Don't fail if we can't write REVISION in haml.gemspec.

doc-src/HAML_CHANGELOG.md

@@ -14,6 +14,8 @@
 
 * Make sure line numbers are reported correctly when filters are being used.
 
+* Make loading the gemspec not crash on read-only filesystems like Heroku's.
+
 ## 2.2.21
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/2.2.21).

doc-src/SASS_CHANGELOG.md

@@ -8,6 +8,8 @@
 * Add a railtie so Haml and Sass will be automatically loaded in Rails 3.
   Thanks to [Daniel Neighman](http://pancakestacks.wordpress.com/).
 
+* Make loading the gemspec not crash on read-only filesystems like Heroku's.
+
 ## 2.2.21
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/2.2.21).

haml.gemspec

@@ -25,14 +25,23 @@ HAML_GEMSPEC = Gem::Specification.new do |spec|
   spec.add_development_dependency 'yard', '>= 0.5.3'
   spec.add_development_dependency 'maruku', '>= 0.5.9'
 
-  # We need the revision file to exist,
-  # so we just create it if it doesn't.
-  # It'll usually just get overwritten, though.
-  File.open('REVISION', 'w') { |f| f.puts "(unknown)" } unless File.exist?('REVISION')
+  have_revision = true
+  unless File.exist?('REVISION')
+    begin
+      # We need the revision file to exist,
+      # so we just create it if it doesn't.
+      # It'll usually just get overwritten, though.
+      File.open('REVISION', 'w') { |f| f.puts "(unknown)" }
+    rescue
+      # If the file can't be created (e.g. on Heroku) continue without it
+      have_revision = false
+    end
+  end
+
   readmes = FileList.new('*') do |list|
     list.exclude(/(^|[^.a-z])[a-z]+/)
     list.exclude('TODO')
-    list.include('REVISION')
+    list.include('REVISION') if have_revision
   end.to_a
   spec.executables = ['haml', 'html2haml', 'sass', 'css2sass']
   spec.files = FileList['rails/init.rb', 'lib/**/*', 'bin/*', 'test/**/*',