editor: Fix crash when copying and pasting using multiple cursors

[timvermeulen]

Fixes a crash when copying and pasting a mixed empty/nonempty multi-cursor selection.

Editor::do_copy is meant to insert a newline after each non-final selection that doesn't copy the entire line, but prev_selection_was_entire_line is currently based on the current selection instead of the previous one. Editor::cut_common does already correctly track this state across loop iterations.

This can lead to an out of bounds crash when pasting because the indexing logic in Editor::do_paste relies on these newlines being added correctly, depending on is_entire_line.

Repro:

foo
bar

1. select foo
2. option-click after bar to add an empty selection

«fooˇ»
barˇ

3. copy
4. paste

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

---

Release Notes:

• Fixed a crash when copying and pasting using multiple cursors.

[ChristopherBiscardi]

This definitely fixes a crash, thanks!

crash log

thread 'main' (57198292) panicked at crates/editor/src/clipboard.rs:110:56:
end byte index 8 is out of bounds of `foobar
`
stack backtrace:
   0: __rustc::rust_begin_unwind
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/std/src/panicking.rs:689:5
   1: core::panicking::panic_fmt
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/panicking.rs:80:14
   2: core::str::slice_error_fail_rt
   3: core::str::slice_error_fail
             at /rustc/59807616e1fa2540724bfbac14d7976d7e4a3860/library/core/src/str/mod.rs:69:5
   4: <core::ops::range::Range<usize> as core::slice::index::SliceIndex<str>>::index
             at /Users/chris/.rustup/toolchains/1.95.0-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/str/traits.rs:241:21
   5: <str as core::ops::index::Index<core::ops::range::Range<usize>>>::index
             at /Users/chris/.rustup/toolchains/1.95.0-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/str/traits.rs:63:15
   6: <editor::Editor>::do_paste::{closure#0}::{closure#2}
             at ./crates/editor/src/clipboard.rs:110:56
   7: <gpui::app::App as gpui::AppContext>::update_entity::<multi_buffer::MultiBuffer, (), <editor::Editor>::do_paste::{closure#0}::{closure#2}>::{closure#0}
             at ./crates/gpui/src/app.rs:2642:26
   8: <gpui::app::App>::update::<(), <gpui::app::App as gpui::AppContext>::update_entity<multi_buffer::MultiBuffer, (), <editor::Editor>::do_paste::{closure#0}::{closure#2}>::{closure#0}>
             at ./crates/gpui/src/app.rs:1031:22
   9: <gpui::app::App as gpui::AppContext>::update_entity::<multi_buffer::MultiBuffer, (), <editor::Editor>::do_paste::{closure#0}::{closure#2}>
             at ./crates/gpui/src/app.rs:2640:14
  10: <gpui::app::context::Context<editor::Editor> as gpui::AppContext>::update_entity::<multi_buffer::MultiBuffer, (), <editor::Editor>::do_paste::{closure#0}::{closure#2}>
             at ./crates/gpui/src/app/context.rs:808:18
  11: <gpui::app::entity_map::Entity<multi_buffer::MultiBuffer>>::update::<(), gpui::app::context::Context<editor::Editor>, <editor::Editor>::do_paste::{closure#0}::{closure#2}>
             at ./crates/gpui/src/app/entity_map.rs:481:12
  12: <editor::Editor>::do_paste::{closure#0}
             at ./crates/editor/src/clipboard.rs:95:29
  13: <editor::Editor>::transact::<<editor::Editor>::do_paste::{closure#0}>::{closure#0}
             at ./crates/editor/src/editor.rs:8346:13
  14: <editor::Editor>::with_selection_effects_deferred::<core::option::Option<clock::Lamport>, <editor::Editor>::transact<<editor::Editor>::do_paste::{closure#0}>::{closure#0}>
             at ./crates/editor/src/selection.rs:102:22
  15: <editor::Editor>::transact::<<editor::Editor>::do_paste::{closure#0}>
             at ./crates/editor/src/editor.rs:8344:14
  16: <editor::Editor>::do_paste
             at ./crates/editor/src/clipboard.rs:76:14
  17: <editor::Editor>::paste_item
             at ./crates/editor/src/clipboard.rs:329:44
  18: <editor::Editor>::paste
             at ./crates/editor/src/clipboard.rs:254:18
  19: <<editor::Editor>::paste as core::ops::function::Fn<(&mut editor::Editor, &editor::actions::Paste, &mut gpui::window::Window, &mut gpui::app::context::Context<editor::Editor>)>>::call
             at /Users/chris/.rustup/toolchains/1.95.0-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/function.rs:79:5
  20: editor::element::register_action::<editor::actions::Paste, <editor::Editor>::paste>::{closure#0}::{closure#0}
             at ./crates/editor/src/element.rs:10641:17
  21: <gpui::app::App as gpui::AppContext>::update_entity::<editor::Editor, (), editor::element::register_action<editor::actions::Paste, <editor::Editor>::paste>::{closure#0}::{closure#0}>::{closure#0}
             at ./crates/gpui/src/app.rs:2642:26
  22: <gpui::app::App>::update::<(), <gpui::app::App as gpui::AppContext>::update_entity<editor::Editor, (), editor::element::register_action<editor::actions::Paste, <editor::Editor>::paste>::{closure#0}::{closure#0}>::{closure#0}>
             at ./crates/gpui/src/app.rs:1031:22
  23: <gpui::app::App as gpui::AppContext>::update_entity::<editor::Editor, (), editor::element::register_action<editor::actions::Paste, <editor::Editor>::paste>::{closure#0}::{closure#0}>
             at ./crates/gpui/src/app.rs:2640:14
  24: <gpui::app::entity_map::Entity<editor::Editor>>::update::<(), gpui::app::App, editor::element::register_action<editor::actions::Paste, <editor::Editor>::paste>::{closure#0}::{closure#0}>
             at ./crates/gpui/src/app/entity_map.rs:481:12
  25: editor::element::register_action::<editor::actions::Paste, <editor::Editor>::paste>::{closure#0}
             at ./crates/editor/src/element.rs:10640:20
  26: <gpui::window::Window>::dispatch_action_on_node_inner
             at ./crates/gpui/src/window.rs:5391:21
  27: <gpui::window::Window>::dispatch_action_on_node
             at ./crates/gpui/src/window.rs:5311:14
  28: <gpui::window::Window>::dispatch_key_event
             at ./crates/gpui/src/window.rs:5146:22
  29: <gpui::window::Window>::dispatch_event
             at ./crates/gpui/src/window.rs:4919:18
  30: <gpui::window::Window>::new::{closure#17}::{closure#0}
             at ./crates/gpui/src/window.rs:1738:61
  31: <gpui::app::App>::update_window_id::<gpui::window::DispatchEventResult, <gpui::window::Window>::new::{closure#17}::{closure#0}>::{closure#0}
             at ./crates/gpui/src/app.rs:1782:26
  32: <gpui::app::App>::update::<core::option::Option<gpui::window::DispatchEventResult>, <gpui::app::App>::update_window_id<gpui::window::DispatchEventResult, <gpui::window::Window>::new::{closure#17}::{closure#0}>::{closure#0}>
             at ./crates/gpui/src/app.rs:1031:22
  33: <gpui::app::App>::update_window_id::<gpui::window::DispatchEventResult, <gpui::window::Window>::new::{closure#17}::{closure#0}>
             at ./crates/gpui/src/app.rs:1776:14
  34: <gpui::app::App as gpui::AppContext>::update_window::<gpui::window::DispatchEventResult, <gpui::window::Window>::new::{closure#17}::{closure#0}>
             at ./crates/gpui/src/app.rs:2670:14
  35: <gpui::app::async_context::AsyncApp as gpui::AppContext>::update_window::<gpui::window::DispatchEventResult, <gpui::window::Window>::new::{closure#17}::{closure#0}>
             at ./crates/gpui/src/app/async_context.rs:94:14
  36: <gpui::window::AnyWindowHandle>::update::<gpui::app::async_context::AsyncApp, gpui::window::DispatchEventResult, <gpui::window::Window>::new::{closure#17}::{closure#0}>
             at ./crates/gpui/src/window.rs:6310:12
  37: <gpui::window::Window>::new::{closure#17}
             at ./crates/gpui/src/window.rs:1738:22
  38: <alloc::boxed::Box<dyn core::ops::function::FnMut<(gpui::interactive::PlatformInput,), Output = gpui::window::DispatchEventResult>> as core::ops::function::FnMut<(gpui::interactive::PlatformInput,)>>::call_mut
             at /Users/chris/.rustup/toolchains/1.95.0-aarch64-apple-darwin/lib/rustlib/src/rust/library/alloc/src/boxed.rs:2247:9
  39: gpui_macos::window::handle_key_event::{closure#0}
             at ./crates/gpui_macos/src/window.rs:2135:14
  40: gpui_macos::window::handle_key_event
             at ./crates/gpui_macos/src/window.rs:2221:27
  41: gpui_macos::window::handle_key_equivalent
             at ./crates/gpui_macos/src/window.rs:2046:5
  42: <unknown>
  43: <unknown>
  44: <unknown>
  45: <unknown>
  46: <unknown>
  47: <unknown>
  48: <unknown>
  49: <() as objc::message::MessageArguments>::invoke::<()>
             at /Users/chris/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/objc-0.2.7/src/message/mod.rs:128:17
  50: objc::message::platform::send_unverified::<objc::runtime::Object, (), ()>
             at /Users/chris/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/objc-0.2.7/src/message/apple/mod.rs:27:9
  51: objc::message::send_message::<objc::runtime::Object, (), ()>
             at /Users/chris/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/objc-0.2.7/src/message/mod.rs:178:5
  52: <*mut objc::runtime::Object as cocoa::appkit::NSApplication>::run
             at /Users/chris/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cocoa-0.26.0/src/appkit.rs:628:9
  53: <gpui_macos::platform::MacPlatform as gpui::platform::Platform>::run
             at ./crates/gpui_macos/src/platform.rs:511:17
  54: <gpui::app::Application>::run::<zed::main::{closure#12}>
             at ./crates/gpui/src/app.rs:231:18
  55: zed::main
             at ./crates/zed/src/main.rs:478:9
  56: <fn() as core::ops::function::FnOnce<()>>::call_once
             at /Users/chris/.rustup/toolchains/1.95.0-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.