Add `PATH` class.

Library/Homebrew/PATH.rb

+class PATH
+  def initialize(*paths)
+    @paths = parse(*paths)
+  end
+
+  def prepend(*paths)
+    @paths.unshift(*parse(*paths))
+    self
+  end
+
+  def append(*paths)
+    @paths.concat(parse(*paths))
+    self
+  end
+
+  def to_ary
+    @paths
+  end
+  alias to_a to_ary
+
+  def to_str
+    @paths.join(File::PATH_SEPARATOR)
+  end
+  alias to_s to_str
+
+  def eql?(other)
+    if other.respond_to?(:to_ary)
+      return true if to_ary == other.to_ary
+    end
+
+    if other.respond_to?(:to_str)
+      return true if to_str == other.to_str
+    end
+
+    false
+  end
+  alias == eql?
+
+  def empty?
+    @paths.empty?
+  end
+
+  def inspect
+    "<PATH##{to_str}>"
+  end
+
+  def validate
+    self.class.new(@paths.select(&File.method(:directory?)))
+  end
+
+  private
+
+  def parse(*paths)
+    paths
+      .flatten
+      .flat_map { |p| p.respond_to?(:to_str) ? p.to_str.split(File::PATH_SEPARATOR): p }
+      .compact
+      .map { |p| p.respond_to?(:to_path) ? p.to_path : p.to_str }
+      .uniq
+  end
+end

Library/Homebrew/global.rb

@@ -3,6 +3,7 @@ require "extend/fileutils"
 require "extend/pathname"
 require "extend/git_repository"
 require "extend/ARGV"
+require "PATH"
 require "extend/string"
 require "os"
 require "utils"

Library/Homebrew/test/PATH_spec.rb

+require "PATH"
+
+describe PATH do
+  describe "#initialize" do
+    it "can take multiple arguments" do
+      expect(described_class.new("/path1", "/path2")).to eq("/path1:/path2")
+    end
+
+    it "can parse a mix of arrays and arguments" do
+      expect(described_class.new(["/path1", "/path2"], "/path3")).to eq("/path1:/path2:/path3")
+    end
+
+    it "splits an existing PATH" do
+      expect(described_class.new("/path1:/path2")).to eq(["/path1", "/path2"])
+    end
+  end
+
+  describe "#to_ary" do
+    it "returns a PATH array" do
+      expect(described_class.new("/path1", "/path2").to_ary).to eq(["/path1", "/path2"])
+    end
+  end
+
+  describe "#to_str" do
+    it "returns a PATH string" do
+      expect(described_class.new("/path1", "/path2").to_str).to eq("/path1:/path2")
+    end
+  end
+
+  describe "#prepend" do
+    it "prepends a path to a PATH" do
+      expect(described_class.new("/path1").prepend("/path2").to_str).to eq("/path2:/path1")
+    end
+  end
+
+  describe "#append" do
+    it "prepends a path to a PATH" do
+      expect(described_class.new("/path1").append("/path2").to_str).to eq("/path1:/path2")
+    end
+  end
+
+  describe "#validate" do
+    it "returns a new PATH without non-existent paths" do
+      allow(File).to receive(:directory?).with("/path1").and_return(true)
+      allow(File).to receive(:directory?).with("/path2").and_return(false)
+
+      path = described_class.new("/path1", "/path2")
+      expect(path.validate.to_ary).to eq(["/path1"])
+      expect(path.to_ary).to eq(["/path1", "/path2"])
+    end
+  end
+end