[ruby/rubygems] Show active overrides when resolution fails

Append the list of currently active overrides (with Gemfile location,
when known) to the SolveFailure message so a user investigating a
"could not find compatible versions" error sees what override changed
the constraint set instead of being misled by the resolver-reported
requirement.

https://github.com/ruby/rubygems/commit/10b8b53270

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

2 files changed, 37 insertions, 0 deletions

diff --git a/lib/bundler/resolver.rb b/lib/bundler/resolver.rb
index 5b575f15e6..fb69becd69 100644
--- a/lib/bundler/resolver.rb
+++ b/lib/bundler/resolver.rb
@@ -122,9 +122,25 @@ module Bundler
         explanation << extended_explanation
       end
 
+      override_summary = override_diagnostic_summary
+      explanation << override_summary if override_summary
+
       raise SolveFailure.new(explanation)
     end
 
+    def override_diagnostic_summary
+      return nil if @base.overrides.empty?
+
+      lines = ["Bundler applied the following overrides while resolving:"]
+      @base.overrides.each do |override|
+        target = override.target == :all ? ":all" : override.target.inspect
+        location = override.source_location_label
+        lines << "  override #{target}, #{override.field}: #{override.operation.inspect}" \
+          "#{location ? " (declared at #{location})" : ""}"
+      end
+      "\n\n#{lines.join("\n")}"
+    end
+
     def find_names_to_relax(incompatibility)
       names_to_unlock = []
       names_to_allow_prereleases_for = []
diff --git a/spec/bundler/install/gemfile/override_spec.rb b/spec/bundler/install/gemfile/override_spec.rb
index 54dd031853..19fa2ee915 100644
--- a/spec/bundler/install/gemfile/override_spec.rb
+++ b/spec/bundler/install/gemfile/override_spec.rb
@@ -318,6 +318,27 @@ RSpec.describe "override DSL" do
     end
   end
 
+  context "diagnostic on resolve failure" do
+    it "lists active overrides with their Gemfile location" do
+      build_repo2 do
+        build_gem "needs_old_ruby", "1.0" do |s|
+          s.required_ruby_version = "= #{Gem.ruby_version}.999"
+        end
+      end
+
+      gemfile <<-G
+        source "https://gem.repo2"
+        override "needs_old_ruby", required_ruby_version: "= #{Gem.ruby_version}.999"
+        gem "needs_old_ruby"
+      G
+
+      bundle :lock, raise_on_error: false
+      expect(err).to include("Bundler applied the following overrides")
+      expect(err).to include("override \"needs_old_ruby\", required_ruby_version:")
+      expect(err).to match(/declared at Gemfile:\d+/)
+    end
+  end
+
   context "install-time compatibility" do
     it "installs a gem whose required_ruby_version excludes the current Ruby when an override removes the constraint" do
       build_repo2 do