[Cache] Ensure to verify cached specification

Even when cached_spec isn't used further with local podspecs, it still must be read from file to verify that it was correctly written before, because that also indicates that the cached pod is valid.

lib/cocoapods/downloader/cache.rb

@@ -76,10 +76,10 @@ module Pod
       #         was found in the download cache.
       #
       def cached_pod(request)
+        cached_spec = cached_spec(request)
         path = path_for_pod(request)
-        spec_path = path_for_spec(request)
-        spec = request.spec || cached_spec(request)
-        return unless spec && path.directory? && spec_path.file?
+        return unless cached_spec && path.directory?
+        spec = request.spec || cached_spec
         Response.new(path, spec, request.params)
       end
 
@@ -92,6 +92,8 @@ module Pod
       def cached_spec(request)
         path = path_for_spec(request)
         path.file? && Specification.from_file(path)
+      rescue JSON::ParserError
+        nil
       end
 
       # @param  [Request] request

spec/unit/downloader/cache_spec.rb

@@ -75,17 +75,7 @@ module Pod
     end
 
     describe 'when the cache is incomplete' do
-      before do
-        [@request, @unreleased_request].each do |request|
-          path_for_pod = @cache.send(:path_for_pod, request)
-          path_for_pod.mkpath
-          Dir.chdir(path_for_pod) do
-            FileUtils.mkdir_p 'Classes'
-            File.open('Classes/a.m', 'w') {}
-          end
-        end
-      end
-
+      shared 'it falls back to download the pod' do
         describe 'when downloading a released pod' do
           it 'does download the source' do
             Downloader::Git.any_instance.expects(:download).never
@@ -103,6 +93,34 @@ module Pod
         end
       end
 
+      before do
+        [@request, @unreleased_request].each do |request|
+          path_for_pod = @cache.send(:path_for_pod, request)
+          path_for_pod.mkpath
+          Dir.chdir(path_for_pod) do
+            FileUtils.mkdir_p 'Classes'
+            File.open('Classes/a.m', 'w') {}
+          end
+        end
+      end
+
+      describe 'because the spec is missing' do
+        behaves_like 'it falls back to download the pod'
+      end
+
+      describe 'because the spec is invalid' do
+        before do
+          [@request, @unreleased_request].each do |request|
+            path_for_spec = @cache.send(:path_for_spec, request)
+            path_for_spec.dirname.mkpath
+            path_for_spec.open('w') { |f| f << '{' }
+          end
+        end
+
+        behaves_like 'it falls back to download the pod'
+      end
+    end
+
     describe 'when the download is cached' do
       before do
         [@request, @unreleased_request].each do |request|