[HooksManager] Show the name of the source for each hook that is run in verbose mode

Huge thanks to @alloy for the `source_location` hint!

The name calculation is wrapped in a lambda so it's not called when it won't be printed out

CHANGELOG.md

@@ -4,6 +4,15 @@ To install or update CocoaPods see this [guide](http://docs.cocoapods.org/guides
 
 To install release candidates run `[sudo] gem install cocoapods --pre`
 
+## Master
+
+##### Enhancements
+
+* Show the name of the source for each hook that is run in verbose mode.  
+  [Samuel Giddins](https://github.com/segiddins)
+  [#2639](https://github.com/CocoaPods/CocoaPods/issues/2639)
+
+
 ## 0.35.0
 
 [CocoaPods](https://github.com/CocoaPods/CocoaPods/compare/0.34.4...0.35.0)

lib/cocoapods/hooks_manager.rb

+require 'rubygems'
+
 module Pod
   # Provides support for the hook system of CocoaPods. The system is designed
   # especially for plugins. Interested clients can register to notifications by
@@ -15,7 +17,7 @@ module Pod
   #
   module HooksManager
     class << self
-      # @return [Hash{Symbol => Proc}] The list of the blocks that are
+      # @return [Hash{Symbol => Array<Proc>}] The list of the blocks that are
       #         registered for each notification name.
       #
       attr_reader :registrations
@@ -52,8 +54,21 @@ module Pod
         if @registrations
           blocks = @registrations[name]
           if blocks
-            blocks.each do |block|
-              block.call(context)
+            pretty_name = name.to_s.gsub('_', ' ')
+            UI.message "- Running #{pretty_name} hooks" do
+              blocks.each do |block|
+                gem_name_lambda = lambda do
+                  file, _line = block.source_location
+                  gem_spec = Gem::Specification.find do |spec|
+                    spec.require_paths.find { |f| file.include? File.join(spec.full_gem_path, f) }
+                  end
+                  gem_name = (gem_spec && gem_spec.name) || File.basename(file, '.rb')
+                end
+
+                UI.message "- #{gem_name_lambda.call}" do
+                  block.call(context)
+                end
+              end
             end
           end
         end

spec/unit/hooks_manager_spec.rb

@@ -60,6 +60,20 @@ module Pod
           @hooks_manager.run(:post_install, nil)
         end
       end
+
+      it 'prints a message in verbose mode when any hooks are run' do
+        config.verbose = true
+        @hooks_manager.register(:post_install) { |_| }
+        @hooks_manager.run(:post_install, Object.new)
+        UI.output.should.match /- Running post install hooks/
+      end
+
+      it 'prints a message in verbose mode for each hook run' do
+        config.verbose = true
+        @hooks_manager.register(:post_install) { |_| }
+        @hooks_manager.run(:post_install, Object.new)
+        UI.output.should.match /- hooks_manager_spec/
+      end
     end
   end
 end