Preserve alias when installing formulae

Part of #567

Library/Homebrew/formula.rb

@@ -58,6 +58,11 @@ class Formula
   # e.g. `this-formula`
   attr_reader :name
 
+  # The name specified when installing this {Formula}.
+  # Could be the name of the {Formula}, or an alias.
+  # e.g. `another-name-for-this-formula`
+  attr_reader :install_name
+
   # The fully-qualified name of this {Formula}.
   # For core formula it's the same as {#name}.
   # e.g. `homebrew/tap-name/this-formula`
@@ -143,9 +148,10 @@ class Formula
   attr_accessor :build
 
   # @private
-  def initialize(name, path, spec)
+  def initialize(name, path, spec, install_name: name)
     @name = name
     @path = path
+    @install_name = install_name
     @revision = self.class.revision || 0
     @version_scheme = self.class.version_scheme || 0
 
@@ -502,6 +508,21 @@ class Formula
     installed_prefixes.map { |dir| Keg.new(dir) }
   end
 
+  # Formula reference to use to get an identical installation of the formula.
+  #
+  # Usually, the formula's path is a good canonical identifier for the formula.
+  # Just using whatever was passed to `brew install` isn't a good idea, because
+  # if it was e.g. a URL, it could end up being downloaded twice.
+  #
+  # However, if the formula was installed with an alias (i.e. `install_name` is
+  # different from `name`), that should be used instead so that information is
+  # preserved. Aliases are looked up in repositories that have already been
+  # tapped, so we don't have to worry about doing extra HTTP requests, or other
+  # expensive operations, when looking them up again.
+  def install_ref
+    install_name == name ? path : install_name
+  end
+
   # The directory where the formula's binaries should be installed.
   # This is symlinked into `HOMEBREW_PREFIX` after installation or with
   # `brew link` for formulae that are not keg-only.

Library/Homebrew/formula_installer.rb

@@ -589,7 +589,7 @@ class FormulaInstaller
       -I #{HOMEBREW_LOAD_PATH}
       --
       #{HOMEBREW_LIBRARY_PATH}/build.rb
-      #{formula.path}
+      #{formula.install_ref}
     ].concat(build_argv)
 
     Sandbox.print_sandbox_message if Sandbox.formula?(formula)

Library/Homebrew/formulary.rb

@@ -68,15 +68,18 @@ class Formulary
     attr_reader :name
     # The formula's ruby file's path or filename
     attr_reader :path
+    # The name used to install the formula
+    attr_reader :install_name
 
     def initialize(name, path)
       @name = name
       @path = path.resolved_path
+      @install_name = name
     end
 
     # Gets the formula instance.
     def get_formula(spec)
-      klass.new(name, path, spec)
+      klass.new(name, path, spec, install_name: install_name)
     end
 
     def klass
@@ -118,6 +121,7 @@ class Formulary
       path = alias_path.resolved_path
       name = path.basename(".rb").to_s
       super name, path
+      @install_name = alias_path.basename.to_s
     end
   end
 

Library/Homebrew/tab.rb

@@ -27,6 +27,7 @@ class Tab < OpenStruct
       "time" => Time.now.to_i,
       "source_modified_time" => formula.source_modified_time.to_i,
       "HEAD" => HOMEBREW_REPOSITORY.git_head,
+      "install_name" => formula.install_name,
       "compiler" => compiler,
       "stdlib" => stdlib,
       "source" => {
@@ -161,6 +162,7 @@ class Tab < OpenStruct
       "time" => nil,
       "source_modified_time" => 0,
       "HEAD" => nil,
+      "install_name" => nil,
       "stdlib" => nil,
       "compiler" => DevelopmentTools.default_compiler,
       "source" => {
@@ -292,6 +294,7 @@ class Tab < OpenStruct
       "time" => time,
       "source_modified_time" => source_modified_time.to_i,
       "HEAD" => self.HEAD,
+      "install_name" => install_name,
       "stdlib" => (stdlib.to_s if stdlib),
       "compiler" => (compiler.to_s if compiler),
       "source" => source

Library/Homebrew/test/fixtures/receipt.json

@@ -11,6 +11,7 @@
   "poured_from_bottle": true,
   "time": 1403827774,
   "HEAD": "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef",
+  "install_name": "test-formula",
   "stdlib": "libcxx",
   "compiler": "clang",
   "source": {

Library/Homebrew/test/test_formula.rb

@@ -8,13 +8,30 @@ class FormulaTests < Homebrew::TestCase
     name = "formula_name"
     path = Formulary.core_path(name)
     spec = :stable
+    install_name = "formula_alias"
 
-    f = klass.new(name, path, spec)
+    f = klass.new(name, path, spec, install_name: install_name)
     assert_equal name, f.name
     assert_equal path, f.path
+    assert_equal install_name, f.install_name
     assert_raises(ArgumentError) { klass.new }
   end
 
+  def test_install_ref_with_alias
+    name = "formula_name"
+    path = Formulary.core_path(name)
+    spec = :stable
+    install_name = "formula_alias"
+
+    f = Testball.new(name, path, spec, install_name: install_name)
+    assert_equal f.install_name, f.install_ref
+  end
+
+  def test_install_ref_with_non_alias
+    f = Testball.new
+    assert_equal f.path, f.install_ref
+  end
+
   def test_prefix
     f = Testball.new
     assert_equal HOMEBREW_CELLAR/f.name/"0.1", f.prefix

Library/Homebrew/test/test_formulary.rb

@@ -86,7 +86,9 @@ class FormularyFactoryTest < Homebrew::TestCase
     alias_dir = CoreTap.instance.alias_dir
     alias_dir.mkpath
     FileUtils.ln_s @path, alias_dir/"foo"
-    assert_kind_of Formula, Formulary.factory("foo")
+    result = Formulary.factory("foo")
+    assert_kind_of Formula, result
+    assert_equal "foo", result.install_name
   ensure
     alias_dir.rmtree
   end

Library/Homebrew/test/test_tab.rb

@@ -43,6 +43,7 @@ class TabTests < Homebrew::TestCase
     assert_nil tab.stable_version
     assert_nil tab.devel_version
     assert_nil tab.head_version
+    assert_nil tab.install_name
     assert_equal DevelopmentTools.default_compiler, tab.cxxstdlib.compiler
     assert_nil tab.cxxstdlib.type
   end
@@ -116,6 +117,7 @@ class TabTests < Homebrew::TestCase
     assert_equal "2.14", tab.stable_version.to_s
     assert_equal "2.15", tab.devel_version.to_s
     assert_equal "HEAD-0000000", tab.head_version.to_s
+    assert_equal "test-formula", tab.install_name
   end
 
   def test_to_json
@@ -133,6 +135,7 @@ class TabTests < Homebrew::TestCase
     assert_equal @tab.stable_version, tab.stable_version
     assert_equal @tab.devel_version, tab.devel_version
     assert_equal @tab.head_version, tab.head_version
+    assert_equal @tab.install_name, tab.install_name
   end
 
   def test_remap_deprecated_options

Library/Homebrew/test/testball.rb

@@ -1,5 +1,5 @@
 class Testball < Formula
-  def initialize(name = "testball", path = Pathname.new(__FILE__).expand_path, spec = :stable)
+  def initialize(name = "testball", path = Pathname.new(__FILE__).expand_path, spec = :stable, install_name: name)
     self.class.instance_eval do
       stable.url "file://#{File.expand_path("..", __FILE__)}/tarballs/testball-0.1.tbz"
       stable.sha256 TESTBALL_SHA256

Library/Homebrew/test/testball_bottle.rb

@@ -1,5 +1,5 @@
 class TestballBottle < Formula
-  def initialize(name = "testball_bottle", path = Pathname.new(__FILE__).expand_path, spec = :stable)
+  def initialize(name = "testball_bottle", path = Pathname.new(__FILE__).expand_path, spec = :stable, install_name: name)
     self.class.instance_eval do
       stable.url "file://#{File.expand_path("..", __FILE__)}/tarballs/testball-0.1.tbz"
       stable.sha256 TESTBALL_SHA256