Handle empty previous ngram context correctly.

Fixes bug where empty previous ngram context not at the
beginning of a sentence incorrectly returned the
beginning-of-sentence marker.

Bug: 19612336
Change-Id: I5ddf3408e20dcedf70487b85c983cd3fc12550e7

2 files changed, 19 insertions, 5 deletions

diff --git a/java/src/com/android/inputmethod/latin/NgramContext.java b/java/src/com/android/inputmethod/latin/NgramContext.java
index c9351586e..aeeff6126 100644
--- a/java/src/com/android/inputmethod/latin/NgramContext.java
+++ b/java/src/com/android/inputmethod/latin/NgramContext.java
@@ -142,8 +142,7 @@ public class NgramContext {
                 }
             }
         }
-        return terms.size() == 0 ? BEGINNING_OF_SENTENCE_TAG
-                : TextUtils.join(CONTEXT_SEPARATOR, terms);
+        return TextUtils.join(CONTEXT_SEPARATOR, terms);
     }
 
     /**
@@ -166,9 +165,7 @@ public class NgramContext {
                 }
             }
         }
-        final String[] contextStringArray = prevTermList.size() == 0 ?
-                new String[] { BEGINNING_OF_SENTENCE_TAG }
-                : prevTermList.toArray(new String[prevTermList.size()]);
+        final String[] contextStringArray = prevTermList.toArray(new String[prevTermList.size()]);
         return contextStringArray;
     }
 
diff --git a/tests/src/com/android/inputmethod/latin/NgramContextTests.java b/tests/src/com/android/inputmethod/latin/NgramContextTests.java
index 97143a3b6..7749bff63 100644
--- a/tests/src/com/android/inputmethod/latin/NgramContextTests.java
+++ b/tests/src/com/android/inputmethod/latin/NgramContextTests.java
@@ -81,15 +81,24 @@ public class NgramContextTests extends AndroidTestCase {
         assertTrue(ngramContext_bos_b.isBeginningOfSentenceContext());
         assertEquals("b", ngramContext_bos_b.getNthPrevWord(2));
         assertEquals("a b <S>", ngramContext_bos_b.extractPrevWordsContext());
+
+        final NgramContext ngramContext_empty = new NgramContext(WordInfo.EMPTY_WORD_INFO);
+        assertEquals("", ngramContext_empty.extractPrevWordsContext());
+        final NgramContext ngramContext_a_empty =
+                ngramContext_empty.getNextNgramContext(new WordInfo("a"));
+        assertEquals("a", ngramContext_a_empty.getNthPrevWord(1));
+        assertEquals("a", ngramContext_a_empty.extractPrevWordsContext());
     }
 
     public void testExtractPrevWordsContextArray() {
         final NgramContext ngramContext_bos =
                 new NgramContext(WordInfo.BEGINNING_OF_SENTENCE_WORD_INFO);
         assertEquals("<S>", ngramContext_bos.extractPrevWordsContext());
+        assertEquals(1, ngramContext_bos.extractPrevWordsContextArray().length);
         final NgramContext ngramContext_a = new NgramContext(new WordInfo("a"));
         final NgramContext ngramContext_b_a =
                 ngramContext_a.getNextNgramContext(new WordInfo("b"));
+        assertEquals(2, ngramContext_b_a.extractPrevWordsContextArray().length);
         assertEquals("b", ngramContext_b_a.getNthPrevWord(1));
         assertEquals("a", ngramContext_b_a.getNthPrevWord(2));
         assertEquals("a", ngramContext_b_a.extractPrevWordsContextArray()[0]);
@@ -98,9 +107,17 @@ public class NgramContextTests extends AndroidTestCase {
         final NgramContext ngramContext_bos_b =
                 ngramContext_b_a.getNextNgramContext(WordInfo.BEGINNING_OF_SENTENCE_WORD_INFO);
         assertTrue(ngramContext_bos_b.isBeginningOfSentenceContext());
+        assertEquals(3, ngramContext_bos_b.extractPrevWordsContextArray().length);
         assertEquals("b", ngramContext_bos_b.getNthPrevWord(2));
         assertEquals("a", ngramContext_bos_b.extractPrevWordsContextArray()[0]);
         assertEquals("b", ngramContext_bos_b.extractPrevWordsContextArray()[1]);
         assertEquals("<S>", ngramContext_bos_b.extractPrevWordsContextArray()[2]);
+
+        final NgramContext ngramContext_empty = new NgramContext(WordInfo.EMPTY_WORD_INFO);
+        assertEquals(0, ngramContext_empty.extractPrevWordsContextArray().length);
+        final NgramContext ngramContext_a_empty =
+                ngramContext_empty.getNextNgramContext(new WordInfo("a"));
+        assertEquals(1, ngramContext_a_empty.extractPrevWordsContextArray().length);
+        assertEquals("a", ngramContext_a_empty.extractPrevWordsContextArray()[0]);
     }
 }