[rubygems/rubygems] Cache commit SHA ref revisions

If the `ref` option is a specific commit SHA, we can check to see if
it's already fetched locally. If it is, then we don't need to re-fetch
it from the remote.

The `ref` option might not be a commit SHA, so we're using the `#commit`
method which returns the full SHA if it's a commit ref, or the locked
revision, or nil.

This is a small improvement that will make `bundle update` slightly
faster in cases for git-sourced gems pinned to a specific commit.

ruby/rubygems@f434c2e66c

Author: thomasmarshall

lib/bundler/source/git/git_proxy.rb

@@ -305,8 +305,8 @@ def git_local(*command, dir: nil)
         end
 
         def has_revision_cached?
-          return unless @revision && path.exist?
-          git("cat-file", "-e", @revision, dir: path)
+          return unless commit && path.exist?
+          git("cat-file", "-e", commit, dir: path)
           true
         rescue GitError
           false

spec/bundler/bundler/source/git/git_proxy_spec.rb

@@ -305,10 +305,21 @@
       context "with a commit ref" do
         let(:ref) { Digest::SHA1.hexdigest("ruby") }
 
-        it "fetches the specific revision" do
-          allow(git_proxy).to receive(:git_local).with("--version").and_return("git version 2.14.0")
-          expect(git_proxy).to receive(:capture).with(["fetch", "--force", "--quiet", "--no-tags", "--depth", "1", "--", uri, "#{ref}:refs/#{ref}-sha"], path).and_return(["", "", clone_result])
-          subject.checkout
+        context "when the revision exists locally" do
+          it "uses the cached revision" do
+            allow(git_proxy).to receive(:git_local).with("--version").and_return("git version 2.14.0")
+            expect(git_proxy).to receive(:git).with("cat-file", "-e", ref, dir: path).and_return(true)
+            subject.checkout
+          end
+        end
+
+        context "when the revision doesn't exist locally" do
+          it "fetches the specific revision" do
+            allow(git_proxy).to receive(:git_local).with("--version").and_return("git version 2.14.0")
+            expect(git_proxy).to receive(:git).with("cat-file", "-e", ref, dir: path).and_raise(Bundler::GitError)
+            expect(git_proxy).to receive(:capture).with(["fetch", "--force", "--quiet", "--no-tags", "--depth", "1", "--", uri, "#{ref}:refs/#{ref}-sha"], path).and_return(["", "", clone_result])
+            subject.checkout
+          end
         end
       end