diagnostic: move some more macOS doctor checks.

Move some `brew doctor` checks that are pretty macOS specific so they
are only run on macOS.

Library/Homebrew/diagnostic.rb

@@ -415,23 +415,6 @@ module Homebrew
         EOS
       end
 
-      def check_homebrew_prefix
-        return if HOMEBREW_PREFIX.to_s == "/usr/local"
-
-        # Allow our Jenkins CI tests to live outside of /usr/local.
-        if ENV["JENKINS_HOME"] &&
-           ENV["GIT_URL"].to_s.start_with?("https://github.com/Homebrew/brew")
-          return
-        end
-
-        <<-EOS.undent
-          Your Homebrew's prefix is not /usr/local.
-          You can install Homebrew anywhere you want but some bottles (binary packages)
-          can only be used with a /usr/local prefix and some formulae (packages)
-          may not build correctly with a non-/usr/local prefix.
-        EOS
-      end
-
       def check_user_path_1
         $seen_prefix_bin = false
         $seen_prefix_sbin = false
@@ -513,33 +496,6 @@ module Homebrew
         EOS
       end
 
-      def check_which_pkg_config
-        binary = which "pkg-config"
-        return if binary.nil?
-
-        mono_config = Pathname.new("/usr/bin/pkg-config")
-        if mono_config.exist? && mono_config.realpath.to_s.include?("Mono.framework")
-          <<-EOS.undent
-            You have a non-Homebrew 'pkg-config' in your PATH:
-              /usr/bin/pkg-config => #{mono_config.realpath}
-
-            This was most likely created by the Mono installer. `./configure` may
-            have problems finding brew-installed packages using this other pkg-config.
-
-            Mono no longer installs this file as of 3.0.4. You should
-            `sudo rm /usr/bin/pkg-config` and upgrade to the latest version of Mono.
-          EOS
-        elsif binary.to_s != "#{HOMEBREW_PREFIX}/bin/pkg-config"
-          <<-EOS.undent
-            You have a non-Homebrew 'pkg-config' in your PATH:
-              #{binary}
-
-            `./configure` may have problems finding brew-installed packages using
-            this other pkg-config.
-          EOS
-        end
-      end
-
       def check_for_gettext
         find_relative_paths("lib/libgettextlib.dylib",
                             "lib/libintl.dylib",
@@ -716,39 +672,6 @@ module Homebrew
         EOS
       end
 
-      def check_filesystem_case_sensitive
-        dirs_to_check = [
-          HOMEBREW_PREFIX,
-          HOMEBREW_REPOSITORY,
-          HOMEBREW_CELLAR,
-          HOMEBREW_TEMP,
-        ]
-        case_sensitive_dirs = dirs_to_check.select do |dir|
-          # We select the dir as being case-sensitive if either the UPCASED or the
-          # downcased variant is missing.
-          # Of course, on a case-insensitive fs, both exist because the os reports so.
-          # In the rare situation when the user has indeed a downcased and an upcased
-          # dir (e.g. /TMP and /tmp) this check falsely thinks it is case-insensitive
-          # but we don't care because: 1. there is more than one dir checked, 2. the
-          # check is not vital and 3. we would have to touch files otherwise.
-          upcased = Pathname.new(dir.to_s.upcase)
-          downcased = Pathname.new(dir.to_s.downcase)
-          dir.exist? && !(upcased.exist? && downcased.exist?)
-        end
-        return if case_sensitive_dirs.empty?
-
-        volumes = Volumes.new
-        case_sensitive_vols = case_sensitive_dirs.map do |case_sensitive_dir|
-          volumes.get_mounts(case_sensitive_dir)
-        end
-        case_sensitive_vols.uniq!
-
-        <<-EOS.undent
-          The filesystem on #{case_sensitive_vols.join(",")} appears to be case-sensitive.
-          The default macOS filesystem is case-insensitive. Please report any apparent problems.
-        EOS
-      end
-
       def check_git_version
         # https://help.github.com/articles/https-cloning-errors
         return unless Utils.git_available?

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

@@ -307,6 +307,77 @@ module Homebrew
           We recommend only installing stable releases of XQuartz.
         EOS
       end
+
+      def check_filesystem_case_sensitive
+        dirs_to_check = [
+          HOMEBREW_PREFIX,
+          HOMEBREW_REPOSITORY,
+          HOMEBREW_CELLAR,
+          HOMEBREW_TEMP,
+        ]
+        case_sensitive_dirs = dirs_to_check.select do |dir|
+          # We select the dir as being case-sensitive if either the UPCASED or the
+          # downcased variant is missing.
+          # Of course, on a case-insensitive fs, both exist because the os reports so.
+          # In the rare situation when the user has indeed a downcased and an upcased
+          # dir (e.g. /TMP and /tmp) this check falsely thinks it is case-insensitive
+          # but we don't care because: 1. there is more than one dir checked, 2. the
+          # check is not vital and 3. we would have to touch files otherwise.
+          upcased = Pathname.new(dir.to_s.upcase)
+          downcased = Pathname.new(dir.to_s.downcase)
+          dir.exist? && !(upcased.exist? && downcased.exist?)
+        end
+        return if case_sensitive_dirs.empty?
+
+        volumes = Volumes.new
+        case_sensitive_vols = case_sensitive_dirs.map do |case_sensitive_dir|
+          volumes.get_mounts(case_sensitive_dir)
+        end
+        case_sensitive_vols.uniq!
+
+        <<-EOS.undent
+          The filesystem on #{case_sensitive_vols.join(",")} appears to be case-sensitive.
+          The default macOS filesystem is case-insensitive. Please report any apparent problems.
+        EOS
+      end
+
+      def check_homebrew_prefix
+        return if HOMEBREW_PREFIX.to_s == "/usr/local"
+
+        <<-EOS.undent
+          Your Homebrew's prefix is not /usr/local.
+          You can install Homebrew anywhere you want but some bottles (binary packages)
+          can only be used with a /usr/local prefix and some formulae (packages)
+          may not build correctly with a non-/usr/local prefix.
+        EOS
+      end
+
+      def check_which_pkg_config
+        binary = which "pkg-config"
+        return if binary.nil?
+
+        mono_config = Pathname.new("/usr/bin/pkg-config")
+        if mono_config.exist? && mono_config.realpath.to_s.include?("Mono.framework")
+          <<-EOS.undent
+            You have a non-Homebrew 'pkg-config' in your PATH:
+              /usr/bin/pkg-config => #{mono_config.realpath}
+
+            This was most likely created by the Mono installer. `./configure` may
+            have problems finding brew-installed packages using this other pkg-config.
+
+            Mono no longer installs this file as of 3.0.4. You should
+            `sudo rm /usr/bin/pkg-config` and upgrade to the latest version of Mono.
+          EOS
+        elsif binary.to_s != "#{HOMEBREW_PREFIX}/bin/pkg-config"
+          <<-EOS.undent
+            You have a non-Homebrew 'pkg-config' in your PATH:
+              #{binary}
+
+            `./configure` may have problems finding brew-installed packages using
+            this other pkg-config.
+          EOS
+        end
+      end
     end
   end
 end

Library/Homebrew/test/diagnostic_spec.rb

@@ -90,13 +90,6 @@ describe Homebrew::Diagnostic::Checks do
     end
   end
 
-  specify "#check_homebrew_prefix" do
-    ENV.delete("JENKINS_HOME")
-    # the integration tests are run in a special prefix
-    expect(subject.check_homebrew_prefix)
-      .to match("Your Homebrew's prefix is not /usr/local.")
-  end
-
   specify "#check_user_path_1" do
     bin = HOMEBREW_PREFIX/"bin"
     sep = File::PATH_SEPARATOR

Library/Homebrew/test/os/mac/diagnostic_spec.rb

@@ -39,4 +39,10 @@ describe Homebrew::Diagnostic::Checks do
     expect(subject.check_xcode_8_without_clt_on_el_capitan)
       .to match("You have Xcode 8 installed without the CLT")
   end
+
+  specify "#check_homebrew_prefix" do
+    # the integration tests are run in a special prefix
+    expect(subject.check_homebrew_prefix)
+      .to match("Your Homebrew's prefix is not /usr/local.")
+  end
 end