Improve error handling for Gitlab::Profiler and improve doc about providing a user

doc/development/profiling.md

@@ -27,6 +27,17 @@ Gitlab::Profiler.profile('/my-user')
 # Returns a RubyProf::Profile where 100 seconds is spent in UsersController#show
 ```
 
+For routes that require authorization you will need to provide a user to
+`Gitlab::Profiler`. You can do this like so:
+
+```ruby
+Gitlab::Profiler.profile('/gitlab-org/gitlab-test', user: User.first)
+```
+
+The user you provide will need to have a [personal access
+token](https://docs.gitlab.com/ce/user/profile/personal_access_tokens.html) in
+the GitLab instance.
+
 Passing a `logger:` keyword argument to `Gitlab::Profiler.profile` will send
 ActiveRecord and ActionController log output to that logger. Further options are
 documented with the method source.

lib/gitlab/profiler.rb

@@ -45,6 +45,7 @@ module Gitlab
 
       if user
         private_token ||= user.personal_access_tokens.active.pluck(:token).first
+        raise 'Your user must have a personal_access_token' unless private_token
       end
 
       headers['Private-Token'] = private_token if private_token

spec/lib/gitlab/profiler_spec.rb

@@ -53,6 +53,15 @@ describe Gitlab::Profiler do
       described_class.profile('/', user: user)
     end
 
+    context 'when providing a user without a personal access token' do
+      it 'raises an error' do
+        user = double(:user)
+        allow(user).to receive_message_chain(:personal_access_tokens, :active, :pluck).and_return([])
+
+        expect { described_class.profile('/', user: user) }.to raise_error('Your user must have a personal_access_token')
+      end
+    end
+
     it 'uses the private_token for auth if both it and user are set' do
       user = double(:user)
       user_token = 'user'