FIX: Don't show the link button in the composer if linking is disabled

app/assets/javascripts/discourse/components/d-editor.js.es6

@@ -45,7 +45,8 @@ const isInside = (text, regex) => {
 
 class Toolbar {
 
-  constructor(site) {
+  constructor(opts) {
+    const { site, siteSettings } = opts;
     this.shortcuts = {};
 
     this.groups = [
@@ -74,7 +75,14 @@ class Toolbar {
       perform: e => e.applySurround('_', '_', 'italic_text')
     });
 
-    this.addButton({id: 'link', group: 'insertions', shortcut: 'K', action: 'showLinkModal'});
+    if (opts.showLink) {
+      this.addButton({
+        id: 'link',
+        group: 'insertions',
+        shortcut: 'K',
+        action: 'showLinkModal'
+      });
+    }
 
     this.addButton({
       id: 'quote',
@@ -108,7 +116,7 @@ class Toolbar {
       perform: e => e.applyList(i => !i ? "1. " : `${parseInt(i) + 1}. `, 'list_item')
     });
 
-    if (Discourse.SiteSettings.support_mixed_text_direction) {
+    if (siteSettings.support_mixed_text_direction) {
       this.addButton({
         id: 'toggle-direction',
         group: 'extras',
@@ -200,6 +208,7 @@ export default Ember.Component.extend({
   lastSel: null,
   _mouseTrap: null,
   emojiPickerIsActive: false,
+  showLink: true,
 
   @computed('placeholder')
   placeholderTranslated(placeholder) {
@@ -279,7 +288,9 @@ export default Ember.Component.extend({
 
   @computed
   toolbar() {
-    const toolbar = new Toolbar(this.site);
+    const toolbar = new Toolbar(
+      this.getProperties('site', 'siteSettings', 'showLink')
+    );
     _createCallbacks.forEach(cb => cb(toolbar));
     this.sendAction('extraButtons', toolbar);
     return toolbar;

app/assets/javascripts/discourse/templates/components/composer-editor.hbs

@@ -11,6 +11,7 @@
   validation=validation
   loading=composer.loading
   forcePreview=forcePreview
+  showLink=currentUser.can_post_link
   composerEvents=true
   onExpandPopupMenuOptions="onExpandPopupMenuOptions"
   onPopupMenuAction=onPopupMenuAction

app/serializers/current_user_serializer.rb

@@ -39,7 +39,12 @@ class CurrentUserSerializer < BasicUserSerializer
              :seen_notification_id,
              :primary_group_id,
              :primary_group_name,
-             :can_create_topic
+             :can_create_topic,
+             :can_post_link
+
+  def can_post_link
+    scope.can_post_link?
+  end
 
   def can_create_topic
     scope.can_create_topic?(nil)

lib/guardian/post_guardian.rb

@@ -1,6 +1,11 @@
 #mixin for all guardian methods dealing with post permissions
 module PostGuardian
 
+  def can_post_link?
+    authenticated? &&
+      @user.has_trust_level?(TrustLevel[SiteSetting.min_trust_to_post_links])
+  end
+
   # 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: {}, can_see_post: nil)

lib/validators/post_validator.rb

@@ -93,7 +93,9 @@ class Validators::PostValidator < ActiveModel::Validator
   end
 
   def can_post_links_validator(post)
-    return if post.link_count == 0 || acting_user_is_trusted?(post, SiteSetting.min_trust_to_post_links) || private_message?(post)
+    return if post.link_count == 0 ||
+      Guardian.new(post.acting_user).can_post_link? ||
+      private_message?(post)
 
     post.errors.add(:base, I18n.t(:links_require_trust))
   end

spec/components/guardian_spec.rb

@@ -26,6 +26,24 @@ describe Guardian do
     expect { Guardian.new(user) }.not_to raise_error
   end
 
+  describe "can_post_link?" do
+    it "returns false for anonymous users" do
+      expect(Guardian.new.can_post_link?).to eq(false)
+    end
+
+    it "returns true for a regular user" do
+      expect(Guardian.new(user).can_post_link?).to eq(true)
+    end
+
+    it "supports customization by site setting" do
+      user.trust_level = 0
+      SiteSetting.min_trust_to_post_links = 0
+      expect(Guardian.new(user).can_post_link?).to eq(true)
+      SiteSetting.min_trust_to_post_links = 1
+      expect(Guardian.new(user).can_post_link?).to eq(false)
+    end
+  end
+
   describe 'post_can_act?' do
     let(:post) { build(:post) }
     let(:user) { build(:user) }