Add metric initializer spec

An empty file in one of the instrumented directories will cause the app
to fail to start when metrics are enabled. Metrics aren't enabled by
default in development or test.

We could handle the empty file case explicitly, but a file could still
not define the constant it is expected to, so instead run the
initializer manually in a spec and check that it succeeds.

config/initializers/metrics.rb

+# Autoload all classes that we want to instrument, and instrument the methods we
+# need. This takes the Gitlab::Metrics::Instrumentation module as an argument so
+# that we can stub it for testing, as it is only called when metrics are
+# enabled.
+#
+# rubocop:disable Metrics/AbcSize
+def instrument_classes(instrumentation)
+  instrumentation.instrument_instance_methods(Gitlab::Shell)
+
+  instrumentation.instrument_methods(Gitlab::Git)
+
+  Gitlab::Git.constants.each do |name|
+    const = Gitlab::Git.const_get(name)
+
+    next unless const.is_a?(Module)
+
+    instrumentation.instrument_methods(const)
+    instrumentation.instrument_instance_methods(const)
+  end
+
+  # Path to search => prefix to strip from constant
+  paths_to_instrument = {
+    ['app', 'finders']                    => ['app', 'finders'],
+    ['app', 'mailers', 'emails']          => ['app', 'mailers'],
+    ['app', 'services', '**']             => ['app', 'services'],
+    ['lib', 'gitlab', 'conflicts']        => ['lib'],
+    ['lib', 'gitlab', 'diff']             => ['lib'],
+    ['lib', 'gitlab', 'email', 'message'] => ['lib'],
+    ['lib', 'gitlab', 'checks']           => ['lib']
+  }
+
+  paths_to_instrument.each do |(path, prefix)|
+    prefix = Rails.root.join(*prefix)
+
+    Dir[Rails.root.join(*path + ['*.rb'])].each do |file_path|
+      path = Pathname.new(file_path).relative_path_from(prefix)
+      const = path.to_s.sub('.rb', '').camelize.constantize
+
+      instrumentation.instrument_methods(const)
+      instrumentation.instrument_instance_methods(const)
+    end
+  end
+
+  instrumentation.instrument_methods(Premailer::Adapter::Nokogiri)
+  instrumentation.instrument_instance_methods(Premailer::Adapter::Nokogiri)
+
+  [
+    :Blame, :Branch, :BranchCollection, :Blob, :Commit, :Diff, :Repository,
+    :Tag, :TagCollection, :Tree
+  ].each do |name|
+    const = Rugged.const_get(name)
+
+    instrumentation.instrument_methods(const)
+    instrumentation.instrument_instance_methods(const)
+  end
+
+  # Instruments all Banzai filters and reference parsers
+  {
+    Filter: Rails.root.join('lib', 'banzai', 'filter', '*.rb'),
+    ReferenceParser: Rails.root.join('lib', 'banzai', 'reference_parser', '*.rb')
+  }.each do |const_name, path|
+    Dir[path].each do |file|
+      klass = File.basename(file, File.extname(file)).camelize
+      const = Banzai.const_get(const_name).const_get(klass)
+
+      instrumentation.instrument_methods(const)
+      instrumentation.instrument_instance_methods(const)
+    end
+  end
+
+  instrumentation.instrument_methods(Banzai::Renderer)
+  instrumentation.instrument_methods(Banzai::Querying)
+
+  instrumentation.instrument_instance_methods(Banzai::ObjectRenderer)
+  instrumentation.instrument_instance_methods(Banzai::Redactor)
+  instrumentation.instrument_methods(Banzai::NoteRenderer)
+
+  [Issuable, Mentionable, Participable].each do |klass|
+    instrumentation.instrument_instance_methods(klass)
+    instrumentation.instrument_instance_methods(klass::ClassMethods)
+  end
+
+  instrumentation.instrument_methods(Gitlab::ReferenceExtractor)
+  instrumentation.instrument_instance_methods(Gitlab::ReferenceExtractor)
+
+  # Instrument the classes used for checking if somebody has push access.
+  instrumentation.instrument_instance_methods(Gitlab::GitAccess)
+  instrumentation.instrument_instance_methods(Gitlab::GitAccessWiki)
+
+  instrumentation.instrument_instance_methods(API::Helpers)
+
+  instrumentation.instrument_instance_methods(RepositoryCheck::SingleRepositoryWorker)
+
+  instrumentation.instrument_instance_methods(Rouge::Plugins::Redcarpet)
+  instrumentation.instrument_instance_methods(Rouge::Formatters::HTMLGitlab)
+
+  [:XML, :HTML].each do |namespace|
+    namespace_mod = Nokogiri.const_get(namespace)
+
+    instrumentation.instrument_methods(namespace_mod)
+    instrumentation.instrument_methods(namespace_mod::Document)
+  end
+
+  instrumentation.instrument_methods(Rinku)
+  instrumentation.instrument_instance_methods(Repository)
+
+  instrumentation.instrument_methods(Gitlab::Highlight)
+  instrumentation.instrument_instance_methods(Gitlab::Highlight)
+
+  # This is a Rails scope so we have to instrument it manually.
+  instrumentation.instrument_method(Project, :visible_to_user)
+end
+# rubocop:enable Metrics/AbcSize
+
 if Gitlab::Metrics.enabled?
   require 'pathname'
   require 'influxdb'
@@ -49,110 +163,7 @@ if Gitlab::Metrics.enabled?
   end
 
   Gitlab::Metrics::Instrumentation.configure do |config|
-    config.instrument_instance_methods(Gitlab::Shell)
-
-    config.instrument_methods(Gitlab::Git)
-
-    Gitlab::Git.constants.each do |name|
-      const = Gitlab::Git.const_get(name)
-
-      next unless const.is_a?(Module)
-
-      config.instrument_methods(const)
-      config.instrument_instance_methods(const)
-    end
-
-    # Path to search => prefix to strip from constant
-    paths_to_instrument = {
-      ['app', 'finders']                    => ['app', 'finders'],
-      ['app', 'mailers', 'emails']          => ['app', 'mailers'],
-      ['app', 'services', '**']             => ['app', 'services'],
-      ['lib', 'gitlab', 'conflicts']        => ['lib'],
-      ['lib', 'gitlab', 'diff']             => ['lib'],
-      ['lib', 'gitlab', 'email', 'message'] => ['lib'],
-      ['lib', 'gitlab', 'checks']           => ['lib']
-    }
-
-    paths_to_instrument.each do |(path, prefix)|
-      prefix = Rails.root.join(*prefix)
-
-      Dir[Rails.root.join(*path + ['*.rb'])].each do |file_path|
-        path = Pathname.new(file_path).relative_path_from(prefix)
-        const = path.to_s.sub('.rb', '').camelize.constantize
-
-        config.instrument_methods(const)
-        config.instrument_instance_methods(const)
-      end
-    end
-
-    config.instrument_methods(Premailer::Adapter::Nokogiri)
-    config.instrument_instance_methods(Premailer::Adapter::Nokogiri)
-
-    [
-      :Blame, :Branch, :BranchCollection, :Blob, :Commit, :Diff, :Repository,
-      :Tag, :TagCollection, :Tree
-    ].each do |name|
-      const = Rugged.const_get(name)
-
-      config.instrument_methods(const)
-      config.instrument_instance_methods(const)
-    end
-
-    # Instruments all Banzai filters and reference parsers
-    {
-      Filter: Rails.root.join('lib', 'banzai', 'filter', '*.rb'),
-      ReferenceParser: Rails.root.join('lib', 'banzai', 'reference_parser', '*.rb')
-    }.each do |const_name, path|
-      Dir[path].each do |file|
-        klass = File.basename(file, File.extname(file)).camelize
-        const = Banzai.const_get(const_name).const_get(klass)
-
-        config.instrument_methods(const)
-        config.instrument_instance_methods(const)
-      end
-    end
-
-    config.instrument_methods(Banzai::Renderer)
-    config.instrument_methods(Banzai::Querying)
-
-    config.instrument_instance_methods(Banzai::ObjectRenderer)
-    config.instrument_instance_methods(Banzai::Redactor)
-    config.instrument_methods(Banzai::NoteRenderer)
-
-    [Issuable, Mentionable, Participable].each do |klass|
-      config.instrument_instance_methods(klass)
-      config.instrument_instance_methods(klass::ClassMethods)
-    end
-
-    config.instrument_methods(Gitlab::ReferenceExtractor)
-    config.instrument_instance_methods(Gitlab::ReferenceExtractor)
-
-    # Instrument the classes used for checking if somebody has push access.
-    config.instrument_instance_methods(Gitlab::GitAccess)
-    config.instrument_instance_methods(Gitlab::GitAccessWiki)
-
-    config.instrument_instance_methods(API::Helpers)
-
-    config.instrument_instance_methods(RepositoryCheck::SingleRepositoryWorker)
-
-    config.instrument_instance_methods(Rouge::Plugins::Redcarpet)
-    config.instrument_instance_methods(Rouge::Formatters::HTMLGitlab)
-
-    [:XML, :HTML].each do |namespace|
-      namespace_mod = Nokogiri.const_get(namespace)
-
-      config.instrument_methods(namespace_mod)
-      config.instrument_methods(namespace_mod::Document)
-    end
-
-    config.instrument_methods(Rinku)
-    config.instrument_instance_methods(Repository)
-
-    config.instrument_methods(Gitlab::Highlight)
-    config.instrument_instance_methods(Gitlab::Highlight)
-
-    # This is a Rails scope so we have to instrument it manually.
-    config.instrument_method(Project, :visible_to_user)
+    instrument_classes(config)
   end
 
   GC::Profiler.enable

spec/initializers/metrics_spec.rb

+require 'spec_helper'
+require_relative '../../config/initializers/metrics'
+
+describe 'instrument_classes', lib: true do
+  let(:config) { double(:config) }
+
+  before do
+    allow(config).to receive(:instrument_method)
+    allow(config).to receive(:instrument_methods)
+    allow(config).to receive(:instrument_instance_methods)
+  end
+
+  it 'can autoload and instrument all files' do
+    expect { instrument_classes(config) }.not_to raise_error
+  end
+end