Add override DSL method to Bundler::Dsl

Introduce Gemfile-level `override target, field: operation, ...` that
collects Bundler::Override instances and forwards them to Definition
via to_definition. Validation and resolver hookup come in later
commits; this commit only wires the entry point.

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

Author: hsbt

bundler/lib/bundler/dsl.rb

@@ -22,7 +22,7 @@ def self.evaluate(gemfile, lockfile, unlock)
     GITHUB_PULL_REQUEST_URL = %r{\Ahttps://github\.com/([A-Za-z0-9_\-\.]+/[A-Za-z0-9_\-\.]+)/pull/(\d+)\z}
     GITLAB_MERGE_REQUEST_URL = %r{\Ahttps://gitlab\.com/([A-Za-z0-9_\-\./]+)/-/merge_requests/(\d+)\z}
 
-    attr_reader :gemspecs, :gemfile
+    attr_reader :gemspecs, :gemfile, :overrides
     attr_accessor :dependencies
 
     def initialize
@@ -40,6 +40,7 @@ def initialize
       @gemfile              = nil
       @gemfiles             = []
       @lockfile             = nil
+      @overrides            = []
       add_git_sources
     end
 
@@ -184,10 +185,18 @@ def github(repo, options = {})
       with_source(git_source) { yield }
     end
 
+    def override(target, **operations)
+      operations.each do |field, operation|
+        @overrides << Override.new(target, field, operation)
+      end
+    end
+
     def to_definition(lockfile, unlock)
       check_primary_source_safety
       lockfile = @lockfile unless @lockfile.nil?
-      Definition.new(lockfile, @dependencies, @sources, unlock, @ruby_version, @optional_groups, @gemfiles)
+      definition = Definition.new(lockfile, @dependencies, @sources, unlock, @ruby_version, @optional_groups, @gemfiles)
+      definition.overrides = @overrides
+      definition
     end
 
     def group(*args, &blk)

spec/bundler/dsl_spec.rb

@@ -366,4 +366,36 @@
       end
     end
   end
+
+  describe "#override" do
+    it "stores an Override for a gem with a version: operation" do
+      subject.override("rails", version: ">= 8.0")
+
+      expect(subject.overrides.size).to eq(1)
+      override = subject.overrides.first
+      expect(override.target).to eq("rails")
+      expect(override.field).to eq(:version)
+      expect(override.operation).to eq(">= 8.0")
+    end
+
+    it "accepts :ignore_upper as the operation" do
+      subject.override("nokogiri", version: :ignore_upper)
+      expect(subject.overrides.first.operation).to eq(:ignore_upper)
+    end
+
+    it "accepts nil as the operation" do
+      subject.override("legacy", version: nil)
+      expect(subject.overrides.first.operation).to be_nil
+    end
+
+    it "appends to overrides across multiple statements" do
+      subject.override("rails", version: ">= 8.0")
+      subject.override("nokogiri", version: :ignore_upper)
+      expect(subject.overrides.map(&:target)).to eq(["rails", "nokogiri"])
+    end
+
+    it "is empty by default" do
+      expect(subject.overrides).to eq([])
+    end
+  end
 end