diagnostic: more porting to generic OS. (#449)

Library/Homebrew/cmd/install.rb

@@ -218,15 +218,9 @@ module Homebrew
     raise "Cannot write to #{HOMEBREW_PREFIX}" unless HOMEBREW_PREFIX.writable_real? || HOMEBREW_PREFIX.to_s == "/usr/local"
   end
 
-  def check_xcode
+  def check_development_tools
     checks = Diagnostic::Checks.new
-    %w[
-      check_for_unsupported_osx
-      check_for_bad_install_name_tool
-      check_for_installed_developer_tools
-      check_xcode_license_approved
-      check_for_osx_gcc_installer
-    ].each do |check|
+    checks.all_development_tools_checks.each do |check|
       out = checks.send(check)
       opoo out unless out.nil?
     end
@@ -252,7 +246,7 @@ module Homebrew
   def perform_preinstall_checks
     check_ppc
     check_writable_install_location
-    check_xcode if MacOS.has_apple_developer_tools?
+    check_development_tools if DevelopmentTools.installed?
     check_cellar
   end
 

Library/Homebrew/diagnostic.rb

@@ -85,6 +85,21 @@ module Homebrew
       end
       ############# END HELPERS
 
+      def all_development_tools_checks
+        %w[
+          check_for_installed_developer_tools
+        ]
+      end
+
+      def check_for_installed_developer_tools
+        return if DevelopmentTools.installed?
+
+        <<-EOS.undent
+          No developer tools installed.
+          Install clang or gcc.
+        EOS
+      end
+
       # See https://github.com/Homebrew/legacy-homebrew/pull/9986
       def check_path_for_trailing_slashes
         all_paths = ENV["PATH"].split(File::PATH_SEPARATOR)

Library/Homebrew/extend/os/mac/diagnostic.rb

@@ -1,6 +1,16 @@
 module Homebrew
   module Diagnostic
     class Checks
+      def all_development_tools_checks
+        %w[
+          check_for_unsupported_osx
+          check_for_bad_install_name_tool
+          check_for_installed_developer_tools
+          check_xcode_license_approved
+          check_for_osx_gcc_installer
+        ]
+      end
+
       def check_for_unsupported_osx
         return if ARGV.homebrew_developer?