[Acknowledgements] Don't crash if the license file doesn't exists.

Closes #828

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ###### Bug fixes
 
+- CocoaPods will not crash anymore if the license file indicated on the spec
+  doesn't exits.
 - Pre install hooks are called before the Pods are cleaned.
 - Fixed and issue which prevent the inclusion of OTHER_CFLAGS and
   OTHER_CPLUSPLUSFLAGS  in the release builds of the Pods project.

lib/cocoapods/generator/acknowledgements.rb

@@ -72,13 +72,19 @@ module Pod
       # @return [Nil] If not license text could be found.
       #
       def license_text(spec)
-        if spec.license
-          if text = spec.license[:text]
-            text
-          elsif license_file = file_accessor(spec).license
-            text = IO.read(license_file)
+        return nil unless spec.license
+        text = spec.license[:text]
+        unless text
+          if license_file = file_accessor(spec).license
+            if license_file.exist?
+              text = IO.read(license_file)
+            else
+              UI.warn "Unable to read the license file `#{license_file }` " \
+              "for the spec `#{spec}`"
+            end
           end
         end
+        text
       end
 
       protected

spec/unit/generator/acknowledgements_spec.rb

@@ -44,6 +44,12 @@ module Pod
         text_from_spec.should == "post v1.0\n"
       end
 
+      it "warns the user if the file specified in the license doesn't exists" do
+        @spec.stubs(:license).returns({ :type => 'MIT', :file => 'MISSING'})
+        text_from_spec = @generator.send(:license_text, @spec)
+        UI.warnings.should.include "Unable to read the license file"
+      end
+
     end
 
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