PERF: Avoid calling expensive `PostGuardian#can_see_post?` multiple times.

Before

```
Your Results: (note for timings- percentile is first, duration is second
in millisecs)
---
topic_admin:
  50: 19
  75: 19
  90: 21
  99: 27
topic:
  50: 56
  75: 62
  90: 64
  99: 99
timings:
  load_rails: 1262
ruby-version: 2.4.1-p111
rss_kb: 198432
pss_kb: 136612
virtual: physical
architecture: amd64
operatingsystem: Ubuntu
memorysize: 15.59 GB
kernelversion: 4.10.0
physicalprocessorcount: 1
processor0: Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
rss_kb_9877: 327892
pss_kb_9877: 263671
rss_kb_9946: 325468
pss_kb_9946: 261671
rss_kb_10153: 326456
pss_kb_10153: 262657
```

After

```
Your Results: (note for timings- percentile is first, duration is second
in millisecs)
---
topic_admin:
  50: 18
  75: 18
  90: 20
  99: 28
topic:
  50: 41
  75: 42
  90: 46
  99: 49
timings:
  load_rails: 1201
ruby-version: 2.4.1-p111
rss_kb: 187936
pss_kb: 123596
virtual: physical
architecture: amd64
operatingsystem: Ubuntu
memorysize: 15.59 GB
kernelversion: 4.10.0
physicalprocessorcount: 1
processor0: Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz
rss_kb_26478: 342360
pss_kb_26478: 276696
rss_kb_26547: 340368
pss_kb_26547: 275930
rss_kb_26747: 338964
pss_kb_26747: 274466
```

app/controllers/post_actions_controller.rb

@@ -13,8 +13,10 @@ class PostActionsController < ApplicationController
     guardian.ensure_post_can_act!(
       @post,
       PostActionType.types[@post_action_type_id],
+      opts: {
         is_warning: params[:is_warning],
         taken_actions: taken
+      }
     )
 
     args = {}

app/helpers/application_helper.rb

@@ -250,7 +250,7 @@ module ApplicationHelper
   end
 
   def crawler_layout?
-    controller.try(:use_crawler_layout?)
+    controller&.use_crawler_layout?
   end
 
   def include_crawler_content?

app/models/topic.rb

@@ -247,7 +247,7 @@ class Topic < ActiveRecord::Base
   def self.visible_post_types(viewed_by = nil)
     types = Post.types
     result = [types[:regular], types[:moderator_action], types[:small_action]]
-    result << types[:whisper] if viewed_by.try(:staff?)
+    result << types[:whisper] if viewed_by&.staff?
     result
   end
 

app/serializers/basic_user_serializer.rb

@@ -9,7 +9,7 @@ class BasicUserSerializer < ApplicationSerializer
     if Hash === object
       User.avatar_template(user[:username], user[:uploaded_avatar_id])
     else
-      user.try(:avatar_template)
+      user&.avatar_template
     end
   end
 

app/serializers/post_serializer.rb

@@ -108,15 +108,15 @@ class PostSerializer < BasicPostSerializer
   end
 
   def moderator?
-    !!(object.try(:user).try(:moderator?))
+    !!(object&.user&.moderator?)
   end
 
   def admin?
-    !!(object.try(:user).try(:admin?))
+    !!(object&.user&.admin?)
   end
 
   def staff?
-    !!(object.try(:user).try(:staff?))
+    !!(object&.user&.staff?)
   end
 
   def yours
@@ -140,7 +140,7 @@ class PostSerializer < BasicPostSerializer
   end
 
   def display_username
-    object.user.try(:name)
+    object.user&.name
   end
 
   def primary_group_name
@@ -154,15 +154,15 @@ class PostSerializer < BasicPostSerializer
   end
 
   def primary_group_flair_url
-    object.user.try(:primary_group).try(:flair_url)
+    object.user&.primary_group&.flair_url
   end
 
   def primary_group_flair_bg_color
-    object.user.try(:primary_group).try(:flair_bg_color)
+    object.user&.primary_group&.flair_bg_color
   end
 
   def primary_group_flair_color
-    object.user.try(:primary_group).try(:flair_color)
+    object.user&.primary_group&.flair_color
   end
 
   def link_counts
@@ -189,11 +189,11 @@ class PostSerializer < BasicPostSerializer
   end
 
   def user_title
-    object.try(:user).try(:title)
+    object&.user&.title
   end
 
   def trust_level
-    object.try(:user).try(:trust_level)
+    object&.user&.trust_level
   end
 
   def reply_to_user
@@ -225,14 +225,18 @@ class PostSerializer < BasicPostSerializer
   # Summary of the actions taken on this post
   def actions_summary
     result = []
-    PostActionType.types.each do |sym, id|
-      next if [:bookmark].include?(sym)
+    can_see_post = scope.can_see_post?(object)
+
+    PostActionType.types.except(:bookmark).each do |sym, id|
       count_col = "#{sym}_count".to_sym
 
       count = object.send(count_col) if object.respond_to?(count_col)
       summary = { id: id, count: count }
       summary[:hidden] = true if sym == :vote
-      summary[:can_act] = true if scope.post_can_act?(object, sym, taken_actions: actions)
+
+      if scope.post_can_act?(object, sym, opts: { taken_actions: actions }, can_see_post: can_see_post)
+        summary[:can_act] = true
+      end
 
       if sym == :notify_user && scope.current_user.present? && scope.current_user == object.user
         summary.delete(:can_act)
@@ -276,7 +280,7 @@ class PostSerializer < BasicPostSerializer
   end
 
   def include_raw?
-    @add_raw.present? && (!object.hidden || scope.user.try(:staff?) || yours)
+    @add_raw.present? && (!object.hidden || scope.user&.staff? || yours)
   end
 
   def include_link_counts?
@@ -326,7 +330,7 @@ class PostSerializer < BasicPostSerializer
   end
 
   def is_auto_generated
-    object.incoming_email.try(:is_auto_generated)
+    object.incoming_email&.is_auto_generated
   end
 
   def include_is_auto_generated?

app/serializers/topic_view_serializer.rb

@@ -83,7 +83,7 @@ class TopicViewSerializer < ApplicationSerializer
 
       result[:allowed_users] = object.topic.allowed_users.select do |user|
         !allowed_user_ids.include?(user.id)
-      end.map do |user|
+      end.map! do |user|
         BasicUserSerializer.new(user, scope: scope, root: false)
       end
     end
@@ -94,7 +94,7 @@ class TopicViewSerializer < ApplicationSerializer
       end
     end
 
-    if object.suggested_topics.try(:topics).present?
+    if object.suggested_topics&.topics.present?
       result[:suggested_topics] = object.suggested_topics.topics.map do |t|
         SuggestedTopicSerializer.new(t, scope: scope, root: false)
       end
@@ -215,7 +215,7 @@ class TopicViewSerializer < ApplicationSerializer
 
   def actions_summary
     result = []
-    return [] unless post = object.posts.try(:first)
+    return [] unless post = object.posts&.first
     PostActionType.topic_flag_types.each do |sym, id|
       result << { id: id,
                   count: 0,

lib/guardian/post_guardian.rb

@@ -3,9 +3,8 @@ module PostGuardian
 
   # Can the user act on the post in a particular way.
   #  taken_actions = the list of actions the user has already taken
-  def post_can_act?(post, action_key, opts = {})
-
-    return false unless can_see_post?(post)
+  def post_can_act?(post, action_key, opts: {}, can_see_post: nil)
+    return false unless (can_see_post.nil? && can_see_post?(post)) || can_see_post
 
     # no warnings except for staff
     return false if (action_key == :notify_user && !is_staff? && opts[:is_warning].present? && opts[:is_warning] == 'true')
@@ -187,7 +186,7 @@ module PostGuardian
   end
 
   def can_vote?(post, opts = {})
-    post_can_act?(post, :vote, opts)
+    post_can_act?(post, :vote, opts: opts)
   end
 
   def can_change_post_owner?

lib/post_action_creator.rb

@@ -7,7 +7,10 @@ class PostActionCreator
   end
 
   def perform(action)
-    guardian.ensure_post_can_act!(@post, action, taken_actions: PostAction.counts_for([@post].compact, @user)[@post.try(:id)])
+    guardian.ensure_post_can_act!(@post, action, opts: {
+      taken_actions: PostAction.counts_for([@post].compact, @user)[@post&.id]
+    })
+
     PostAction.act(@user, @post, action)
   end
 

spec/components/guardian_spec.rb

@@ -57,11 +57,15 @@ describe Guardian do
     end
 
     it "returns false when you've already done it" do
-      expect(Guardian.new(user).post_can_act?(post, :like, taken_actions: { PostActionType.types[:like] => 1 })).to be_falsey
+      expect(Guardian.new(user).post_can_act?(post, :like, opts: {
+        taken_actions: { PostActionType.types[:like] => 1 }
+      })).to be_falsey
     end
 
     it "returns false when you already flagged a post" do
-      expect(Guardian.new(user).post_can_act?(post, :off_topic, taken_actions: { PostActionType.types[:spam] => 1 })).to be_falsey
+      expect(Guardian.new(user).post_can_act?(post, :off_topic, opts: {
+        taken_actions: { PostActionType.types[:spam] => 1 }
+      })).to be_falsey
     end
 
     it "returns false for notify_user if private messages are disabled" do
@@ -863,11 +867,15 @@ describe Guardian do
       end
 
       it "doesn't allow voting if the user has an action from voting already" do
-        expect(guardian.post_can_act?(post, :vote, taken_actions: { PostActionType.types[:vote] => 1 })).to be_falsey
+        expect(guardian.post_can_act?(post, :vote, opts: {
+          taken_actions: { PostActionType.types[:vote] => 1 }
+        })).to be_falsey
       end
 
       it "allows voting if the user has performed a different action" do
-        expect(guardian.post_can_act?(post, :vote, taken_actions: { PostActionType.types[:like] => 1 })).to be_truthy
+        expect(guardian.post_can_act?(post, :vote, opts: {
+          taken_actions: { PostActionType.types[:like] => 1 }
+        })).to be_truthy
       end
 
       it "isn't allowed on archived topics" do

spec/controllers/post_actions_controller_spec.rb

@@ -53,7 +53,11 @@ describe PostActionsController do
 
       it "passes a list of taken actions through" do
         PostAction.create(post_id: @post.id, user_id: @user.id, post_action_type_id: PostActionType.types[:inappropriate])
-        Guardian.any_instance.expects(:post_can_act?).with(@post, :off_topic, has_entry(taken_actions: has_key(PostActionType.types[:inappropriate])))
+
+        Guardian.any_instance.expects(:post_can_act?).with(@post, :off_topic,
+          has_entry(opts: has_entry(taken_actions: has_key(PostActionType.types[:inappropriate])))
+        )
+
         xhr :post, :create, id: @post.id, post_action_type_id: PostActionType.types[:off_topic]
       end