Add --number option for showing line numbers. Also adds related options:

    - minus line foreground color
    - plus line foreground color
    - center divider color
    - right divider color
    - center divider string
    - right divider string

README.md

@@ -230,6 +230,10 @@ FLAGS:
                                      those modes. It can also be used to experiment with different RGB hex codes by
                                      combining this option with --minus-color, --minus-emph-color, --plus-color, --plus-
                                      emph-color.
+    -n, --number                     Display line numbers next to the diff. The first column contains line numbers in
+                                     the previous version of the file, and the second column contains line number in the
+                                     new version of the file. A blank cell in the first or second column indicates that
+                                     the line does not exist in that file (it was added or removed, respectively)
     -V, --version                    Prints version information
 
 OPTIONS:
@@ -251,6 +255,24 @@ OPTIONS:
             0.3]
         --minus-color <minus_color>                The background color to use for removed lines.
         --minus-emph-color <minus_emph_color>      The background color to use for emphasized sections of removed lines.
+
+        --number-divider-center-foreground-color <number-divider-center-foreground-color>
+            Color for the center dividing line of the line numbers section, if --number is set. Defaults to the
+            configured hunk_color
+        --number-divider-center-string <number-divider-center-string>
+            String to use as the center divider of the line numbers section, if --number is set [default: ⋮]
+        --number-divider-right-foreground-color <number-divider-right-foreground-color>
+            Color for the right dividing line of the line numbers section, if --number is set. Defaults to the
+            configured hunk_color
+        --number-divider-right-string <number-divider-right-string>
+            String to use as the right divider of the line numbers section, if --number is set [default: │]
+        --number-minus-foreground-color <number-minus-foreground-color>
+            Color for the left (minus) column of line numbers (--number), if --number is set. Defaults to the configured
+            hunk_color
+        --number-plus-foreground-color <number-plus-foreground-color>
+            Color for the right (plus) column of line numbers (--number), if --number is set. Defaults to the configured
+            hunk_color
+
         --paging <paging_mode>
             Whether to use a pager when displaying output. Options are: auto, always, and never. The default pager is
             `less`: this can be altered by setting the environment variables BAT_PAGER or PAGER (BAT_PAGER has

src/cli.rs

@@ -210,6 +210,42 @@ pub struct Opt {
     /// or PAGER (BAT_PAGER has priority).
     #[structopt(long = "paging", default_value = "auto")]
     pub paging_mode: String,
+
+    /// Display line numbers next to the diff. The first column contains line
+    /// numbers in the previous version of the file, and the second column contains
+    /// line number in the new version of the file. A blank cell in the first or
+    /// second column indicates that the line does not exist in that file (it was
+    /// added or removed, respectively).
+    #[structopt(short = "n", long = "number")]
+    pub show_line_numbers: bool,
+
+    /// Color for the left (minus) column of line numbers (--number), if --number is set.
+    /// Defaults to --hunk-color.
+    #[structopt(long = "number-minus-foreground-color")]
+    pub number_minus_foreground_color: Option<String>,
+
+    /// Color for the right (plus) column of line numbers (--number), if --number is set.
+    /// Defaults to --hunk-color.
+    #[structopt(long = "number-plus-foreground-color")]
+    pub number_plus_foreground_color: Option<String>,
+
+    /// Color for the right dividing line of the line numbers section, if --number is set.
+    /// Defaults to --hunk-color.
+    #[structopt(long = "number-right-divider-foreground-color")]
+    pub number_right_divider_foreground_color: Option<String>,
+
+    /// Color for the center dividing line of the line numbers section, if --number is set.
+    /// Defaults to --hunk-color.
+    #[structopt(long = "number-center-divider-foreground-color")]
+    pub number_center_divider_foreground_color: Option<String>,
+
+    /// String to use as the center divider of the line numbers section, if --number is set.
+    #[structopt(long = "number-center-divider-string", default_value = "⋮")]
+    pub number_center_divider_string: String,
+
+    /// String to use as the right divider of the line numbers section, if --number is set.
+    #[structopt(long = "number-right-divider-string", default_value = "│")]
+    pub number_right_divider_string: String,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq)]

src/config.rs

@@ -38,6 +38,13 @@ pub struct Config<'a> {
     pub no_style: Style,
     pub max_buffered_lines: usize,
     pub paging_mode: PagingMode,
+    pub show_line_numbers: bool,
+    pub number_minus_foreground_color: Color,
+    pub number_plus_foreground_color: Color,
+    pub number_right_divider_foreground_color: Color,
+    pub number_center_divider_foreground_color: Color,
+    pub number_center_divider_string: &'a str,
+    pub number_right_divider_string: &'a str,
 }
 
 #[allow(dead_code)]
@@ -153,6 +160,29 @@ pub fn get_config<'a>(
         no_style: style::get_no_style(),
         max_buffered_lines: 32,
         paging_mode,
+        show_line_numbers: opt.show_line_numbers,
+        number_minus_foreground_color: color_from_rgb_or_ansi_code_with_default(
+            opt.number_minus_foreground_color.as_deref(),
+            Some(color_from_rgb_or_ansi_code(&opt.hunk_color)),
+        )
+        .unwrap(),
+        number_plus_foreground_color: color_from_rgb_or_ansi_code_with_default(
+            opt.number_plus_foreground_color.as_deref(),
+            Some(color_from_rgb_or_ansi_code(&opt.hunk_color)),
+        )
+        .unwrap(),
+        number_right_divider_foreground_color: color_from_rgb_or_ansi_code_with_default(
+            opt.number_right_divider_foreground_color.as_deref(),
+            Some(color_from_rgb_or_ansi_code(&opt.hunk_color)),
+        )
+        .unwrap(),
+        number_center_divider_foreground_color: color_from_rgb_or_ansi_code_with_default(
+            opt.number_center_divider_foreground_color.as_deref(),
+            Some(color_from_rgb_or_ansi_code(&opt.hunk_color)),
+        )
+        .unwrap(),
+        number_center_divider_string: opt.number_center_divider_string.as_ref(),
+        number_right_divider_string: opt.number_right_divider_string.as_ref(),
     }
 }
 

src/delta.rs

@@ -256,7 +256,9 @@ fn handle_hunk_meta_line(
         cli::SectionStyle::Plain => panic!(),
         cli::SectionStyle::Omit => return Ok(()),
     };
-    let (raw_code_fragment, line_number) = parse::parse_hunk_metadata(&line);
+    let (raw_code_fragment, line_numbers) = parse::parse_hunk_metadata(&line);
+    painter.minus_line_number = line_numbers[0];
+    painter.plus_line_number = line_numbers.last().copied().unwrap();
     let code_fragment = prepare(raw_code_fragment, false, config);
     if !code_fragment.is_empty() {
         let syntax_style_sections = Painter::get_line_syntax_style_sections(
@@ -271,6 +273,7 @@ fn handle_hunk_meta_line(
                 style::NO_BACKGROUND_COLOR_STYLE_MODIFIER,
                 &code_fragment,
             )]],
+            vec![(None, None)],
             &mut painter.output_buffer,
             config,
             "",
@@ -288,11 +291,19 @@ fn handle_hunk_meta_line(
         )?;
         painter.output_buffer.clear();
     }
-    writeln!(
-        painter.writer,
-        "\n{}",
-        paint::paint_text_foreground(line_number, config.hunk_color, config.true_color)
-    )?;
+    if config.show_line_numbers {
+        writeln!(painter.writer, "",)?;
+    } else {
+        writeln!(
+            painter.writer,
+            "\n{}",
+            paint::paint_text_foreground(
+                &format!("{}", painter.plus_line_number),
+                config.hunk_color,
+                config.true_color
+            )
+        )?;
+    }
     Ok(())
 }
 
@@ -350,12 +361,18 @@ fn handle_hunk_line(
             Painter::paint_lines(
                 vec![syntax_style_sections],
                 vec![diff_style_sections],
+                vec![(
+                    Some(painter.minus_line_number),
+                    Some(painter.plus_line_number),
+                )],
                 &mut painter.output_buffer,
                 config,
                 prefix,
                 style::NO_BACKGROUND_COLOR_STYLE_MODIFIER,
                 None,
             );
+            painter.minus_line_number += 1;
+            painter.plus_line_number += 1;
             state
         }
         _ => {

src/paint.rs

@@ -25,6 +25,8 @@ pub struct Painter<'a> {
     pub highlighter: HighlightLines<'a>,
     pub config: &'a config::Config<'a>,
     pub output_buffer: String,
+    pub minus_line_number: usize,
+    pub plus_line_number: usize,
 }
 
 impl<'a> Painter<'a> {
@@ -45,6 +47,8 @@ impl<'a> Painter<'a> {
             highlighter: dummy_highlighter,
             writer,
             config,
+            minus_line_number: 0,
+            plus_line_number: 0,
         }
     }
 
@@ -79,11 +83,23 @@ impl<'a> Painter<'a> {
         );
         let (minus_line_diff_style_sections, plus_line_diff_style_sections) =
             Self::get_diff_style_sections(&self.minus_lines, &self.plus_lines, self.config);
+
+        let mut minus_line_numbers = Vec::new();
+        let mut plus_line_numbers = Vec::new();
+        for _line in &self.minus_lines {
+            minus_line_numbers.push((Some(self.minus_line_number), None));
+            self.minus_line_number += 1;
+        }
+        for _line in &self.plus_lines {
+            plus_line_numbers.push((None, Some(self.plus_line_number)));
+            self.plus_line_number += 1;
+        }
         // TODO: lines and style sections contain identical line text
         if !self.minus_lines.is_empty() {
             Painter::paint_lines(
                 minus_line_syntax_style_sections,
                 minus_line_diff_style_sections,
+                minus_line_numbers,
                 &mut self.output_buffer,
                 self.config,
                 self.config.minus_line_marker,
@@ -95,6 +111,7 @@ impl<'a> Painter<'a> {
             Painter::paint_lines(
                 plus_line_syntax_style_sections,
                 plus_line_diff_style_sections,
+                plus_line_numbers,
                 &mut self.output_buffer,
                 self.config,
                 self.config.plus_line_marker,
@@ -111,6 +128,7 @@ impl<'a> Painter<'a> {
     pub fn paint_lines(
         syntax_style_sections: Vec<Vec<(Style, &str)>>,
         diff_style_sections: Vec<Vec<(StyleModifier, &str)>>,
+        line_number_sections: Vec<(Option<usize>, Option<usize>)>,
         output_buffer: &mut String,
         config: &config::Config,
         prefix: &str,
@@ -119,8 +137,11 @@ impl<'a> Painter<'a> {
     ) {
         let background_style = config.no_style.apply(background_style_modifier);
         let background_ansi_style = to_ansi_style(background_style, config.true_color);
-        for (syntax_sections, diff_sections) in
-            syntax_style_sections.iter().zip(diff_style_sections.iter())
+
+        for ((syntax_sections, diff_sections), line_numbers) in syntax_style_sections
+            .iter()
+            .zip(diff_style_sections.iter())
+            .zip(line_number_sections.iter())
         {
             let mut ansi_strings = Vec::new();
             if prefix != "" {
@@ -151,6 +172,10 @@ impl<'a> Painter<'a> {
                 {
                     line.truncate(line.len() - ANSI_SGR_RESET.len());
                 }
+
+                if config.show_line_numbers {
+                    output_buffer.push_str(&format_line_numbers(*line_numbers, config));
+                }
                 output_buffer.push_str(&line);
                 output_buffer.push_str(ANSI_CSI_ERASE_IN_LINE);
                 output_buffer.push_str(ANSI_SGR_RESET);
@@ -282,6 +307,42 @@ pub fn color_from_ansi_name(name: &str) -> Option<Color> {
     ansi_color_name_to_number(name).and_then(color_from_ansi_number)
 }
 
+fn _paint_line_numbers(line_number: Option<usize>, color: Color, true_color: bool) -> String {
+    let formatted = match line_number {
+        Some(x) => format!("{:^4}", x),
+        None => format!("    "),
+    };
+    paint_text_foreground(&formatted, color, true_color)
+}
+
+pub fn format_line_numbers(
+    line_numbers: (Option<usize>, Option<usize>),
+    config: &config::Config,
+) -> String {
+    let (minus_line_number, plus_line_number) = line_numbers;
+    let minus = _paint_line_numbers(
+        minus_line_number,
+        config.number_minus_foreground_color,
+        config.true_color,
+    );
+    let plus = _paint_line_numbers(
+        plus_line_number,
+        config.number_plus_foreground_color,
+        config.true_color,
+    );
+    let divider_center = paint_text_foreground(
+        config.number_center_divider_string,
+        config.number_center_divider_foreground_color,
+        config.true_color,
+    );
+    let divider_right = paint_text_foreground(
+        config.number_right_divider_string,
+        config.number_right_divider_foreground_color,
+        config.true_color,
+    );
+    format!("{}{}{}{}", minus, divider_center, plus, divider_right)
+}
+
 /// Convert 8-bit ANSI code to #RGBA string with ANSI code in red channel and 0 in alpha channel.
 // See https://github.com/sharkdp/bat/pull/543
 pub fn color_from_ansi_number(n: u8) -> Option<Color> {