Check GitHub for issues relating to build failures

Uses the GitHub issue search API, so it's very neat and concise. However you can get false positives, so it's not 100% useful. Still I think it is more useful than before, which was, nothing.

A further issue is it depends on the ticket at GitHub using the formula's proper name. So we should ensure this as we can.

Finally, it does add a possibly large delay to clean exit after a build error. We may want to fiddle with timeouts if it becomes troublesome.

Library/Homebrew/brew.h.rb

@@ -212,6 +212,28 @@ rescue FormulaUnavailableError
   end
 end
 
+def issues_for_formula name
+  # bit basic as depends on the issue at github having the exact name of the
+  # formula in it. Which for stuff like objective-caml is unlikely. So we
+  # really should search for aliases too.
+
+  name = f.name if Formula === name
+
+  require 'open-uri'
+  require 'yaml'
+
+  issues = []
+
+  open("http://github.com/api/v2/yaml/issues/search/mxcl/homebrew/open/"+name) do |f|
+    YAML::load(f.read)['issues'].each do |issue|
+      issues << 'http://github.com/mxcl/homebrew/issues/#issue/%s' % issue['number']
+    end
+  end
+
+  issues
+rescue
+  []
+end
 
 def clean f
   Cleaner.new f

bin/brew

@@ -326,12 +326,18 @@ rescue Interrupt => e
   exit 130
 rescue BuildError => e
   e.backtrace[1] =~ %r{Library/Formula/(.+)\.rb:(\d+)}
-  puts "http://github.com/mxcl/homebrew/blob/master/Library/Formula/#{$1}.rb#L#{$2}"
+  formula_name = $1
+  puts "http://github.com/mxcl/homebrew/blob/master/Library/Formula/#{formula_name}.rb#L#{$2}"
   ohai "Environment"
   dump_config
   puts "Exit status: #{e.status.exitstatus}"
   onoe e
   puts PLEASE_REPORT_BUG
+  # this feature can be slow (depends on network conditions and if github is up)
+  # so ideally we'd show feedback, eg. "checking for existin issues..." and
+  # then replace that string with the following when the github api returns
+  issues = issues_for_formula(formula_name)
+  puts "These existing issues may help you:", *issues unless issues.empty?
   exit 1
 rescue RuntimeError, SystemCallError => e
   onoe e