Fix panic on ctrl-w empty document

helix-core/src/words.rs

@@ -25,7 +25,7 @@ pub fn nth_prev_word_boundary(slice: RopeSlice, mut char_idx: usize, count: usiz
         }
     }
 
-    if with_end {
+    if with_end || char_idx == 0 {
         char_idx
     } else {
         char_idx + 1
@@ -37,7 +37,7 @@ fn different_prev_word_boundary() {
     use ropey::Rope;
     let t = |x, y| {
         let text = Rope::from(x);
-        let out = nth_prev_word_boundary(text.slice(..), text.len_chars() - 1, 1);
+        let out = nth_prev_word_boundary(text.slice(..), text.len_chars().saturating_sub(1), 1);
         assert_eq!(text.slice(..out), y, r#"from "{}""#, x);
     };
     t("abcd\nefg\nwrs", "abcd\nefg\n");
@@ -47,6 +47,7 @@ fn different_prev_word_boundary() {
     t("hello, world", "hello, ");
     t("hello, ", "hello");
     t("hello", "");
+    t(",", "");
     t("こんにちは、世界！", "こんにちは、世界");
     t("こんにちは、世界", "こんにちは、");
     t("こんにちは、", "こんにちは");
@@ -56,10 +57,12 @@ fn different_prev_word_boundary() {
     t("お前はもう死んでいる", "");
     t("その300円です", ""); // TODO: should stop at 300
     t("唱k", ""); // TODO: should stop at 唱
+    t("，", "");
     t("1 + 1 = 2", "1 + 1 = ");
     t("1 + 1 =", "1 + 1 ");
     t("1 + 1", "1 + ");
     t("1 + ", "1 ");
     t("1 ", "");
     t("1+1=2", "1+1=");
+    t("", "");
 }