Support selective highlighting of lines

Instead of highlighting all lines when not all of them are
needed, only highlight specific lines.

The `BlobPresenter#highlight` method has been updated to
support `since` and `to` params. These params will be used to
limit the content to be highlighted.

Modify `Gitlab::Highlight` to support `since` param which will
then be used to determine the starting line number.

2 files changed, 23 insertions, 19 deletions

diff --git a/app/presenters/blob_presenter.rb b/app/presenters/blob_presenter.rb
index 2cf3278d240..f85c1a237a6 100644
--- a/app/presenters/blob_presenter.rb
+++ b/app/presenters/blob_presenter.rb
@@ -3,12 +3,13 @@
 class BlobPresenter < Gitlab::View::Presenter::Delegated
   presents :blob
 
-  def highlight(plain: nil)
+  def highlight(since: nil, to: nil, plain: nil)
     load_all_blob_data
 
     Gitlab::Highlight.highlight(
       blob.path,
-      blob.data,
+      limited_blob_data(since: since, to: to),
+      since: since,
       language: blob.language_from_gitattributes,
       plain: plain
     )
@@ -23,4 +24,18 @@ class BlobPresenter < Gitlab::View::Presenter::Delegated
   def load_all_blob_data
     blob.load_all_data! if blob.respond_to?(:load_all_data!)
   end
+
+  def limited_blob_data(since: nil, to: nil)
+    return blob.data if since.blank? || to.blank?
+
+    limited_blob_lines(since, to).join
+  end
+
+  def limited_blob_lines(since, to)
+    all_lines[since - 1..to - 1]
+  end
+
+  def all_lines
+    @all_lines ||= blob.data.lines
+  end
 end
diff --git a/app/presenters/blobs/unfold_presenter.rb b/app/presenters/blobs/unfold_presenter.rb
index 21a1e1309e0..f4672d22fc9 100644
--- a/app/presenters/blobs/unfold_presenter.rb
+++ b/app/presenters/blobs/unfold_presenter.rb
@@ -21,20 +21,19 @@ module Blobs
       load_all_blob_data
 
       @subject = blob
-      @all_lines = blob.data.lines
       super(params)
 
       if full?
-        self.attributes = { since: 1, to: @all_lines.size, bottom: false, unfold: false, offset: 0, indent: 0 }
+        self.attributes = { since: 1, to: all_lines.size, bottom: false, unfold: false, offset: 0, indent: 0 }
       end
     end
 
     # Returns an array of Gitlab::Diff::Line with match line added
     def diff_lines
-      diff_lines = lines.map.with_index do |line, index|
-        full_line = limited_blob_lines[index].delete("\n")
+      diff_lines = limited_blob_lines(since, to).map.with_index do |line, index|
+        full_line = line.delete("\n")
 
-        Gitlab::Diff::Line.new(full_line, nil, nil, nil, nil, rich_text: line)
+        Gitlab::Diff::Line.new(full_line, nil, nil, nil, nil, rich_text: lines[index])
       end
 
       add_match_line(diff_lines)
@@ -43,7 +42,7 @@ module Blobs
     end
 
     def lines
-      @lines ||= limit(highlight.lines).map(&:html_safe)
+      @lines ||= highlight(since: since, to: to).lines.map(&:html_safe)
     end
 
     def match_line_text
@@ -59,7 +58,7 @@ module Blobs
     def add_match_line(diff_lines)
       return unless unfold?
 
-      if bottom? && to < @all_lines.size
+      if bottom? && to < all_lines.size
         old_pos = to - offset
         new_pos = to
       elsif since != 1
@@ -73,15 +72,5 @@ module Blobs
 
       bottom? ? diff_lines.push(match_line) : diff_lines.unshift(match_line)
     end
-
-    def limited_blob_lines
-      @limited_blob_lines ||= limit(@all_lines)
-    end
-
-    def limit(lines)
-      return lines if full?
-
-      lines[since - 1..to - 1]
-    end
   end
 end