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Fix two-thumb backspace fragment modes #8

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Merged
AsafMah merged 2 commits into from
May 25, 2026
Merged

Fix two-thumb backspace fragment modes #8

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d61c264
Fix two-thumb backspace fragment modes
AsafMah May 24, 2026
eea68f0
Update backspace install validation log
AsafMah May 25, 2026
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138 changes: 109 additions & 29 deletions app/src/main/java/helium314/keyboard/latin/inputlogic/InputLogic.java
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Original file line number Diff line number Diff line change
Expand Up @@ -134,7 +134,11 @@ public final class InputLogic {
// character at a time. The list is kept in sync with {@code mWordComposer.getTypedWord()}:
// entries past the current length are filtered at read time, and the list is cleared
// outright whenever the composing word is committed or reset.
private final java.util.ArrayList<Integer> mGestureFragmentBoundaries = new java.util.ArrayList<>();
private final ArrayList<Integer> mGestureFragmentBoundaries = new ArrayList<>();
/** Fragment lengths within the most recent gesture-driven commit. The last entry includes
* the trailing autospace if one was inserted. Used by "Delete last fragment" after the
* composing word has already been auto-committed. */
private final ArrayList<Integer> mLastGestureCommittedFragmentLengths = new ArrayList<>();

// ---- Unified combining-mode state machine ----------------------------------------------
// After every composing-word-extending event (tap of a letter OR gesture completion),
Expand Down Expand Up @@ -882,8 +886,7 @@ public void onCancelBatchInput(final LatinIME.UIHandler handler) {
// composing word is committed or reset; stale entries beyond the current length are
// filtered in {@link #tryFragmentBackspace} as a defensive measure.

/** Record a fragment boundary at the current composing-word length. No-op when not in manual+fragment mode. */
private void recordFragmentBoundaryIfTracking(final SettingsValues sv) {
private boolean shouldTrackFragmentBoundaries(final SettingsValues sv) {
// Two paths into fragment tracking:
// * Legacy manual-spacing mode (#1.1) — gated on both prefs.
// * Multi-part word composition (#1.6) — combining mode is the trigger; fragment
Expand All @@ -893,9 +896,20 @@ private void recordFragmentBoundaryIfTracking(final SettingsValues sv) {
final boolean multipartTracking = sv.mMultipartAutoExtendInCombining
&& sv.mCombiningGraceMs > 0
&& sv.mGestureFragmentBackspace;
if (!legacyTracking && !multipartTracking) return;
return legacyTracking || multipartTracking;
}

/** Record a fragment boundary at the current composing-word length. No-op when not in fragment mode. */
private void recordFragmentBoundaryIfTracking(final SettingsValues sv) {
if (!shouldTrackFragmentBoundaries(sv)) return;
if (!mWordComposer.isComposingWord()) return;
final int len = mWordComposer.getTypedWord().length();
recordFragmentBoundaryIfTracking(sv, mWordComposer.getTypedWord().length());
}

/** Record a fragment boundary at a known composing-word length. */
private void recordFragmentBoundaryIfTracking(final SettingsValues sv, final int len) {
if (!shouldTrackFragmentBoundaries(sv)) return;
if (len <= 0) return;
// Don't record duplicates (e.g. the same fragment appended twice in quick succession).
if (!mGestureFragmentBoundaries.isEmpty()
&& mGestureFragmentBoundaries.get(mGestureFragmentBoundaries.size() - 1) == len) {
Expand All @@ -909,6 +923,13 @@ private void clearFragmentBoundaries() {
if (!mGestureFragmentBoundaries.isEmpty()) mGestureFragmentBoundaries.clear();
}

private void clearCommittedGestureBackspaceState() {
mLastGestureCommittedLength = 0;
if (!mLastGestureCommittedFragmentLengths.isEmpty()) {
mLastGestureCommittedFragmentLengths.clear();
}
}

// ---- Unified combining-mode helpers --------------------------------------------------

/**
Expand All @@ -925,7 +946,7 @@ private void enterCombiningMode(final SettingsValues settingsValues, final boole
// next-word predictions" one-shot — the user moved on to typing the next word.
mAutospaceAlternativesPending = false;
mAutoCommitRevertLength = 0;
mLastGestureCommittedLength = 0;
clearCommittedGestureBackspaceState();
mAutospaceJustWritten = false;
final int baseGraceMs = settingsValues.mCombiningGraceMs;
if (baseGraceMs <= 0) return;
Expand Down Expand Up @@ -955,7 +976,7 @@ private void enterJoinNextMode(final SettingsValues settingsValues) {
OneShotSpaceAction.armJoinNext();
mAutospaceAlternativesPending = false;
mAutoCommitRevertLength = 0;
mLastGestureCommittedLength = 0;
clearCommittedGestureBackspaceState();
mAutospaceJustWritten = false;
if (Constants.CODE_SPACE == mConnection.getCodePointBeforeCursor()
&& !mWordComposer.isComposingWord()) {
Expand Down Expand Up @@ -1018,7 +1039,7 @@ void cancelCombiningMode() {
// represent the user explicitly leaving the just-auto-committed context.
mAutospaceAlternativesPending = false;
mAutoCommitRevertLength = 0;
mLastGestureCommittedLength = 0;
clearCommittedGestureBackspaceState();
mAutospaceJustWritten = false;
mCombiningWordHasGestureFragment = false;
if (mInCombiningMode) {
Expand Down Expand Up @@ -1097,6 +1118,8 @@ private void onCombiningGraceExpired() {
// commit itself doesn't move the cursor. We need the typed-word length plus whatever
// chars the autospace path writes to know how much to undo on a suggestion-pick.
final String typedWordAtCommit = mWordComposer.getTypedWord();
final ArrayList<Integer> fragmentLengthsAtCommit =
getFragmentLengthsForCommit(typedWordAtCommit.length());
final int cursorBefore = mConnection.getExpectedSelectionEnd();
mConnection.beginBatchEdit();
if (sv.mCombiningAutocorrectOnAutospace) {
Expand Down Expand Up @@ -1184,6 +1207,21 @@ private void onCombiningGraceExpired() {
// 0 for tap-only commits, where char-by-char delete is the right behavior.
if (wordHadGestureFragment) {
mLastGestureCommittedLength = writtenChars;
mLastGestureCommittedFragmentLengths.clear();
if (!fragmentLengthsAtCommit.isEmpty()) {
final int committedDelta = committedLen - typedWordAtCommit.length();
final int lastIndex = fragmentLengthsAtCommit.size() - 1;
final int adjustedLastFragmentLen =
fragmentLengthsAtCommit.get(lastIndex) + committedDelta + autospaceChars;
if (adjustedLastFragmentLen > 0) {
fragmentLengthsAtCommit.set(lastIndex, adjustedLastFragmentLen);
mLastGestureCommittedFragmentLengths.addAll(fragmentLengthsAtCommit);
} else if (writtenChars > 0) {
mLastGestureCommittedFragmentLengths.add(writtenChars);
}
} else if (writtenChars > 0) {
mLastGestureCommittedFragmentLengths.add(writtenChars);
}
}
// "keep_alternatives" — fall through, do nothing.
}
Expand All @@ -1204,6 +1242,7 @@ private boolean tryFragmentBackspace(final SettingsValues sv) {
&& sv.mCombiningGraceMs > 0
&& sv.mGestureFragmentBackspace;
if (!legacyTracking && !multipartTracking) return false;
if (sv.mCombiningBackspaceDeletesGestureWord) return false;
if (mGestureFragmentBoundaries.isEmpty()) return false;
if (!mWordComposer.isComposingWord()) {
clearFragmentBoundaries();
Expand All @@ -1214,16 +1253,24 @@ private boolean tryFragmentBackspace(final SettingsValues sv) {
final int currentLen = mWordComposer.getTypedWord().length();
// Filter out stale boundaries past the current length.
while (!mGestureFragmentBoundaries.isEmpty()
&& mGestureFragmentBoundaries.get(mGestureFragmentBoundaries.size() - 1) >= currentLen) {
&& mGestureFragmentBoundaries.get(mGestureFragmentBoundaries.size() - 1) > currentLen) {
mGestureFragmentBoundaries.remove(mGestureFragmentBoundaries.size() - 1);
}
if (mGestureFragmentBoundaries.isEmpty()) return false;

// Pop one boundary and shrink to the previous one (or 0 if no more).
mGestureFragmentBoundaries.remove(mGestureFragmentBoundaries.size() - 1);
final int newLen = mGestureFragmentBoundaries.isEmpty()
? 0
: mGestureFragmentBoundaries.get(mGestureFragmentBoundaries.size() - 1);
final int lastBoundary = mGestureFragmentBoundaries.get(mGestureFragmentBoundaries.size() - 1);
final int newLen;
if (lastBoundary == currentLen) {
// The last marker is the end of the current fragment. Pop it and shrink to the
// previous marker, or to 0 for a single-fragment word.
mGestureFragmentBoundaries.remove(mGestureFragmentBoundaries.size() - 1);
newLen = mGestureFragmentBoundaries.isEmpty()
? 0
: mGestureFragmentBoundaries.get(mGestureFragmentBoundaries.size() - 1);
} else {
// Defensive fallback for words whose current fragment end was not recorded.
newLen = lastBoundary;
}

final String oldWord = mWordComposer.getTypedWord();
final String newWord = newLen <= 0
Expand All @@ -1250,6 +1297,22 @@ private boolean tryFragmentBackspace(final SettingsValues sv) {
return true;
}

private ArrayList<Integer> getFragmentLengthsForCommit(final int currentLen) {
final ArrayList<Integer> fragmentLengths = new ArrayList<>();
if (currentLen <= 0) return fragmentLengths;
int previousBoundary = 0;
for (int i = 0; i < mGestureFragmentBoundaries.size(); ++i) {
final int boundary = mGestureFragmentBoundaries.get(i);
if (boundary <= previousBoundary || boundary > currentLen) continue;
fragmentLengths.add(boundary - previousBoundary);
previousBoundary = boundary;
}
if (previousBoundary < currentLen) {
fragmentLengths.add(currentLen - previousBoundary);
}
return fragmentLengths;
}

// TODO: on the long term, this method should become private, but it will be
// difficult.
// Especially, how do we deal with InputMethodService.onDisplayCompletions?
Expand Down Expand Up @@ -2236,6 +2299,8 @@ private void handleBackspaceEvent(final Event event, final InputTransaction inpu
// clears it. If non-zero (the previous commit was a gesture), this backspace MIGHT
// delete the whole word — see further down, after the autocorrect-revert branch.
final int gestureCommittedLen = mLastGestureCommittedLength;
final ArrayList<Integer> gestureCommittedFragmentLengths =
new ArrayList<>(mLastGestureCommittedFragmentLengths);
// Combining mode: a backspace always cancels the pending commit. The user is
// explicitly retracting input; we don't want the timer to fire mid-correction.
cancelCombiningMode();
Expand Down Expand Up @@ -2298,15 +2363,13 @@ private void handleBackspaceEvent(final Event event, final InputTransaction inpu
StatsUtils.onBackspaceWordDelete(rejectedSuggestion.length());
} else if ((inputTransaction.getSettingsValues().mGestureManualSpacing
|| inputTransaction.getSettingsValues().mCombiningGraceMs > 0)
&& inputTransaction.getSettingsValues().mCombiningBackspaceDeletesGestureWord) {
&& inputTransaction.getSettingsValues().mCombiningBackspaceDeletesGestureWord
&& inputTransaction.getSettingsValues().mCombiningBackspaceDeletesComposingText) {
final int wordLength = mWordComposer.getTypedWord().length();
if (inputTransaction.getSettingsValues().mCombiningBackspaceDeletesComposingText) {
mConnection.beginBatchEdit();
mConnection.deleteTextBeforeCursor(wordLength);
mConnection.endBatchEdit();
} else {
mConnection.finishComposingText();
}
mConnection.beginBatchEdit();
mConnection.deleteTextBeforeCursor(wordLength);
mConnection.finishComposingText();
mConnection.endBatchEdit();
mWordComposer.reset();
deletedWholeComposingWord = true;
StatsUtils.onBackspaceWordDelete(wordLength);
Expand Down Expand Up @@ -2348,6 +2411,21 @@ private void handleBackspaceEvent(final Event event, final InputTransaction inpu
// words don't qualify — gestureCommittedLen is 0 for those. We delete via
// deleteTextBeforeCursor instead of the usual single-char path so the user
// doesn't have to mash backspace to undo a swiped word.
final int gestureCommittedFragmentLen = gestureCommittedFragmentLengths.isEmpty()
? 0
: gestureCommittedFragmentLengths.remove(gestureCommittedFragmentLengths.size() - 1);
if (gestureCommittedFragmentLen > 0
&& inputTransaction.getSettingsValues().mGestureFragmentBackspace
&& !inputTransaction.getSettingsValues().mCombiningBackspaceDeletesGestureWord) {
mConnection.beginBatchEdit();
mConnection.deleteTextBeforeCursor(gestureCommittedFragmentLen);
mConnection.endBatchEdit();
mLastGestureCommittedFragmentLengths.clear();
mLastGestureCommittedFragmentLengths.addAll(gestureCommittedFragmentLengths);
StatsUtils.onBackspaceWordDelete(gestureCommittedFragmentLen);
inputTransaction.setRequiresUpdateSuggestions();
return;
}
if (gestureCommittedLen > 0
&& inputTransaction.getSettingsValues().mCombiningBackspaceDeletesGestureWord) {
mConnection.beginBatchEdit();
Expand Down Expand Up @@ -3678,17 +3756,19 @@ public void onUpdateTailBatchInputCompleted(final SettingsValues settingsValues,
} else {
setSuggestedWords(SuggestedWords.getEmptyInstance());
}
// PREF_GESTURE_FRAGMENT_BACKSPACE: record this gesture as a fragment boundary
// so backspace can pop the whole word at once. When extending an existing
// composing word, both the prior fragments AND this new one are already in the
// boundaries list (prior fragments were recorded at their own append time);
// recordFragmentBoundaryIfTracking adds the NEW boundary at the end. No-op if
// PREF_GESTURE_FRAGMENT_BACKSPACE isn't on.
// PREF_GESTURE_FRAGMENT_BACKSPACE: make sure the previous word length is present
// (fresh gesture words did not have an earlier extension point), then record this
// gesture's end so backspace can pop exactly one fragment.
if (!usedMergedTrail) {
recordFragmentBoundaryIfTracking(settingsValues, prevTypedWord.length());
}
recordFragmentBoundaryIfTracking(settingsValues);
} else {
// Non-extend path replaces the whole composing word each gesture; any prior
// fragment boundaries become meaningless.
// fragment boundaries become meaningless, then the new gesture becomes the only
// fragment currently available to pop.
clearFragmentBoundaries();
recordFragmentBoundaryIfTracking(settingsValues);
}
// Tap-promotion-extend is a one-shot decision per gesture; clear the flag so the
// next gesture re-evaluates the timing.
Expand Down
2 changes: 1 addition & 1 deletion app/src/main/res/values/strings.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -294,7 +294,7 @@
<string name="two_thumb_backspace_behavior">Backspace behavior</string>
<string name="two_thumb_backspace_behavior_summary">Choose what backspace removes while using manual spacing or delayed autospace.</string>
<string name="two_thumb_backspace_normal">Delete one character</string>
<string name="two_thumb_backspace_fragment">Delete last word part</string>
<string name="two_thumb_backspace_fragment">Delete last fragment</string>
<string name="two_thumb_backspace_word">Delete whole word</string>
<string name="multipart_join_key_mode">Explicit "join next" modifier</string>
<string name="multipart_join_key_mode_summary">Force the next input to extend the current word regardless of timing.</string>
Expand Down
85 changes: 83 additions & 2 deletions app/src/test/java/helium314/keyboard/latin/InputLogicTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -390,7 +390,7 @@ class InputLogicTest {
assertEquals("", composingText)
}

@Test fun wholeWordBackspaceCanKeepManualSpacingComposingTextInEditor() {
@Test fun wholeWordBackspaceWithLiveComposingDeleteOffFallsBackToOneCharacter() {
reset()
latinIME.prefs().edit {
putBoolean(Settings.PREF_GESTURE_MANUAL_SPACING, true)
Expand All @@ -405,7 +405,88 @@ class InputLogicTest {

functionalKeyPress(KeyCode.DELETE)

assertEquals("hello", textBeforeCursor)
assertEquals("hell", textBeforeCursor)
assertEquals("hell", composingText)
}

@Test fun fragmentBackspaceDeletesOnlySwipeFragment() {
reset()
latinIME.prefs().edit {
putBoolean(Settings.PREF_GESTURE_MANUAL_SPACING, true)
putBoolean(Settings.PREF_GESTURE_FRAGMENT_BACKSPACE, true)
putBoolean(Settings.PREF_COMBINING_BACKSPACE_DELETES_GESTURE_WORD, false)
}

gestureInput("fire")
assertEquals("fire", textBeforeCursor)
assertEquals("fire", composingText)

functionalKeyPress(KeyCode.DELETE)

assertEquals("", textBeforeCursor)
assertEquals("", composingText)
}

@Test fun fragmentBackspaceDeletesLastSwipeFragmentInMultipartWord() {
reset()
latinIME.prefs().edit {
putBoolean(Settings.PREF_GESTURE_MANUAL_SPACING, true)
putBoolean(Settings.PREF_GESTURE_FRAGMENT_BACKSPACE, true)
putBoolean(Settings.PREF_COMBINING_BACKSPACE_DELETES_GESTURE_WORD, false)
}

gestureInput("fire")
gestureInput("truck")
assertEquals("firetruck", textBeforeCursor)
assertEquals("firetruck", composingText)

functionalKeyPress(KeyCode.DELETE)

assertEquals("fire", textBeforeCursor)
assertEquals("fire", composingText)
}

@Test fun fragmentBackspaceDeletesLastSwipeFragmentAfterAutospaceCommit() {
reset()
latinIME.prefs().edit {
putInt(Settings.PREF_COMBINING_GRACE_MS, 1000)
putBoolean(Settings.PREF_GESTURE_MANUAL_SPACING, false)
putBoolean(Settings.PREF_GESTURE_FRAGMENT_BACKSPACE, true)
putBoolean(Settings.PREF_COMBINING_BACKSPACE_DELETES_GESTURE_WORD, false)
}

gestureInput("fire")
gestureInput("truck")
expireCombiningGrace()
assertEquals("firetruck ", textBeforeCursor)
assertEquals("", composingText)

functionalKeyPress(KeyCode.DELETE)

assertEquals("fire", textBeforeCursor)
assertEquals("", composingText)

functionalKeyPress(KeyCode.DELETE)

assertEquals("", textBeforeCursor)
assertEquals("", composingText)
}

@Test fun wholeWordBackspaceWithLiveComposingDeleteOnClearsComposingSpan() {
reset()
latinIME.prefs().edit {
putBoolean(Settings.PREF_GESTURE_MANUAL_SPACING, true)
putBoolean(Settings.PREF_GESTURE_FRAGMENT_BACKSPACE, false)
putBoolean(Settings.PREF_COMBINING_BACKSPACE_DELETES_GESTURE_WORD, true)
putBoolean(Settings.PREF_COMBINING_BACKSPACE_DELETES_COMPOSING_TEXT, true)
}

chainInput("hello")
functionalKeyPress(KeyCode.DELETE)
chainInput("hi")
functionalKeyPress(KeyCode.DELETE)

assertEquals("", textBeforeCursor)
assertEquals("", composingText)
}

Expand Down
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