Use CLD3 (#2949)

Compact Language Detector v3 (CLD3) is the successor of CLD2, which was
used in the previous implementation. CLD3 includes improvements since CLD2,
and supports newer compilers. On the other hand, it has additional
requirements and cld3-ruby, the FFI of CLD3 for Ruby, is still new and may
be still inmature.

Though CLD3 is named after CLD2, it is implemented with a neural network
model, different from the old implementation, which is based on a Naïve
Bayesian classifier.

CLD3 supports newer compilers, such as GCC 6. CLD2 is not compatible with
GCC 6 because it assigns negative values to varibales typed unsigned.
(see internal/cld_generated_cjk_uni_prop_80.cc) The support for GCC 6 and
newer compilers are essential today, when some server operating system
such as Ubuntu Server 16.10 has GCC 6 by default.

On the one hand, CLD3 requires C++11 support. Environments with old
compilers such as Ubuntu Server 14.04 needs to update the system or install
a newer compiler.

CLD3 needs protocol buffers as a new dependency. However,it is not
considered problematic because major server operating systems, CentOS and
Ubuntu Server provide them.

The FFI cld3-ruby was written by me (Akihiko Odaki) for use in Mastodon.
It is still new and may be inmature, but confirmed to pass existing tests.

7 files changed, 23 insertions, 15 deletions

diff --git a/.travis.yml b/.travis.yml
index 632074874..f18da476b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -13,9 +13,9 @@ env:
     - LOCAL_DOMAIN=cb6e6126.ngrok.io
     - LOCAL_HTTPS=true
     - RAILS_ENV=test
-    - CXX=g++-4.8
     - NOKOGIRI_USE_SYSTEM_LIBRARIES=true
     - PARALLEL_TEST_PROCESSORS=2
+    - "PATH=$HOME:$PATH"
 
 addons:
   postgresql: 9.4
@@ -24,8 +24,10 @@ addons:
     - ubuntu-toolchain-r-test
     - trusty-media
     packages:
-    - g++-4.8
     - ffmpeg
+    - g++-6
+    - libprotobuf-dev
+    - protobuf-compiler
 
 rvm:
   - 2.3.4
@@ -43,6 +45,7 @@ install:
 before_script:
   - bundle exec rake parallel:create parallel:load_schema parallel:prepare
   - bundle exec rails assets:precompile
+  - ln -s /usr/bin/x86_64-linux-gnu-g++-6 "$HOME/g++"
 
 script:
   - bundle exec parallel_test spec/ --group-by filesize --type rspec
diff --git a/Dockerfile b/Dockerfile
index 3e4727258..e2926725a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -16,7 +16,8 @@ RUN echo "@edge https://nl.alpinelinux.org/alpine/edge/main" >> /etc/apk/reposit
     libxml2-dev \
     libxslt-dev \
     python \
-    build-base" \
+    build-base \
+    protobuf-dev" \
  && apk -U upgrade && apk add \
     $BUILD_DEPS \
     nodejs@edge \
@@ -29,6 +30,7 @@ RUN echo "@edge https://nl.alpinelinux.org/alpine/edge/main" >> /etc/apk/reposit
     file \
     imagemagick@edge \
     ca-certificates \
+    protobuf \
  && npm install -g npm@3 && npm install -g yarn \
  && update-ca-certificates \
  && rm -rf /tmp/* /var/cache/apk/*
diff --git a/Gemfile b/Gemfile
index 3651ad8b0..9c22b3c42 100644
--- a/Gemfile
+++ b/Gemfile
@@ -19,7 +19,7 @@ gem 'paperclip', '~> 5.1'
 gem 'paperclip-av-transcoder'
 
 gem 'addressable'
-gem 'cld2', require: 'cld'
+gem 'cld3', '~> 3.1.0'
 gem 'devise'
 gem 'devise-two-factor'
 gem 'doorkeeper'
diff --git a/Gemfile.lock b/Gemfile.lock
index 1baf6bec5..059fbab0e 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -99,8 +99,8 @@ GEM
       rack-test (>= 0.5.4)
       xpath (~> 2.0)
     chunky_png (1.3.8)
-    cld2 (1.0.3)
-      ffi (~> 1.9.3)
+    cld3 (3.1.0)
+      ffi (>= 1.1.0, < 1.10.0)
     climate_control (0.1.0)
     cocaine (0.5.8)
       climate_control (>= 0.0.3, < 1.0)
@@ -480,7 +480,7 @@ DEPENDENCIES
   capistrano-rbenv
   capistrano-yarn
   capybara
-  cld2
+  cld3 (~> 3.1.0)
   devise
   devise-two-factor
   doorkeeper
diff --git a/Vagrantfile b/Vagrantfile
index b2ebbb83f..f2302b24f 100644
--- a/Vagrantfile
+++ b/Vagrantfile
@@ -33,7 +33,9 @@ sudo apt-get install \
   redis-tools \
   postgresql \
   postgresql-contrib \
+  protobuf-compiler \
   yarn \
+  libprotobuf-dev \
   libreadline-dev \
   -y
 
diff --git a/app/lib/language_detector.rb b/app/lib/language_detector.rb
index ca5cb2591..1c22a9ccc 100644
--- a/app/lib/language_detector.rb
+++ b/app/lib/language_detector.rb
@@ -6,6 +6,7 @@ class LanguageDetector
   def initialize(text, account = nil)
     @text = text
     @account = account
+    @identifier = CLD3::NNetLanguageIdentifier.new(1, 2048)
   end
 
   def to_iso_s
@@ -15,15 +16,15 @@ class LanguageDetector
   private
 
   def detected_language_code
-    detected_language[:code].to_sym if detected_language_reliable?
+    result.language.to_sym if detected_language_reliable?
   end
 
-  def detected_language
-    @_detected_language ||= CLD.detect_language(text_without_urls)
+  def result
+    @result ||= @identifier.find_language(text_without_urls)
   end
 
   def detected_language_reliable?
-    detected_language[:reliable]
+    result.reliable?
   end
 
   def text_without_urls
diff --git a/spec/lib/language_detector_spec.rb b/spec/lib/language_detector_spec.rb
index 18ab5aee6..e543edd49 100644
--- a/spec/lib/language_detector_spec.rb
+++ b/spec/lib/language_detector_spec.rb
@@ -24,15 +24,15 @@ describe LanguageDetector do
     end
 
     describe 'when language can\'t be detected' do
-      it 'confirm language engine cant detect' do
-        result = CLD.detect_language('')
-        expect(result[:reliable]).to be false
+      it 'uses default locale when sent an empty document' do
+        result = described_class.new('').to_iso_s
+        expect(result).to eq :en
       end
 
       describe 'because of a URL' do
         it 'uses default locale when sent just a URL' do
           string = 'http://example.com/media/2kFTgOJLXhQf0g2nKB4'
-          cld_result = CLD.detect_language(string)[:code]
+          cld_result = CLD3::NNetLanguageIdentifier.new(0, 2048).find_language(string)
           expect(cld_result).not_to eq :en
 
           result = described_class.new(string).to_iso_s