[Elasticsearch] Improve code search for camel case

changelogs/unreleased-ee/improve_code_search_for_camel_case.yml

+---
+title: "[Elasticsearch] Improve code search for camel case"
+merge_request:
+author:

lib/elasticsearch/git/model.rb

@@ -33,7 +33,7 @@ module Elasticsearch
               code_analyzer: {
                 type: 'custom',
                 tokenizer: 'standard',
-                filter: %w(code lowercase asciifolding),
+                filter: %w(code edgeNGram_filter lowercase asciifolding),
                 char_filter: ["code_mapping"]
               },
               code_search_analyzer: {
@@ -61,8 +61,14 @@ module Elasticsearch
                 preserve_original: 1,
                 patterns: [
                   "(\\p{Ll}+|\\p{Lu}\\p{Ll}+|\\p{Lu}+)",
-                  "(\\d+)"
+                  "(\\d+)",
+                  "(?=([\\p{Lu}]+[\\p{L}]+))"
                 ]
+              },
+              edgeNGram_filter: {
+                type: 'edgeNGram',
+                min_gram: 2,
+                max_gram: 40
               }
             },
             char_filter: {

spec/lib/gitlab/elastic/search_results_spec.rb

@@ -399,6 +399,45 @@ describe Gitlab::Elastic::SearchResults, lib: true do
 
       expect(results.blobs_count).to eq 0
     end
+
+    context 'Searches CamelCased methods' do
+      before do
+        project_1.repository.create_file(
+          user,
+          'test.txt',
+          ' function writeStringToFile(){} ',
+          message: 'added test file',
+          branch_name: 'master')
+
+        project_1.repository.index_blobs
+
+        Gitlab::Elastic::Helper.refresh_index
+      end
+
+      def search_for(term)
+        blobs = described_class.new(user, term, [project_1.id]).objects('blobs')
+
+        blobs.map do |blob|
+          blob["_source"]["blob"]["path"]
+        end
+      end
+
+      it 'find by first word' do
+        expect(search_for('write')).to include('test.txt')
+      end
+
+      it 'find by first two words' do
+        expect(search_for('writeString')).to include('test.txt')
+      end
+
+      it 'find by last two words' do
+        expect(search_for('ToFile')).to include('test.txt')
+      end
+
+      it 'find by exact match' do
+        expect(search_for('writeStringToFile')).to include('test.txt')
+      end
+    end
   end
 
   describe 'Wikis' do