Raise error if item rep path does not start with slash

lib/nanoc/base/services/item_rep_router.rb

@@ -9,6 +9,12 @@ def initialize(output_path, rep_a, rep_b)
       end
     end
 
+    class RouteWithoutSlashError < ::Nanoc::Error
+      def initialize(output_path, rep)
+        super("The item representation #{rep.inspect} is routed to #{output_path}, which does not start with a slash, as required.")
+      end
+    end
+
     def initialize(reps, action_provider, site)
       @reps = reps
       @action_provider = action_provider
@@ -29,6 +35,10 @@ def route_rep(rep, path, snapshot_name, paths_to_reps)
       return if basic_path.nil?
       basic_path = basic_path.encode('UTF-8')
 
+      unless basic_path.start_with?('/')
+        raise RouteWithoutSlashError.new(basic_path, rep)
+      end
+
       # Check for duplicate paths
       if paths_to_reps.key?(basic_path)
         raise IdenticalRoutesError.new(basic_path, paths_to_reps[basic_path], rep)

spec/nanoc/base/services/item_rep_router_spec.rb

@@ -81,6 +81,14 @@
           expect(paths_to_reps).to have_key('/foo/index.html')
         end
 
+        context 'path does not start with a slash' do
+          let(:basic_path) { 'foo/index.html' }
+
+          it 'errors' do
+            expect { subject }.to raise_error(Nanoc::Int::ItemRepRouter::RouteWithoutSlashError)
+          end
+        end
+
         context 'path is not UTF-8' do
           let(:basic_path) { '/foo/index.html'.encode('ISO-8859-1') }
 

spec/nanoc/regressions/gh_1015_spec.rb

@@ -0,0 +1,17 @@
+describe 'GH-1015', site: true, stdio: true do
+  before do
+    File.write('content/foo.md', 'I am foo!')
+
+    File.write('Rules', <<EOS)
+  compile '/foo.*' do
+    filter :erb, stuff: self
+    write 'foo.html'
+  end
+EOS
+  end
+
+  it 'errors' do
+    expect { Nanoc::CLI.run(%w(compile --verbose)) }.to raise_exception(Nanoc::Int::ItemRepRouter::RouteWithoutSlashError)
+    expect(File.file?('outputfoo.html')).not_to be
+  end
+end