DSL method "apply" to specify patch files

The "apply" DSL method can be called from patch-do blocks to specify
the paths within an archive of the desired patch files, which will be
applied in the order in which they were supplied to the "apply" calls.
If "apply" isn't used, raise an error whenever the extracted directory
doesn't contain exactly one file.

The "apply" method can be called zero or more times within a patch-do
block with the following syntaxes supported:

    apply "single_apply"
    apply "multiple_apply_1", "multiple_apply_2"
    apply [array_of_apply]

If apply must be used, a single call using the second syntax above is
usually best practice. Each apply leaf should be the relative path to a
specific patch file in the extracted directory.

For example, if extracting this-v123-patches.tar.gz gives you

    this-123
    this-123/.DS_Store
    this-123/LICENSE.txt
    this-123/patches
    this-123/patches/A.diff
    this-123/patches/B.diff
    this-123/patches/C.diff
    this-123/README.txt

and you want to apply only B.diff and C.diff, then you need to use
"patches/B.diff" and "patches/C.diff" for the lowest-level apply leaves.

The code was provided by Xu Cheng. Any mistakes are mine.

1 files changed, 24 insertions, 4 deletions

diff --git a/Library/Homebrew/patch.rb b/Library/Homebrew/patch.rb
index 3c5bd42ea..ebfb8e347 100644
--- a/Library/Homebrew/patch.rb
+++ b/Library/Homebrew/patch.rb
@@ -112,7 +112,7 @@ class ExternalPatch
 
   def initialize(strip, &block)
     @strip    = strip
-    @resource = Resource.new("patch", &block)
+    @resource = Resource::Patch.new(&block)
   end
 
   def external?
@@ -127,9 +127,25 @@ class ExternalPatch
   def apply
     dir = Pathname.pwd
     resource.unpack do
-      # Assumption: the only file in the staging directory is the patch
-      patchfile = Pathname.pwd.children.first
-      dir.cd { safe_system "/usr/bin/patch", "-g", "0", "-f", "-#{strip}", "-i", patchfile }
+      patch_dir = Pathname.pwd
+      if patch_files.empty?
+        children = patch_dir.children
+        if (children.count == 1 && children.first.file?)
+          patch_files << children.first.basename
+        else
+          raise MissingApplyError, <<-EOS.undent
+            There should be exactly one patch file in the staging directory unless
+            the "apply" method was used one or more times in the patch-do block.
+          EOS
+        end
+      end
+      dir.cd do
+        patch_files.each do |patch_file|
+          ohai "Applying #{patch_file}"
+          patch_file = patch_dir/patch_file
+          safe_system "/usr/bin/patch", "-g", "0", "-f", "-#{strip}", "-i", patch_file
+        end
+      end
     end
   end
 
@@ -141,6 +157,10 @@ class ExternalPatch
     resource.fetch
   end
 
+  def patch_files
+    resource.patch_files
+  end
+
   def verify_download_integrity(fn)
     resource.verify_download_integrity(fn)
   end