Install content-addressable gemspecs under specifications/<ruby_abi>/

A content-addressable gemspec in the flat specifications/ directory
poisons a shared GEM_HOME for older RubyGems: the stub line carries the
content address where the platform used to be, so an older StubLine
parses it as platform unknown and derives a gem_dir that does not exist.
gem list shows the gem while gem "name" raises MissingSpecError.

Older RubyGems globs specifications/*.gemspec non-recursively
(Gem::Util.glob_files_in_dir), so a subdirectory is invisible to it by
construction: nothing to parse, nothing to misinterpret.
specifications/default/ and plugins/<ruby_abi>/ are the existing
precedents.

The read side only adds the running Ruby's ABI subdirectory, so a CA
build for another ABI sharing the GEM_HOME is never an activation
candidate. This also fixes two CA builds of one name-version having
identical sort_obj values, where Dependency#to_spec could activate a
~> X.Y.0 build on a different Ruby with no warning.

Layout:

  GEM_HOME/
    specifications/
      rake-13.3.1.gemspec                # ordinary gems, unchanged
      3.4/
        nokogiri-1.19.4-86e5e59f.gemspec # CA gems, ABI-scoped
    gems/
      nokogiri-1.19.4-86e5e59f/          # payload location unchanged

Gem::SpecificationRecord is the single home for layout knowledge:

- dirs_from expands each path to the flat specifications directory
  plus specifications/<Gem.ruby_abi> (read side, running Ruby)
- abi_scoped_spec_dir? classifies a directory as ABI-scoped only when
  its basename is ABI-shaped AND its parent is named specifications,
  so unrelated paths like /tmp/3.4 are never misclassified
- specification_dir_for maps a spec to its one directory (write side,
  keyed by the spec's pinned ABI, mirroring plugin_stub_dir_for)

Installer#spec_file delegates to specification_dir_for; write_spec
creates the ABI directory lazily via ensure_writable_dir and clamps it
to --dir-mode only after the gemspec is written, matching the
gem_dir/build_info_dir two-step (and surviving read-only dir modes).

Specification#base_dir strips the extra path level for specs loaded
from an ABI-scoped directory (like default_gem?), and #spec_dir points
back at it, so uninstall and pristine work unchanged.

Installer#installed_specs and RequestSet#specs_in glob through
dirs_from so already-installed CA gems are recognized.

Out of scope, tracked as follow-ups: gem doctor, bundle clean,
gem contents --spec-dir, and migration of legacy flat CA gemspecs
written by earlier 4.1.0.dev builds.

Assisted-By: devx/8371356f-3924-46a0-be8e-70db09fa3352

Author: jenshenny

lib/bundler/endpoint_specification.rb

@@ -161,7 +161,8 @@ def _remote_specification
     end
 
     def local_specification_path
-      "#{base_dir}/specifications/#{full_name}.gemspec"
+      File.join(Gem::SpecificationRecord.specification_dir_for(self, base_dir),
+                "#{full_name}.gemspec")
     end
 
     def parse_metadata(data)

lib/bundler/rubygems_ext.rb

@@ -45,6 +45,21 @@ def self.content_addressed_row?(suffix, platform, required_ruby_version = nil, v
     end
   end
 
+  # Can be removed once RubyGems 4.0.0 support is dropped
+  class SpecificationRecord
+    unless respond_to?(:specification_dir_for)
+      def self.specification_dir_for(spec, base_dir)
+        File.join(base_dir, "specifications")
+      end
+    end
+
+    unless respond_to?(:dirs_from)
+      def self.dirs_from(paths)
+        paths.map {|path| File.join(path, "specifications") }
+      end
+    end
+  end
+
   # Can be removed once RubyGems 3.5.11 support is dropped
   unless Gem.respond_to?(:freebsd_platform?)
     def self.freebsd_platform?

lib/bundler/rubygems_integration.rb

@@ -111,7 +111,7 @@ def gem_cache
 
     def spec_cache_dirs
       @spec_cache_dirs ||= begin
-        dirs = gem_path.map {|dir| File.join(dir, "specifications") }
+        dirs = gem_path.flat_map {|dir| Gem::SpecificationRecord.dirs_from([dir]) }
         dirs << Gem.spec_cache_dir
         dirs.uniq.select {|dir| File.directory? dir }
       end

lib/rubygems/commands/lock_command.rb

@@ -100,8 +100,8 @@ def execute
   end
 
   def spec_path(gem_full_name)
-    gemspecs = Gem.path.map do |path|
-      File.join path, "specifications", "#{gem_full_name}.gemspec"
+    gemspecs = Gem::SpecificationRecord.dirs_from(Gem.path).map do |spec_dir|
+      File.join spec_dir, "#{gem_full_name}.gemspec"
     end
 
     gemspecs.find {|path| File.exist? path }

lib/rubygems/content_address.rb

@@ -53,9 +53,11 @@ def self.ruby_abi_for(required_ruby_version)
     return nil if requirements.size != 1
 
     op, version = requirements.first
-    return nil if op != "~>" || version.segments.size != 3 || version.segments[2] != 0
+    segments = version.segments
+    return nil if op != "~>" || segments.size != 3 || segments[2] != 0
+    return nil unless segments[0].is_a?(Integer) && segments[1].is_a?(Integer)
 
-    version.segments[0..1].join(".")
+    segments[0..1].join(".")
   end
 
   ##

lib/rubygems/installer.rb

@@ -308,7 +308,11 @@ def install
 
     say clean_text(spec.post_install_message.to_s) if options[:post_install_message] && !spec.post_install_message.nil?
 
-    Gem::Specification.add_spec(spec) unless @install_dir
+    if incompatible_abi_install?
+      say "#{spec.full_name} is scoped to Ruby ABI #{spec.ruby_abi} and will not be visible to the running Ruby (ABI #{Gem.ruby_abi})"
+    else
+      Gem::Specification.add_spec(spec) unless @install_dir
+    end
 
     load_plugin unless options[:install_plugin] == false
 
@@ -357,9 +361,11 @@ def installed_specs
     @installed_specs ||= begin
       specs = []
 
-      Gem::Util.glob_files_in_dir("*.gemspec", File.join(gem_home, "specifications")).each do |path|
-        spec = Gem::Specification.load path
-        specs << spec if spec
+      Gem::SpecificationRecord.dirs_from([gem_home]).each do |dir|
+        Gem::Util.glob_files_in_dir("*.gemspec", dir).each do |path|
+          spec = Gem::Specification.load path
+          specs << spec if spec
+        end
       end
 
       specs
@@ -395,7 +401,7 @@ def installation_satisfies_dependency?(dependency)
   #
 
   def spec_file
-    File.join gem_home, "specifications", "#{spec.full_name}.gemspec"
+    File.join Gem::SpecificationRecord.specification_dir_for(spec, gem_home), "#{spec.full_name}.gemspec"
   end
 
   def default_spec_dir
@@ -419,7 +425,24 @@ def default_spec_file
   def write_spec
     spec.installed_by_version = Gem.rubygems_version
 
-    Gem.write_binary(spec_file, spec.to_ruby_for_cache)
+    spec_file = self.spec_file
+    spec_dir = File.dirname spec_file
+    dir_mode = options[:dir_mode]
+    content_addressed = Gem::ContentAddress.content_addressed?(spec)
+
+    if File.directory? spec_dir
+      if content_addressed && dir_mode && !File.writable?(spec_dir)
+        File.chmod(0o755, spec_dir)
+      end
+    else
+      ensure_writable_dir spec_dir
+    end
+
+    begin
+      Gem.write_binary(spec_file, spec.to_ruby_for_cache)
+    ensure
+      File.chmod(dir_mode, spec_dir) if dir_mode && content_addressed
+    end
   end
 
   ##
@@ -973,6 +996,10 @@ def ensure_writable_dir(dir) # :nodoc:
 
   private
 
+  def incompatible_abi_install?
+    Gem::ContentAddress.content_addressed?(spec) && spec.ruby_abi != Gem.ruby_abi
+  end
+
   def assign_content_address
     address = @package.content_address
     expected = options[:content_address]

lib/rubygems/package.rb

@@ -556,7 +556,7 @@ def extract_tar_gz(io, destination_dir, pattern = "*") # :nodoc:
       end
     end
 
-    if dir_mode
+    if dir_mode && !directories.empty?
       File.chmod(dir_mode, *directories)
     end
   end

lib/rubygems/request_set.rb

@@ -518,8 +518,10 @@ def specs
   end
 
   def specs_in(dir)
-    Gem::Util.glob_files_in_dir("*.gemspec", File.join(dir, "specifications")).map do |g|
-      Gem::Specification.load g
+    Gem::SpecificationRecord.dirs_from([dir]).flat_map do |spec_dir|
+      Gem::Util.glob_files_in_dir("*.gemspec", spec_dir).map do |g|
+        Gem::Specification.load g
+      end
     end
   end
 

lib/rubygems/resolver/lock_specification.rb

@@ -30,7 +30,11 @@ def initialize(set, name, version, sources, platform)
   def install(options = {})
     destination = options[:install_dir] || Gem.dir
 
-    if File.exist? File.join(destination, "specifications", spec.spec_name)
+    installed = Gem::SpecificationRecord.dirs_from([destination]).any? do |spec_dir|
+      File.exist? File.join(spec_dir, spec.spec_name)
+    end
+
+    if installed
       yield nil
       return
     end

lib/rubygems/specification.rb

@@ -1263,7 +1263,11 @@ def self.reset
   # Keeps track of all currently known specifications
 
   def self.specification_record
-    @specification_record ||= Gem::SpecificationRecord.new(dirs)
+    @specification_record ||= Gem::SpecificationRecord.new(
+      Gem::SpecificationRecord.dirs_with_abi(
+        (defined?(@@dirs) ? @@dirs : nil) || Gem::SpecificationRecord.dirs_from(gem_path)
+      )
+    )
   end
 
   # DOC: This method needs documented or nodoc'd
@@ -2026,13 +2030,19 @@ def initialize_copy(other_spec)
 
   def base_dir
     return Gem.dir unless loaded_from
-    @base_dir ||= if default_gem?
+    @base_dir ||= if default_gem? || loaded_from_abi_scoped_spec_dir?
       File.dirname File.dirname File.dirname loaded_from
     else
       File.dirname File.dirname loaded_from
     end
   end
 
+  def loaded_from_abi_scoped_spec_dir?
+    !loaded_from.nil? &&
+      Gem::SpecificationRecord.abi_scoped_spec_dir?(File.dirname(loaded_from))
+  end
+  private :loaded_from_abi_scoped_spec_dir?
+
   def inspect # :nodoc:
     if $DEBUG
       super
@@ -2330,9 +2340,16 @@ def source # :nodoc:
   ##
   # Returns the full path to the directory containing this spec's
   # gemspec file. eg: /usr/local/lib/ruby/gems/1.8/specifications
+  #
+  # Content-addressable gemspecs live in the ABI-scoped subdirectory,
+  # eg: /usr/local/lib/ruby/gems/1.8/specifications/3.4
 
   def spec_dir
-    @spec_dir ||= File.join base_dir, "specifications"
+    @spec_dir ||= if loaded_from && Gem::ContentAddress.content_addressed?(self)
+      File.dirname loaded_from
+    else
+      Gem::SpecificationRecord.specification_dir_for(self, base_dir)
+    end
   end
 
   ##