Ensure Cache#inspect doesn't block concurrent cache writes

Object#inspect recursively inspects instance variables, exposing all
internal state, including sensitive internal cache objects. Override
Cache#inspect to give a high-level summary that never interferes with
concurrent cache writes.

2 files changed, 11 insertions, 0 deletions

diff --git a/actionview/lib/action_view/template/resolver.rb b/actionview/lib/action_view/template/resolver.rb
index f33acc2103..c5e69b1833 100644
--- a/actionview/lib/action_view/template/resolver.rb
+++ b/actionview/lib/action_view/template/resolver.rb
@@ -55,6 +55,10 @@ module ActionView
         @query_cache = SmallCache.new
       end
 
+      def inspect
+        "#<#{self.class.name}:0x#{(object_id << 1).to_s(16)} keys=#{@data.size} queries=#{@query_cache.size}>"
+      end
+
       # Cache the templates returned by the block
       def cache(key, name, prefix, partial, locals)
         if Resolver.caching?
diff --git a/actionview/test/template/resolver_cache_test.rb b/actionview/test/template/resolver_cache_test.rb
new file mode 100644
index 0000000000..1081c13db0
--- /dev/null
+++ b/actionview/test/template/resolver_cache_test.rb
@@ -0,0 +1,7 @@
+require 'abstract_unit'
+
+class ResolverCacheTest < ActiveSupport::TestCase
+  def test_inspect_shields_cache_internals
+    assert_match %r(#<ActionView::Resolver:0x[0-9a-f]+ @cache=#<ActionView::Resolver::Cache:0x[0-9a-f]+ keys=0 queries=0>>), ActionView::Resolver.new.inspect
+  end
+end