[ruby/rubygems] Reject duplicate target+field in override DSL

Two override statements that target the same gem and the same field
make it ambiguous which operation should win. Raise ArgumentError
when the new (target, field) pair already exists in the recorded
overrides, leaving the previously recorded entry untouched.

https://github.com/ruby/rubygems/commit/1c90030cf9

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2 files changed, 28 insertions, 0 deletions

diff --git a/lib/bundler/dsl.rb b/lib/bundler/dsl.rb
index 2f9d1f9054..7f14c0dca0 100644
--- a/lib/bundler/dsl.rb
+++ b/lib/bundler/dsl.rb
@@ -198,6 +198,7 @@ module Bundler
       operations.each do |field, operation|
         validate_override_field!(field)
         validate_override_operation!(operation)
+        validate_override_uniqueness!(target, field)
       end
 
       operations.each do |field, operation|
@@ -290,6 +291,11 @@ module Bundler
       end
     end
 
+    def validate_override_uniqueness!(target, field)
+      return unless @overrides.any? {|o| o.target == target && o.field == field }
+      raise ArgumentError, "duplicate override for #{target.inspect} `#{field}:`"
+    end
+
     def add_dependency(name, version = nil, options = {})
       options["gemfile"] = @gemfile
       options["source"] ||= @source
diff --git a/spec/bundler/bundler/dsl_spec.rb b/spec/bundler/bundler/dsl_spec.rb
index 86bcb3be8d..39f745c05e 100644
--- a/spec/bundler/bundler/dsl_spec.rb
+++ b/spec/bundler/bundler/dsl_spec.rb
@@ -447,5 +447,27 @@ RSpec.describe Bundler::Dsl do
       end.to raise_error(ArgumentError, /unsupported override field/)
       expect(subject.overrides).to eq([])
     end
+
+    it "raises ArgumentError when the same target and field are overridden twice" do
+      subject.override("rails", version: ">= 8.0")
+      expect do
+        subject.override("rails", version: :ignore_upper)
+      end.to raise_error(ArgumentError, /duplicate override for "rails" `version:`/)
+    end
+
+    it "keeps the original override when a duplicate is rejected" do
+      subject.override("rails", version: ">= 8.0")
+      expect do
+        subject.override("rails", version: :ignore_upper)
+      end.to raise_error(ArgumentError)
+      expect(subject.overrides.size).to eq(1)
+      expect(subject.overrides.first.operation).to eq(">= 8.0")
+    end
+
+    it "allows different targets with the same field" do
+      subject.override("rails", version: ">= 8.0")
+      subject.override("nokogiri", version: :ignore_upper)
+      expect(subject.overrides.size).to eq(2)
+    end
   end
 end