printer: trim line terminator before finding submatches

This fixes a bug where PCRE2 look-around could change the result of a
match if it observed a line terminator in the printer. And in
particular, this is precisely how the searcher operates: the line is
considered unto itself *without* the line terminator.

Fixes #1401

crates/printer/src/util.rs

@@ -418,7 +418,12 @@ where
             bytes = &bytes[..range.end + MAX_LOOK_AHEAD];
         }
     } else {
-        bytes = &bytes[..range.end];
+        // When searching a single line, we should remove the line terminator.
+        // Otherwise, it's possible for the regex (via look-around) to observe
+        // the line terminator and not match because of it.
+        let mut m = Match::new(0, range.end);
+        trim_line_terminator(searcher, bytes, &mut m);
+        bytes = &bytes[..m.end()];
     }
     matcher
         .find_iter_at(bytes, range.start, |m| {
@@ -429,3 +434,21 @@ where
         })
         .map_err(io::Error::error_message)
 }
+
+/// Given a buf and some bounds, if there is a line terminator at the end of
+/// the given bounds in buf, then the bounds are trimmed to remove the line
+/// terminator.
+pub fn trim_line_terminator(
+    searcher: &Searcher,
+    buf: &[u8],
+    line: &mut Match,
+) {
+    let lineterm = searcher.line_terminator();
+    if lineterm.is_suffix(&buf[*line]) {
+        let mut end = line.end() - 1;
+        if lineterm.is_crlf() && end > 0 && buf.get(end - 1) == Some(&b'\r') {
+            end -= 1;
+        }
+        *line = line.with_end(end);
+    }
+}