From 0ddb2c9acc2f0e594df4bf8eb5b52589b32a8835 Mon Sep 17 00:00:00 2001
From: Patrick Linnane <patrick@linnane.io>
Date: Wed, 20 May 2026 21:19:02 -0700
Subject: [PATCH 1/3] pathname: eagerly initialize lazy instance variables

Continues d57efd9ea2 by initialising the lazy memoised instance
variables defined in `extend/pathname.rb` and `DiskUsageExtension`
(`@magic_number`, `@file_type`, `@zipinfo`, `@which_install_info`,
`@disk_usage`, `@file_count`) up front via a new prepended
`EagerInitializeExtension` module, so every `Pathname` instance
shares the same object shape and we no longer hit:

    warning: The class Pathname reached 8 shape variations,
    instance variables accesses will be slower and memory usage
    increased.
---
 Library/Homebrew/extend/pathname.rb           |  2 ++
 .../pathname/eager_initialize_extension.rb    | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 Library/Homebrew/extend/pathname/eager_initialize_extension.rb

diff --git a/Library/Homebrew/extend/pathname.rb b/Library/Homebrew/extend/pathname.rb
index e329ca97282a9..175f834c879d7 100644
--- a/Library/Homebrew/extend/pathname.rb
+++ b/Library/Homebrew/extend/pathname.rb
@@ -3,6 +3,7 @@
 
 require "system_command"
 require "extend/pathname/disk_usage_extension"
+require "extend/pathname/eager_initialize_extension"
 require "extend/pathname/observer_pathname_extension"
 require "extend/pathname/write_mkpath_extension"
 require "utils/output"
@@ -29,6 +30,7 @@ class Pathname
   include SystemCommand::Mixin
   include DiskUsageExtension
   include Utils::Output::Mixin
+  prepend EagerInitializeExtension
 
   sig { void }
   def self.activate_extensions!
diff --git a/Library/Homebrew/extend/pathname/eager_initialize_extension.rb b/Library/Homebrew/extend/pathname/eager_initialize_extension.rb
new file mode 100644
index 0000000000000..f7d7c1c17bbee
--- /dev/null
+++ b/Library/Homebrew/extend/pathname/eager_initialize_extension.rb
@@ -0,0 +1,19 @@
+# typed: strict
+# frozen_string_literal: true
+
+module EagerInitializeExtension
+  extend T::Helpers
+
+  requires_ancestor { Pathname }
+
+  sig { params(args: T.untyped).void }
+  def initialize(*args)
+    @magic_number = T.let(nil, T.nilable(String))
+    @file_type = T.let(nil, T.nilable(String))
+    @zipinfo = T.let(nil, T.nilable(T::Array[String]))
+    @which_install_info = T.let(nil, T.nilable(String))
+    @disk_usage = T.let(nil, T.nilable(Integer))
+    @file_count = T.let(nil, T.nilable(Integer))
+    super
+  end
+end

From 3af57b9692d9be50e58519970af752d737e20501 Mon Sep 17 00:00:00 2001
From: Patrick Linnane <patrick@linnane.io>
Date: Wed, 20 May 2026 21:48:11 -0700
Subject: [PATCH 2/3] pathname: spec EagerInitializeExtension ivar
 pre-allocation

Lock the eager-init invariant so adding a new lazy memoised ivar to
`Pathname`/`DiskUsageExtension` without updating
`EagerInitializeExtension` (and thus reintroducing shape churn) is
caught in CI.
---
 Library/Homebrew/test/pathname_spec.rb | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Library/Homebrew/test/pathname_spec.rb b/Library/Homebrew/test/pathname_spec.rb
index 4f498505dd3de..71bbd9903314c 100644
--- a/Library/Homebrew/test/pathname_spec.rb
+++ b/Library/Homebrew/test/pathname_spec.rb
@@ -12,6 +12,16 @@
   let(:file) { src/"foo" }
   let(:dir) { src/"bar" }
 
+  describe EagerInitializeExtension do
+    it "defines the lazy memoised ivars on every new Pathname" do
+      pathname = Pathname.new(file.to_s)
+      [:@magic_number, :@file_type, :@zipinfo, :@which_install_info, :@disk_usage, :@file_count].each do |ivar|
+        expect(pathname.instance_variable_defined?(ivar)).to be(true), "expected #{ivar} to be defined"
+        expect(pathname.instance_variable_get(ivar)).to be_nil
+      end
+    end
+  end
+
   describe DiskUsageExtension do
     before do
       mkdir_p dir/"a-directory"

From 9bc2ff4bae52a2af9e23064d9e7d9491b63c75e0 Mon Sep 17 00:00:00 2001
From: Patrick Linnane <patrick@linnane.io>
Date: Thu, 21 May 2026 08:13:14 -0700
Subject: [PATCH 3/3] pathname: document EagerInitializeExtension rationale

Explain why the module exists (shape cache warning) and the
contract for adding/removing lazy memoised ivars on `Pathname`
or its mixed-in extensions, per review feedback.
---
 .../Homebrew/extend/pathname/eager_initialize_extension.rb   | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Library/Homebrew/extend/pathname/eager_initialize_extension.rb b/Library/Homebrew/extend/pathname/eager_initialize_extension.rb
index f7d7c1c17bbee..14c689ebcf61e 100644
--- a/Library/Homebrew/extend/pathname/eager_initialize_extension.rb
+++ b/Library/Homebrew/extend/pathname/eager_initialize_extension.rb
@@ -1,6 +1,11 @@
 # typed: strict
 # frozen_string_literal: true
 
+# Eagerly initialises {Pathname}'s lazy memoised ivars so every instance
+# shares one object shape, avoiding Ruby's shape-variation warning.
+#
+# Any new `@x ||= ...` ivar added to {Pathname} or its mixed-in extensions
+# must also be added to `#initialize` below to keep the shape stable.
 module EagerInitializeExtension
   extend T::Helpers