Skip redundant leading empty lines when applying diffs to empty files

Author: robertpiosik

apps/editor/src/commands/apply-chat-response-command/utils/edit-formats/diffs/diff-processor.spec.ts

@@ -236,5 +236,19 @@ describe('diff-processor', () => {
 
       expect(result).toBe(expected)
     })
+    it('applies diff with a redundant new empty line correctly', async () => {
+      const test_case = 'redundant-new-empty-line'
+      const original = load_test_case_file('', test_case, 'original.txt')
+      const diff = load_test_case_file('', test_case, 'diff.txt')
+      const expected = load_test_case_file('', test_case, 'expected.txt')
+
+      const result = apply_diff({
+        original_code: original,
+        diff_patch: diff
+      })
+
+      expect(result).toBe(expected)
+    })
+
   })
 })

apps/editor/src/commands/apply-chat-response-command/utils/edit-formats/diffs/diff-processor.ts

@@ -25,6 +25,7 @@ export const apply_diff = (params: {
     let has_additions = false
     let in_hunk = false
     const result_lines: string[] = []
+    let seen_content = false
 
     for (const line of patch_lines) {
       if (line.startsWith('@@')) {
@@ -33,13 +34,27 @@ export const apply_diff = (params: {
       }
       if (!in_hunk) continue
 
+      let line_to_add: string | null = null
+      let is_addition = false
+
       if (line.startsWith('+')) {
-        result_lines.push(line.substring(1))
+        line_to_add = line.substring(1)
+        is_addition = true
         has_additions = true
       } else if (line.startsWith(' ')) {
-        result_lines.push(line.substring(1))
+        line_to_add = line.substring(1)
       } else if (line == '') {
-        result_lines.push('')
+        line_to_add = ''
+      }
+
+      if (line_to_add !== null) {
+        if (!seen_content) {
+          if (!is_addition && line_to_add.trim() == '') {
+            continue
+          }
+          seen_content = true
+        }
+        result_lines.push(line_to_add)
       }
     }
 

apps/editor/src/commands/apply-chat-response-command/utils/edit-formats/diffs/test-cases/redundant-new-empty-line/diff.txt

@@ -0,0 +1,5 @@
+--- a/index.ts
++++ b/index.ts
+@@ -1,2 +1,2 @@
+
++export * from './b'

apps/editor/src/commands/apply-chat-response-command/utils/edit-formats/diffs/test-cases/redundant-new-empty-line/expected.txt

@@ -0,0 +1 @@
+export * from './b'