Fix suggestion on lines that are not part of an MR

Return the `text` as plain string in the response instead of
including HTML tags but keep `rich_text` as is.

The fix is to modify `Blob::UnfoldPresenter#diff_files` to map
each raw diff line (limited by the range specified) to a
corresponding line in an array of highlighted lines to use as
`rich_text`.

app/presenters/blob_presenter.rb

@@ -4,7 +4,7 @@ class BlobPresenter < Gitlab::View::Presenter::Delegated
   presents :blob
 
   def highlight(plain: nil)
-    blob.load_all_data! if blob.respond_to?(:load_all_data!)
+    load_all_blob_data
 
     Gitlab::Highlight.highlight(
       blob.path,
@@ -17,4 +17,10 @@ class BlobPresenter < Gitlab::View::Presenter::Delegated
   def web_url
     Gitlab::Routing.url_helpers.project_blob_url(blob.repository.project, File.join(blob.commit_id, blob.path))
   end
+
+  private
+
+  def load_all_blob_data
+    blob.load_all_data! if blob.respond_to?(:load_all_data!)
+  end
 end

app/presenters/blobs/unfold_presenter.rb

@@ -16,8 +16,12 @@ module Blobs
     attribute :indent, Integer, default: 0
 
     def initialize(blob, params)
+      # Load all blob data first as we need to ensure they're all loaded first
+      # so we can accurately show the rest of the diff when unfolding.
+      load_all_blob_data
+
       @subject = blob
-      @all_lines = highlight.lines
+      @all_lines = blob.data.lines
       super(params)
 
       if full?
@@ -25,10 +29,12 @@ module Blobs
       end
     end
 
-    # Converts a String array to Gitlab::Diff::Line array, with match line added
+    # Returns an array of Gitlab::Diff::Line with match line added
     def diff_lines
-      diff_lines = lines.map do |line|
-        Gitlab::Diff::Line.new(line, nil, nil, nil, nil, rich_text: line)
+      diff_lines = lines.map.with_index do |line, index|
+        full_line = limited_blob_lines[index].delete("\n")
+
+        Gitlab::Diff::Line.new(full_line, nil, nil, nil, nil, rich_text: line)
       end
 
       add_match_line(diff_lines)
@@ -37,11 +43,7 @@ module Blobs
     end
 
     def lines
-      strong_memoize(:lines) do
-        lines = @all_lines
-        lines = lines[since - 1..to - 1] unless full?
-        lines.map(&:html_safe)
-      end
+      @lines ||= limit(highlight.lines).map(&:html_safe)
     end
 
     def match_line_text
@@ -71,5 +73,15 @@ 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

changelogs/unreleased/57953-fix-unfolded-diff-suggestions.yml

+---
+title: Fix suggestion on lines that are not part of an MR
+merge_request: 30606
+author:
+type: fixed

spec/presenters/blobs/unfold_presenter_spec.rb

@@ -54,8 +54,10 @@ describe Blobs::UnfoldPresenter do
         expect(lines.size).to eq(total_lines)
 
         lines.each.with_index do |line, index|
-          expect(line.text).to include("LC#{index + 1}")
-          expect(line.text).to eq(line.rich_text)
+          line_number = index + 1
+
+          expect(line.text).to eq(line_number.to_s)
+          expect(line.rich_text).to include("LC#{line_number}")
           expect(line.type).to be_nil
         end
       end