Fix Korean IME arrow key inserting character at wrong position by drvoss · Pull Request #20039 · microsoft/terminal

drvoss · 2026-03-31T02:24:44Z

Summary of the Pull Request

Fix a regression introduced in v1.24 where pressing an arrow key during Korean IME composition caused the committed character to be inserted at the wrong cursor position.

References and Relevant Issues

Closes #20038
Related to #19738 (Remove TF_TMAE_UIELEMENTENABLEDONLY).

Detailed Description of the Pull Request / Additional comments

Before #19738, the Korean IME activated through IMM32 (excluded from TSF by TF_TMAE_UIELEMENTENABLEDONLY) and was not affected by TermControl::_KeyHandler forwarding keys to the PTY during composition. After #19738, the Korean IME activates through TSF, making a missing composition guard in _KeyHandler visible as a bug.

The sequence of events that causes the bug:

User presses Left arrow during active Korean IME composition (e.g. composing 가).
_KeyHandler calls _TrySendKeyEvent(VK_LEFT) which enqueues \x1b[D to the PTY input queue. The cursor moves.
TSF processes the key. The Korean IME sees the arrow and ends the composition.
OnEndComposition schedules _doCompositionUpdate with TF_ES_ASYNC.
The async session fires, reads finalized text 가, calls HandleOutput("가").
PTY processes [\x1b[D, "가"]: cursor moves left first, then 가 is inserted at the wrong (already-moved) position.

The fix adds a guard before _TrySendKeyEvent:

cpp if (GetTSFHandle().HasActiveComposition()) { return true; }

This mirrors the existing behavior in conhost v1 (src/interactivity/win32/windowio.cpp lines 361-364). When TSF has an active composition, key events are suppressed from the PTY. The Korean IME re-injects navigation and confirmation keys after the composition ends, at which point HasActiveComposition() returns false and they are forwarded normally.

Historical note: This guard was not needed before PR #17067 (v1.22) because the old implementation used WinRT CoreTextServices via XAML (TSFInputControl.xaml). The XAML framework intercepted composition key events before _KeyHandler. The new custom Win32 TSF context in #17067 no longer does this. The bug was latent from v1.22 but only became visible for Korean in v1.24 when #19738 removed TF_TMAE_UIELEMENTENABLEDONLY.

Validation Steps Performed

Open Windows Terminal with Korean IME (Dubeolsik layout).
Type rk to begin composing 가 (composition active, syllable not yet committed).
Press the Left arrow key.
Before fix: 가 is inserted one cell to the left of the intended position.
After fix: 가 is inserted at the correct position, then cursor moves left.

Also verified:

Normal Korean text input (typing without arrow keys) still works correctly.
Arrow key navigation when no composition is active still works correctly.
English and other IME input is not affected.

PR Checklist

Closes Korean IME (v1.24+): Arrow key during composition inserts character at wrong position #20038
Tests added/passed
Documentation updated (not required for this fix)
Schema updated (not required for this fix)

When an arrow key is pressed during an active Korean IME composition, _KeyHandler was forwarding the key to the PTY immediately via _TrySendKeyEvent. This moved the cursor before the async TSF edit session had a chance to commit the finalized text, causing the committed character to land at the wrong position. The fix adds a guard that mirrors the existing behavior in the conhost v1 key handler (src/interactivity/win32/windowio.cpp lines 361-364): suppress all key events from being forwarded to the PTY while TSF has an active composition. The IME re-injects navigation and confirmation keys after the composition ends, at which point HasActiveComposition() returns false and they are forwarded normally. Historical note: this guard was not needed before PR microsoft#17067 (v1.22) because the old TSF implementation used WinRT CoreTextServices via XAML (TSFInputControl.xaml/.cpp). In that model the XAML framework handled composition key events before they reached _KeyHandler, so _KeyHandler never received them during composition. The new custom Win32 TSF context introduced in microsoft#17067 no longer intercepts keys at the XAML level, making _KeyHandler responsible for this check. The bug was not visible in v1.22-v1.23 for Korean because the Korean IME was excluded from the TSF path by TF_TMAE_UIELEMENTENABLEDONLY. It became visible in v1.24 when PR microsoft#19738 removed that flag, causing the Korean IME to activate through TSF for the first time. Closes microsoft#20038

DHowett

@lhecker this makes sense to me - you agree?

DHowett · 2026-03-31T22:04:22Z

/azp run

azure-pipelines · 2026-03-31T22:04:33Z

Azure Pipelines successfully started running 1 pipeline(s).

lhecker

Thank you for investigating this for us!

Fix a regression introduced in v1.24 where pressing an arrow key during Korean IME composition caused the committed character to be inserted at the wrong cursor position. Before #19738, the Korean IME activated through IMM32 (excluded from TSF by `TF_TMAE_UIELEMENTENABLEDONLY`) and was not affected by `TermControl::_KeyHandler` forwarding keys to the PTY during composition. After #19738, the Korean IME activates through TSF, making a missing composition guard in `_KeyHandler` visible as a bug. The sequence of events that causes the bug: 1. User presses Left arrow during active Korean IME composition (e.g. composing `가`). 2. `_KeyHandler` calls `_TrySendKeyEvent(VK_LEFT)` which enqueues `\x1b[D` to the PTY input queue. The cursor moves. 3. TSF processes the key. The Korean IME sees the arrow and ends the composition. 4. `OnEndComposition` schedules `_doCompositionUpdate` with `TF_ES_ASYNC`. 5. The async session fires, reads finalized text `가`, calls `HandleOutput("가")`. 6. PTY processes `[\x1b[D, "가"]`: cursor moves left first, then `가` is inserted at the wrong (already-moved) position. The fix adds a guard before `_TrySendKeyEvent`, which mirrors the existing behavior in conhost (windowio.cpp). When TSF has an active composition, key events are not converted into input. The Korean IME re-injects navigation and confirmation keys after the composition ends, at which point `HasActiveComposition()` returns false and they are forwarded normally. **Historical note:** This guard was not needed before PR #17067 (v1.22) because the old implementation used WinRT `CoreTextServices` via XAML (`TSFInputControl.xaml`). The XAML framework intercepted composition key events before `_KeyHandler`. The new custom Win32 TSF context in #17067 no longer does this. The bug was latent from v1.22 but only became visible for Korean in v1.24 when #19738 removed `TF_TMAE_UIELEMENTENABLEDONLY`. ## Validation Steps Performed 1. Open Windows Terminal with Korean IME (Dubeolsik layout). 2. Type `rk` to begin composing `가` (composition active, syllable not yet committed). 3. Press the Left arrow key. 4. Before fix: `가` is inserted one cell to the left of the intended position. 5. After fix: `가` is inserted at the correct position, then cursor moves left. Also verified: - Normal Korean text input (typing without arrow keys) still works correctly. - Arrow key navigation when no composition is active still works correctly. - English and other IME input is not affected. Closes #20038 Refs #19738 (cherry picked from commit 14f4271) Service-Card-Id: PVTI_lADOAF3p4s4BQX0-zgo0JpM Service-Version: 1.25

Fix a regression introduced in v1.24 where pressing an arrow key during Korean IME composition caused the committed character to be inserted at the wrong cursor position. Before #19738, the Korean IME activated through IMM32 (excluded from TSF by `TF_TMAE_UIELEMENTENABLEDONLY`) and was not affected by `TermControl::_KeyHandler` forwarding keys to the PTY during composition. After #19738, the Korean IME activates through TSF, making a missing composition guard in `_KeyHandler` visible as a bug. The sequence of events that causes the bug: 1. User presses Left arrow during active Korean IME composition (e.g. composing `가`). 2. `_KeyHandler` calls `_TrySendKeyEvent(VK_LEFT)` which enqueues `\x1b[D` to the PTY input queue. The cursor moves. 3. TSF processes the key. The Korean IME sees the arrow and ends the composition. 4. `OnEndComposition` schedules `_doCompositionUpdate` with `TF_ES_ASYNC`. 5. The async session fires, reads finalized text `가`, calls `HandleOutput("가")`. 6. PTY processes `[\x1b[D, "가"]`: cursor moves left first, then `가` is inserted at the wrong (already-moved) position. The fix adds a guard before `_TrySendKeyEvent`, which mirrors the existing behavior in conhost (windowio.cpp). When TSF has an active composition, key events are not converted into input. The Korean IME re-injects navigation and confirmation keys after the composition ends, at which point `HasActiveComposition()` returns false and they are forwarded normally. **Historical note:** This guard was not needed before PR #17067 (v1.22) because the old implementation used WinRT `CoreTextServices` via XAML (`TSFInputControl.xaml`). The XAML framework intercepted composition key events before `_KeyHandler`. The new custom Win32 TSF context in #17067 no longer does this. The bug was latent from v1.22 but only became visible for Korean in v1.24 when #19738 removed `TF_TMAE_UIELEMENTENABLEDONLY`. ## Validation Steps Performed 1. Open Windows Terminal with Korean IME (Dubeolsik layout). 2. Type `rk` to begin composing `가` (composition active, syllable not yet committed). 3. Press the Left arrow key. 4. Before fix: `가` is inserted one cell to the left of the intended position. 5. After fix: `가` is inserted at the correct position, then cursor moves left. Also verified: - Normal Korean text input (typing without arrow keys) still works correctly. - Arrow key navigation when no composition is active still works correctly. - English and other IME input is not affected. Closes #20038 Refs #19738 (cherry picked from commit 14f4271) Service-Card-Id: PVTI_lADOAF3p4s4BBcTlzgo0JpQ Service-Version: 1.24

This commit fixes a regression in v1.24, where composing Korean text in-between existing characters causes text to the right to be hidden. This is problematic for the Korean IME, because it commonly inserts the composed syllable between existing characters. The fix compresses (removes/absorbs) available whitespace to the right of the composition to make space for any existing text. This means that a composition now virtually acts in insert mode. Closes #20040 Refs #19738 Refs #20039 ## Validation Steps Performed 1. Korean IME: compose `ㄷ` between `가` and `나` → display shows `가ㄷ나`, `나` visible. 2. TUI box (vim prompt with padding): compose inside padded text box → border preserved in place. 3. Composition at end of line (no chars to right): unaffected. 4. English and other IME input: not affected (no active composition row). Co-authored-by: jason <drvoss@users.noreply.github.com> Co-authored-by: Leonard Hecker <lhecker@microsoft.com>

This commit fixes a regression in v1.24, where composing Korean text in-between existing characters causes text to the right to be hidden. This is problematic for the Korean IME, because it commonly inserts the composed syllable between existing characters. The fix compresses (removes/absorbs) available whitespace to the right of the composition to make space for any existing text. This means that a composition now virtually acts in insert mode. Closes #20040 Refs #19738 Refs #20039 ## Validation Steps Performed 1. Korean IME: compose `ㄷ` between `가` and `나` → display shows `가ㄷ나`, `나` visible. 2. TUI box (vim prompt with padding): compose inside padded text box → border preserved in place. 3. Composition at end of line (no chars to right): unaffected. 4. English and other IME input: not affected (no active composition row). Co-authored-by: jason <drvoss@users.noreply.github.com> Co-authored-by: Leonard Hecker <lhecker@microsoft.com> (cherry picked from commit 7a83c0f) Service-Card-Id: PVTI_lADOAF3p4s4BQX0-zgo0JpY Service-Version: 1.25

This commit fixes a regression in v1.24, where composing Korean text in-between existing characters causes text to the right to be hidden. This is problematic for the Korean IME, because it commonly inserts the composed syllable between existing characters. The fix compresses (removes/absorbs) available whitespace to the right of the composition to make space for any existing text. This means that a composition now virtually acts in insert mode. Closes #20040 Refs #19738 Refs #20039 1. Korean IME: compose `ㄷ` between `가` and `나` → display shows `가ㄷ나`, `나` visible. 2. TUI box (vim prompt with padding): compose inside padded text box → border preserved in place. 3. Composition at end of line (no chars to right): unaffected. 4. English and other IME input: not affected (no active composition row). Co-authored-by: jason <drvoss@users.noreply.github.com> Co-authored-by: Leonard Hecker <lhecker@microsoft.com> (cherry picked from commit 7a83c0f) Service-Card-Id: PVTI_lADOAF3p4s4BBcTlzgo0Jpc Service-Version: 1.24

…osoft#20041) This commit fixes a regression in v1.24, where composing Korean text in-between existing characters causes text to the right to be hidden. This is problematic for the Korean IME, because it commonly inserts the composed syllable between existing characters. The fix compresses (removes/absorbs) available whitespace to the right of the composition to make space for any existing text. This means that a composition now virtually acts in insert mode. Closes microsoft#20040 Refs microsoft#19738 Refs microsoft#20039 ## Validation Steps Performed 1. Korean IME: compose `ㄷ` between `가` and `나` → display shows `가ㄷ나`, `나` visible. 2. TUI box (vim prompt with padding): compose inside padded text box → border preserved in place. 3. Composition at end of line (no chars to right): unaffected. 4. English and other IME input: not affected (no active composition row). Co-authored-by: jason <drvoss@users.noreply.github.com> Co-authored-by: Leonard Hecker <lhecker@microsoft.com>

drvoss mentioned this pull request Mar 31, 2026

Fix Korean IME overlay hiding characters to the right of cursor #20041

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DHowett reviewed Mar 31, 2026

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DHowett enabled auto-merge (squash) March 31, 2026 22:07

lhecker approved these changes Mar 31, 2026

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DHowett merged commit 14f4271 into microsoft:main Mar 31, 2026
14 of 16 checks passed

dongy703 mentioned this pull request May 19, 2026

Korean IME: composing character still moves to wrong position on arrow key press (v1.24.11321.0) #20244

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Fix Korean IME arrow key inserting character at wrong position#20039

Fix Korean IME arrow key inserting character at wrong position#20039
DHowett merged 1 commit into
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drvoss:fix/korean-ime-composition-key-forward

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drvoss commented Mar 31, 2026

Summary of the Pull Request

References and Relevant Issues

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

PR Checklist

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