Avoid duplicate relative path prefix in bundle exec

When bundle exec resolves an explicit relative path like ./script and falls back to Kernel.exec, Bundler currently prepends another ./ because the resolved path is not absolute. That turns ./script into ././script, which leaks into the executed process as an unexpectedly modified argv[0].

Only prepend ./ for non-absolute paths that do not already begin with a relative path marker. This preserves the existing behavior for bare executables found in the current directory while leaving explicit relative paths unchanged.

Add a regression spec that disables exec-load so the Kernel.exec path is exercised and verifies that ./script remains ./script.

Closes #8930

Author: samuel-williams-shopify

bundler/lib/bundler/cli/exec.rb

@@ -23,7 +23,7 @@ def run
           bin_path.delete_suffix!(".bat") if Gem.win_platform?
           kernel_load(bin_path, *args)
         else
-          bin_path = "./" + bin_path unless File.absolute_path?(bin_path)
+          bin_path = "./" + bin_path unless File.absolute_path?(bin_path) || bin_path.start_with?(".")
           kernel_exec(bin_path, *args)
         end
       else

spec/commands/exec_spec.rb

@@ -341,6 +341,19 @@
     expect(out).to include(rubylib)
   end
 
+  it "does not duplicate a relative path prefix when exec'ing to a relative path" do
+    skip "https://github.com/ruby/rubygems/issues/3351" if Gem.win_platform?
+
+    create_file("script", "#!/usr/bin/env ruby\nputs $0")
+
+    install_gemfile <<-G
+      source "https://gem.repo1"
+    G
+
+    bundle "exec ./script", env: { "BUNDLE_DISABLE_EXEC_LOAD" => "true" }
+    expect(out).to eq("./script")
+  end
+
   it "errors nicely when the argument doesn't exist" do
     install_gemfile <<-G
       source "https://gem.repo1"