Add a --background option

Improves #55

CHANGELOG.md

@@ -23,6 +23,9 @@ more discoverable.
 Added a `--color` option which allows explicitly enabling/disabling
 colour output.
 
+Added a `--background` option which controls whether difftastic uses
+bright or dark colours.
+
 ## 0.17 (released 25 January 2022)
 
 ### Diffing

src/inline.rs

@@ -4,7 +4,7 @@ use crate::{
     context::{calculate_after_context, calculate_before_context, opposite_positions},
     hunks::Hunk,
     lines::{format_line_num, MaxLine},
-    style::{self, apply_colors},
+    style::{self, apply_colors, BackgroundColor},
     syntax::MatchedPos,
 };
 use colored::*;
@@ -17,9 +17,10 @@ pub fn display(
     hunks: &[Hunk],
     display_path: &str,
     lang_name: &str,
+    background: BackgroundColor,
 ) -> String {
-    let lhs_colored = apply_colors(lhs_src, true, lhs_positions);
-    let rhs_colored = apply_colors(rhs_src, false, rhs_positions);
+    let lhs_colored = apply_colors(lhs_src, true, background, lhs_positions);
+    let rhs_colored = apply_colors(rhs_src, false, background, rhs_positions);
 
     let lhs_lines: Vec<_> = lhs_colored.lines().collect();
     let rhs_lines: Vec<_> = rhs_colored.lines().collect();
@@ -30,7 +31,13 @@ pub fn display(
     let opposite_to_rhs = opposite_positions(rhs_positions);
 
     for (i, hunk) in hunks.iter().enumerate() {
-        res.push_str(&style::header(display_path, i + 1, hunks.len(), lang_name));
+        res.push_str(&style::header(
+            display_path,
+            i + 1,
+            hunks.len(),
+            lang_name,
+            background,
+        ));
         res.push('\n');
 
         let hunk_lines = hunk.lines.clone();

src/main.rs

@@ -47,6 +47,7 @@ use atty::Stream;
 use clap::{crate_authors, crate_description, crate_version, App, AppSettings, Arg};
 use sliders::fix_all_sliders;
 use std::{env, path::Path};
+use style::BackgroundColor;
 use summary::DiffResult;
 use syntax::init_next_prev;
 use typed_arena::Arena;
@@ -93,6 +94,7 @@ enum ColorOutput {
 
 enum Mode {
     Diff {
+        background_color: BackgroundColor,
         color_output: ColorOutput,
         display_width: usize,
         display_path: String,
@@ -145,6 +147,12 @@ fn app() -> clap::App<'static> {
                 .value_name("WHEN")
                 .help("When to use color output.")
         )
+        .arg(
+            Arg::new("background").long("background")
+                .default_value("dark")
+                .possible_values(["dark", "light"])
+                .help("Set the background color. Difftastic will prefer brighter colours on dark backgrounds.")
+        )
         .arg(
             Arg::new("paths")
                 .multiple_values(true)
@@ -230,7 +238,18 @@ fn parse_args() -> Mode {
         ColorOutput::Auto
     };
 
+    let background_color = if let Some(background) = matches.value_of("background") {
+        if background == "light" {
+            BackgroundColor::Light
+        } else {
+            BackgroundColor::Dark
+        }
+    } else {
+        BackgroundColor::Dark
+    };
+
     Mode::Diff {
+        background_color,
         color_output,
         display_width,
         display_path,
@@ -292,6 +311,7 @@ fn main() {
             }
         }
         Mode::Diff {
+            background_color,
             color_output,
             display_width,
             display_path,
@@ -306,11 +326,11 @@ fn main() {
 
             if lhs_path.is_dir() && rhs_path.is_dir() {
                 for diff_result in diff_directories(lhs_path, rhs_path) {
-                    print_diff_result(display_width, &diff_result);
+                    print_diff_result(display_width, background_color, &diff_result);
                 }
             } else {
                 let diff_result = diff_file(&display_path, lhs_path, rhs_path);
-                print_diff_result(display_width, &diff_result);
+                print_diff_result(display_width, background_color, &diff_result);
             }
         }
     };
@@ -432,9 +452,12 @@ fn diff_directories(lhs_dir: &Path, rhs_dir: &Path) -> Vec<DiffResult> {
     res
 }
 
-fn print_diff_result(display_width: usize, summary: &DiffResult) {
+fn print_diff_result(display_width: usize, background: BackgroundColor, summary: &DiffResult) {
     if summary.binary {
-        println!("{}", style::header(&summary.path, 1, 1, "binary"));
+        println!(
+            "{}",
+            style::header(&summary.path, 1, 1, "binary", background)
+        );
         return;
     }
 
@@ -452,7 +475,10 @@ fn print_diff_result(display_width: usize, summary: &DiffResult) {
 
     let lang_name = summary.language.clone().unwrap_or_else(|| "text".into());
     if hunks.is_empty() {
-        println!("{}", style::header(&summary.path, 1, 1, &lang_name));
+        println!(
+            "{}",
+            style::header(&summary.path, 1, 1, &lang_name, background)
+        );
         if lang_name == "text" {
             println!("No changes.\n");
         } else {
@@ -472,6 +498,7 @@ fn print_diff_result(display_width: usize, summary: &DiffResult) {
                 &hunks,
                 &summary.path,
                 &lang_name,
+                background
             )
         );
     } else {
@@ -480,6 +507,7 @@ fn print_diff_result(display_width: usize, summary: &DiffResult) {
             side_by_side::display_hunks(
                 &hunks,
                 display_width,
+                background,
                 &summary.path,
                 &lang_name,
                 &summary.lhs_src,

src/side_by_side.rs

@@ -11,7 +11,7 @@ use crate::{
     hunks::{matched_lines_for_hunk, Hunk},
     lines::{codepoint_len, format_line_num, LineNumber},
     positions::SingleLineSpan,
-    style::{self, apply_colors, color_positions, split_and_apply, Style},
+    style::{self, apply_colors, color_positions, split_and_apply, BackgroundColor, Style},
     syntax::{zip_pad_shorter, MatchedPos},
 };
 
@@ -45,11 +45,17 @@ fn format_missing_line_num(prev_num: LineNumber, column_width: usize) -> String
 }
 
 /// Display `src` in a single column (e.g. a file removal or addition).
-fn display_single_column(display_path: &str, lang_name: &str, src: &str, color: Color) -> String {
+fn display_single_column(
+    display_path: &str,
+    lang_name: &str,
+    src: &str,
+    color: Color,
+    background: BackgroundColor,
+) -> String {
     let column_width = format_line_num(src.lines().count().into()).len();
 
     let mut result = String::with_capacity(src.len());
-    result.push_str(&style::header(display_path, 1, 1, lang_name));
+    result.push_str(&style::header(display_path, 1, 1, lang_name, background));
     result.push('\n');
 
     for (i, line) in src.lines().enumerate() {
@@ -69,6 +75,7 @@ fn display_line_nums(
     lhs_line_num: Option<LineNumber>,
     rhs_line_num: Option<LineNumber>,
     widths: &Widths,
+    background: BackgroundColor,
     lhs_has_novel: bool,
     rhs_has_novel: bool,
     prev_lhs_line_num: Option<LineNumber>,
@@ -78,7 +85,12 @@ fn display_line_nums(
         Some(line_num) => {
             let s = format_line_num_padded(line_num, widths.lhs_line_nums);
             if lhs_has_novel {
-                s.red().bold().to_string()
+                // TODO: factor out applying colours to line numbers.
+                match background {
+                    BackgroundColor::Dark => s.bright_red(),
+                    BackgroundColor::Light => s.red(),
+                }
+                .to_string()
             } else {
                 s
             }
@@ -92,7 +104,11 @@ fn display_line_nums(
         Some(line_num) => {
             let s = format_line_num_padded(line_num, widths.rhs_line_nums);
             if rhs_has_novel {
-                s.green().bold().to_string()
+                match background {
+                    BackgroundColor::Dark => s.bright_green(),
+                    BackgroundColor::Light => s.green(),
+                }
+                .to_string()
             } else {
                 s
             }
@@ -175,13 +191,14 @@ fn lines_with_novel(
 /// Calculate positions of highlights on both sides. This includes
 /// both syntax highlighting and added/removed content highlighting.
 fn highlight_positions(
+    background: BackgroundColor,
     lhs_mps: &[MatchedPos],
     rhs_mps: &[MatchedPos],
 ) -> (
     HashMap<LineNumber, Vec<(SingleLineSpan, Style)>>,
     HashMap<LineNumber, Vec<(SingleLineSpan, Style)>>,
 ) {
-    let lhs_positions = color_positions(true, lhs_mps);
+    let lhs_positions = color_positions(true, background, lhs_mps);
     // Preallocate the hashmap assuming the average line will have 2 items on it.
     let mut lhs_styles: HashMap<LineNumber, Vec<(SingleLineSpan, Style)>> =
         HashMap::with_capacity(lhs_positions.len() / 2);
@@ -190,7 +207,7 @@ fn highlight_positions(
         styles.push((span, style));
     }
 
-    let rhs_positions = color_positions(false, rhs_mps);
+    let rhs_positions = color_positions(false, background, rhs_mps);
     let mut rhs_styles: HashMap<LineNumber, Vec<(SingleLineSpan, Style)>> =
         HashMap::with_capacity(rhs_positions.len() / 2);
     for (span, style) in rhs_positions {
@@ -228,6 +245,7 @@ fn highlight_as_novel(
 pub fn display_hunks(
     hunks: &[Hunk],
     display_width: usize,
+    background: BackgroundColor,
     display_path: &str,
     lang_name: &str,
     lhs_src: &str,
@@ -235,18 +253,32 @@ pub fn display_hunks(
     lhs_mps: &[MatchedPos],
     rhs_mps: &[MatchedPos],
 ) -> String {
-    let lhs_colored_src = apply_colors(lhs_src, true, lhs_mps);
-    let rhs_colored_src = apply_colors(rhs_src, false, rhs_mps);
+    let lhs_colored_src = apply_colors(lhs_src, true, background, lhs_mps);
+    let rhs_colored_src = apply_colors(rhs_src, false, background, rhs_mps);
 
     if lhs_src.is_empty() {
-        return display_single_column(display_path, lang_name, &rhs_colored_src, Color::Green);
+        // TODO: use BrightGreen on dark backgrounds.
+        // TODO: this doesn't need the coloured source as it applies colours.
+        return display_single_column(
+            display_path,
+            lang_name,
+            &rhs_colored_src,
+            Color::Green,
+            background,
+        );
     }
     if rhs_src.is_empty() {
-        return display_single_column(display_path, lang_name, &lhs_colored_src, Color::Red);
+        return display_single_column(
+            display_path,
+            lang_name,
+            &lhs_colored_src,
+            Color::Red,
+            background,
+        );
     }
 
     // TODO: this is largely duplicating the `apply_colors` logic.
-    let (lhs_highlights, rhs_highlights) = highlight_positions(lhs_mps, rhs_mps);
+    let (lhs_highlights, rhs_highlights) = highlight_positions(background, lhs_mps, rhs_mps);
     let lhs_lines = split_on_newlines(lhs_src);
     let rhs_lines = split_on_newlines(rhs_src);
     let lhs_colored_lines = split_on_newlines(&lhs_colored_src);
@@ -262,7 +294,13 @@ pub fn display_hunks(
     let mut out_lines: Vec<String> = vec![];
 
     for (i, hunk) in hunks.iter().enumerate() {
-        out_lines.push(style::header(display_path, i + 1, hunks.len(), lang_name));
+        out_lines.push(style::header(
+            display_path,
+            i + 1,
+            hunks.len(),
+            lang_name,
+            background,
+        ));
 
         let aligned_lines = matched_lines_for_hunk(&matched_lines, hunk);
         let no_lhs_changes = hunk.lines.iter().all(|(l, _)| l.is_none());
@@ -288,6 +326,7 @@ pub fn display_hunks(
                 lhs_line_num,
                 rhs_line_num,
                 &widths,
+                background,
                 lhs_line_novel,
                 rhs_line_novel,
                 prev_lhs_line_num,
@@ -365,7 +404,11 @@ pub fn display_hunks(
                         );
                         if let Some(line_num) = lhs_line_num {
                             if lhs_lines_with_novel.contains(&line_num) {
-                                s = s.red().bold().to_string()
+                                s = match background {
+                                    BackgroundColor::Dark => s.bright_red(),
+                                    BackgroundColor::Light => s.red(),
+                                }
+                                .to_string();
                             }
                         }
                         s
@@ -380,7 +423,11 @@ pub fn display_hunks(
                         );
                         if let Some(line_num) = rhs_line_num {
                             if rhs_lines_with_novel.contains(&line_num) {
-                                s = s.green().bold().to_string();
+                                s = match background {
+                                    BackgroundColor::Dark => s.bright_green(),
+                                    BackgroundColor::Light => s.green(),
+                                }
+                                .to_string();
                             }
                         }
                         s
@@ -430,7 +477,13 @@ mod tests {
     #[test]
     fn test_display_single_column() {
         // Basic smoke test.
-        let res = display_single_column("foo.py", "Python", "print(123)\n", Color::Green);
+        let res = display_single_column(
+            "foo.py",
+            "Python",
+            "print(123)\n",
+            Color::Green,
+            BackgroundColor::Dark,
+        );
         assert!(res.len() > 10);
     }
 
@@ -493,6 +546,7 @@ mod tests {
         display_hunks(
             &hunks,
             80,
+            BackgroundColor::Dark,
             "foo.el",
             "Emacs Lisp",
             "foo",

src/style.rs

@@ -11,6 +11,12 @@ use std::{
     collections::HashMap,
 };
 
+#[derive(Clone, Copy, Debug)]
+pub enum BackgroundColor {
+    Dark,
+    Light,
+}
+
 #[derive(Clone, Copy, Debug)]
 pub struct Style {
     foreground: Option<Color>,
@@ -192,15 +198,35 @@ fn apply(s: &str, styles: &[(SingleLineSpan, Style)]) -> String {
     res
 }
 
-pub fn color_positions(is_lhs: bool, positions: &[MatchedPos]) -> Vec<(SingleLineSpan, Style)> {
+pub fn color_positions(
+    is_lhs: bool,
+    background: BackgroundColor,
+    positions: &[MatchedPos],
+) -> Vec<(SingleLineSpan, Style)> {
+    let red = match background {
+        BackgroundColor::Dark => Color::BrightRed,
+        BackgroundColor::Light => Color::Red,
+    };
+    let green = match background {
+        BackgroundColor::Dark => Color::BrightGreen,
+        BackgroundColor::Light => Color::Green,
+    };
+    let novel_color = if is_lhs { red } else { green };
+
     let mut styles = vec![];
     for pos in positions {
         let line_pos = pos.pos;
         let style = match pos.kind {
             MatchKind::Unchanged { highlight, .. } => Style {
                 foreground: match highlight {
-                    TokenKind::Atom(AtomKind::String) => Some(Color::Magenta),
-                    TokenKind::Atom(AtomKind::Comment) => Some(Color::Cyan),
+                    TokenKind::Atom(AtomKind::String) => Some(match background {
+                        BackgroundColor::Dark => Color::BrightMagenta,
+                        BackgroundColor::Light => Color::Magenta,
+                    }),
+                    TokenKind::Atom(AtomKind::Comment) => Some(match background {
+                        BackgroundColor::Dark => Color::BrightCyan,
+                        BackgroundColor::Light => Color::Cyan,
+                    }),
                     _ => None,
                 },
                 background: None,
@@ -212,7 +238,7 @@ pub fn color_positions(is_lhs: bool, positions: &[MatchedPos]) -> Vec<(SingleLin
                 dimmed: false,
             },
             MatchKind::Novel { highlight, .. } => Style {
-                foreground: Some(if is_lhs { Color::Red } else { Color::Green }),
+                foreground: Some(novel_color),
                 background: None,
                 bold: match highlight {
                     TokenKind::Delimiter => true,
@@ -223,13 +249,13 @@ pub fn color_positions(is_lhs: bool, positions: &[MatchedPos]) -> Vec<(SingleLin
                 dimmed: false,
             },
             MatchKind::ChangedCommentPart { .. } => Style {
-                foreground: Some(if is_lhs { Color::Red } else { Color::Green }),
+                foreground: Some(novel_color),
                 background: None,
                 bold: true,
                 dimmed: false,
             },
             MatchKind::UnchangedCommentPart { .. } => Style {
-                foreground: Some(if is_lhs { Color::Red } else { Color::Green }),
+                foreground: Some(novel_color),
                 background: None,
                 bold: false,
                 dimmed: false,
@@ -240,15 +266,30 @@ pub fn color_positions(is_lhs: bool, positions: &[MatchedPos]) -> Vec<(SingleLin
     styles
 }
 
-pub fn apply_colors(s: &str, is_lhs: bool, positions: &[MatchedPos]) -> String {
-    let styles = color_positions(is_lhs, positions);
+pub fn apply_colors(
+    s: &str,
+    is_lhs: bool,
+    background: BackgroundColor,
+    positions: &[MatchedPos],
+) -> String {
+    let styles = color_positions(is_lhs, background, positions);
     apply(s, &styles)
 }
 
-pub fn header(file_name: &str, hunk_num: usize, hunk_total: usize, language_name: &str) -> String {
+pub fn header(
+    file_name: &str,
+    hunk_num: usize,
+    hunk_total: usize,
+    language_name: &str,
+    background: BackgroundColor,
+) -> String {
     format!(
         "{} --- {}/{} --- {}",
-        file_name.yellow().bold(),
+        match background {
+            BackgroundColor::Dark => file_name.bright_yellow(),
+            BackgroundColor::Light => file_name.yellow(),
+        }
+        .bold(),
         hunk_num,
         hunk_total,
         language_name