Support safe.bareRepository=explicit in git sources

lib/bundler/source/git/git_proxy.rb

@@ -507,7 +507,15 @@ def capture3_args_for(cmd, dir)
 
           return ["git", *opts, *cmd] unless dir
 
-          ["git", "-C", dir.to_s, *opts, *cmd]
+          # With safe.bareRepository=explicit, git refuses to discover a bare
+          # repository from -C, so the cache clone is named with --git-dir.
+          # Working trees, like a local override, still go through -C.
+          location = bare_repo?(dir) ? "--git-dir" : "-C"
+          ["git", location, dir.to_s, *opts, *cmd]
+        end
+
+        def bare_repo?(dir)
+          File.exist?(File.join(dir, "objects")) && File.exist?(File.join(dir, "HEAD"))
         end
 
         def extra_clone_args

spec/install/gemfile/git_spec.rb

@@ -31,6 +31,17 @@
       expect(out).to eq("WIN")
     end
 
+    it "installs and updates gems when git only accepts explicit bare repositories" do
+      git "config --global safe.bareRepository explicit"
+
+      install_base_gemfile
+      expect(the_bundle).to include_gems("foo 1.0")
+
+      update_git "foo", "1.1", path: lib_path("foo-1.0")
+      bundle "update foo"
+      expect(the_bundle).to include_gems("foo 1.1")
+    end
+
     it "points the installed copy's origin at the real remote, not the local cache" do
       install_base_gemfile