Do not re-resume suggestion if it's not needed.

This is much better interface-wise. It eliminates all blinking
of the line in the practice.

Bug: 8874148
Bug: 8864306
Change-Id: I87754e44784327c2e9c8b162d598d145e20668e8

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,

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;

tests/src/com/android/inputmethod/latin/WordComposerTests.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin;
+
+import android.test.AndroidTestCase;
+import android.test.suitebuilder.annotation.SmallTest;
+
+/**
+ * Unit tests for WordComposer.
+ */
+@SmallTest
+public class WordComposerTests extends AndroidTestCase {
+    public void testMoveCursor() {
+        final WordComposer wc = new WordComposer();
+        final String STR_WITHIN_BMP = "abcdef";
+        wc.setComposingWord(STR_WITHIN_BMP, null);
+        assertEquals(wc.size(),
+                STR_WITHIN_BMP.codePointCount(0, STR_WITHIN_BMP.length()));
+        assertFalse(wc.isCursorFrontOrMiddleOfComposingWord());
+        wc.setCursorPositionWithinWord(2);
+        assertTrue(wc.isCursorFrontOrMiddleOfComposingWord());
+        // Move the cursor to after the 'd'
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(2));
+        assertTrue(wc.isCursorFrontOrMiddleOfComposingWord());
+        // Move the cursor to after the 'e'
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(1));
+        assertTrue(wc.isCursorFrontOrMiddleOfComposingWord());
+        assertEquals(wc.size(), 6);
+        // Move the cursor to after the 'f'
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(1));
+        assertFalse(wc.isCursorFrontOrMiddleOfComposingWord());
+        // Move the cursor past the end of the word
+        assertFalse(wc.moveCursorByAndReturnIfInsideComposingWord(1));
+        assertFalse(wc.moveCursorByAndReturnIfInsideComposingWord(15));
+
+        // \uD861\uDED7 is 𨛗, a character outside the BMP
+        final String STR_WITH_SUPPLEMENTARY_CHAR = "abcde\uD861\uDED7fgh";
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        assertEquals(wc.size(), STR_WITH_SUPPLEMENTARY_CHAR.codePointCount(0,
+                        STR_WITH_SUPPLEMENTARY_CHAR.length()));
+        assertFalse(wc.isCursorFrontOrMiddleOfComposingWord());
+        wc.setCursorPositionWithinWord(3);
+        assertTrue(wc.isCursorFrontOrMiddleOfComposingWord());
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(6));
+        assertTrue(wc.isCursorFrontOrMiddleOfComposingWord());
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(1));
+        assertFalse(wc.isCursorFrontOrMiddleOfComposingWord());
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        wc.setCursorPositionWithinWord(3);
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(7));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        wc.setCursorPositionWithinWord(3);
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(7));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        wc.setCursorPositionWithinWord(3);
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(-3));
+        assertFalse(wc.moveCursorByAndReturnIfInsideComposingWord(-1));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        wc.setCursorPositionWithinWord(3);
+        assertFalse(wc.moveCursorByAndReturnIfInsideComposingWord(-9));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(-10));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        assertFalse(wc.moveCursorByAndReturnIfInsideComposingWord(-11));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(0));
+
+        wc.setComposingWord(STR_WITH_SUPPLEMENTARY_CHAR, null);
+        wc.setCursorPositionWithinWord(2);
+        assertTrue(wc.moveCursorByAndReturnIfInsideComposingWord(0));
+    }
+}