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>

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
+  # Ignore CannotInstallFormulaError and let caller handle it.
-    ofail e.message
   end
 end

Library/Homebrew/cmd/reinstall.rb

@@ -1,4 +1,3 @@
-require 'cmd/uninstall'
 require 'cmd/install'
 
 module Homebrew extend self
@@ -6,9 +5,6 @@ module Homebrew extend self
     # At first save the named formulae and remove them from ARGV
     named = ARGV.named
     ARGV.delete_if { |arg| named.include? arg }
-    # We add --force because then uninstall always succeeds and so reinstall
-    # works for formulae not yet installed.
-    ARGV << "--force"
     clean_ARGV = ARGV.clone
 
     # Add the used_options for each named formula separately so
@@ -21,13 +17,65 @@ module Homebrew extend self
       if tab.built_as_bottle and not tab.poured_from_bottle
         ARGV << '--build-bottle'
       end
-      # Todo: Be as smart as upgrade to restore the old state if reinstall fails.
+
-      self.uninstall
+      canonical_name = Formula.canonical_name(name)
-      # Don't display --force in options; user didn't request it so a bit scary.
+      formula = Formula.factory(canonical_name)
-      options_only = ARGV.options_only
+
-      options_only.delete "--force"
+      if not formula.installed?
-      oh1 "Reinstalling #{name} #{options_only*' '}"
+        if force_new_install?
-      self.install
+          oh1 "Force installing new formula: #{name}"
+          self.install_formula formula
+          next
+        else
+          raise <<-EOS.undent
+          #{formula} is not installed. Please install it first or use
+          "--force-new-install" flag.
+          EOS
+        end
+      end
+
+      linked_keg_ref = HOMEBREW_REPOSITORY/'opt'/canonical_name
+      keg = Keg.new(linked_keg_ref.realpath)
+
+      begin
+        oh1 "Reinstalling #{name} #{ARGV.options_only*' '}"
+        quarantine keg
+        self.install_formula formula
+      rescue Exception => e
+        ofail e.message unless e.message.empty?
+        restore_quarantine keg, formula
+        raise 'Reinstallation abort.'
+      else
+        remove_quarantine keg
+      end
     end
   end
+
+  def force_new_install?
+    ARGV.include? '--force-new-install'
+  end
+
+  def quarantine keg
+    keg.unlink
+
+    path = Pathname.new(keg.to_s)
+    path.rename quarantine_path(path)
+  end
+
+  def restore_quarantine keg, formula
+    path = Pathname.new(quarantine_path(keg))
+    if path.directory?
+      path.rename keg.to_s
+      keg.link unless formula.keg_only?
+    end
+  end
+
+  def remove_quarantine keg
+    path = Pathname.new(quarantine_path(keg))
+    path.rmtree
+  end
+
+  def quarantine_path path
+    path.to_s + '.reinstall'
+  end
 end