From f18cbd2066d114ad3dec053c2df4845f4621dc6a Mon Sep 17 00:00:00 2001
From: Phoenix Eliot <phoenixjeliot@gmail.com>
Date: Tue, 11 Jan 2022 14:16:35 -0500
Subject: [PATCH] Add helpful error message when attempting to run `brew cask`

---
 Library/Homebrew/brew.rb     | 4 ++++
 Library/Homebrew/commands.rb | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/Library/Homebrew/brew.rb b/Library/Homebrew/brew.rb
index 945c14dea1..865fefda9f 100644
--- a/Library/Homebrew/brew.rb
+++ b/Library/Homebrew/brew.rb
@@ -86,6 +86,10 @@ begin
   require "commands"
   require "settings"
 
+  # Print an error message and exit if the command is no longer supported
+  unsupported_cmd_message = Commands.unsupported_cmd?(cmd)
+  odie unsupported_cmd_message if unsupported_cmd_message
+
   internal_cmd = Commands.valid_internal_cmd?(cmd) || Commands.valid_internal_dev_cmd?(cmd) if cmd
 
   unless internal_cmd
diff --git a/Library/Homebrew/commands.rb b/Library/Homebrew/commands.rb
index e9450b3fed..c67e5dbeff 100644
--- a/Library/Homebrew/commands.rb
+++ b/Library/Homebrew/commands.rb
@@ -30,6 +30,13 @@ module Commands
     "lc"          => "livecheck",
     "tc"          => "typecheck",
   }.freeze
+  HOMEBREW_UNSUPPORTED_COMMAND_MESSAGES = {
+    "cask" => "`brew cask <command>` is no longer supported. Use `brew <command> --cask` instead.",
+  }.freeze
+
+  def unsupported_cmd?(cmd)
+    HOMEBREW_UNSUPPORTED_COMMAND_MESSAGES.fetch(cmd, nil)
+  end
 
   def valid_internal_cmd?(cmd)
     require?(HOMEBREW_CMD_PATH/cmd)