macOS: IME text committed after the marked text is cleared isn't lost (winit#4650) (#676)

winit 0.30.13 reports insertText as Ime::Commit only while marked text is
left, and after any commit it swallows the next key. Real paths where that
loses text:

- input methods that end a composition with unmarkText, then insertText
  (rust-windowing/winit#3925): the committed text was dropped;
- Apple Korean 2-Set, for the key typed after a syllable: on 한 then 5 it
  calls setMarkedText("한"), insertText("한"), setMarkedText(""),
  insertText("5"), so the 5 (or ;, or any key that ends the syllable) was
  dropped;
- a commit made outside a key press (a candidate clicked with the mouse,
  dictation): no key follows to reset the state, so the next key (for
  example Backspace) was swallowed.

vendor/winit now commits when a composition was started (pending_commit,
set in setMarkedText, cleared by the commit and when IME is disallowed);
other insertText calls still reach the app as KeyboardInput. A commit
outside keyDown clears the marked text and returns to the ground state.
validAttributesForMarkedText lists the underline and marked-clause
attributes, which some input methods need before they compose.

This is rust-windowing/winit#4650, the 0.30 backport of #4651 (merged on
winit master), plus the part of #4748 that fixes #4651's out-of-key-press
case (#4748's other parts are not included). One correction: upstream
spells the underline attribute "NSUnderlineStyle", but AppKit's
NSUnderlineStyleAttributeName is "NSUnderline" (printed on macOS 14), so
the AppKit value is used.

Checked with the real input methods on macOS 14.7.1 (a scratch winit app fed
key events through AppKit): with the patch 한+5 and 한+; commit the 5 and ;,
unmarkText-then-insertText commits, and Backspace after a commit outside a
key press is delivered; ABC typing, held keys, Japanese (日本, あ), Cangjie
(日) and Korean composition give the same events as before. A test fails if
a re-vendored winit loses the patch.

Co-authored-by: Claude Opus 5.5 <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>

apps/pdfcraft/tests/winit_macos_ime_commit.rs

@@ -0,0 +1,19 @@
+//! vendor/winit patch (6) (vendor/README.md).
+
+#[test]
+fn winit_commits_macos_compositions_that_end_without_marked_text() {
+    // winit 0.30.13 treats `insertText` as an IME commit only while marked text is left. Input
+    // methods that end a composition with `unmarkText` first lost the committed text, and Apple
+    // Korean, which clears its marked text before inserting the key typed after a syllable (`한`
+    // then `5`), lost that key. vendor/winit commits when a composition was started
+    // (`pending_commit`, rust-windowing/winit#4650, the 0.30 backport of #4651 on winit master), and
+    // a commit outside a key press no longer swallows the next key (#4748). A re-vendored copy
+    // without the patch would silently bring the bug back: re-apply the patch, or drop the copy once
+    // a winit 0.30 release has the fix.
+    let root = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../..");
+    let view = std::fs::read_to_string(root.join("vendor/winit/src/platform_impl/macos/view.rs")).unwrap();
+    assert!(view.contains("if pending_commit && ime_enabled && !is_control {"), "insertText commits only while marked text is left");
+    assert!(view.contains("self.ivars().pending_commit.set(true);"), "setMarkedText no longer starts a pending commit");
+    assert!(view.contains("self.ivars().in_key_down.set(true);"), "a commit outside a key press swallows the next key again");
+    assert!(view.contains("NSString::from_str(\"NSUnderline\")"), "validAttributesForMarkedText lost the underline attribute");
+}