Improve diff performance by eliminating redundant checks for text blobs

On a merge request with over 1000 changed files, there were redundant
calls to blob_text_viewable?, which incurred about 7% of the time.

Improves #14775

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.11.0 (unreleased)
   - Fix the title of the toggle dropdown button. !5515 (herminiotorres)
+  - Improve diff performance by eliminating redundant checks for text blobs
   - Remove magic comments (`# encoding: UTF-8`) from Ruby files. !5456 (winniehell)
   - Fix CI status icon link underline (ClemMakesApps)
   - Cache the commit author in RequestStore to avoid extra lookups in PostReceive

app/helpers/blob_helper.rb

@@ -13,7 +13,7 @@ module BlobHelper
     blob = project.repository.blob_at(ref, path) rescue nil
-    return unless blob && blob_text_viewable?(blob)
+    return unless blob
     from_mr = options[:from_merge_request_id]
     link_opts = {}

app/views/projects/blob/_actions.html.haml

@@ -16,6 +16,7 @@
 - if current_user
   .btn-group{ role: "group" }
-    = edit_blob_link
+    - if blob_text_viewable?(@blob)
+      = edit_blob_link
     = replace_blob_link
     = delete_blob_link

app/views/projects/diffs/_file.html.haml

@@ -9,10 +9,11 @@
             = icon('comment')
           \
-        - if editable_diff?(diff_file)
-          = edit_blob_link(@merge_request.source_project,
-              @merge_request.source_branch, diff_file.new_path,
-              from_merge_request_id: @merge_request.id)
+          - if editable_diff?(diff_file)
+            = edit_blob_link(@merge_request.source_project,
+                @merge_request.source_branch, diff_file.new_path,
+                from_merge_request_id: @merge_request.id,
+                skip_visible_check: true)
         = view_file_btn(diff_commit.id, diff_file, project)

spec/helpers/blob_helper_spec.rb

 require 'spec_helper'
 describe BlobHelper do
+  include TreeHelper
+
   let(:blob_name) { 'test.lisp' }
   let(:no_context_content) { ":type \"assem\"))" }
   let(:blob_content) { "(make-pathname :defaults name\n#{no_context_content}" }
@@ -65,4 +67,20 @@ describe BlobHelper do
       expect(sanitize_svg(blob).data).to eq(expected)
     end
   end
+
+  describe "#edit_blob_link" do
+    let(:project) { create(:project) }
+
+    before do
+      allow(self).to receive(:current_user).and_return(double)
+    end
+
+    it 'verifies blob is text' do
+      expect(self).not_to receive(:blob_text_viewable?)
+
+      button = edit_blob_link(project, 'refs/heads/master', 'README.md')
+
+      expect(button).to start_with('<button')
+    end
+  end
 end