Label filter doesn't work as expected for non-latin characters

Summary

On the right hand side of the issue details page, we have the "Labels" section on the sidebar. If One clicks the "Edit" link on this section, a filterable multi-select box (type-a-head) renders and we can type in, to filter the existing labels.

In Turkish, we have the letter İ which is the capital form of the letter i. Therefore, on our Gitlab instance we have the following labels:

• İyileştirme
• Potansiyel İyileştirme

We cannot filter down to these labels by using the Turkish letters they contain.

Steps to reproduce

1. Create two labels with the texts "İyileştirme" and "Potansiyel İyileştirme"
2. Edit an issue and click the Edit link on the Labels section of the right sidebar.
3. Type İ on the label filter input. Neither "İyileştirme" nor "Potansiyel İyileştirme" matches.
4. Type iyi on the label filter input. It does match "Potansiyel İyileştirme" but not "İyileştirme".
5. Type le on the label filter input. It matches both "Potansiyel İyileştirme" and "İyileştirme" labels.

Outcomes of steps (3) and (4) should be like step (5)'s, typing either İ or iyi should match both "İyileştirme" and "Potansiyel İyileştirme".

Example Project

alaattink/gitlab-label-filtering-bug#1

What is the current bug behavior?

Labels cannot be filtered with the non-latin characters they have especially with the letter İ.

What is the expected correct behavior?

Labels should be filtered with any letter combination they contain.

Relevant logs and/or screenshots

Results of GitLab environment info

Expand for output related to GitLab environment info

System information
System:		Ubuntu 16.04
Current User:	git
Using RVM:	no
Ruby Version:	2.3.6p384
Gem Version:	2.6.13
Bundler Version:1.13.7
Rake Version:	12.3.0
Redis Version:	3.2.11
Git Version:	2.14.3
Sidekiq Version:5.0.5
Go Version:	unknown
GitLab information
Version:	10.5.4
Revision:	8d768f9
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
URL:		https://gitlab..com
HTTP Clone URL:	https://gitlab..com/some-group/some-project.git
SSH Clone URL:	git@gitlab.*****.com:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers: google_oauth2
GitLab Shell
Version:	6.0.3
Repository storage paths:

• default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

Checking GitLab Shell ...
GitLab Shell version >= 6.0.3 ? ... OK (6.0.3)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
3/3 ... ok
3/4 ... ok
5/6 ... ok
5/7 ... ok
12/9 ... ok
12/10 ... ok
12/11 ... ok
12/12 ... ok
12/13 ... ok
12/14 ... ok
12/15 ... ok
14/16 ... ok
13/18 ... ok
14/19 ... ok
13/20 ... ok
13/21 ... ok
5/22 ... ok
13/23 ... ok
13/24 ... ok
13/25 ... ok
13/26 ... ok
13/27 ... ok
13/28 ... ok
13/29 ... ok
16/30 ... ok
15/31 ... ok
16/33 ... ok
16/34 ... ok
16/35 ... ok
13/36 ... ok
12/37 ... ok
12/38 ... ok
12/39 ... ok
12/40 ... ok
19/41 ... ok
12/42 ... ok
18/43 ... ok
18/44 ... ok
18/45 ... ok
18/46 ... ok
20/47 ... ok
10/48 ... ok
16/49 ... ok
5/50 ... ok
18/52 ... ok
18/53 ... ok
18/54 ... ok
18/55 ... ok
18/56 ... ok
18/57 ... ok
18/58 ... ok
18/59 ... ok
18/60 ... ok
23/62 ... ok
23/63 ... ok
24/64 ... ok
23/65 ... ok
23/66 ... ok
23/67 ... ok
23/68 ... ok
23/72 ... ok
23/80 ... ok
23/81 ... ok
23/82 ... ok
5/101 ... ok
24/102 ... repository is empty
10/108 ... repository is empty
23/110 ... ok
24/114 ... ok
3/117 ... ok
18/118 ... ok
23/124 ... ok
16/133 ... repository is empty
16/134 ... ok
16/135 ... ok
16/136 ... ok
16/137 ... ok
26/138 ... ok
5/139 ... ok
27/140 ... ok
24/141 ... ok
27/144 ... ok
24/145 ... repository is empty
24/146 ... ok
28/147 ... repository is empty
30/148 ... ok
10/149 ... repository is empty
16/150 ... ok
16/151 ... ok
33/152 ... ok
16/153 ... ok
30/154 ... ok
30/155 ... ok
16/156 ... ok
21/159 ... ok
35/161 ... ok
35/162 ... ok
35/163 ... ok
35/164 ... ok
35/165 ... ok
35/168 ... ok
35/174 ... ok
16/230 ... ok
7/232 ... ok
7/233 ... ok
18/234 ... ok
16/241 ... ok
7/242 ... ok
21/245 ... repository is empty
23/246 ... ok
39/248 ... ok
39/249 ... ok
39/250 ... ok
15/251 ... ok
16/252 ... ok
16/253 ... ok
24/254 ... ok
40/256 ... ok
2/257 ... ok
40/258 ... ok
24/259 ... ok
42/260 ... ok
42/261 ... ok
42/262 ... ok
42/265 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Sidekiq ...
Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Reply by email is disabled in config/gitlab.yml
Checking LDAP ...
LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
3/3 ... yes
3/4 ... yes
5/6 ... yes
5/7 ... yes
12/9 ... yes
12/10 ... yes
12/11 ... yes
12/12 ... yes
12/13 ... yes
12/14 ... yes
12/15 ... yes
14/16 ... yes
13/18 ... yes
14/19 ... yes
13/20 ... yes
13/21 ... yes
5/22 ... yes
13/23 ... yes
13/24 ... yes
13/25 ... yes
13/26 ... yes
13/27 ... yes
13/28 ... yes
13/29 ... yes
16/30 ... yes
15/31 ... yes
16/33 ... yes
16/34 ... yes
16/35 ... yes
13/36 ... yes
12/37 ... yes
12/38 ... yes
12/39 ... yes
12/40 ... yes
19/41 ... yes
12/42 ... yes
18/43 ... yes
18/44 ... yes
18/45 ... yes
18/46 ... yes
20/47 ... yes
10/48 ... yes
16/49 ... yes
5/50 ... yes
18/52 ... yes
18/53 ... yes
18/54 ... yes
18/55 ... yes
18/56 ... yes
18/57 ... yes
18/58 ... yes
18/59 ... yes
18/60 ... yes
23/62 ... yes
23/63 ... yes
24/64 ... yes
23/65 ... yes
23/66 ... yes
23/67 ... yes
23/68 ... yes
23/72 ... yes
23/80 ... yes
23/81 ... yes
23/82 ... yes
5/101 ... yes
24/102 ... yes
10/108 ... yes
23/110 ... yes
24/114 ... yes
3/117 ... yes
18/118 ... yes
23/124 ... yes
16/133 ... yes
16/134 ... yes
16/135 ... yes
16/136 ... yes
16/137 ... yes
26/138 ... yes
5/139 ... yes
27/140 ... yes
24/141 ... yes
27/144 ... yes
24/145 ... yes
24/146 ... yes
28/147 ... yes
30/148 ... yes
10/149 ... yes
16/150 ... yes
16/151 ... yes
33/152 ... yes
16/153 ... yes
30/154 ... yes
30/155 ... yes
16/156 ... yes
21/159 ... yes
35/161 ... yes
35/162 ... yes
35/163 ... yes
35/164 ... yes
35/165 ... yes
35/168 ... yes
35/174 ... yes
16/230 ... yes
7/232 ... yes
7/233 ... yes
18/234 ... yes
16/241 ... yes
7/242 ... yes
21/245 ... yes
23/246 ... yes
39/248 ... yes
39/249 ... yes
39/250 ... yes
15/251 ... yes
16/252 ... yes
16/253 ... yes
24/254 ... yes
40/256 ... yes
2/257 ... yes
40/258 ... yes
24/259 ... yes
42/260 ... yes
42/261 ... yes
42/262 ... yes
42/265 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.3.6)
Git version >= 2.9.5 ? ... yes (2.14.3)
Git user has default SSH configuration? ... yes
Active users: ... 15
Checking GitLab ... Finished

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)