conflicts: allow stripped trailing whitespace in diffs

Some editors strip trailing whitespace on save, which breaks any diffs
which have context lines, since the parsing function expects them to
start with a space. There's no visual difference between " \n" and "\n",
so it seems reasonable to accept both.

lib/src/conflicts.rs

@@ -467,6 +467,12 @@ fn parse_conflict_hunk(input: &[u8]) -> Merge<BString> {
                 } else if let Some(rest) = line.strip_prefix(b" ") {
                     removes.last_mut().unwrap().extend_from_slice(rest);
                     adds.last_mut().unwrap().extend_from_slice(rest);
+                } else if line == b"\n" || line == b"\r\n" {
+                    // Some editors strip trailing whitespace, so " \n" might become "\n". It would
+                    // be unfortunate if this prevented the conflict from being parsed, so we add
+                    // the empty line to the "remove" and "add" as if there was a space in front
+                    removes.last_mut().unwrap().extend_from_slice(line);
+                    adds.last_mut().unwrap().extend_from_slice(line);
                 } else {
                     // Doesn't look like a valid conflict
                     return Merge::resolved(BString::new(vec![]));

lib/tests/test_conflicts.rs

@@ -768,8 +768,8 @@ fn test_parse_conflict_crlf_markers() {
 
 #[test]
 fn test_parse_conflict_diff_stripped_whitespace() {
-    // Conflict parsing fails since diff contains empty line without leading space
-    assert_eq!(
+    // Should be able to parse conflict even if diff contains empty line
+    insta::assert_debug_snapshot!(
         parse_conflict(
             indoc! {b"
             line 1
@@ -788,7 +788,25 @@ fn test_parse_conflict_diff_stripped_whitespace() {
             "},
             2
         ),
-        None
+        @r#"
+    Some(
+        [
+            Resolved(
+                "line 1\n",
+            ),
+            Conflicted(
+                [
+                    "line 2\n\nleft\n\r\nline 4\n",
+                    "line 2\n\nline 3\n\r\nline 4\n",
+                    "right\n",
+                ],
+            ),
+            Resolved(
+                "line 5\n",
+            ),
+        ],
+    )
+    "#
     );
 }