Stop supporting `brew install --force'

Rationale: it breaks stuff. You should not be able to install over something already installed *and* linked. brew now prompts you to unlink the existing linked keg first.

I came to fix this because I discovered that `brew install foo` works without --force provided foo's formula version is different to that which is installed and linked. I'm not sure if this was intentionally broken, but it led to at least two tickets I found where people were getting crazy issues trying to install over the top of already installed previous versions.

So I also fixed a whole category of other issues, mostly by moving error handling into FormulaInstaller. Now error's can be caught in Homebrew.install and handled on a formula-by-formula basis. I will next port this behaviour to upgrade.

1 files changed, 1 insertions, 4 deletions

diff --git a/Library/Homebrew/exceptions.rb b/Library/Homebrew/exceptions.rb
index 6db601fe1..df334582c 100644
--- a/Library/Homebrew/exceptions.rb
+++ b/Library/Homebrew/exceptions.rb
@@ -42,10 +42,7 @@ module Homebrew
   end
 end
 
-class FormulaAlreadyInstalledError < Homebrew::InstallationError
-  def message
-    "Formula already installed: #{formula}"
-  end
+class CannotInstallFormulaError < RuntimeError
 end
 
 class FormulaInstallationAlreadyAttemptedError < Homebrew::InstallationError