Fix another bug in -o/--only-matching.

The handling of the -o/--only-matching was incorrect. We cannot ever
re-run regexes on a *subset* of a matched line, because it doesn't take
into account zero width assertions on the edges of the regex. This
occurs whenever an end user uses an assertion explicity, but also occurs
when one is used implicitly, e.g., with the `-w` flag.

This instead reuses the initial matched range from the first regex
match. We also apply this fix to coloring.

Fixes #493

src/printer.rs

@@ -3,7 +3,7 @@ use std::fmt;
 use std::path::Path;
 use std::str::FromStr;
 
-use regex::bytes::{Regex, Replacer, Captures};
+use regex::bytes::{Captures, Regex, Replacer};
 use termcolor::{Color, ColorSpec, ParseColorError, WriteColor};
 
 use pathutil::strip_prefix;
@@ -242,15 +242,17 @@ impl<W: WriteColor> Printer<W> {
         line_number: Option<u64>,
     ) {
         if !self.line_per_match && !self.only_matching {
-            let column = re.find(&buf[start..end])
-                           .map(|m| m.start()).unwrap_or(0);
+            let mat = re
+                .find(&buf[start..end])
+                .map(|m| (m.start(), m.end()))
+                .unwrap_or((0, 0));
             return self.write_match(
-                re, path, buf, start, end, line_number, column);
+                re, path, buf, start, end, line_number, mat.0, mat.1);
         }
         for m in re.find_iter(&buf[start..end]) {
-            let column = m.start();
             self.write_match(
-                re, path.as_ref(), buf, start, end, line_number, column);
+                re, path.as_ref(), buf, start, end,
+                line_number, m.start(), m.end());
         }
     }
 
@@ -262,7 +264,8 @@ impl<W: WriteColor> Printer<W> {
         start: usize,
         end: usize,
         line_number: Option<u64>,
-        column: usize,
+        match_start: usize,
+        match_end: usize,
     ) {
         if self.heading && self.with_filename && !self.has_printed {
             self.write_file_sep();
@@ -276,7 +279,7 @@ impl<W: WriteColor> Printer<W> {
             self.line_number(line_number, b':');
         }
         if self.column {
-            self.column_number(column as u64 + 1, b':');
+            self.column_number(match_start as u64 + 1, b':');
         }
         if self.replace.is_some() {
             let mut count = 0;
@@ -297,19 +300,21 @@ impl<W: WriteColor> Printer<W> {
                 self.write_eol();
             }
         } else {
-            let line_buf = if self.only_matching {
-                let start_offset = start + column;
-                let m = re.find(&buf[start_offset..end]).unwrap();
-                &buf[start_offset + m.start()..start_offset + m.end()]
+            if self.only_matching {
+                let buf = &buf[start + match_start..start + match_end];
+                self.write_matched_line(re, buf, true);
             } else {
-                &buf[start..end]
-            };
-            self.write_matched_line(re, line_buf);
-            // write_matched_line guarantees to write a newline.
+                self.write_matched_line(re, &buf[start..end], false);
+            }
         }
     }
 
-    fn write_matched_line(&mut self, re: &Regex, buf: &[u8]) {
+    fn write_matched_line(
+        &mut self,
+        re: &Regex,
+        buf: &[u8],
+        only_match: bool,
+    ) {
         if self.max_columns.map_or(false, |m| buf.len() > m) {
             let count = re.find_iter(buf).count();
             let msg = format!("[Omitted long line with {} matches]", count);
@@ -319,6 +324,8 @@ impl<W: WriteColor> Printer<W> {
         }
         if !self.wtr.supports_color() || self.colors.matched().is_none() {
             self.write(buf);
+        } else if only_match {
+            self.write_colored(buf, |colors| colors.matched());
         } else {
             let mut last_written = 0;
             for m in re.find_iter(buf) {

tests/tests.rs

@@ -1079,7 +1079,8 @@ clean!(regression_428_color_context_path, "foo", ".", |wd: WorkDir, mut cmd: Com
 });
 
 // See: https://github.com/BurntSushi/ripgrep/issues/428
-clean!(regression_428_unrecognized_style, "Sherlok", ".", |wd: WorkDir, mut cmd: Command| {
+clean!(regression_428_unrecognized_style, "Sherlok", ".",
+|wd: WorkDir, mut cmd: Command| {
     cmd.arg("--colors=match:style:");
     wd.assert_err(&mut cmd);
 
@@ -1091,6 +1092,15 @@ Unrecognized style attribute ''. Choose from: nobold, bold, nointense, intense.
     assert_eq!(err, expected);
 });
 
+// See: https://github.com/BurntSushi/ripgrep/issues/493
+clean!(regression_493, " 're ", "input.txt", |wd: WorkDir, mut cmd: Command| {
+    wd.create("input.txt", "peshwaship 're seminomata");
+    cmd.arg("-o").arg("-w");
+
+    let lines: String = wd.stdout(&mut cmd);
+    assert_eq!(lines, " 're \n");
+});
+
 // See: https://github.com/BurntSushi/ripgrep/issues/1
 clean!(feature_1_sjis, "Шерлок Холмс", ".", |wd: WorkDir, mut cmd: Command| {
     let sherlock =