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

CHANGELOG.md

@@ -71,6 +71,8 @@ Bug fixes:
   Document cygwin path translation behavior in the FAQ.
 * [BUG #1311](https://github.com/BurntSushi/ripgrep/issues/1311):
   Fix multi-line bug where a search & replace for `\n` didn't work as expected.
+* [BUG #1401](https://github.com/BurntSushi/ripgrep/issues/1401):
+  Fix buggy interaction between PCRE2 look-around and `-o/--only-matching`.
 * [BUG #1412](https://github.com/BurntSushi/ripgrep/issues/1412):
   Fix multi-line bug with searches using look-around past matching lines.
 * [BUG #1642](https://github.com/BurntSushi/ripgrep/issues/1642):

crates/printer/src/standard.rs

@@ -17,7 +17,8 @@ use color::ColorSpecs;
 use counter::CounterWriter;
 use stats::Stats;
 use util::{
-    find_iter_at_in_context, trim_ascii_prefix, PrinterPath, Replacer, Sunk,
+    find_iter_at_in_context, trim_ascii_prefix, trim_line_terminator,
+    PrinterPath, Replacer, Sunk,
 };
 
 /// The configuration for the standard printer.
@@ -1547,17 +1548,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
     }
 
     fn trim_line_terminator(&self, buf: &[u8], line: &mut Match) {
-        let lineterm = self.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);
-        }
+        trim_line_terminator(&self.searcher, buf, line);
     }
 
     fn has_line_terminator(&self, buf: &[u8]) -> bool {

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);
+    }
+}

tests/regression.rs

@@ -806,7 +806,32 @@ rgtest!(r1389_bad_symlinks_no_biscuit, |dir: Dir, mut cmd: TestCommand| {
     eqnice!("mylink/file.txt:test\n", stdout);
 });
 
-// printf "foo\nbar\n" | rg -PU '(?<=foo\n)bar' -r quux
+// See: https://github.com/BurntSushi/ripgrep/issues/1401
+rgtest!(r1401_look_ahead_only_matching_1, |dir: Dir, mut cmd: TestCommand| {
+    // Only PCRE2 supports look-around.
+    if !dir.is_pcre2() {
+        return;
+    }
+    dir.create("ip.txt", "foo 42\nxoyz\ncat\tdog\n");
+    cmd.args(&["-No", r".*o(?!.*\s)", "ip.txt"]);
+    eqnice!("xo\ncat\tdo\n", cmd.stdout());
+
+    let mut cmd = dir.command();
+    cmd.args(&["-No", r".*o(?!.*[ \t])", "ip.txt"]);
+    eqnice!("xo\ncat\tdo\n", cmd.stdout());
+});
+
+// See: https://github.com/BurntSushi/ripgrep/issues/1401
+rgtest!(r1401_look_ahead_only_matching_2, |dir: Dir, mut cmd: TestCommand| {
+    // Only PCRE2 supports look-around.
+    if !dir.is_pcre2() {
+        return;
+    }
+    dir.create("ip.txt", "foo 42\nxoyz\ncat\tdog\nfoo");
+    cmd.args(&["-No", r".*o(?!.*\s)", "ip.txt"]);
+    eqnice!("xo\ncat\tdo\nfoo\n", cmd.stdout());
+});
+
 // See: https://github.com/BurntSushi/ripgrep/issues/1412
 rgtest!(r1412_look_behind_no_replacement, |dir: Dir, mut cmd: TestCommand| {
     // Only PCRE2 supports look-around.