Make reinstall transaction safe.

* Aborting during reinstall will now restore the originally installed
  keg.
  - Change install code to pass on CannotInstallFormulaError exception
    to caller so it can be reused in reinstall.
* Add "--force-new-install" flag to force installing a new formula.

Closes Homebrew/homebrew#22190.

Signed-off-by: Samuel John <github@SamuelJohn.de>

1 files changed, 8 insertions, 3 deletions

diff --git a/Library/Homebrew/cmd/install.rb b/Library/Homebrew/cmd/install.rb
index 46bc59b91..2fe22cfa4 100644
--- a/Library/Homebrew/cmd/install.rb
+++ b/Library/Homebrew/cmd/install.rb
@@ -19,7 +19,13 @@ module Homebrew extend self
     end unless ARGV.force?
 
     perform_preinstall_checks
-    ARGV.formulae.each { |f| install_formula(f) }
+    ARGV.formulae.each do |f|
+      begin
+        install_formula(f)
+      rescue CannotInstallFormulaError => e
+        ofail e.message
+      end
+    end
   end
 
   def check_ppc
@@ -80,7 +86,6 @@ module Homebrew extend self
     # another formula. In that case, don't generate an error, just move on.
   rescue FormulaAlreadyInstalledError => e
     opoo e.message
-  rescue CannotInstallFormulaError => e
-    ofail e.message
+  # Ignore CannotInstallFormulaError and let caller handle it.
   end
 end