utils/path: add child_of? method

Library/Homebrew/test/utils/path_spec.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require "utils/path"
+
+RSpec.describe Utils::Path do
+  describe "::child_of?" do
+    it "recognizes a path as its own child" do
+      expect(described_class.child_of?("/foo/bar", "/foo/bar")).to be(true)
+    end
+
+    it "recognizes a path that is a child of the parent" do
+      expect(described_class.child_of?("/foo", "/foo/bar")).to be(true)
+    end
+
+    it "recognizes a path that is a grandchild of the parent" do
+      expect(described_class.child_of?("/foo", "/foo/bar/baz")).to be(true)
+    end
+
+    it "does not recognize a path that is not a child" do
+      expect(described_class.child_of?("/foo", "/bar/baz")).to be(false)
+    end
+
+    it "handles . and .. in paths correctly" do
+      expect(described_class.child_of?("/foo", "/foo/./bar")).to be(true)
+      expect(described_class.child_of?("/foo/bar", "/foo/../foo/bar/baz")).to be(true)
+    end
+
+    it "handles relative paths correctly" do
+      expect(described_class.child_of?("foo", "./bar/baz")).to be(false)
+      expect(described_class.child_of?("../foo", "./bar/baz/../../../foo/bar/baz")).to be(true)
+    end
+  end
+end

Library/Homebrew/utils/path.rb

@@ -0,0 +1,14 @@
+# typed: strict
+# frozen_string_literal: true
+
+module Utils
+  module Path
+    sig { params(parent: T.any(Pathname, String), child: T.any(Pathname, String)).returns(T::Boolean) }
+    def self.child_of?(parent, child)
+      parent_pathname = Pathname(parent).expand_path
+      child_pathname = Pathname(child).expand_path
+      child_pathname.ascend { |p| return true if p == parent_pathname }
+      false
+    end
+  end
+end