Improve the error message displayed when branch creation fails.

Note: This feature was developed independently on master while this was
in review. I've removed the conflicting bits and left the relevant
additions, mainly a test for `Gitlab::Git::Hook`. The original commit
message follows:

1. `gitlab-shell` outputs errors to `stderr`, but we weren't using this
   information, prior to this commit. Now we capture the `stderr`, and
   display it in the flash message when branch creation fails.

2. This can be used to display better errors for other git operation
   failures with small tweaks.

3. The return value of `Gitlab::Git::Hook#trigger` is changed from a
   simple `true`/`false` to a tuple of `[status, errors]`. All usages
   and tests have been updated to reflect this change.

4. This is only relevant to branch creation _from the Web UI_, since SSH
   and HTTP pushes access `gitlab-shell` either directly or through
   `gitlab-workhorse`.

5. A few minor changes need to be made on the `gitlab-shell` end. Right
   now, the `stderr` message it outputs is prefixed by "GitLab: ", which
   shows up in our flash message. This is better removed.

app/views/projects/protected_branches/index.html.haml

@@ -4,17 +4,17 @@
   .col-lg-3
     %h4.prepend-top-0
       = page_title
-    %p Keep stable branches secure and force developers to use Merge Requests
-  .col-lg-9
-    %h5.prepend-top-0
-      Protect a branch
-    .account-well.append-bottom-default
-      %p.light-header.append-bottom-0 Protected branches are designed to
+    %p Keep stable branches secure and force developers to use merge requests.
+    %p.prepend-top-20
+      Protected branches are designed to:
       %ul
         %li prevent pushes from everybody except #{link_to "masters", help_page_path("permissions", "permissions"), class: "vlink"}
         %li prevent anyone from force pushing to the branch
         %li prevent anyone from deleting the branch
       %p.append-bottom-0 Read more about #{link_to "project permissions", help_page_path("permissions", "permissions"), class: "underlined-link"}
+  .col-lg-9
+    %h5.prepend-top-0
+      Protect a branch
     - if can? current_user, :admin_project, @project
       = form_for [@project.namespace.becomes(Namespace), @project, @protected_branch] do |f|
         = form_errors(@protected_branch)
@@ -35,7 +35,7 @@
             = f.label :developers_can_push, "Developers can push", class: "label-light append-bottom-0"
             %p.light.append-bottom-0
               Allow developers to push to this branch
-        = f.submit "Protect", class: "btn-create btn"
+        = f.submit "Protect", class: "btn-create btn protect-branch-btn", disabled: true
     %hr
     = render "branches_list"
 

lib/gitlab/git/hook.rb

@@ -14,7 +14,7 @@ module Gitlab
       end
 
       def trigger(gl_id, oldrev, newrev, ref)
-        return true unless exists?
+        return [true, nil] unless exists?
 
         case name
         when "pre-receive", "post-receive"
@@ -68,13 +68,10 @@ module Gitlab
       end
 
       def call_update_hook(gl_id, oldrev, newrev, ref)
-        status = nil
-
         Dir.chdir(repo_path) do
-          status = system({ 'GL_ID' => gl_id }, path, ref, oldrev, newrev)
+          stdout, stderr, status = Open3.capture3({ 'GL_ID' => gl_id }, path, ref, oldrev, newrev)
+          [status.success?, stderr.presence || stdout]
         end
-
-        [status, nil]
       end
 
       def retrieve_error_message(stderr, stdout)

spec/lib/gitlab/git/hook_spec.rb

+require 'spec_helper'
+require 'fileutils'
+
+describe Gitlab::Git::Hook, lib: true do
+  describe "#trigger" do
+    let(:project) { create(:project) }
+    let(:user) { create(:user) }
+
+    def create_hook(name)
+      FileUtils.mkdir_p(File.join(project.repository.path, 'hooks'))
+      File.open(File.join(project.repository.path, 'hooks', name), 'w', 0755) do |f|
+        f.write('exit 0')
+      end
+    end
+
+    def create_failing_hook(name)
+      FileUtils.mkdir_p(File.join(project.repository.path, 'hooks'))
+      File.open(File.join(project.repository.path, 'hooks', name), 'w', 0755) do |f|
+        f.write(<<-HOOK)
+          echo 'regular message from the hook'
+          echo 'error message from the hook' 1>&2
+          exit 1
+        HOOK
+      end
+    end
+
+    ['pre-receive', 'post-receive', 'update'].each do |hook_name|
+
+      context "when triggering a #{hook_name} hook" do
+        context "when the hook is successful" do
+          it "returns success with no errors" do
+            create_hook(hook_name)
+            hook = Gitlab::Git::Hook.new(hook_name, project.repository.path)
+            blank = Gitlab::Git::BLANK_SHA
+            ref = Gitlab::Git::BRANCH_REF_PREFIX + 'new_branch'
+
+            status, errors = hook.trigger(Gitlab::GlId.gl_id(user), blank, blank, ref)
+            expect(status).to be true
+            expect(errors).to be_blank
+          end
+        end
+
+        context "when the hook is unsuccessful" do
+          it "returns failure with errors" do
+            create_failing_hook(hook_name)
+            hook = Gitlab::Git::Hook.new(hook_name, project.repository.path)
+            blank = Gitlab::Git::BLANK_SHA
+            ref = Gitlab::Git::BRANCH_REF_PREFIX + 'new_branch'
+
+            status, errors = hook.trigger(Gitlab::GlId.gl_id(user), blank, blank, ref)
+            expect(status).to be false
+            expect(errors).to eq("error message from the hook\n")
+          end
+        end
+      end
+    end
+
+    context "when the hook doesn't exist" do
+      it "returns success with no errors" do
+        hook = Gitlab::Git::Hook.new('unknown_hook', project.repository.path)
+        blank = Gitlab::Git::BLANK_SHA
+        ref = Gitlab::Git::BRANCH_REF_PREFIX + 'new_branch'
+
+        status, errors = hook.trigger(Gitlab::GlId.gl_id(user), blank, blank, ref)
+        expect(status).to be true
+        expect(errors).to be_nil
+      end
+    end
+  end
+end

spec/support/test_env.rb

@@ -63,7 +63,7 @@ module TestEnv
   end
 
   def disable_pre_receive
-    allow_any_instance_of(Gitlab::Git::Hook).to receive(:trigger).and_return(true)
+    allow_any_instance_of(Gitlab::Git::Hook).to receive(:trigger).and_return([true, nil])
   end
 
   # Clean /tmp/tests