Bug report: IME/dead-key composition broken in Controlled wrapper (react-codemirror2 v9.0.1 + CodeMirror 5.65.20 + React 18)

[mblagojevic10]

We’ve run into an issue with IME/dead-key composition (international keyboard accents) when using react-codemirror2 (Controlled) on React 18.

Environment

• react-codemirror2: 9.0.1
• codemirror: 5.65.20
• React: 18.x
• Browser/OS: reproducible in modern browsers (we initially noticed it with an international keyboard layout)

What’s broken

IME/dead-key composition does not commit correctly in the Controlled wrapper.
Example: typing ' followed by e should produce é, but instead composition appears to remain active and the final composed character is not committed as expected.

Steps to reproduce

1. Render a <Controlled /> editor with value bound to component state.
2. Focus the editor.
3. Switch to an international keyboard layout that supports dead-keys (e.g., US-International).
4. Type: ' then e.
5. Observe that the composition does not commit to é correctly (and/or subsequent edits behave incorrectly).

Suspected root cause

In the Controlled implementation, the wrapper currently cancels every beforeChange (data.cancel()) and then uses a “mirror” editor to compute the next value. This seems to break IME/dead-key composition (origin *compose), because:

• cancelling the beforeChange prevents CodeMirror from completing the composition lifecycle
• syncing value via setValue() during composition can also reset the input state

It looks like composition should be treated as a special case:

• do not cancel changes when data.origin === "*compose" (or when the editor is currently composing)
• avoid applying external value updates (setValue) while composing; instead defer until compositionend

Expected behavior

Dead-key/IME composition should work normally in Controlled mode (i.e., ' + e produces é and composition ends properly), regardless of React version or role/account type in the host app.

If you’d like, I can provide a minimal reproduction repo or a patch showing a composition-safe approach (skip cancel for *compose and defer external sync until compositionend).

Thanks!
Miloš

[mblagojevic10]

Additionally, on macOS, the system “double space” shortcut (inserting a period, i.e., “. ”) does not work inside the editor, which suggests general issues with native composition/text input behaviors.