Fix auto-indent when pasting multi-line content that was copied start… (#26246)

Closes https://github.com/zed-industries/zed/issues/24914 (again)

Release Notes:

- Fixed an issue where multi-line pasted content was auto-indented
incorrectly if copied from the middle of an existing line.

crates/editor/src/editor.rs

@@ -1012,8 +1012,8 @@ pub struct ClipboardSelection {
     pub len: usize,
     /// Whether this was a full-line selection.
     pub is_entire_line: bool,
-    /// The column where this selection originally started.
-    pub start_column: u32,
+    /// The indentation of the first line when this content was originally copied.
+    pub first_line_indent: u32,
 }
 
 #[derive(Debug)]
@@ -2354,7 +2354,7 @@ impl Editor {
     pub fn edit_with_block_indent<I, S, T>(
         &mut self,
         edits: I,
-        original_start_columns: Vec<u32>,
+        original_indent_columns: Vec<Option<u32>>,
         cx: &mut Context<Self>,
     ) where
         I: IntoIterator<Item = (Range<S>, T)>,
@@ -2369,7 +2369,7 @@ impl Editor {
             buffer.edit(
                 edits,
                 Some(AutoindentMode::Block {
-                    original_start_columns,
+                    original_indent_columns,
                 }),
                 cx,
             )
@@ -3480,7 +3480,7 @@ impl Editor {
 
     pub fn insert(&mut self, text: &str, window: &mut Window, cx: &mut Context<Self>) {
         let autoindent = text.is_empty().not().then(|| AutoindentMode::Block {
-            original_start_columns: Vec::new(),
+            original_indent_columns: Vec::new(),
         });
         self.insert_with_autoindent_mode(text, autoindent, window, cx);
     }
@@ -8704,7 +8704,9 @@ impl Editor {
                 clipboard_selections.push(ClipboardSelection {
                     len,
                     is_entire_line,
-                    start_column: selection.start.column,
+                    first_line_indent: buffer
+                        .indent_size_for_line(MultiBufferRow(selection.start.row))
+                        .len,
                 });
             }
         }
@@ -8783,7 +8785,7 @@ impl Editor {
                 clipboard_selections.push(ClipboardSelection {
                     len,
                     is_entire_line,
-                    start_column: start.column,
+                    first_line_indent: buffer.indent_size_for_line(MultiBufferRow(start.row)).len,
                 });
             }
         }
@@ -8813,8 +8815,8 @@ impl Editor {
                 let old_selections = this.selections.all::<usize>(cx);
                 let all_selections_were_entire_line =
                     clipboard_selections.iter().all(|s| s.is_entire_line);
-                let first_selection_start_column =
-                    clipboard_selections.first().map(|s| s.start_column);
+                let first_selection_indent_column =
+                    clipboard_selections.first().map(|s| s.first_line_indent);
                 if clipboard_selections.len() != old_selections.len() {
                     clipboard_selections.drain(..);
                 }
@@ -8829,21 +8831,21 @@ impl Editor {
 
                     let mut start_offset = 0;
                     let mut edits = Vec::new();
-                    let mut original_start_columns = Vec::new();
+                    let mut original_indent_columns = Vec::new();
                     for (ix, selection) in old_selections.iter().enumerate() {
                         let to_insert;
                         let entire_line;
-                        let original_start_column;
+                        let original_indent_column;
                         if let Some(clipboard_selection) = clipboard_selections.get(ix) {
                             let end_offset = start_offset + clipboard_selection.len;
                             to_insert = &clipboard_text[start_offset..end_offset];
                             entire_line = clipboard_selection.is_entire_line;
                             start_offset = end_offset + 1;
-                            original_start_column = Some(clipboard_selection.start_column);
+                            original_indent_column = Some(clipboard_selection.first_line_indent);
                         } else {
                             to_insert = clipboard_text.as_str();
                             entire_line = all_selections_were_entire_line;
-                            original_start_column = first_selection_start_column
+                            original_indent_column = first_selection_indent_column
                         }
 
                         // If the corresponding selection was empty when this slice of the
@@ -8859,7 +8861,7 @@ impl Editor {
                         };
 
                         edits.push((range, to_insert));
-                        original_start_columns.extend(original_start_column);
+                        original_indent_columns.push(original_indent_column);
                     }
                     drop(snapshot);
 
@@ -8867,7 +8869,7 @@ impl Editor {
                         edits,
                         if auto_indent_on_paste {
                             Some(AutoindentMode::Block {
-                                original_start_columns,
+                                original_indent_columns,
                             })
                         } else {
                             None