Log build environment on failure

Library/Homebrew/cmd/--env.rb

@@ -30,7 +30,7 @@ module Homebrew
       ACLOCAL_PATH PATH CPATH].select { |key| env.key?(key) }
   end
 
-  def dump_build_env env
+  def dump_build_env env, f=$stdout
     keys = build_env_keys(env)
     keys -= %w[CC CXX OBJC OBJCXX] if env["CC"] == env["HOMEBREW_CC"]
 
@@ -41,7 +41,7 @@ module Homebrew
       when "CC", "CXX", "LD"
         s << " => #{Pathname.new(value).realpath}" if File.symlink?(value)
       end
-      puts s
+      f.puts s
     end
   end
 end

Library/Homebrew/formula.rb

@@ -686,9 +686,17 @@ class Formula
         log.flush
         Kernel.system "/usr/bin/tail", "-n", "5", logfn unless verbose
         log.puts
-        require 'cmd/config'
+
+        require "cmd/config"
+        require "cmd/--env"
+
+        env = ENV.to_hash
+
         Homebrew.dump_verbose_config(log)
-        raise BuildError.new(self, cmd, args, ENV.to_hash)
+        log.puts
+        Homebrew.dump_build_env(env, log)
+
+        raise BuildError.new(self, cmd, args, env)
       end
     ensure
       log.close