Update behavior of --show-themes to rely on the computed is_light_mode

value to determine whether to show light or dark themes by default

2 files changed, 11 insertions, 8 deletions

diff --git a/src/cli.rs b/src/cli.rs
index 60a4d5a7..e90c26d7 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -201,13 +201,11 @@ https://github.com/dandavison/delta/issues.
 pub struct Opt {
     /// Use default colors appropriate for a light terminal background. For more control, see the
     /// style options and --syntax-theme.
-    /// When passed in with --show-themes, only light themes will be displayed.
     #[structopt(long = "light")]
     pub light: bool,
 
     /// Use default colors appropriate for a dark terminal background. For more control, see the
     /// style options and --syntax-theme.
-    /// When passed in with --show-themes, only dark themes will be displayed.
     #[structopt(long = "dark")]
     pub dark: bool,
 
@@ -271,11 +269,13 @@ pub struct Opt {
     #[structopt(long = "show-syntax-themes")]
     pub show_syntax_themes: bool,
 
-    /// Show all available delta themes, each with an example of highlighted diff output.
+    /// Show available delta themes with an example of highlighted diff output.
     /// If diff output is supplied on standard input then this will be used for the demo. For
     /// example: `git show --color=always | delta --show-themes`.
-    /// When used with the --dark or --light command line arguments, will only show dark or
-    /// light themes, respectively.
+    /// By default, if delta is configured to use a light theme (as set by the user or inferred by the
+    /// BAT_THEME), only displays light themes, otherwise will only display dark themes, unless the
+    /// --dark or --light command line arguments are included.
+    /// If both --dark and --light command line arguments are included, will display all themes.
     #[structopt(long = "show-themes")]
     pub show_themes: bool,
 
diff --git a/src/main.rs b/src/main.rs
index dcc6ed48..c99fb464 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -68,7 +68,7 @@ fn run_app() -> std::io::Result<i32> {
         show_syntax_themes()?;
         return Ok(0);
     } else if opt.show_themes {
-        show_themes(opt.dark, opt.light)?;
+        show_themes(opt.dark, opt.light, opt.computed.is_light_mode)?;
         return Ok(0);
     }
 
@@ -312,7 +312,7 @@ where
     }
 }
 
-fn show_themes(dark: bool, light: bool) -> std::io::Result<()> {
+fn show_themes(dark: bool, light: bool, computed_theme_is_light: bool) -> std::io::Result<()> {
     use bytelines::ByteLines;
     use sample_diff::DIFF;
     use std::io::BufReader;
@@ -343,7 +343,10 @@ fn show_themes(dark: bool, light: bool) -> std::io::Result<()> {
         let is_light_theme = opt.light;
         let config = config::Config::from(opt);
 
-        if (dark && is_dark_theme) || (light && is_light_theme) || (!dark && !light) {
+        if (!computed_theme_is_light && is_dark_theme)
+            || (computed_theme_is_light && is_light_theme)
+            || (dark && light)
+        {
             writeln!(writer, "\n\nTheme: {}\n", title_style.paint(theme))?;
 
             if let Err(error) = delta(ByteLines::new(BufReader::new(&input[0..])), writer, &config)