superenv: filter -I/-L paths on dependencies

Previously, superenv did not try to filter -I or -L flags
based on the list of requested dependencies; as a result, buildsystems
which opportunistically discover Homebrew-installed libraries were able
to link against them even under superenv.

This adds a list of all requested dependencies to the superenv environment,
and compares all -I and -L flags against those; any Cellar and opt paths
found which resolve to unrequested dependencies are filtered out.

Library/ENV/4.3/cc

@@ -14,8 +14,8 @@ require "pathname"
 require "set"
 
 class Cmd
-  attr_reader :config, :prefix, :cellar, :tmpdir, :sysroot
+  attr_reader :config, :prefix, :cellar, :opt, :tmpdir, :sysroot, :deps
-  attr_reader :archflags, :optflags
+  attr_reader :archflags, :optflags, :keg_regex
 
   def initialize(arg0, args)
     @arg0 = arg0
@@ -23,10 +23,14 @@ class Cmd
     @config = ENV.fetch("HOMEBREW_CCCFG") { "" }
     @prefix = ENV["HOMEBREW_PREFIX"]
     @cellar = ENV["HOMEBREW_CELLAR"]
+    @opt = ENV["HOMEBREW_OPT"]
     @tmpdir = ENV["HOMEBREW_TEMP"]
     @sysroot = ENV["HOMEBREW_SDKROOT"]
     @archflags = ENV.fetch("HOMEBREW_ARCHFLAGS") { "" }.split(" ")
     @optflags = ENV.fetch("HOMEBREW_OPTFLAGS") { "" }.split(" ")
+    @deps = Set.new(ENV.fetch("HOMEBREW_DEPENDENCIES") { "" }.split(","))
+    # matches opt or cellar prefix and formula name
+    @keg_regex = %r[(#{Regexp.escape(opt)}|#{Regexp.escape(cellar)})/([\w\-_\+]+)]
   end
 
   def mode
@@ -197,7 +201,16 @@ class Cmd
   end
 
   def keep?(path)
-    path.start_with?(prefix, cellar, tmpdir) || !path.start_with?("/opt", "/sw", "/usr/X11")
+    # first two paths: reject references to Cellar or opt paths
+    # for unspecified dependencies
+    if path.start_with?(cellar) || path.start_with?(opt)
+      dep = path[keg_regex, 2]
+      dep && @deps.include?(dep)
+    elsif path.start_with?(prefix)
+      true
+    else
+      !path.start_with?("/opt", "/sw", "/usr/X11")
+    end
   end
 
   def cflags

Library/Homebrew/extend/ENV/super.rb

@@ -53,6 +53,7 @@ module Superenv
     self["HOMEBREW_BREW_FILE"] = HOMEBREW_BREW_FILE.to_s
     self["HOMEBREW_PREFIX"] = HOMEBREW_PREFIX.to_s
     self["HOMEBREW_CELLAR"] = HOMEBREW_CELLAR.to_s
+    self["HOMEBREW_OPT"] = "#{HOMEBREW_PREFIX}/opt"
     self["HOMEBREW_TEMP"] = HOMEBREW_TEMP.to_s
     self["HOMEBREW_SDKROOT"] = effective_sysroot
     self["HOMEBREW_OPTFLAGS"] = determine_optflags
@@ -66,6 +67,7 @@ module Superenv
     self["HOMEBREW_ISYSTEM_PATHS"] = determine_isystem_paths
     self["HOMEBREW_INCLUDE_PATHS"] = determine_include_paths
     self["HOMEBREW_LIBRARY_PATHS"] = determine_library_paths
+    self["HOMEBREW_DEPENDENCIES"] = determine_dependencies
 
     if MacOS::Xcode.without_clt? || (MacOS::Xcode.installed? && MacOS::Xcode.version.to_i >= 7)
       self["MACOSX_DEPLOYMENT_TARGET"] = MacOS.version.to_s
@@ -184,6 +186,10 @@ module Superenv
     paths.to_path_s
   end
 
+  def determine_dependencies
+    deps.map {|d| d.name}.join(",")
+  end
+
   def determine_cmake_prefix_path
     paths = keg_only_deps.map { |d| d.opt_prefix.to_s }
     paths << HOMEBREW_PREFIX.to_s