Don't wrap pasted code when it's already inside code tags

app/assets/javascripts/copy_as_gfm.js

@@ -299,12 +299,29 @@ class CopyAsGFM {
     const clipboardData = e.originalEvent.clipboardData;
     if (!clipboardData) return;
 
+    const text = clipboardData.getData('text/plain');
     const gfm = clipboardData.getData('text/x-gfm');
     if (!gfm) return;
 
     e.preventDefault();
 
-    window.gl.utils.insertText(e.target, gfm);
+    window.gl.utils.insertText(e.target, (textBefore, textAfter) => {
+      // If the text before the cursor contains an odd number of backticks,
+      // we are either inside an inline code span that starts with 1 backtick
+      // or a code block that starts with 3 backticks.
+      // This logic still holds when there are one or more _closed_ code spans
+      // or blocks that will have 2 or 6 backticks.
+      // This will break down when the actual code block contains an uneven
+      // number of backticks, but this is a rare edge case.
+      const backtickMatch = textBefore.match(/`/g);
+      const insideCodeBlock = backtickMatch && (backtickMatch.length % 2) === 1;
+
+      if (insideCodeBlock) {
+        return text;
+      }
+
+      return gfm;
+    });
   }
 
   static transformGFMSelection(documentFragment) {

app/assets/javascripts/lib/utils/common_utils.js

@@ -198,10 +198,12 @@
 
       const textBefore = value.substring(0, selectionStart);
       const textAfter = value.substring(selectionEnd, value.length);
-      const newText = textBefore + text + textAfter;
+
+      const insertedText = text instanceof Function ? text(textBefore, textAfter) : text;
+      const newText = textBefore + insertedText + textAfter;
 
       target.value = newText;
-      target.selectionStart = target.selectionEnd = selectionStart + text.length;
+      target.selectionStart = target.selectionEnd = selectionStart + insertedText.length;
 
       // Trigger autosave
       $(target).trigger('input');

changelogs/unreleased/dm-paste-code-inside-gfm-code.yml

+---
+title: Don't wrap pasted code when it's already inside code tags
+merge_request:
+author: