Remove a dependency on gitlab-gollum-lib

Removing this dependency also allows us to remove a transitive
dependency on gitlab_grit - which is the whole point of this exercise.

I don't think we can EOL gitlab_grit until it's removed as a dependency
from gitaly-ruby, but this at least gets it out of gitlab-ce.

Gemfile

@@ -79,10 +79,6 @@ gem 'gpgme'
 gem 'gitlab_omniauth-ldap', '~> 2.0.4', require: 'omniauth-ldap'
 gem 'net-ldap'
 
-# Git Wiki
-# Only used to compute wiki page slugs
-gem 'gitlab-gollum-lib', '~> 4.2', require: false
-
 # API
 gem 'grape', '~> 1.1'
 gem 'grape-entity', '~> 0.7.1'

Gemfile.lock

@@ -278,19 +278,6 @@ GEM
       google-protobuf (~> 3.1)
       grpc (~> 1.10)
     github-markup (1.7.0)
-    gitlab-gollum-lib (4.2.7.5)
-      gemojione (~> 3.2)
-      github-markup (~> 1.6)
-      gollum-grit_adapter (~> 1.0)
-      nokogiri (>= 1.6.1, < 2.0)
-      rouge (~> 3.1)
-      sanitize (~> 4.6.4)
-      stringex (~> 2.6)
-    gitlab-grit (2.8.2)
-      charlock_holmes (~> 0.6)
-      diff-lcs (~> 1.1)
-      mime-types (>= 1.16)
-      posix-spawn (~> 0.3)
     gitlab-markup (1.6.4)
     gitlab-sidekiq-fetcher (0.3.0)
       sidekiq (~> 5)
@@ -305,8 +292,6 @@ GEM
       rubyntlm (~> 0.5)
     globalid (0.4.1)
       activesupport (>= 4.2.0)
-    gollum-grit_adapter (1.0.1)
-      gitlab-grit (~> 2.7, >= 2.7.1)
     gon (6.2.0)
       actionpack (>= 3.0)
       multi_json
@@ -596,7 +581,6 @@ GEM
     pg (0.18.4)
     po_to_json (1.0.1)
       json (>= 1.6.0)
-    posix-spawn (0.3.13)
     powerpack (0.1.1)
     premailer (1.10.4)
       addressable
@@ -867,7 +851,6 @@ GEM
     state_machines-activerecord (0.5.1)
       activerecord (>= 4.1, < 6.0)
       state_machines-activemodel (>= 0.5.0)
-    stringex (2.8.4)
     sys-filesystem (1.1.6)
       ffi
     sysexits (1.2.0)
@@ -1022,7 +1005,6 @@ DEPENDENCIES
   gettext_i18n_rails_js (~> 1.3)
   gitaly-proto (~> 0.118.1)
   github-markup (~> 1.7.0)
-  gitlab-gollum-lib (~> 4.2)
   gitlab-markup (~> 1.6.4)
   gitlab-sidekiq-fetcher
   gitlab-styles (~> 2.4)

Gemfile.rails5.lock

@@ -281,19 +281,6 @@ GEM
       google-protobuf (~> 3.1)
       grpc (~> 1.10)
     github-markup (1.7.0)
-    gitlab-gollum-lib (4.2.7.5)
-      gemojione (~> 3.2)
-      github-markup (~> 1.6)
-      gollum-grit_adapter (~> 1.0)
-      nokogiri (>= 1.6.1, < 2.0)
-      rouge (~> 3.1)
-      sanitize (~> 4.6.4)
-      stringex (~> 2.6)
-    gitlab-grit (2.8.2)
-      charlock_holmes (~> 0.6)
-      diff-lcs (~> 1.1)
-      mime-types (>= 1.16)
-      posix-spawn (~> 0.3)
     gitlab-markup (1.6.4)
     gitlab-sidekiq-fetcher (0.3.0)
       sidekiq (~> 5)
@@ -308,8 +295,6 @@ GEM
       rubyntlm (~> 0.5)
     globalid (0.4.1)
       activesupport (>= 4.2.0)
-    gollum-grit_adapter (1.0.1)
-      gitlab-grit (~> 2.7, >= 2.7.1)
     gon (6.2.0)
       actionpack (>= 3.0)
       multi_json
@@ -600,7 +585,6 @@ GEM
     pg (0.18.4)
     po_to_json (1.0.1)
       json (>= 1.6.0)
-    posix-spawn (0.3.13)
     powerpack (0.1.1)
     premailer (1.10.4)
       addressable
@@ -875,7 +859,6 @@ GEM
     state_machines-activerecord (0.5.1)
       activerecord (>= 4.1, < 6.0)
       state_machines-activemodel (>= 0.5.0)
-    stringex (2.8.4)
     sys-filesystem (1.1.6)
       ffi
     sysexits (1.2.0)
@@ -1031,7 +1014,6 @@ DEPENDENCIES
   gettext_i18n_rails_js (~> 1.3)
   gitaly-proto (~> 0.118.1)
   github-markup (~> 1.7.0)
-  gitlab-gollum-lib (~> 4.2)
   gitlab-markup (~> 1.6.4)
   gitlab-sidekiq-fetcher
   gitlab-styles (~> 2.4)

lib/gitlab/git/wiki.rb

-# We only need Gollum::Page so let's not load all of gollum-lib.
-require 'gollum-lib/pagination'
-require 'gollum-lib/wiki'
-require 'gollum-lib/page'
-
 module Gitlab
   module Git
     class Wiki
@@ -18,6 +13,38 @@ module Gitlab
       end
       PageBlob = Struct.new(:name)
 
+      # GollumSlug inlines just enough knowledge from Gollum::Page to generate a
+      # slug, which is used when previewing pages that haven't been persisted
+      class GollumSlug
+        class << self
+          def format_to_ext(format)
+            format == :markdown ? 'md' : format.to_s
+          end
+
+          def cname(name, char_white_sub = '-', char_other_sub = '-')
+            if name.respond_to?(:gsub)
+              name.gsub(/\s/, char_white_sub).gsub(/[<>+]/, char_other_sub)
+            else
+              ''
+            end
+          end
+
+          def generate(title, format)
+            name = cname(title) + '.' + format_to_ext(format)
+            blob = PageBlob.new(name)
+
+            path =
+              if blob.name.include?('/')
+                blob.name.sub(%r{/[^/]+$}, '/')
+              else
+                ''
+              end
+
+            path + cname(name)
+          end
+        end
+      end
+
       attr_reader :repository
 
       def self.default_ref
@@ -90,15 +117,7 @@ module Gitlab
       end
 
       def preview_slug(title, format)
-        # Adapted from gollum gem (Gollum::Wiki#preview_page) to avoid
-        # using Rugged through a Gollum::Wiki instance
-        page_class = Gollum::Page
-        page = page_class.new(nil)
-        ext = page_class.format_to_ext(format.to_sym)
-        name = page_class.cname(title) + '.' + ext
-        blob = PageBlob.new(name)
-        page.populate(blob)
-        page.url_path
+        GollumSlug.generate(title, format)
       end
 
       def page_formatted_data(title:, dir: nil, version: nil)