Re-work ARGV filtering to properly handle --HEAD

Previously, stripping arguments like `--HEAD` for dependencies failed because
that flag affects the installation prefix encoded into formula objects. The
previous implementation of `ARGV` filtering tried to contain all changes to a
single method call before the `FormulaInstaller` forks. This update spreads
things out a bit:

  - The Homebrew `ARGV` extension adds a new method, `filter_for_dependencies`
    which strips flags like `--HEAD`, yields to a block, then restores the
    original contents of ARGV.

  - The `explicitly_requested?` test, which returns true or false depending on
    if a formula object is a member of `ARGV.formulae`, is now a method of
    `Formula` objects.

  - `FormulaInstaller` objects now execute the installation of dependencies
    inside an `ARGV.filter_for_dependencies` block if the dependency was
    `explicitly_requested?`.

Fixes Homebrew/homebrew#8668.
Closes Homebrew/homebrew#7724.

1 files changed, 18 insertions, 0 deletions

diff --git a/Library/Homebrew/extend/ARGV.rb b/Library/Homebrew/extend/ARGV.rb
index e46c0b038..9a86e86ec 100644
--- a/Library/Homebrew/extend/ARGV.rb
+++ b/Library/Homebrew/extend/ARGV.rb
@@ -96,6 +96,24 @@ module HomebrewArgvExtension
     Homebrew.help_s
   end
 
+  def filter_for_dependencies
+    # Clears some flags that affect installation, yields to a block, then
+    # restores to original state.
+    old_args = clone
+
+    %w[
+      --debug -d
+      --fresh
+      --interactive -i
+      --verbose -v
+      --HEAD
+    ].each {|flag| delete flag}
+
+    yield
+
+    replace old_args
+  end
+
   private
 
   def downcased_unique_named