Underline highlighted lines in ANSI theme (#1985)

* Underline highlighted lines in ANSI theme

* add test for ansi highlight underline, fix underscore in plain

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Features
 
 - New style component `header-filesize` to show size of the displayed file in the header. See #1988 (@mdibaiee)
+- Use underline for line highlighting on ANSI, see #1730 (@mdibaiee)
 
 ## Bugfixes
 

src/printer.rs

@@ -463,6 +463,10 @@ impl<'a> Printer for InteractivePrinter<'a> {
         let highlight_this_line =
             self.config.highlighted_lines.0.check(line_number) == RangeCheckResult::InRange;
 
+        if highlight_this_line && self.config.theme == "ansi" {
+            self.ansi_style.update("^[4m");
+        }
+
         let background_color = self
             .background_color_highlight
             .filter(|_| highlight_this_line);
@@ -649,6 +653,11 @@ impl<'a> Printer for InteractivePrinter<'a> {
             writeln!(handle)?;
         }
 
+        if highlight_this_line && self.config.theme == "ansi" {
+            self.ansi_style.update("^[24m");
+            write!(handle, "\x1B[24m")?;
+        }
+
         Ok(())
     }
 }

tests/integration_tests.rs

@@ -1290,6 +1290,25 @@ fn grid_for_file_without_newline() {
         .stderr("");
 }
 
+// For ANSI theme, use underscore as a highlighter
+#[test]
+fn ansi_highlight_underline() {
+    bat()
+        .arg("--paging=never")
+        .arg("--color=never")
+        .arg("--terminal-width=80")
+        .arg("--wrap=never")
+        .arg("--decorations=always")
+        .arg("--theme=ansi")
+        .arg("--style=plain")
+        .arg("--highlight-line=1")
+        .write_stdin("Ansi Underscore Test\nAnother Line")
+        .assert()
+        .success()
+        .stdout("\x1B[4mAnsi Underscore Test\n\x1B[24mAnother Line")
+        .stderr("");
+}
+
 // Ensure that ANSI passthrough is emitted properly for both wrapping and non-wrapping printer.
 #[test]
 fn ansi_passthrough_emit() {