GitDownloadStrategy optimization

The current series of fetch invocations in GitDownloadStrategy has the
unfortunate behavior of fetching full history even in shallow clones
that only need the history between the clone point and the remote HEAD.
It should be possible to determine if it is actually necessary to fetch
the full history, including all tags, and if it is not to avoid this
overhead.

Fixes Homebrew/homebrew#11958, and several other recurring problems.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

1 files changed, 27 insertions, 16 deletions

diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 6b8aff900..6a5dd6ac7 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -324,14 +324,10 @@ class GitDownloadStrategy < AbstractDownloadStrategy
   end
 
   def support_depth?
-    !commit_history_required? and depth_supported_host?
+    @spec != :revision and host_supports_depth?
   end
 
-  def commit_history_required?
-    @spec == :sha
-  end
-
-  def depth_supported_host?
+  def host_supports_depth?
     @url =~ %r(git://) or @url =~ %r(https://github.com/)
   end
 
@@ -352,16 +348,31 @@ class GitDownloadStrategy < AbstractDownloadStrategy
 
     unless @clone.exist?
       # Note: first-time checkouts are always done verbosely
-      git_args = %w(git clone)
-      git_args << "--depth" << "1" if support_depth?
-      git_args << @url << @clone
-      safe_system(*git_args)
+      clone_args = %w[git clone]
+      clone_args << '--single-branch'
+      clone_args << '--depth' << '1' if support_depth?
+
+      case @spec
+      when :branch, :tag
+        clone_args << '--branch' << @ref
+      end
+
+      clone_args << @url << @clone
+      safe_system(*clone_args)
     else
       puts "Updating #{@clone}"
       Dir.chdir(@clone) do
-        safe_system 'git', 'remote', 'set-url', 'origin', @url
-        quiet_safe_system 'git', 'fetch', 'origin'
-        quiet_safe_system 'git', 'fetch', '--tags' if @spec == :tag
+        safe_system 'git', 'config', 'remote.origin.url', @url
+
+        safe_system 'git', 'config', 'remote.origin.fetch', case @spec
+          when :branch then "+refs/heads/#{@ref}:refs/remotes/origin/#{@ref}"
+          when :tag then "+refs/tags/#{@ref}:refs/tags/#{@ref}"
+          else '+refs/heads/master:refs/remotes/origin/master'
+          end
+
+        git_args = %w[git fetch origin]
+        git_args << '--depth' << '1' if support_depth?
+        quiet_safe_system(*git_args)
       end
     end
   end
@@ -373,9 +384,9 @@ class GitDownloadStrategy < AbstractDownloadStrategy
         ohai "Checking out #{@spec} #{@ref}"
         case @spec
         when :branch
-          nostdout { quiet_safe_system 'git', 'checkout', "origin/#{@ref}" }
-        when :tag, :sha
-          nostdout { quiet_safe_system 'git', 'checkout', @ref }
+          nostdout { quiet_safe_system 'git', 'checkout', "origin/#{@ref}", '--' }
+        when :tag, :revision
+          nostdout { quiet_safe_system 'git', 'checkout', @ref, '--' }
         end
       else
         # otherwise the checkout-index won't checkout HEAD