Fix bundle config gemfile unset behavior

bundler/lib/bundler/cli.rb

@@ -61,14 +61,18 @@ def initialize(*args)
 
       current_cmd = args.last[:current_command].name
 
-      Bundler.configure_custom_gemfile(options[:gemfile])
-
-      # lock --lockfile works differently than install --lockfile
-      unless current_cmd == "lock"
-        custom_lockfile = options[:lockfile] || ENV["BUNDLE_LOCKFILE"] || Bundler.settings[:lockfile]
-        if custom_lockfile && !custom_lockfile.empty?
-          Bundler::SharedHelpers.set_env "BUNDLE_LOCKFILE", File.expand_path(custom_lockfile)
-          reset_settings = true
+      # `bundle config` manages stored settings, so avoid promoting settings
+      # like `gemfile` or `lockfile` to environment variables before it runs.
+      unless current_cmd == "config"
+        Bundler.configure_custom_gemfile(options[:gemfile])
+
+        # lock --lockfile works differently than install --lockfile
+        unless current_cmd == "lock"
+          custom_lockfile = options[:lockfile] || ENV["BUNDLE_LOCKFILE"] || Bundler.settings[:lockfile]
+          if custom_lockfile && !custom_lockfile.empty?
+            Bundler::SharedHelpers.set_env "BUNDLE_LOCKFILE", File.expand_path(custom_lockfile)
+            reset_settings = true
+          end
         end
       end
 

spec/commands/config_spec.rb

@@ -577,6 +577,36 @@
 end
 
 RSpec.describe "setting gemfile via config" do
+  context "when a default Gemfile exists" do
+    before do
+      gemfile <<-G
+        source "https://gem.repo1"
+      G
+
+      gemfile bundled_app("foo/bar_gemfile"), <<-G
+        source "https://gem.repo1"
+      G
+    end
+
+    it "reports the local gemfile setting without promoting it to the environment" do
+      bundle "config set gemfile foo/bar_gemfile"
+
+      bundle "config list"
+      expect(out).to include("Set for your local app (#{bundled_app(".bundle/config")}): \"foo/bar_gemfile\"")
+      expect(out).not_to include("Set via BUNDLE_GEMFILE")
+    end
+
+    it "unsets the local gemfile setting from the app config" do
+      bundle "config set gemfile foo/bar_gemfile"
+
+      bundle "config unset gemfile"
+      bundle "config get gemfile"
+
+      expect(out).to include("You have not configured a value for `gemfile`")
+      expect(File.read(bundled_app(".bundle/config"))).not_to include("BUNDLE_GEMFILE")
+    end
+  end
+
   context "when only the non-default Gemfile exists" do
     it "persists the gemfile location to .bundle/config" do
       gemfile bundled_app("NotGemfile"), <<-G