2 files changed, 40 insertions, 1 deletions

diff --git a/java/src/com/android/inputmethod/latin/LatinIME.java b/java/src/com/android/inputmethod/latin/LatinIME.java
index 0560cf528..f3fc3177b 100644
--- a/java/src/com/android/inputmethod/latin/LatinIME.java
+++ b/java/src/com/android/inputmethod/latin/LatinIME.java
@@ -961,7 +961,11 @@ public class LatinIME extends InputMethodService implements KeyboardActionListen
             // TODO: is it still necessary to test for composingSpan related stuff?
             final boolean selectionChangedOrSafeToReset = selectionChanged
                     || (!mWordComposer.isComposingWord()) || noComposingSpan;
-            if (selectionChangedOrSafeToReset) {
+            final boolean hasOrHadSelection = (oldSelStart != oldSelEnd
+                    || newSelStart != newSelEnd);
+            final int moveAmount = newSelStart - oldSelStart;
+            if (selectionChangedOrSafeToReset && (hasOrHadSelection
+                    || !mWordComposer.moveCursorByAndReturnIfInsideComposingWord(moveAmount))) {
                 // If we are composing a word and moving the cursor, we would want to set a
                 // suggestion span for recorrection to work correctly. Unfortunately, that
                 // would involve the keyboard committing some new text, which would move the
@@ -2535,6 +2539,7 @@ public class LatinIME extends InputMethodService implements KeyboardActionListen
             }
         }
         mWordComposer.setComposingWord(typedWord, mKeyboardSwitcher.getKeyboard());
+        // TODO: this is in chars but the callee expects code points!
         mWordComposer.setCursorPositionWithinWord(numberOfCharsInWordBeforeCursor);
         mConnection.setComposingRegion(
                 mLastSelectionStart - numberOfCharsInWordBeforeCursor,
diff --git a/java/src/com/android/inputmethod/latin/WordComposer.java b/java/src/com/android/inputmethod/latin/WordComposer.java
index e078f03f4..2babe8b0c 100644
--- a/java/src/com/android/inputmethod/latin/WordComposer.java
+++ b/java/src/com/android/inputmethod/latin/WordComposer.java
@@ -192,6 +192,40 @@ public final class WordComposer {
         return mCursorPositionWithinWord != mCodePointSize;
     }
 
+    /**
+     * When the cursor is moved by the user, we need to update its position.
+     * If it falls inside the currently composing word, we don't reset the composition, and
+     * only update the cursor position.
+     *
+     * @param expectedMoveAmount How many java chars to move the cursor. Negative values move
+     * the cursor backward, positive values move the cursor forward.
+     * @return true if the cursor is still inside the composing word, false otherwise.
+     */
+    public boolean moveCursorByAndReturnIfInsideComposingWord(final int expectedMoveAmount) {
+        int actualMoveAmountWithinWord = 0;
+        int cursorPos = mCursorPositionWithinWord;
+        if (expectedMoveAmount >= 0) {
+            // Moving the cursor forward for the expected amount or until the end of the word has
+            // been reached, whichever comes first.
+            while (actualMoveAmountWithinWord < expectedMoveAmount && cursorPos < mCodePointSize) {
+                actualMoveAmountWithinWord += Character.charCount(mPrimaryKeyCodes[cursorPos]);
+                ++cursorPos;
+            }
+        } else {
+            // Moving the cursor backward for the expected amount or until the start of the word
+            // has been reached, whichever comes first.
+            while (actualMoveAmountWithinWord > expectedMoveAmount && cursorPos > 0) {
+                --cursorPos;
+                actualMoveAmountWithinWord -= Character.charCount(mPrimaryKeyCodes[cursorPos]);
+            }
+        }
+        // If the actual and expected amounts differ, we crossed the start or the end of the word
+        // so the result would not be inside the composing word.
+        if (actualMoveAmountWithinWord != expectedMoveAmount) return false;
+        mCursorPositionWithinWord = cursorPos;
+        return true;
+    }
+
     public void setBatchInputPointers(final InputPointers batchPointers) {
         mInputPointers.set(batchPointers);
         mIsBatchMode = true;