limit
+
           query.length >= min_chars_for_partial_matching
         end
 
@@ -35,14 +39,14 @@ module Gitlab
         # query - The text to search for.
         # lower_exact_match - When set to `true` we'll fall back to using
         #                     `LOWER(column) = query` instead of using `ILIKE`.
-        def fuzzy_arel_match(column, query, lower_exact_match: false)
+        def fuzzy_arel_match(column, query, lower_exact_match: false, use_minimum_char_limit: true)
           query = query.squish
           return unless query.present?
 
-          words = select_fuzzy_words(query)
+          words = select_fuzzy_words(query, use_minimum_char_limit: use_minimum_char_limit)
 
           if words.any?
-            words.map { |word| arel_table[column].matches(to_pattern(word)) }.reduce(:and)
+            words.map { |word| arel_table[column].matches(to_pattern(word, use_minimum_char_limit: use_minimum_char_limit)) }.reduce(:and)
           else
             # No words of at least 3 chars, but we can search for an exact
             # case insensitive match with the query as a whole
@@ -56,7 +60,7 @@ module Gitlab
           end
         end
 
-        def select_fuzzy_words(query)
+        def select_fuzzy_words(query, use_minimum_char_limit: true)
           quoted_words = query.scan(REGEX_QUOTED_WORD)
 
           query = quoted_words.reduce(query) { |q, quoted_word| q.sub(quoted_word, '') }
@@ -67,7 +71,7 @@ module Gitlab
 
           words.concat(quoted_words)
 
-          words.select { |word| partial_matching?(word) }
+          words.select { |word| partial_matching?(word, use_minimum_char_limit: use_minimum_char_limit) }
         end
       end
     end

spec/lib/gitlab/sql/pattern_spec.rb

@@ -10,6 +10,12 @@ describe Gitlab::SQL::Pattern do
       it 'returns exact matching pattern' do
         expect(to_pattern).to eq('12')
       end
+
+      context 'and ignore_minimum_char_limit is true' do
+        it 'returns partial matching pattern' do
+          expect(User.to_pattern(query, use_minimum_char_limit:  false)).to eq('%12%')
+        end
+      end
     end
 
     context 'when a query with a escape character is shorter than 3 chars' do
@@ -18,6 +24,12 @@ describe Gitlab::SQL::Pattern do
       it 'returns sanitized exact matching pattern' do
         expect(to_pattern).to eq('\_2')
       end
+
+      context 'and ignore_minimum_char_limit is true' do
+        it 'returns sanitized partial matching pattern' do
+          expect(User.to_pattern(query, use_minimum_char_limit:  false)).to eq('%\_2%')
+        end
+      end
     end
 
     context 'when a query is equal to 3 chars' do

spec/models/concerns/issuable_spec.rb

@@ -223,6 +223,16 @@ describe Issuable do
       expect(issuable_class.full_search(searchable_issue2.description.downcase)).to eq([searchable_issue2])
     end
 
+    it 'returns issues with a fuzzy matching description for a query shorter than 3 chars if told to do so' do
+      search = searchable_issue2.description.downcase.scan(/\w+/).sample[-1]
+
+      expect(issuable_class.full_search(search, use_minimum_char_limit: false)).to include(searchable_issue2)
+    end
+
+    it 'returns issues with a fuzzy matching title for a query shorter than 3 chars if told to do so' do
+      expect(issuable_class.full_search('i', use_minimum_char_limit: false)).to include(searchable_issue)
+    end
+
     context 'when matching columns is "title"' do
       it 'returns issues with a matching title' do
         expect(issuable_class.full_search(searchable_issue.title, matched_columns: 'title'))