Don't attempt installation multiple times

When a dependency of a formula specified on the command-line is also
specified, *after* the dependent formula, installation proceeds as part
of the dependent's dependency tree and then is attempted again because
the user asked for it explicitly. This results in the installer raising
a CannotInstallFormulaError because it has already been installed.

For example:

  $ brew install graphviz pkg-config
  ==> Installing graphviz dependency: pkg-config
  ...
  ==> Installing graphviz
  ...
  Error: pkg-config-0.27.1 already installed

We already have a mechanism for dealing with this, but it does not kick
in early enough. Move the installation attempt check into
FormulaInstaller#check_install_sanity and catch the exception in the
appropriate places.

Fixes Homebrew/homebrew#16957.

1 files changed, 12 insertions, 8 deletions

diff --git a/Library/Homebrew/cmd/install.rb b/Library/Homebrew/cmd/install.rb
index 90acb0774..ef01d0452 100644
--- a/Library/Homebrew/cmd/install.rb
+++ b/Library/Homebrew/cmd/install.rb
@@ -78,16 +78,20 @@ module Homebrew extend self
     unless formulae.empty?
       perform_preinstall_checks
       formulae.each do |f|
-        begin
-          fi = FormulaInstaller.new(f)
-          fi.install
-          fi.caveats
-          fi.finish
-        rescue CannotInstallFormulaError => e
-          ofail e.message
-        end
+        install_formula(f)
       end
     end
   end
 
+  def install_formula f
+    fi = FormulaInstaller.new(f)
+    fi.install
+    fi.caveats
+    fi.finish
+  rescue FormulaInstallationAlreadyAttemptedError
+    # We already attempted to install f as part of the dependency tree of
+    # another formula. In that case, don't generate an error, just move on.
+  rescue CannotInstallFormulaError => e
+    ofail e.message
+  end
 end