brew: warn about 10.11 unsupported

Issue a warning about Homebrew's very basic support for 10.11 at this point
in time on each run of `brew`.

Closes Homebrew/homebrew#40536.

Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/Library/brew.rb b/Library/brew.rb
index 8b8376422..1441f347b 100755
--- a/Library/brew.rb
+++ b/Library/brew.rb
@@ -50,6 +50,15 @@ if OS.mac? and MacOS.version < "10.6"
   EOABORT
 end
 
+if OS.mac? && MacOS.version == "10.11"
+  opoo <<-EOS.undent
+    Although Homebrew has added initial recognition of 10.11, it is unsupported.
+    You may encounter breakage or other failure and there is no guarantee
+    Homebrew can resolve those issues until El Capitan is stable.
+
+  EOS
+end
+
 # Many Pathname operations use getwd when they shouldn't, and then throw
 # odd exceptions. Reduce our support burden by showing a user-friendly error.
 Dir.getwd rescue abort "The current working directory doesn't exist, cannot proceed."