limit amount of matches during replacement

Skip matches beyond the original range when
replacing a buffer with captures.

crates/matcher/src/lib.rs

@@ -41,6 +41,7 @@ implementations.
 use std::fmt;
 use std::io;
 use std::ops;
+use std::ops::Range;
 use std::u64;
 
 use crate::interpolate::interpolate;
@@ -942,6 +943,33 @@ pub trait Matcher {
         Ok(())
     }
 
+    /// Same as replace_with_captures_at, but limits the replacements to the
+    /// given range. Matches beyond the end of the range are skipped.
+    fn replace_with_captures_in_range<F>(
+        &self,
+        haystack: &[u8],
+        range: &Range<usize>,
+        caps: &mut Self::Captures,
+        dst: &mut Vec<u8>,
+        mut append: F,
+    ) -> Result<(), Self::Error>
+    where
+        F: FnMut(&Self::Captures, &mut Vec<u8>) -> bool,
+    {
+        let mut last_match = range.start;
+        self.captures_iter_at(haystack, range.start, caps, |caps| {
+            let m = caps.get(0).unwrap();
+            if m.start >= range.end {
+                return false;
+            }
+            dst.extend(&haystack[last_match..m.start]);
+            last_match = m.end;
+            append(caps, dst)
+        })?;
+        dst.extend(&haystack[last_match..range.end]);
+        Ok(())
+    }
+
     /// Returns true if and only if the matcher matches the given haystack.
     ///
     /// By default, this method is implemented by calling `shortest_match`.

crates/printer/src/util.rs

@@ -1,4 +1,5 @@
 use std::borrow::Cow;
+use std::cmp::max;
 use std::fmt;
 use std::io;
 use std::path::Path;
@@ -63,13 +64,9 @@ impl<M: Matcher> Replacer<M> {
         // See the giant comment in 'find_iter_at_in_context' below for why we
         // do this dance.
         let is_multi_line = searcher.multi_line_with_matcher(&matcher);
-        let mut extension_len = 0;
         if is_multi_line {
             if subject[range.end..].len() >= MAX_LOOK_AHEAD {
-                extension_len = MAX_LOOK_AHEAD;
                 subject = &subject[..range.end + MAX_LOOK_AHEAD];
-            } else {
-                extension_len = subject.len() - range.end;
             }
         } else {
             // When searching a single line, we should remove the line
@@ -87,9 +84,9 @@ impl<M: Matcher> Replacer<M> {
             matches.clear();
 
             matcher
-                .replace_with_captures_at(
+                .replace_with_captures_in_range(
                     subject,
-                    range.start,
+                    &range,
                     caps,
                     dst,
                     |caps, dst| {
@@ -107,14 +104,7 @@ impl<M: Matcher> Replacer<M> {
                 )
                 .map_err(io::Error::error_message)?;
 
-            if is_multi_line {
-                // Remove the subject buffer beyond the range.end.
-                // NOTE: could this be a bug with the current replace functionality?
-                // As an example, running `rg -U '\.\nA' --replace 'BB' -C 2` in this repo produces
-                // spurious extra lines of output in the replacement, as the extra bytes where
-                // not removed. This seems to fix that, but it's not pretty and might be wrong.
-                dst.truncate(dst.len() - extension_len);
-            } else {
+            if !is_multi_line {
                 // Restore the line terminator.
                 dst.extend(searcher.line_terminator().as_bytes());
             }