From 69d7ea7b606f2321307623795c152ccffc1d01e5 Mon Sep 17 00:00:00 2001
From: Smit Barmase <heysmitbarmase@gmail.com>
Date: Sat, 5 Apr 2025 05:14:15 +0530
Subject: [PATCH] buffer: Fix broken auto indent when pasting code starting
 with new line (#28134)

Closes #26907

Currently, in case of new line to find delta, it is comparing old first
line indent with new second line indent. This results into incorrect
indentation. This PR fixes this delta calculation by passing correct
second line indent in that particular case.

- [X] Add Test

Before:


https://github.com/user-attachments/assets/065deba0-be19-4643-a784-d248a8e7c891

After:


https://github.com/user-attachments/assets/a0037043-4bd8-460f-b8ba-b7da7bdbe1ea

Release Notes:

- Fixed issue where pasting code starting with new line resulted
incorrect auto indent.
---
 crates/language/src/buffer.rs       | 11 +++++--
 crates/language/src/buffer_tests.rs | 50 +++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/crates/language/src/buffer.rs b/crates/language/src/buffer.rs
index bf2b414976..5e3cb56a49 100644
--- a/crates/language/src/buffer.rs
+++ b/crates/language/src/buffer.rs
@@ -2210,7 +2210,12 @@ impl Buffer {
                         original_indent_columns,
                     } = &mode
                     {
-                        original_indent_column = Some(
+                        original_indent_column = Some(if new_text.starts_with('\n') {
+                            indent_size_for_text(
+                                new_text[range_of_insertion_to_indent.clone()].chars(),
+                            )
+                            .len
+                        } else {
                             original_indent_columns
                                 .get(ix)
                                 .copied()
@@ -2220,8 +2225,8 @@ impl Buffer {
                                         new_text[range_of_insertion_to_indent.clone()].chars(),
                                     )
                                     .len
-                                }),
-                        );
+                                })
+                        });
 
                         // Avoid auto-indenting the line after the edit.
                         if new_text[range_of_insertion_to_indent.clone()].ends_with('\n') {
diff --git a/crates/language/src/buffer_tests.rs b/crates/language/src/buffer_tests.rs
index 76316b2640..dbe54b5c6d 100644
--- a/crates/language/src/buffer_tests.rs
+++ b/crates/language/src/buffer_tests.rs
@@ -1712,6 +1712,56 @@ fn test_autoindent_block_mode(cx: &mut App) {
     });
 }
 
+#[gpui::test]
+fn test_autoindent_block_mode_with_newline(cx: &mut App) {
+    init_settings(cx, |_| {});
+
+    cx.new(|cx| {
+        let text = r#"
+            fn a() {
+                b();
+            }
+        "#
+        .unindent();
+        let mut buffer = Buffer::local(text, cx).with_language(Arc::new(rust_lang()), cx);
+
+        // First line contains just '\n', it's indentation is stored in "original_indent_columns"
+        let original_indent_columns = vec![Some(4)];
+        let inserted_text = r#"
+
+                c();
+                    d();
+                        e();
+        "#
+        .unindent();
+        buffer.edit(
+            [(Point::new(2, 0)..Point::new(2, 0), inserted_text.clone())],
+            Some(AutoindentMode::Block {
+                original_indent_columns: original_indent_columns.clone(),
+            }),
+            cx,
+        );
+
+        // While making edit, we ignore first line as it only contains '\n'
+        // hence second line indent is used to calculate delta
+        assert_eq!(
+            buffer.text(),
+            r#"
+            fn a() {
+                b();
+
+                c();
+                    d();
+                        e();
+            }
+            "#
+            .unindent()
+        );
+
+        buffer
+    });
+}
+
 #[gpui::test]
 fn test_autoindent_block_mode_without_original_indent_columns(cx: &mut App) {
     init_settings(cx, |_| {});