Do not generate digests if filename contains a digest

lib/sprockets/asset.rb

@@ -64,7 +64,11 @@ def to_hash
     #
     # Returns String.
     def digest_path
-      logical_path.sub(/\.(\w+)$/) { |ext| "-#{etag}#{ext}" }
+      if DigestUtils.already_digested?(@name)
+        logical_path
+      else
+        logical_path.sub(/\.(\w+)$/) { |ext| "-#{etag}#{ext}" }
+      end
     end
 
     # Public: Return load path + logical path with digest spliced in.

lib/sprockets/digest_utils.rb

@@ -179,6 +179,19 @@ def hexdigest_integrity_uri(hexdigest)
       integrity_uri(unpack_hexdigest(hexdigest))
     end
 
+    # Internal: Checks an asset name for a valid digest
+    #
+    # name - The name of the asset
+    #
+    # Returns true if the name contains a digest recognized by one of the valid digest classes
+    def already_digested?(name)
+      return if name.nil?
+
+      if hexdigest = name.scan(/[a-fA-F0-9]+\z/).last
+        detect_digest_class(unpack_hexdigest(hexdigest))
+      end
+    end
+
     private
       def build_digest(obj)
         digest = digest_class.new

test/fixtures/asset/application-d41d8cd98f00b204e9800998ecf8427e.js

@@ -0,0 +1,6 @@
+// =require "project"
+// =require "users"
+
+document.on('dom:loaded', function() {
+  $('search').focus();
+});

test/test_asset.rb

@@ -1124,6 +1124,26 @@ def read(logical_path)
   end
 end
 
+class PreDigestedAssetTest < Sprockets::TestCase
+  def setup
+    @env = Sprockets::Environment.new
+    @env.append_path(fixture_path('asset'))
+    @env.cache = {}
+
+    @pipeline = nil
+    @asset = @env['application.js']
+  end
+
+  test "digest path" do
+    assert_equal "application-d41d8cd98f00b204e9800998ecf8427e.js",
+      asset("application-d41d8cd98f00b204e9800998ecf8427e.js").digest_path
+  end
+
+  def asset(logical_path, options = {})
+    @env.find_asset(logical_path, **{pipeline: @pipeline}.merge(options))
+  end
+end
+
 
 class DebugAssetTest < Sprockets::TestCase
   def setup

test/test_digest_utils.rb

@@ -94,4 +94,22 @@ def test_hexdigest_integrity_uri
     assert_equal "sha512-+uuYUxxe7oWIShQrWEmMn/fixz/rxDP4qcAZddXLDM3nN8/tpk1ZC2jXQk6N+mXE65jwfzNVUJL/qjA3y9KbuQ==",
       hexdigest_integrity_uri(sha512)
   end
+
+  def test_already_digested
+    md5    = Digest::MD5.new.hexdigest
+    sha1   = Digest::SHA1.new.hexdigest
+    sha256 = Digest::SHA256.new.hexdigest
+    sha384 = Digest::SHA384.new.hexdigest
+    sha512 = Digest::SHA512.new.hexdigest
+
+    refute already_digested?(nil)
+    refute already_digested?("application-d41d8cd98f00b204e9800998ecf8427e-")
+    refute already_digested?("application-d41d8cd98f00b204e9800998ecf8427z")
+
+    assert already_digested?("application-" + md5)
+    assert already_digested?("application-" + sha1)
+    assert already_digested?("application-" + sha256)
+    assert already_digested?("application-" + sha384)
+    assert already_digested?("application-" + sha512)
+  end
 end