Properly parse .ruby-version file (#9012)

In ccb965e, I used
Bundler::RubyVersion.from_string, but this method is used to parse the
Ruby version present in the Gemfile, of the form `ruby 3.3.0p0`, while
we want to parse `3.3.0` or `ruby-3.3.0`.

The code is lifted from `Bundler::RubyDsl#normalize_ruby_file`, so it
only supports either `ruby-{version}` or `ruby {version}` or a plain
version. That's what `ruby file: ".ruby-version"` supports.

Co-authored-by: Jenny Shen <jenny.shen@shopify.com>

bundler/helpers/v2/monkey_patches/definition_ruby_version_patch.rb

@@ -6,7 +6,14 @@
 module BundlerDefinitionRubyVersionPatch
   def ruby_version
     super || begin
-      Bundler::RubyVersion.from_string(File.read(".ruby-version", chomp: true))
+      file_content = Bundler.read_file(".ruby-version")
+      ruby_version =
+        if /^ruby(-|\s+)([^\s#]+)/ =~ file_content
+          ::Regexp.last_match(2)
+        else
+          file_content.strip
+        end
+      Bundler::RubyVersion.new(ruby_version, nil, nil, nil) if ruby_version
     rescue SystemCallError
       # .ruby-version doesn't exist, fallback to the Ruby Dependabot runs
     end

bundler/helpers/v2/spec/ruby_version_spec.rb

@@ -0,0 +1,40 @@
+# typed: false
+# frozen_string_literal: true
+
+require "native_spec_helper"
+require "shared_contexts"
+
+RSpec.describe BundlerDefinitionRubyVersionPatch do
+  include_context "in a temporary bundler directory"
+  include_context "stub rubygems compact index"
+
+  let(:project_name) { "ruby_version_implied" }
+  before do
+    @ui = Bundler.ui
+    Bundler.ui = Bundler::UI::Silent.new
+  end
+  after { Bundler.ui = @ui }
+
+  it "updates to the most recent version" do
+    in_tmp_folder do
+      File.delete(".ruby-version")
+      definition = Bundler::Definition.build("Gemfile", "Gemfile.lock", gems: ["statesman"])
+      definition.resolve_remotely!
+      specs = definition.resolve["statesman"]
+      expect(specs.size).to eq(1)
+      spec = specs.first
+      expect(spec.version).to eq("7.2.0")
+    end
+  end
+
+  it "doesn't update to a version that is not compatible with the Ruby version implied by .ruby-version" do
+    in_tmp_folder do
+      definition = Bundler::Definition.build("Gemfile", "Gemfile.lock", gems: ["statesman"])
+      definition.resolve_remotely!
+      specs = definition.resolve["statesman"]
+      expect(specs.size).to eq(1)
+      spec = specs.first
+      expect(spec.version).to eq("2.0.1")
+    end
+  end
+end

bundler/spec/fixtures/projects/bundler2/ruby_version_implied/.ruby-version

@@ -0,0 +1 @@
+2.1.10

bundler/spec/fixtures/projects/bundler2/ruby_version_implied/Gemfile

@@ -0,0 +1,4 @@
+source "https://rubygems.org"
+
+gem "business"
+gem "statesman"

bundler/spec/fixtures/projects/bundler2/ruby_version_implied/Gemfile.lock

@@ -0,0 +1,15 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    business (1.12.0)
+    statesman (2.0.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  business
+  statesman
+
+BUNDLED WITH
+   2.5.3