Fix config location edge caseapp_config_path_absolute

If `BUNDLE_APP_CONFIG` is set to an absolute path, and there's no
Gemfile up in the directory hierarchy, bundler would end up using the
default config location instead of the customized one.

This commit fixes that.

2 files changed, 18 insertions, 2 deletions

diff --git a/lib/bundler.rb b/lib/bundler.rb
index df345539c8..f081d4d63f 100644
--- a/lib/bundler.rb
+++ b/lib/bundler.rb
@@ -285,7 +285,13 @@ module Bundler
 
     def app_config_path
       if app_config = ENV["BUNDLE_APP_CONFIG"]
-        Pathname.new(app_config).expand_path(root)
+        app_config_pathname = Pathname.new(app_config)
+
+        if app_config_pathname.absolute?
+          app_config_pathname
+        else
+          app_config_pathname.expand_path(root)
+        end
       else
         root.join(".bundle")
       end
diff --git a/spec/commands/config_spec.rb b/spec/commands/config_spec.rb
index 7a45dd0dd7..3a6b72d988 100644
--- a/spec/commands/config_spec.rb
+++ b/spec/commands/config_spec.rb
@@ -35,7 +35,7 @@ RSpec.describe ".bundle/config" do
     end
   end
 
-  describe "location" do
+  describe "location with a gemfile" do
     before :each do
       gemfile <<-G
         source "#{file_uri_for(gem_repo1)}"
@@ -64,6 +64,16 @@ RSpec.describe ".bundle/config" do
     end
   end
 
+  describe "location without a gemfile" do
+    it "works with an absolute path" do
+      ENV["BUNDLE_APP_CONFIG"] = tmp("foo/bar").to_s
+      bundle "config set --local path vendor/bundle"
+
+      expect(bundled_app(".bundle")).not_to exist
+      expect(tmp("foo/bar/config")).to exist
+    end
+  end
+
   describe "global" do
     before(:each) do
       install_gemfile <<-G