fix crashes on prev_boundary

jmuk · jmuk · commit fb5d7b6714d2 · 2018-03-16T13:34:53.000-07:00
Fixes #38, #39
diff --git a/src/grapheme.rs b/src/grapheme.rs
@@ -624,6 +624,9 @@ impl GraphemeCursor {
         if self.offset == 0 {
             return Ok(None);
         }
+        if self.offset == chunk_start {
+            return Err(GraphemeIncomplete::PrevChunk);
+        }
         let mut iter = chunk[..self.offset - chunk_start].chars().rev();
         let mut ch = iter.next().unwrap();
         loop {
@@ -647,6 +650,7 @@ impl GraphemeCursor {
                     self.decide(true);
                 } else {
                     self.resuming = true;
+                    self.cat_after = Some(gr::grapheme_category(ch));
                     return Err(GraphemeIncomplete::PrevChunk);
                 }
             }
@@ -659,3 +663,19 @@ impl GraphemeCursor {
         }
     }
 }
+
+#[test]
+fn test_grapheme_cursor_prev_boundary() {
+    let s = "abcd";
+    let mut c = GraphemeCursor::new(3, s.len(), true);
+    assert_eq!(c.prev_boundary(&s[2..], 2), Err(GraphemeIncomplete::PrevChunk));
+    assert_eq!(c.prev_boundary(&s[..2], 0), Ok(Some(2)));
+}
+
+#[test]
+fn test_grapheme_cursor_prev_boundary_chunk_start() {
+    let s = "abcd";
+    let mut c = GraphemeCursor::new(2, s.len(), true);
+    assert_eq!(c.prev_boundary(&s[2..], 2), Err(GraphemeIncomplete::PrevChunk));
+    assert_eq!(c.prev_boundary(&s[..2], 0), Ok(Some(1)));
+}
