Verify that all 'live' branches actually exist

Fail if there is a branch in the 'live' list that is not also in the
'branches' list.

.rubocop.yml

@@ -17,6 +17,9 @@ Style/TrailingCommaInArrayLiteral:
 Style/TrailingCommaInHashLiteral:
   EnforcedStyleForMultiline: comma
 
+Style/WordArray:
+  Enabled: false
+
 Metrics/AbcSize:
   Max: 20
 

integtest/spec/all_books_spec.rb

@@ -718,6 +718,27 @@ def self.setup_example(repo, lang, hash)
     end
   end
 
+  context 'when a live branch is not in the list of branches' do
+    convert_before do |src, dest|
+      repo = src.repo_with_index 'repo', 'some text'
+
+      book = src.book 'Test'
+      book.source repo, 'index.asciidoc'
+      book.branches = ['master']
+      book.live_branches = ['newer', 'master', 'missing']
+      dest.prepare_convert_all(src.conf).convert(expect_failure: true)
+    end
+    it 'fails with an appropriate error status' do
+      puts outputs
+      expect(statuses[0]).to eq(2)
+    end
+    it 'logs the missing file' do
+      expect(outputs[0]).to include(<<~LOG.strip)
+        Live branch(es) <newer, missing> not in <branches> in book <Test>
+      LOG
+    end
+  end
+
   context 'when run with --announce_preview' do
     target_branch = 'foo_1'
     preview_location = "http://#{target_branch}.docs-preview.app.elstc.co/guide"

lib/ES/Book.pm

@@ -117,6 +117,22 @@ sub new {
     die "Current branch <$current> is not in <branches> in book <$title>"
         unless $branch_titles{$current};
 
+    my $live_branches = $args{live};
+    # If `live` is defined, check if there are any specified branches that
+    # aren't in the list of branches being built.
+    my @difference;
+    foreach my $item (@$live_branches) {
+        push @difference, $item unless grep { $item eq $_ } @branches;
+    }
+
+    # print "Branches: ", join(", ", @branches), "\n";
+    # print "Live: ", join(", ", @$live_branches), "\n";
+    # print "Difference: ", join(", ", @difference), "\n";
+
+    my $missing = join ", ", @difference;
+    die "Live branch(es) <$missing> not in <branches> in book <$title>"
+        if $difference[0];
+
     my $tags = $args{tags}
         or die "No <tags> specified for book <$title>";
 

schema.yaml

@@ -66,6 +66,7 @@ book:
     current: include("branch")
 
     # List of branches shown by default in the dropdown (and are still receiving updates)
+    # All items in this list must also be in `branches`.
     # TODO: Change this to be a list of versions.
     live: list(include("branch"), required=False)