From cf3486f98a5ddc8eae3c511f759471eff79cfcf8 Mon Sep 17 00:00:00 2001
From: Martin Afanasjew <martin@afanasjew.de>
Date: Tue, 19 Apr 2016 07:33:13 +0200
Subject: [PATCH] help: show command-specific help for invalid usage

Instead of always printing the generic help text, print command-specific
help if it is available and a command raised the `UsageError` exception.
Put the error message underneath the help text (was above) to avoid that
it scrolls off the screen.

Thereby fix a regression where handling the invalid usage would fail to
access `ARGV.usage` removed in c6536066dc39da653d265640c6ba6046bb5def98.
---
 Library/Homebrew/cmd/help.rb | 8 ++++++++
 Library/brew.rb              | 4 ++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Library/Homebrew/cmd/help.rb b/Library/Homebrew/cmd/help.rb
index c8fc334308..b8dcad3d57 100644
--- a/Library/Homebrew/cmd/help.rb
+++ b/Library/Homebrew/cmd/help.rb
@@ -40,6 +40,14 @@ module Homebrew
       path = command_path(cmd)
     end
 
+    # Display command-specific (or generic) help in response to `UsageError`.
+    if (error_message = flags[:usage_error])
+      $stderr.puts path ? command_help(path) : HOMEBREW_HELP
+      $stderr.puts
+      onoe error_message
+      exit 1
+    end
+
     # Handle `brew` (no arguments).
     if flags[:empty_argv]
       $stderr.puts HOMEBREW_HELP
diff --git a/Library/brew.rb b/Library/brew.rb
index eb4fe06061..222b432acd 100644
--- a/Library/brew.rb
+++ b/Library/brew.rb
@@ -118,8 +118,8 @@ rescue FormulaUnspecifiedError
 rescue KegUnspecifiedError
   abort "This command requires a keg argument"
 rescue UsageError
-  onoe "Invalid usage"
-  abort ARGV.usage
+  require "cmd/help"
+  Homebrew.help cmd, :usage_error => "Invalid usage"
 rescue SystemExit => e
   onoe "Kernel.exit" if ARGV.verbose? && !e.success?
   $stderr.puts e.backtrace if ARGV.debug?