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

    - format string for specifying minus number line
    - format string for specifying plus number line
    - minus number style
    - plus number style
    - minus format string style
    - plus format string style

7 files changed, 338 insertions, 21 deletions

diff --git a/src/cli.rs b/src/cli.rs
index 479eea8f..0226832d 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -127,6 +127,24 @@ within a style string):
    Specifying colors like this is useful if your terminal only supports 256 colors (i.e. doesn\'t
    support 24-bit color).
 
+LINE NUMBERS
+------------
+
+Options that have a name like --*-format allow you to specify a string to display for the line
+number columns. The string should specify the location of the line number using the placeholder
+%ln.
+
+For example, to display the line numbers divided by specific characters:
+
+    8 ⋮   9 │ Here is an output line
+    9 ⋮  10 │ Here is another output line
+   10 ⋮  11 │ Here is the line number
+
+you would use the following input:
+
+--number-minus-format '%ln ⋮'
+--number-plus-format '%ln │'
+
 If something isn't working correctly, or you have a feature request, please open an issue at
 https://github.com/dandavison/delta/issues.
 "
@@ -245,6 +263,52 @@ pub struct Opt {
     /// given.
     pub hunk_header_decoration_style: 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,
+
+    /// Style (foreground, background, attributes) for the left (minus) column of line numbers
+    /// (--number), if --number is set. See STYLES section.
+    /// Defaults to --hunk-style.
+    #[structopt(long = "number-minus-style", default_value = "auto")]
+    pub number_minus_style: String,
+
+    /// Style (foreground, background, attributes) for the right (plus) column of line numbers
+    /// (--number), if --number is set. See STYLES section.
+    /// Defaults to --hunk-style.
+    #[structopt(long = "number-plus-style", default_value = "auto")]
+    pub number_plus_style: String,
+
+    /// Format string for the left (minus) column of line numbers (--number), if --number is set.
+    /// Should include the placeholder %ln to indicate the position of the line number.
+    /// See the LINE NUMBERS section.
+    /// Defaults to '%ln⋮'
+    #[structopt(long = "number-minus-format", default_value = "%ln⋮")]
+    pub number_minus_format: String,
+
+    /// Format string for the right (plus) column of line numbers (--number), if --number is set.
+    /// Should include the placeholder %ln to indicate the position of the line number.
+    /// See the LINE NUMBERS section.
+    /// Defaults to '%ln│ '
+    #[structopt(long = "number-plus-format", default_value = "%ln│ ")]
+    pub number_plus_format: String,
+
+    /// Style (foreground, background, attributes) for the left (minus) line number format string
+    /// (--number), if --number is set. See STYLES section.
+    /// Defaults to --hunk-style.
+    #[structopt(long = "number-minus-format-style", default_value = "auto")]
+    pub number_minus_format_style: String,
+
+    /// Style (foreground, background, attributes) for the right (plus) line number format string
+    /// (--number), if --number is set. See STYLES section.
+    /// Defaults to --hunk-style.
+    #[structopt(long = "number-plus-format-style", default_value = "auto")]
+    pub number_plus_format_style: String,
+
     #[structopt(long = "color-only")]
     /// Do not alter the input in any way other than applying colors. Equivalent to
     /// `--keep-plus-minus-markers --width variable --tabs 0 --commit-decoration ''
diff --git a/src/config.rs b/src/config.rs
index 4c522ea8..a248f294 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -41,12 +41,19 @@ pub struct Config<'a> {
     pub navigate: bool,
     pub null_style: Style,
     pub null_syntect_style: SyntectStyle,
+    pub number_minus_format: String,
+    pub number_minus_format_style: Style,
+    pub number_minus_style: Style,
+    pub number_plus_format: String,
+    pub number_plus_format_style: Style,
+    pub number_plus_style: Style,
     pub paging_mode: PagingMode,
     pub plus_emph_style: Style,
     pub plus_file: Option<PathBuf>,
     pub plus_line_marker: &'a str,
     pub plus_non_emph_style: Style,
     pub plus_style: Style,
+    pub show_line_numbers: bool,
     pub syntax_dummy_theme: SyntaxTheme,
     pub syntax_set: SyntaxSet,
     pub syntax_theme: Option<SyntaxTheme>,
@@ -120,6 +127,17 @@ pub fn get_config<'a>(
     let (commit_style, file_style, hunk_header_style) =
         make_commit_file_hunk_header_styles(&opt, true_color);
 
+    let (
+        number_minus_format_style,
+        number_minus_style,
+        number_plus_format_style,
+        number_plus_style,
+    ) = make_line_number_styles(
+        &opt,
+        hunk_header_style.decoration_ansi_term_style(),
+        true_color,
+    );
+
     let syntax_theme = if syntax_theme::is_no_syntax_highlighting_theme_name(&syntax_theme_name) {
         None
     } else {
@@ -164,12 +182,19 @@ pub fn get_config<'a>(
         navigate: opt.navigate,
         null_style: Style::new(),
         null_syntect_style: SyntectStyle::default(),
+        number_minus_format: opt.number_minus_format,
+        number_minus_format_style: number_minus_format_style,
+        number_minus_style: number_minus_style,
+        number_plus_format: opt.number_plus_format,
+        number_plus_format_style: number_plus_format_style,
+        number_plus_style: number_plus_style,
         paging_mode,
         plus_emph_style,
         plus_file: opt.plus_file.map(|s| s.clone()),
         plus_line_marker,
         plus_non_emph_style,
         plus_style,
+        show_line_numbers: opt.show_line_numbers,
         syntax_dummy_theme,
         syntax_set,
         syntax_theme,
@@ -264,6 +289,60 @@ fn make_hunk_styles<'a>(
     )
 }
 
+fn make_line_number_styles<'a>(
+    opt: &'a cli::Opt,
+    default_style: Option<ansi_term::Style>,
+    true_color: bool,
+) -> (Style, Style, Style, Style) {
+    let (default_foreground, default_background) = match default_style {
+        Some(default_style) => (default_style.foreground, default_style.background),
+        None => (None, None),
+    };
+
+    let number_minus_format_style = Style::from_str(
+        &opt.number_minus_format_style,
+        default_foreground,
+        default_background,
+        None,
+        true_color,
+        false,
+    );
+
+    let number_minus_style = Style::from_str(
+        &opt.number_minus_style,
+        default_foreground,
+        default_background,
+        None,
+        true_color,
+        false,
+    );
+
+    let number_plus_format_style = Style::from_str(
+        &opt.number_plus_format_style,
+        default_foreground,
+        default_background,
+        None,
+        true_color,
+        false,
+    );
+
+    let number_plus_style = Style::from_str(
+        &opt.number_plus_style,
+        default_foreground,
+        default_background,
+        None,
+        true_color,
+        false,
+    );
+
+    (
+        number_minus_format_style,
+        number_minus_style,
+        number_plus_format_style,
+        number_plus_style,
+    )
+}
+
 fn make_commit_file_hunk_header_styles(opt: &cli::Opt, true_color: bool) -> (Style, Style, Style) {
     (
         Style::from_str_with_handling_of_special_decoration_attributes_and_respecting_deprecated_foreground_color_arg(
diff --git a/src/delta.rs b/src/delta.rs
index bab26679..b498bd0a 100644
--- a/src/delta.rs
+++ b/src/delta.rs
@@ -369,7 +369,9 @@ fn handle_hunk_header_line(
             draw::write_no_decoration
         }
     };
-    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[line_numbers.len() - 1];
     if config.hunk_header_style.is_raw {
         writeln!(painter.writer)?;
         draw_fn(
@@ -397,6 +399,7 @@ fn handle_hunk_header_line(
             Painter::paint_lines(
                 syntax_style_sections,
                 vec![vec![(config.hunk_header_style, &lines[0])]],
+                vec![None],
                 &mut painter.output_buffer,
                 config,
                 "",
@@ -418,10 +421,14 @@ fn handle_hunk_header_line(
             };
         }
     };
-    match config.hunk_header_style.decoration_ansi_term_style() {
-        Some(style) => writeln!(painter.writer, "{}", style.paint(line_number))?,
-        None => writeln!(painter.writer, "{}", line_number)?,
-    };
+
+    if !config.show_line_numbers {
+        let line_number = &format!("{}", painter.plus_line_number);
+        match config.hunk_header_style.decoration_ansi_term_style() {
+            Some(style) => writeln!(painter.writer, "{}", style.paint(line_number))?,
+            None => writeln!(painter.writer, "{}", line_number)?,
+        }
+    }
     Ok(())
 }
 
@@ -474,6 +481,10 @@ fn handle_hunk_line(
             Painter::paint_lines(
                 syntax_style_sections,
                 vec![diff_style_sections],
+                vec![Some((
+                    Some(painter.minus_line_number),
+                    Some(painter.plus_line_number),
+                ))],
                 &mut painter.output_buffer,
                 config,
                 prefix,
@@ -481,6 +492,8 @@ fn handle_hunk_line(
                 config.zero_style,
                 None,
             );
+            painter.minus_line_number += 1;
+            painter.plus_line_number += 1;
             state
         }
         _ => {
diff --git a/src/paint.rs b/src/paint.rs
index bfd029ef..b18a4399 100644
--- a/src/paint.rs
+++ b/src/paint.rs
@@ -1,3 +1,5 @@
+use lazy_static::lazy_static;
+use regex::Regex;
 use std::io::Write;
 
 use ansi_term;
@@ -22,6 +24,8 @@ 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> {
@@ -37,6 +41,8 @@ impl<'a> Painter<'a> {
             highlighter: dummy_highlighter,
             writer,
             config,
+            minus_line_number: 0,
+            plus_line_number: 0,
         }
     }
 
@@ -71,11 +77,23 @@ 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((Some(self.minus_line_number), None)));
+            self.minus_line_number += 1;
+        }
+        for _line in &self.plus_lines {
+            plus_line_numbers.push(Some((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,
@@ -88,6 +106,7 @@ 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,
@@ -105,6 +124,7 @@ impl<'a> Painter<'a> {
     pub fn paint_lines(
         syntax_style_sections: Vec<Vec<(SyntectStyle, &str)>>,
         diff_style_sections: Vec<Vec<(Style, &str)>>,
+        line_number_sections: Vec<Option<(Option<usize>, Option<usize>)>>,
         output_buffer: &mut String,
         config: &config::Config,
         prefix: &str,
@@ -120,8 +140,11 @@ impl<'a> Painter<'a> {
         // 2. We must ensure that we fill rightwards with the appropriate
         //    non-emph background color. In that case we don't use the last
         //    style of the line, because this might be emph.
-        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 non_emph_style = if style_sections_contain_more_than_one_style(diff_sections) {
                 non_emph_style // line contains an emph section
@@ -130,6 +153,45 @@ impl<'a> Painter<'a> {
             };
             let mut ansi_strings = Vec::new();
             let mut handled_prefix = false;
+            if config.show_line_numbers && line_numbers.is_some() {
+                let (minus, plus) = line_numbers.unwrap();
+                let (minus_before, minus_number, minus_after) =
+                    get_line_number_components(minus, &config.number_minus_format);
+                let (plus_before, plus_number, plus_after) =
+                    get_line_number_components(plus, &config.number_plus_format);
+
+                ansi_strings.push(
+                    config
+                        .number_minus_format_style
+                        .ansi_term_style
+                        .paint(minus_before),
+                );
+                ansi_strings.push(
+                    config
+                        .number_minus_style
+                        .ansi_term_style
+                        .paint(minus_number),
+                );
+                ansi_strings.push(
+                    config
+                        .number_minus_format_style
+                        .ansi_term_style
+                        .paint(minus_after),
+                );
+                ansi_strings.push(
+                    config
+                        .number_plus_format_style
+                        .ansi_term_style
+                        .paint(plus_before),
+                );
+                ansi_strings.push(config.number_plus_style.ansi_term_style.paint(plus_number));
+                ansi_strings.push(
+                    config
+                        .number_plus_format_style
+                        .ansi_term_style
+                        .paint(plus_after),
+                );
+            }
             for (section_style, mut text) in superimpose_style_sections(
                 syntax_sections,
                 diff_sections,
@@ -499,3 +561,40 @@ mod superimpose_style_sections {
         }
     }
 }
+
+lazy_static! {
+    static ref LINE_NUMBER_REGEXP: Regex =
+        Regex::new(r"(?P<before>.*)(?P<ln>%ln)(?P<after>.*)").unwrap();
+}
+
+fn format_line_number(line_number: Option<usize>) -> String {
+    match line_number {
+        Some(x) => format!("{:^4}", x),
+        None => format!("    "),
+    }
+}
+
+fn get_line_number_components(
+    number: Option<usize>,
+    number_format: &str,
+) -> (String, String, String) {
+    let _caps = LINE_NUMBER_REGEXP.captures(number_format);
+
+    let caps = match _caps {
+        Some(_) => _caps.unwrap(),
+        None => return (number_format.to_string(), "".to_string(), "".to_string()),
+    };
+
+    let before = caps.name("before").unwrap().as_str();
+    let ln = caps.name("ln");
+    let after = caps.name("after").unwrap().as_str();
+    let display_number = match ln {
+        Some(_) => number,
+        None => None,
+    };
+    (
+        before.to_string(),
+        format_line_number(display_number),
+        after.to_string(),
+    )
+}
diff --git a/src/parse.rs b/src/parse.rs
index 7bccd658..5cc11232 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -1,3 +1,5 @@
+use lazy_static::lazy_static;
+use regex::Regex;
 use std::path::Path;
 
 use crate::config::Config;
@@ -87,17 +89,36 @@ pub fn get_file_change_description_from_file_paths(
     }
 }
 
+lazy_static! {
+    static ref HUNK_METADATA_REGEXP: Regex =
+        Regex::new(r"@+ (?P<lns>([-+]\d+(?:,\d+)? ){2,4})@+(?P<cf>.*\s?)").unwrap();
+}
+
+lazy_static! {
+    static ref LINE_NUMBER_REGEXP: Regex = Regex::new(r"[-+]").unwrap();
+}
+
+fn _make_line_number_vec(line: &str) -> Vec<usize> {
+    let mut numbers = Vec::<usize>::new();
+
+    for s in LINE_NUMBER_REGEXP.split(line) {
+        let number = s.split(',').nth(0).unwrap().split_whitespace().nth(0);
+        match number {
+            Some(number) => numbers.push(number.parse::<usize>().unwrap()),
+            None => continue,
+        }
+    }
+    return numbers;
+}
+
 /// Given input like
 /// "@@ -74,15 +74,14 @@ pub fn delta("
-/// Return " pub fn delta("
-pub fn parse_hunk_metadata(line: &str) -> (&str, &str) {
-    let mut iter = line.split("@@").skip(1);
-    let line_number = iter
-        .next()
-        .and_then(|s| s.split('+').nth(1).and_then(|s| s.split(',').next()))
-        .unwrap_or("");
-    let code_fragment = iter.next().unwrap_or("");
-    (code_fragment, line_number)
+/// Return " pub fn delta(" and a vector of line numbers
+pub fn parse_hunk_metadata(line: &str) -> (&str, Vec<usize>) {
+    let caps = HUNK_METADATA_REGEXP.captures(line).unwrap();
+    let line_numbers = _make_line_number_vec(caps.name("lns").unwrap().as_str());
+    let code_fragment = caps.name("cf").unwrap().as_str();
+    return (code_fragment, line_numbers);
 }
 
 /// Attempt to parse input as a file path and return extension as a &str.
@@ -249,9 +270,42 @@ mod tests {
 
     #[test]
     fn test_parse_hunk_metadata() {
-        assert_eq!(
-            parse_hunk_metadata("@@ -74,15 +75,14 @@ pub fn delta(\n"),
-            (" pub fn delta(\n", "75")
-        );
+        let parsed = parse_hunk_metadata("@@ -74,15 +75,14 @@ pub fn delta(\n");
+        let code_fragment = parsed.0;
+        let line_numbers = parsed.1;
+        assert_eq!(code_fragment, " pub fn delta(\n",);
+        assert_eq!(line_numbers[0], 74,);
+        assert_eq!(line_numbers[1], 75,);
+    }
+
+    #[test]
+    fn test_parse_hunk_metadata_added_file() {
+        let parsed = parse_hunk_metadata("@@ -1,22 +0,0 @@");
+        let code_fragment = parsed.0;
+        let line_numbers = parsed.1;
+        assert_eq!(code_fragment, "",);
+        assert_eq!(line_numbers[0], 1,);
+        assert_eq!(line_numbers[1], 0,);
+    }
+
+    #[test]
+    fn test_parse_hunk_metadata_deleted_file() {
+        let parsed = parse_hunk_metadata("@@ -0,0 +1,3 @@");
+        let code_fragment = parsed.0;
+        let line_numbers = parsed.1;
+        assert_eq!(code_fragment, "",);
+        assert_eq!(line_numbers[0], 0,);
+        assert_eq!(line_numbers[1], 1,);
+    }
+
+    #[test]
+    fn test_parse_hunk_metadata_merge() {
+        let parsed = parse_hunk_metadata("@@@ -293,11 -358,15 +358,16 @@@ dependencies =");
+        let code_fragment = parsed.0;
+        let line_numbers = parsed.1;
+        assert_eq!(code_fragment, " dependencies =",);
+        assert_eq!(line_numbers[0], 293,);
+        assert_eq!(line_numbers[1], 358,);
+        assert_eq!(line_numbers[2], 358,);
     }
 }
diff --git a/src/rewrite.rs b/src/rewrite.rs
index ab75508e..c7db5fae 100644
--- a/src/rewrite.rs
+++ b/src/rewrite.rs
@@ -49,7 +49,8 @@ fn _rewrite_options_to_honor_git_config(
             ("dark", dark),
             ("navigate", navigate),
             ("color-only", color_only),
-            ("keep-plus-minus-markers", keep_plus_minus_markers)
+            ("keep-plus-minus-markers", keep_plus_minus_markers),
+            ("number", show_line_numbers)
         ],
         opt,
         git_config,
@@ -76,6 +77,12 @@ fn _rewrite_options_to_honor_git_config(
             ("minus-emph-style", minus_emph_style),
             ("minus-non-emph-style", minus_non_emph_style),
             ("minus-style", minus_style),
+            ("number-minus-format", number_minus_format),
+            ("number-minus-format-style", number_minus_format_style),
+            ("number-minus-style", number_minus_style),
+            ("number-plus-format", number_plus_format),
+            ("number-plus-format-style", number_plus_format_style),
+            ("number-plus-style", number_plus_style),
             ("paging-mode", paging_mode),
             ("plus-emph-style", plus_emph_style),
             ("plus-non-emph-style", plus_non_emph_style),
diff --git a/src/tests/ansi_test_utils.rs b/src/tests/ansi_test_utils.rs
index 5beb3f4e..7d0ccf36 100644
--- a/src/tests/ansi_test_utils.rs
+++ b/src/tests/ansi_test_utils.rs
@@ -107,6 +107,7 @@ pub mod ansi_test_utils {
         paint::Painter::paint_lines(
             vec![syntax_style_sections],
             vec![vec![(syntax_highlighted_style, lines[0])]],
+            vec![None],
             &mut output_buffer,
             config,
             "",