ruby 1.9: don't choke on course import with '~' filename

work around the issue where creating a temp file whose basename
starts with '~' fails on ruby 1.9

ruby issue: https://bugs.ruby-lang.org/issues/7547

test plan: try to import the course linked in the ticket

fixes #CNVS-2922

Change-Id: Iafbbae05c90dbef22e73e6311379e3aeee0a5f32
Reviewed-on: https://gerrit.instructure.com/16796
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Adam Phillipps <adam@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>

lib/unzip_attachment.rb

@@ -110,7 +110,8 @@ class UnzipAttachment
         # Hyphenate the path.  So, /some/file/path becomes some-file-path
         # Since Tempfile guarantees that the names are unique, we don't
         # have to worry about what this name actually is.
-        Tempfile.open(filename) do |f|
+        # NOTE: strip leading ~ as workaround for https://bugs.ruby-lang.org/issues/7547
+        Tempfile.open(filename.sub(/^~/, '')) do |f|
           begin
             entry.extract(f.path) { true }
             # This is where the attachment actually happens.  See file_in_context.rb

spec/lib/unzip_attachment_spec.rb

@@ -131,6 +131,13 @@ describe UnzipAttachment do
       end
     end
 
+    it "should not fall over when facing a filename starting with ~" do
+      filename = fixture_filename('tilde.zip')
+      ua = UnzipAttachment.new(:course => @course, :filename => filename)
+      lambda { ua.process }.should_not raise_error
+      @course.attachments.map(&:display_name).should == ['~tilde']
+    end
+
     describe 'validations' do
 
       let(:filename) { fixture_filename('huge_zip.zip') }