add line highlight

src/app.rs

@@ -64,6 +64,9 @@ pub struct Config<'a> {
 
     /// The syntax highlighting theme
     pub theme: String,
+
+    /// A line to highlight
+    pub highlight_line: Option<usize>,
 }
 
 fn is_truecolor_terminal() -> bool {
@@ -182,6 +185,7 @@ impl App {
                 .or_else(|| env::var("BAT_THEME").ok())
                 .unwrap_or(String::from(BAT_THEME_DEFAULT)),
             line_range: transpose(self.matches.value_of("line-range").map(LineRange::from))?,
+            highlight_line: self.matches.value_of("highlight-line").and_then(|w| w.parse().ok()),
             output_components,
         })
     }

src/clap_app.rs

@@ -141,6 +141,17 @@ pub fn build_app(interactive_output: bool) -> ClapApp<'static, 'static> {
                      '--line-range 40:' prints lines 40 to the end of the file",
                 ),
         )
+        .arg(
+            Arg::with_name("highlight-line")
+                .long("highlight-line")
+                .overrides_with("highlight-line")
+                .takes_value(true)
+                .value_name("n")
+                .help("Highlight a line.")
+                .long_help(
+                    "Highlight the nth line. The background color is changed to create contrast.",
+                ),
+        )
         .arg(
             Arg::with_name("color")
                 .long("color")

src/printer.rs

@@ -7,6 +7,7 @@ use ansi_term::Style;
 use console::AnsiCodeIterator;
 
 use syntect::easy::HighlightLines;
+use syntect::highlighting::Color;
 use syntect::highlighting::Theme;
 use syntect::parsing::SyntaxSet;
 
@@ -79,6 +80,7 @@ pub struct InteractivePrinter<'a> {
     pub line_changes: Option<LineChanges>,
     highlighter: Option<HighlightLines<'a>>,
     syntax_set: &'a SyntaxSet,
+    background_highlight: Option<Color>,
 }
 
 impl<'a> InteractivePrinter<'a> {
@@ -90,6 +92,8 @@ impl<'a> InteractivePrinter<'a> {
     ) -> Self {
         let theme = assets.get_theme(&config.theme);
 
+        let background_highlight = theme.settings.line_highlight;
+
         let colors = if config.colored_output {
             Colors::colored(theme, config.true_color)
         } else {
@@ -156,6 +160,7 @@ impl<'a> InteractivePrinter<'a> {
             line_changes,
             highlighter,
             syntax_set: &assets.syntax_set,
+            background_highlight,
         }
     }
 
@@ -296,6 +301,18 @@ impl<'a> Printer for InteractivePrinter<'a> {
             }
         }
 
+        // Line highlighting
+        let background = match self.config.highlight_line {
+            Some(line) => {
+                if line_number == line {
+                    self.background_highlight
+                } else {
+                    None
+                }
+             }
+            _ => None
+        };
+
         // Line contents.
         if self.config.output_wrap == OutputWrap::None {
             let true_color = self.config.true_color;
@@ -306,7 +323,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
                 write!(
                     handle,
                     "{}",
-                    as_terminal_escaped(style, &*text, true_color, colored_output,)
+                    as_terminal_escaped(style, &*text, true_color, colored_output, background)
                 )?;
             }
 
@@ -362,6 +379,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
                                             ),
                                             self.config.true_color,
                                             self.config.colored_output,
+                                            background
                                         )
                                     )?;
                                     break;
@@ -401,6 +419,7 @@ impl<'a> Printer for InteractivePrinter<'a> {
                                         ),
                                         self.config.true_color,
                                         self.config.colored_output,
+                                        background
                                     ),
                                     panel_wrap.clone().unwrap()
                                 )?;

src/terminal.rs

@@ -18,8 +18,9 @@ pub fn as_terminal_escaped(
     text: &str,
     true_color: bool,
     colored: bool,
+    background_color: Option<highlighting::Color>,
 ) -> String {
-    let style = if !colored {
+    let mut style = if !colored {
         Style::default()
     } else {
         let color = to_ansi_color(style.foreground, true_color);
@@ -35,5 +36,6 @@ pub fn as_terminal_escaped(
         }
     };
 
+    style.background = background_color.map(|c| to_ansi_color(c, true_color));
     style.paint(text).to_string()
 }