rgs: added multiline window limit and in-file result indexing (work in progress)

Cargo.toml

@@ -30,7 +30,7 @@ rust-version = "1.85"
 [[bin]]
 bench = false
 path = "crates/core/main.rs"
-name = "rg"
+name = "rgs"
 
 [[test]]
 name = "integration"

crates/core/flags/complete/rg.zsh

@@ -96,6 +96,8 @@ _rg() {
     + '(file-name)' # File-name options
     {-H,--with-filename}'[show file name for matches]'
     {-I,--no-filename}"[don't show file name for matches]"
+    '--in-file-index[show per-file match index in output]'
+    '--no-in-file-index[hide per-file match index in output]'
 
     + '(file-system)' # File system options
     "--one-file-system[don't descend into directories on other file systems]"
@@ -210,6 +212,7 @@ _rg() {
 
     + '(multiline)' # Multiline options
     {-U,--multiline}'[permit matching across multiple lines]'
+    '--multiline-window=[limit multiline matches to NUM lines (with -U)]:number of lines'
     $no'(multiline-dotall)--no-multiline[restrict matches to at most one line each]'
 
     + '(multiline-dotall)' # Multiline DOTALL options

crates/core/flags/defs.rs

@@ -97,6 +97,7 @@ pub(super) const FLAGS: &[&dyn Flag] = &[
     &MaxFilesize,
     &Mmap,
     &Multiline,
+    &MultilineWindow,
     &MultilineDotall,
     &NoConfig,
     &NoIgnore,
@@ -142,6 +143,7 @@ pub(super) const FLAGS: &[&dyn Flag] = &[
     &Unrestricted,
     &Version,
     &Vimgrep,
+    &InFileIndex,
     &WithFilename,
     &WithFilenameNo,
     &WordRegexp,
@@ -4209,6 +4211,59 @@ fn test_multiline() {
     assert_eq!(false, args.multiline);
 }
 
+/// --multiline-window
+#[derive(Debug)]
+struct MultilineWindow;
+
+impl Flag for MultilineWindow {
+    fn is_switch(&self) -> bool {
+        false
+    }
+    fn name_long(&self) -> &'static str {
+        "multiline-window"
+    }
+    fn doc_variable(&self) -> Option<&'static str> {
+        Some("NUM")
+    }
+    fn doc_category(&self) -> Category {
+        Category::Search
+    }
+    fn doc_short(&self) -> &'static str {
+        r"Limit multiline matches to a fixed number of lines."
+    }
+    fn doc_long(&self) -> &'static str {
+        r#"
+Limit the maximum number of lines that a multiline match may span to
+\fINUM\fP (use \fB--multiline-window=\fP\fINUM\fP).
+.sp
+This flag requires \flag{multiline}. Matches are found as if the file being
+searched were limited to \fINUM\fP lines at a time, which can prevent
+unintended long matches while still enabling multi-line searching.
+.sp
+The value of \fINUM\fP must be at least 1.
+"#
+    }
+
+    fn update(&self, v: FlagValue, args: &mut LowArgs) -> anyhow::Result<()> {
+        let lines = convert::usize(&v.unwrap_value())?;
+        if lines == 0 {
+            anyhow::bail!("--multiline-window must be at least 1");
+        }
+        args.multiline_window = Some(lines);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+#[test]
+fn test_multiline_window() {
+    let args = parse_low_raw(None::<&str>).unwrap();
+    assert_eq!(None, args.multiline_window);
+
+    let args = parse_low_raw(["--multiline-window=2"]).unwrap();
+    assert_eq!(Some(2), args.multiline_window);
+}
+
 /// --multiline-dotall
 #[derive(Debug)]
 struct MultilineDotall;
@@ -7401,6 +7456,53 @@ fn test_vimgrep() {
     assert_eq!(true, args.vimgrep);
 }
 
+/// --in-file-index
+#[derive(Debug)]
+struct InFileIndex;
+
+impl Flag for InFileIndex {
+    fn is_switch(&self) -> bool {
+        true
+    }
+    fn name_long(&self) -> &'static str {
+        "in-file-index"
+    }
+    fn name_negated(&self) -> Option<&'static str> {
+        Some("no-in-file-index")
+    }
+    fn doc_category(&self) -> Category {
+        Category::Output
+    }
+    fn doc_short(&self) -> &'static str {
+        r"Prefix matches with an index per file."
+    }
+    fn doc_long(&self) -> &'static str {
+        r"
+When enabled, ripgrep prefixes each matching line with an index that is
+incremented per file. The format is \fIFILE\fP[\fIN\fP]:\fILINE\fP:, which can
+disambiguate multi-line matches that print the same line multiple times.
+"
+    }
+
+    fn update(&self, v: FlagValue, args: &mut LowArgs) -> anyhow::Result<()> {
+        args.in_file_index = v.unwrap_switch();
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+#[test]
+fn test_in_file_index() {
+    let args = parse_low_raw(None::<&str>).unwrap();
+    assert_eq!(false, args.in_file_index);
+
+    let args = parse_low_raw(["--in-file-index"]).unwrap();
+    assert_eq!(true, args.in_file_index);
+
+    let args = parse_low_raw(["--in-file-index", "--no-in-file-index"]).unwrap();
+    assert_eq!(false, args.in_file_index);
+}
+
 /// --with-filename
 #[derive(Debug)]
 struct WithFilename;

crates/core/flags/hiargs.rs

@@ -61,6 +61,7 @@ pub(crate) struct HiArgs {
     ignore_file_case_insensitive: bool,
     ignore_file: Vec<PathBuf>,
     include_zero: bool,
+    in_file_index: bool,
     invert_match: bool,
     is_terminal_stdout: bool,
     line_number: bool,
@@ -73,6 +74,7 @@ pub(crate) struct HiArgs {
     mode: Mode,
     multiline: bool,
     multiline_dotall: bool,
+    multiline_window: Option<usize>,
     no_ignore_dot: bool,
     no_ignore_exclude: bool,
     no_ignore_files: bool,
@@ -140,6 +142,9 @@ impl HiArgs {
         }
 
         let mut state = State::new()?;
+        if low.multiline_window.is_some() && !low.multiline {
+            anyhow::bail!("--multiline-window requires --multiline");
+        }
         let patterns = Patterns::from_low_args(&mut state, &mut low)?;
         let paths = Paths::from_low_args(&mut state, &patterns, &mut low)?;
 
@@ -278,6 +283,7 @@ impl HiArgs {
             ignore_file: low.ignore_file,
             ignore_file_case_insensitive: low.ignore_file_case_insensitive,
             include_zero: low.include_zero,
+            in_file_index: low.in_file_index,
             invert_match: low.invert_match,
             is_terminal_stdout: state.is_terminal_stdout,
             line_number,
@@ -289,6 +295,7 @@ impl HiArgs {
             mmap_choice,
             multiline: low.multiline,
             multiline_dotall: low.multiline_dotall,
+            multiline_window: low.multiline_window,
             no_ignore_dot: low.no_ignore_dot,
             no_ignore_exclude: low.no_ignore_exclude,
             no_ignore_files: low.no_ignore_files,
@@ -616,6 +623,7 @@ impl HiArgs {
             .column(self.column)
             .heading(self.heading)
             .hyperlink(self.hyperlink_config.clone())
+            .in_file_index(self.in_file_index)
             .max_columns_preview(self.max_columns_preview)
             .max_columns(self.max_columns)
             .only_matching(self.only_matching)
@@ -723,6 +731,7 @@ impl HiArgs {
             .invert_match(self.invert_match)
             .line_number(self.line_number)
             .multi_line(self.multiline)
+            .multiline_window(self.multiline_window)
             .memory_map(self.mmap_choice.clone())
             .stop_on_nonmatch(self.stop_on_nonmatch);
         match self.context {

crates/core/flags/lowargs.rs

@@ -65,6 +65,7 @@ pub(crate) struct LowArgs {
     pub(crate) ignore_file: Vec<PathBuf>,
     pub(crate) ignore_file_case_insensitive: bool,
     pub(crate) include_zero: bool,
+    pub(crate) in_file_index: bool,
     pub(crate) invert_match: bool,
     pub(crate) line_number: Option<bool>,
     pub(crate) logging: Option<LoggingMode>,
@@ -76,6 +77,7 @@ pub(crate) struct LowArgs {
     pub(crate) mmap: MmapMode,
     pub(crate) multiline: bool,
     pub(crate) multiline_dotall: bool,
+    pub(crate) multiline_window: Option<usize>,
     pub(crate) no_config: bool,
     pub(crate) no_ignore_dot: bool,
     pub(crate) no_ignore_exclude: bool,

crates/printer/src/standard.rs

@@ -39,6 +39,7 @@ struct Config {
     stats: bool,
     heading: bool,
     path: bool,
+    in_file_index: bool,
     only_matching: bool,
     per_match: bool,
     per_match_one_line: bool,
@@ -64,6 +65,7 @@ impl Default for Config {
             stats: false,
             heading: false,
             path: true,
+            in_file_index: false,
             only_matching: false,
             per_match: false,
             per_match_one_line: false,
@@ -231,6 +233,12 @@ impl StandardBuilder {
         self
     }
 
+    /// When enabled, prefix matching lines with a per-file match index.
+    pub fn in_file_index(&mut self, yes: bool) -> &mut StandardBuilder {
+        self.config.in_file_index = yes;
+        self
+    }
+
     /// Only print the specific matches instead of the entire line containing
     /// each match. Each match is printed on its own line. When multi line
     /// search is enabled, then matches spanning multiple lines are printed
@@ -528,6 +536,7 @@ impl<W: WriteColor> Standard<W> {
             path: None,
             start_time: Instant::now(),
             match_count: 0,
+            in_file_index: 0,
             binary_byte_offset: None,
             stats,
             needs_match_granularity,
@@ -564,6 +573,7 @@ impl<W: WriteColor> Standard<W> {
             path: Some(ppath),
             start_time: Instant::now(),
             match_count: 0,
+            in_file_index: 0,
             binary_byte_offset: None,
             stats,
             needs_match_granularity,
@@ -644,6 +654,7 @@ pub struct StandardSink<'p, 's, M: Matcher, W> {
     path: Option<PrinterPath<'p>>,
     start_time: Instant,
     match_count: u64,
+    in_file_index: u64,
     binary_byte_offset: Option<u64>,
     stats: Option<Stats>,
     needs_match_granularity: bool,
@@ -769,6 +780,7 @@ impl<'p, 's, M: Matcher, W: WriteColor> Sink for StandardSink<'p, 's, M, W> {
         mat: &SinkMatch<'_>,
     ) -> Result<bool, io::Error> {
         self.match_count += 1;
+        self.in_file_index += 1;
 
         self.record_matches(
             searcher,
@@ -842,6 +854,7 @@ impl<'p, 's, M: Matcher, W: WriteColor> Sink for StandardSink<'p, 's, M, W> {
         self.standard.wtr.borrow_mut().reset_count();
         self.start_time = Instant::now();
         self.match_count = 0;
+        self.in_file_index = 0;
         self.binary_byte_offset = None;
         Ok(true)
     }
@@ -956,6 +969,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
             self.sunk.absolute_byte_offset(),
             self.sunk.line_number(),
             None,
+            self.in_file_index(),
         )?;
         self.write_line(self.sunk.bytes())
     }
@@ -981,6 +995,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                 absolute_byte_offset,
                 self.sunk.line_number().map(|n| n + i as u64),
                 None,
+                self.in_file_index(),
             )?;
             absolute_byte_offset += line.len() as u64;
 
@@ -1001,6 +1016,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                     self.sunk.absolute_byte_offset() + m.start() as u64,
                     self.sunk.line_number(),
                     Some(m.start() as u64 + 1),
+                    self.in_file_index(),
                 )?;
 
                 let buf = &self.sunk.bytes()[m];
@@ -1012,6 +1028,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                     self.sunk.absolute_byte_offset() + m.start() as u64,
                     self.sunk.line_number(),
                     Some(m.start() as u64 + 1),
+                    self.in_file_index(),
                 )?;
                 self.write_colored_line(&[m], self.sunk.bytes())?;
             }
@@ -1020,6 +1037,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                 self.sunk.absolute_byte_offset(),
                 self.sunk.line_number(),
                 Some(self.sunk.matches()[0].start() as u64 + 1),
+                self.in_file_index(),
             )?;
             self.write_colored_line(self.sunk.matches(), self.sunk.bytes())?;
         }
@@ -1048,6 +1066,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                 self.sunk.absolute_byte_offset() + line.start() as u64,
                 self.sunk.line_number().map(|n| n + count),
                 Some(matches[0].start() as u64 + 1),
+                self.in_file_index(),
             )?;
             count += 1;
             self.trim_ascii_prefix(bytes, &mut line);
@@ -1093,6 +1112,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                         self.sunk.absolute_byte_offset() + m.start() as u64,
                         self.sunk.line_number().map(|n| n + count),
                         Some(m.start() as u64 + 1),
+                        self.in_file_index(),
                     )?;
 
                     let this_line = line.with_end(upto);
@@ -1131,6 +1151,7 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
                     self.sunk.absolute_byte_offset() + line.start() as u64,
                     self.sunk.line_number().map(|n| n + count),
                     Some(m.start().saturating_sub(line.start()) as u64 + 1),
+                    self.in_file_index(),
                 )?;
                 count += 1;
                 self.trim_line_terminator(bytes, &mut line);
@@ -1178,10 +1199,11 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
         absolute_byte_offset: u64,
         line_number: Option<u64>,
         column: Option<u64>,
+        in_file_index: Option<u64>,
     ) -> io::Result<()> {
         let mut prelude = PreludeWriter::new(self);
         prelude.start(line_number, column)?;
-        prelude.write_path()?;
+        prelude.write_path(in_file_index)?;
         prelude.write_line_number(line_number)?;
         prelude.write_column_number(column)?;
         prelude.write_byte_offset(absolute_byte_offset)?;
@@ -1532,6 +1554,14 @@ impl<'a, M: Matcher, W: WriteColor> StandardImpl<'a, M, W> {
         self.sunk.context_kind().is_some()
     }
 
+    fn in_file_index(&self) -> Option<u64> {
+        if self.is_context() || !self.config().in_file_index {
+            None
+        } else {
+            Some(self.sink.in_file_index)
+        }
+    }
+
     /// Return the underlying configuration for this printer.
     fn config(&self) -> &'a Config {
         &self.sink.standard.config
@@ -1657,16 +1687,27 @@ impl<'a, M: Matcher, W: WriteColor> PreludeWriter<'a, M, W> {
     /// separator. (If a path terminator is set, then that is used instead of
     /// the field separator.)
     #[inline(always)]
-    fn write_path(&mut self) -> io::Result<()> {
+    fn write_path(&mut self, in_file_index: Option<u64>) -> io::Result<()> {
         // The prelude doesn't handle headings, only what comes before a match
         // on the same line. So if we are emitting paths in headings, we should
         // not do it here on each line.
-        if self.config().heading {
+        if self.config().heading && in_file_index.is_none() {
+            return Ok(());
+        }
+        let path = self.std.path();
+        if path.is_none() && in_file_index.is_none() {
             return Ok(());
         }
-        let Some(path) = self.std.path() else { return Ok(()) };
         self.write_separator()?;
+        if let Some(path) = path {
             self.std.write_path(path)?;
+        }
+        if let Some(index) = in_file_index {
+            self.std.write_spec(self.config().colors.path(), b"[")?;
+            let n = DecimalFormatter::new(index);
+            self.std.write_spec(self.config().colors.path(), n.as_bytes())?;
+            self.std.write_spec(self.config().colors.path(), b"]")?;
+        }
 
         self.next_separator = if self.config().path_terminator.is_some() {
             PreludeSeparator::PathTerminator

crates/searcher/src/searcher/core.rs

@@ -212,6 +212,18 @@ impl<'s, M: Matcher, S: Sink> Core<'s, M, S> {
         consumed
     }
 
+    pub(crate) fn advance_buffer(&mut self, buf: &[u8], consumed: usize) {
+        if consumed == 0 {
+            return;
+        }
+        self.count_lines(buf, consumed);
+        self.absolute_byte_offset += consumed as u64;
+        self.last_line_counted = 0;
+        self.last_line_visited =
+            self.last_line_visited.saturating_sub(consumed);
+        self.set_pos(self.pos().saturating_sub(consumed));
+    }
+
     pub(crate) fn detect_binary(
         &mut self,
         buf: &[u8],

crates/searcher/src/searcher/glue.rs

@@ -1,7 +1,9 @@
 use grep_matcher::Matcher;
 
+use std::collections::VecDeque;
+
 use crate::{
-    line_buffer::{DEFAULT_BUFFER_CAPACITY, LineBufferReader},
+    line_buffer::{DEFAULT_BUFFER_CAPACITY, LineBufferReader, alloc_error},
     lines::{self, LineStep},
     searcher::{Config, Range, Searcher, core::Core},
     sink::{Sink, SinkError},
@@ -138,6 +140,348 @@ impl<'s, M: Matcher, S: Sink> SliceByLine<'s, M, S> {
     }
 }
 
+#[derive(Debug)]
+pub(crate) struct WindowedMultiLine<'s, M, S> {
+    config: &'s Config,
+    core: Core<'s, M, S>,
+    window_lines: usize,
+    buf: Vec<u8>,
+    buf_start: usize,
+    line_lens: VecDeque<usize>,
+    abs_start: u64,
+    current_index: usize,
+    eof: bool,
+}
+
+impl<'s, M: Matcher, S: Sink> WindowedMultiLine<'s, M, S> {
+    pub(crate) fn new(
+        searcher: &'s Searcher,
+        matcher: M,
+        window_lines: usize,
+        write_to: S,
+    ) -> WindowedMultiLine<'s, M, S> {
+        debug_assert!(searcher.multi_line_with_matcher(&matcher));
+        debug_assert!(window_lines > 0);
+
+        WindowedMultiLine {
+            config: &searcher.config,
+            core: Core::new(searcher, matcher, write_to, true),
+            window_lines,
+            buf: Vec::new(),
+            buf_start: 0,
+            line_lens: VecDeque::new(),
+            abs_start: 0,
+            current_index: 0,
+            eof: false,
+        }
+    }
+
+    pub(crate) fn run_reader<R: std::io::Read>(
+        mut self,
+        mut rdr: LineBufferReader<'s, R>,
+    ) -> Result<(), S::Error> {
+        if self.core.begin()? {
+            let mut already_binary = rdr.binary_byte_offset().is_some();
+            while self.fill_reader(&mut rdr, &mut already_binary)?
+                || !self.line_lens.is_empty()
+            {
+                if !self.process_current_line()? {
+                    break;
+                }
+            }
+        }
+        let byte_count = self.byte_count();
+        let binary_byte_offset = self.core.binary_byte_offset();
+        self.core.finish(byte_count, binary_byte_offset)
+    }
+
+    pub(crate) fn run_slice(mut self, slice: &'s [u8]) -> Result<(), S::Error> {
+        if self.core.begin()? {
+            let binary_upto =
+                std::cmp::min(slice.len(), DEFAULT_BUFFER_CAPACITY);
+            let binary_range = Range::new(0, binary_upto);
+            if !self.core.detect_binary(slice, &binary_range)? {
+                let mut stepper = LineStep::new(
+                    self.config.line_term.as_byte(),
+                    0,
+                    slice.len(),
+                );
+                while let Some(line) = stepper.next_match(slice) {
+                    self.push_line(&slice[line])?;
+                }
+                self.eof = true;
+                while !self.line_lens.is_empty() {
+                    if !self.process_current_line()? {
+                        break;
+                    }
+                }
+            }
+        }
+        let byte_count = self.byte_count();
+        let binary_byte_offset = self.core.binary_byte_offset();
+        self.core.finish(byte_count, binary_byte_offset)
+    }
+
+    fn fill_reader<R: std::io::Read>(
+        &mut self,
+        rdr: &mut LineBufferReader<'s, R>,
+        already_binary: &mut bool,
+    ) -> Result<bool, S::Error> {
+        while !self.eof
+            && self.line_lens.len() < self.current_index + self.window_lines
+        {
+            let didread = match rdr.fill() {
+                Err(err) => return Err(S::Error::error_io(err)),
+                Ok(didread) => didread,
+            };
+            if !*already_binary {
+                if let Some(offset) = rdr.binary_byte_offset() {
+                    *already_binary = true;
+                    if !self.core.binary_data(offset)? {
+                        self.eof = true;
+                        return Ok(false);
+                    }
+                }
+            }
+            if !didread {
+                self.eof = true;
+                break;
+            }
+            let buf = rdr.buffer();
+            let mut stepper = LineStep::new(
+                self.config.line_term.as_byte(),
+                0,
+                buf.len(),
+            );
+            while let Some(line) = stepper.next_match(buf) {
+                let bytes = &buf[line];
+                self.push_line(bytes)?;
+            }
+            rdr.consume(buf.len());
+        }
+        Ok(!self.eof)
+    }
+
+    fn push_line(&mut self, line: &[u8]) -> Result<(), S::Error> {
+        self.buf.extend_from_slice(line);
+        self.line_lens.push_back(line.len());
+        if let Some(limit) = self.config.heap_limit {
+            let used = self.buf.len() - self.buf_start;
+            if used > limit {
+                return Err(S::Error::error_io(alloc_error(limit)));
+            }
+        }
+        Ok(())
+    }
+
+    fn process_current_line(&mut self) -> Result<bool, S::Error> {
+        if self.current_index >= self.line_lens.len() {
+            return Ok(false);
+        }
+        let window_end =
+            std::cmp::min(self.line_lens.len(), self.current_index + self.window_lines);
+        let window_start_off = self.line_offset(self.current_index);
+        let window_end_off = self.line_offset(window_end);
+        let line0_len = self.line_lens[self.current_index];
+
+        {
+            let buffer = &self.buf[self.buf_start..];
+            let window_bytes =
+                &self.buf[self.buf_start + window_start_off
+                    ..self.buf_start + window_end_off];
+            if self.config.invert_match {
+                if !sink_inverted_line(
+                    &mut self.core,
+                    self.config,
+                    buffer,
+                    window_bytes,
+                    window_start_off,
+                    line0_len,
+                )? {
+                    return Ok(false);
+                }
+            } else if !sink_matched_line(
+                &mut self.core,
+                self.config,
+                buffer,
+                window_bytes,
+                window_start_off,
+                line0_len,
+            )? {
+                return Ok(false);
+            }
+
+            let drop_upto = window_start_off + line0_len;
+            if self.config.passthru {
+                if !self.core.other_context_by_line(buffer, drop_upto)? {
+                    return Ok(false);
+                }
+            } else if !self.core.after_context_by_line(buffer, drop_upto)? {
+                return Ok(false);
+            }
+        }
+
+        self.current_index += 1;
+        if self.current_index > self.config.before_context {
+            let drop_len = self.line_lens.pop_front().unwrap();
+            self.shift_buffer(drop_len);
+            self.current_index -= 1;
+        }
+
+        if self.eof && self.current_index >= self.line_lens.len() {
+            let buffer = &self.buf[self.buf_start..];
+            if self.config.passthru {
+                if !self.core.other_context_by_line(buffer, buffer.len())? {
+                    return Ok(false);
+                }
+            } else if !self.core.after_context_by_line(buffer, buffer.len())? {
+                return Ok(false);
+            }
+            return Ok(false);
+        }
+        Ok(true)
+    }
+
+    fn line_offset(&self, idx: usize) -> usize {
+        self.line_lens.iter().take(idx).sum()
+    }
+
+    fn shift_buffer(&mut self, consumed: usize) {
+        let buffer = &self.buf[self.buf_start..];
+        self.core.advance_buffer(buffer, consumed);
+        self.buf_start += consumed;
+        self.abs_start += consumed as u64;
+        if self.buf_start > 0 && self.buf_start > self.buf.len() / 2 {
+            self.buf.copy_within(self.buf_start.., 0);
+            let new_len = self.buf.len() - self.buf_start;
+            self.buf.truncate(new_len);
+            self.buf_start = 0;
+        }
+    }
+
+    fn byte_count(&mut self) -> u64 {
+        match self.core.binary_byte_offset() {
+            Some(offset) if offset < self.core.pos() as u64 => offset,
+            _ => self.abs_start + (self.buf.len() - self.buf_start) as u64,
+        }
+    }
+}
+
+fn sink_matched_line<M: Matcher, S: Sink>(
+    core: &mut Core<'_, M, S>,
+    config: &Config,
+    buffer: &[u8],
+    window_bytes: &[u8],
+    window_start_off: usize,
+    line0_len: usize,
+) -> Result<bool, S::Error> {
+    let mut pos = 0;
+    let mut last_match: Option<Range> = None;
+        while let Some(mat) = find_in_window(core, window_bytes, pos)? {
+            if mat.start() >= line0_len {
+                break;
+            }
+            let line = lines::locate(
+                window_bytes,
+                config.line_term.as_byte(),
+                mat,
+            )
+            .offset(window_start_off);
+            match last_match.take() {
+                None => {
+                    last_match = Some(line);
+                }
+                Some(last) => {
+                    if last.end() >= line.start() {
+                        last_match = Some(last.with_end(line.end()));
+                    } else {
+                        if !sink_context(core, config, buffer, &last)? {
+                            return Ok(false);
+                        }
+                        if !core.matched(buffer, &last)? {
+                            return Ok(false);
+                        }
+                        last_match = Some(line);
+                    }
+                }
+            }
+            pos = mat.end();
+            if mat.is_empty() && pos < window_bytes.len() {
+                pos += 1;
+            }
+        }
+        if let Some(last) = last_match.take() {
+            if !sink_context(core, config, buffer, &last)? {
+                return Ok(false);
+            }
+            if !core.matched(buffer, &last)? {
+                return Ok(false);
+            }
+        }
+        Ok(true)
+}
+
+fn sink_inverted_line<M: Matcher, S: Sink>(
+    core: &mut Core<'_, M, S>,
+    config: &Config,
+    buffer: &[u8],
+    window_bytes: &[u8],
+    window_start_off: usize,
+    line0_len: usize,
+) -> Result<bool, S::Error> {
+        let mut pos = 0;
+        while let Some(mat) = find_in_window(core, window_bytes, pos)? {
+            if mat.start() >= line0_len {
+                break;
+            }
+            if mat.start() < line0_len {
+                return Ok(true);
+            }
+            pos = mat.end();
+            if mat.is_empty() && pos < window_bytes.len() {
+                pos += 1;
+            }
+        }
+        let line = Range::new(window_start_off, window_start_off + line0_len);
+        if !sink_context(core, config, buffer, &line)? {
+            return Ok(false);
+        }
+        if !core.matched(buffer, &line)? {
+            return Ok(false);
+        }
+        Ok(true)
+}
+
+fn find_in_window<M: Matcher, S: Sink>(
+    core: &mut Core<'_, M, S>,
+    window_bytes: &[u8],
+    pos: usize,
+) -> Result<Option<Range>, S::Error> {
+    core.find(&window_bytes[pos..])
+        .map(|m| m.map(|m| m.offset(pos)))
+}
+
+fn sink_context<M: Matcher, S: Sink>(
+    core: &mut Core<'_, M, S>,
+    config: &Config,
+    buffer: &[u8],
+    range: &Range,
+) -> Result<bool, S::Error> {
+    if config.passthru {
+        if !core.other_context_by_line(buffer, range.start())? {
+            return Ok(false);
+        }
+    } else {
+        if !core.after_context_by_line(buffer, range.start())? {
+            return Ok(false);
+        }
+        if !core.before_context_by_line(buffer, range.start())? {
+            return Ok(false);
+        }
+    }
+    Ok(true)
+}
+
 #[derive(Debug)]
 pub(crate) struct MultiLine<'s, M, S> {
     config: &'s Config,
@@ -518,6 +862,37 @@ byte count:366
             .test();
     }
 
+    #[test]
+    fn multi_line_window_limits_match() {
+        let haystack = "a\nb\nc\nd\n";
+        let matcher = RegexMatcher::new("a\nb\nc");
+
+        let mut builder = SearcherBuilder::new();
+        builder.multi_line(true).multiline_window(Some(2)).line_number(false);
+        let mut sink = KitchenSink::new();
+        let mut searcher = builder.build();
+        searcher
+            .search_slice(&matcher, haystack.as_bytes(), &mut sink)
+            .unwrap();
+        let got = String::from_utf8(sink.as_bytes().to_vec()).unwrap();
+        let exp = format!("\nbyte count:{}\n", haystack.len());
+        assert_eq!(exp, got);
+
+        let mut builder = SearcherBuilder::new();
+        builder.multi_line(true).multiline_window(Some(3)).line_number(false);
+        let mut sink = KitchenSink::new();
+        let mut searcher = builder.build();
+        searcher
+            .search_slice(&matcher, haystack.as_bytes(), &mut sink)
+            .unwrap();
+        let exp = format!(
+            "0:a\n2:b\n4:c\n\nbyte count:{}\n",
+            haystack.len()
+        );
+        let got = String::from_utf8(sink.as_bytes().to_vec()).unwrap();
+        assert_eq!(exp, got);
+    }
+
     #[test]
     fn multi_line_overlap2() {
         let haystack = "xxx\nabc\ndefabc\ndefxxx\nxxx";

crates/searcher/src/searcher/mod.rs

@@ -16,7 +16,7 @@ use crate::{
         self, BufferAllocation, DEFAULT_BUFFER_CAPACITY, LineBuffer,
         LineBufferBuilder, LineBufferReader, alloc_error,
     },
-    searcher::glue::{MultiLine, ReadByLine, SliceByLine},
+    searcher::glue::{MultiLine, ReadByLine, SliceByLine, WindowedMultiLine},
     sink::{Sink, SinkError},
 };
 
@@ -172,6 +172,8 @@ pub struct Config {
     binary: BinaryDetection,
     /// Whether to enable matching across multiple lines.
     multi_line: bool,
+    /// The maximum number of lines a multi-line match may span.
+    multiline_window: Option<usize>,
     /// An encoding that, when present, causes the searcher to transcode all
     /// input from the encoding to UTF-8.
     encoding: Option<Encoding>,
@@ -197,6 +199,7 @@ impl Default for Config {
             mmap: MmapChoice::default(),
             binary: BinaryDetection::default(),
             multi_line: false,
+            multiline_window: None,
             encoding: None,
             bom_sniffing: true,
             stop_on_nonmatch: false,
@@ -390,6 +393,15 @@ impl SearcherBuilder {
         self
     }
 
+    /// Limit multi-line matches to a window of at most `line_count` lines.
+    pub fn multiline_window(
+        &mut self,
+        line_count: Option<usize>,
+    ) -> &mut SearcherBuilder {
+        self.config.multiline_window = line_count;
+        self
+    }
+
     /// Whether to include a fixed number of lines after every match.
     ///
     /// When this is set to a non-zero number, then the searcher will report
@@ -694,6 +706,13 @@ impl Searcher {
         // enabled. This pre-allocates a buffer roughly the size of the file,
         // which isn't possible when searching an arbitrary std::io::Read.
         if self.multi_line_with_matcher(&matcher) {
+            if self.config.multiline_window.is_some() {
+                log::trace!(
+                    "{:?}: searching via windowed multiline strategy",
+                    path
+                );
+                return self.search_reader(matcher, file, write_to);
+            }
             log::trace!(
                 "{:?}: reading entire file on to heap for mulitline",
                 path
@@ -744,6 +763,18 @@ impl Searcher {
             .map_err(S::Error::error_io)?;
 
         if self.multi_line_with_matcher(&matcher) {
+            if let Some(window_lines) = self.config.multiline_window {
+                let mut line_buffer = self.line_buffer.borrow_mut();
+                let rdr = LineBufferReader::new(decoder, &mut *line_buffer);
+                log::trace!("generic reader: searching via windowed multiline");
+                return WindowedMultiLine::new(
+                    self,
+                    matcher,
+                    window_lines,
+                    write_to,
+                )
+                .run_reader(rdr);
+            }
             log::trace!(
                 "generic reader: reading everything to heap for multiline"
             );
@@ -786,6 +817,16 @@ impl Searcher {
             return self.search_reader(matcher, slice, write_to);
         }
         if self.multi_line_with_matcher(&matcher) {
+            if let Some(window_lines) = self.config.multiline_window {
+                log::trace!("slice reader: searching via windowed multiline");
+                return WindowedMultiLine::new(
+                    self,
+                    matcher,
+                    window_lines,
+                    write_to,
+                )
+                .run_slice(slice);
+            }
             log::trace!("slice reader: searching via multiline strategy");
             MultiLine::new(self, matcher, slice, write_to).run()
         } else {
@@ -865,6 +906,12 @@ impl Searcher {
         self.config.multi_line
     }
 
+    /// Returns the maximum number of lines a multi-line match may span.
+    #[inline]
+    pub fn multiline_window(&self) -> Option<usize> {
+        self.config.multiline_window
+    }
+
     /// Returns true if and only if this searcher is configured to stop when it
     /// finds a non-matching line after a matching one.
     #[inline]