address code review feedback from #3553

- change site:reset to site:after_reset
- raise an exception when registering uncallable hook
- set default hook priority at the public API level

features/hooks.feature

@@ -2,11 +2,11 @@ Feature: Hooks
   As a plugin author
   I want to be able to run code during various stages of the build process
 
-  Scenario: Run some code on site reset
+  Scenario: Run some code after site reset
     Given I have a _plugins directory
     And I have a "_plugins/ext.rb" file with content:
     """
-    Jekyll::Hooks.register :site, :reset do |site|
+    Jekyll::Hooks.register :site, :after_reset do |site|
       pageklass = Class.new(Jekyll::Page) do
         def initialize(site, base)
           @site = site

lib/jekyll/hooks.rb

@@ -20,7 +20,7 @@ module Jekyll
     # initial empty hooks
     @registry = {
       :site => {
-        reset: [],
+        after_reset: [],
         post_read: [],
         pre_render: [],
         post_write: [],
@@ -48,23 +48,23 @@ module Jekyll
     @hook_priority = {}
 
     NotAvailable = Class.new(RuntimeError)
+    Uncallable = Class.new(RuntimeError)
 
-    # register hook(s) to be called later
-    def self.register(owners, event, priority: nil, &block)
+    # register hook(s) to be called later, public API
+    def self.register(owners, event, priority: DEFAULT_PRIORITY, &block)
       Array(owners).each do |owner|
-        register_one(owner, event, priority: priority_value(priority), &block)
+        register_one(owner, event, priority_value(priority), &block)
       end
     end
 
     # Ensure the priority is a Fixnum
-    def self.priority_value(priority=nil)
-      return DEFAULT_PRIORITY unless priority
+    def self.priority_value(priority)
       return priority if priority.is_a?(Fixnum)
       PRIORITY_MAP[priority] || DEFAULT_PRIORITY
     end
 
-    # register a single hook to be called later
-    def self.register_one(owner, event, priority: nil, &block)
+    # register a single hook to be called later, internal API
+    def self.register_one(owner, event, priority, &block)
       unless @registry[owner]
         raise NotAvailable, "Hooks are only available for the following " <<
           "classes: #{@registry.keys.inspect}"
@@ -75,6 +75,10 @@ module Jekyll
           "following hooks #{@registry[owner].keys.inspect}"
       end
 
+      unless block.respond_to? :call
+        raise Uncallable, "Hooks must respond to :call"
+      end
+
       insert_hook owner, event, priority, &block
     end
 

lib/jekyll/site.rb

@@ -76,7 +76,7 @@ module Jekyll
         raise ArgumentError, "limit_posts must be a non-negative number"
       end
 
-      Jekyll::Hooks.trigger self, :reset
+      Jekyll::Hooks.trigger self, :after_reset
     end
 
     # Load necessary libraries, plugins, converters, and generators.

site/_docs/plugins.md

@@ -520,7 +520,7 @@ The complete list of available hooks is below:
         <p><code>:site</code></p>
       </td>
       <td>
-        <p><code>:reset</code></p>
+        <p><code>:after_reset</code></p>
       </td>
       <td>
         <p>Just after site reset</p>