feat(ui): respect NO_COLOR environment variable (#804)

* feat(ui) Respect NO_COLOR environment variable

* Add NO_COLOR to man and readme

* chore: generate completions & manpage

* Really update manpage this time

* Add `enpty` color scheme to readme

* Rename "empty" color theme to "none"

This seems a better wording for what this theme is. However, empty is
still supported for backwards compatibility (though not mentioned in
readme and manpage, but it wasn't mentioned before anyway)
Since `ColorTheme::empty` is private, I felt it's okay to rename too to
follow suite.

* Add details to related readme paragraph

---------

Co-authored-by: Skim bot <skim-bot@skim-rs.github.io>
Co-authored-by: LoricAndre <57358788+LoricAndre@users.noreply.github.com>

README.md

@@ -319,6 +319,8 @@ limited to the default appearance - Skim supports comprehensive customization of
 --color=[BASE_SCHEME][,COLOR:ANSI]
 ```
 
+Skim also respects the `NO_COLOR` environment variable. Set it to anything and `sk` (and many other terminal apps) will disable all colored output. See [no-color.org](https://no-color.org/) for more details.
+
 ### Available Base Color Schemes
 
 Skim comes with several built-in color schemes that you can use as a starting point:
@@ -328,6 +330,7 @@ sk --color=dark      # Default dark theme (256 colors)
 sk --color=light     # Light theme (256 colors)
 sk --color=16        # Simple 16-color theme
 sk --color=bw        # Minimal black & white theme (no colors, just styles)
+sk --color=none      # Minimal black & white theme (no colors, no styles)
 sk --color=molokai   # Molokai-inspired theme (256 colors)
 ```
 

man/man1/sk.1

@@ -12,6 +12,10 @@ sk is a general purpose command\-line fuzzy finder.
 .PP
 ENVIRONMENT VARIABLES
 .PP
+NO_COLOR
+.PP
+If set and not empty, sk will not use any colors in the output.
+.PP
 SKIM_DEFAULT_COMMAND
 .PP
 Default command to use when input is tty. On *nix systems, sk runs the command with sh \-c, so make  sure  that it\*(Aqs POSIX\-compliant.
@@ -426,6 +430,7 @@ Base Color Schemes
 \- light: 256\-color light theme
 \- 16: Basic 16\-color theme
 \- bw: Minimal black & white theme (no colors, just styles)
+\- none: Minimal black & white theme (no colors, no styles). Default when NO_COLOR is set
 \- molokai: Molokai\-inspired 256\-color theme
 
 Color Customization

skim/src/options.rs

@@ -19,6 +19,10 @@ use crate::{CaseMatching, FuzzyAlgorithm, Selector};
 ///
 /// # ENVIRONMENT VARIABLES
 ///
+/// ## NO_COLOR
+///
+/// If set and not empty, sk will not use any colors in the output.
+///
 /// ## SKIM_DEFAULT_COMMAND
 ///
 /// Default command to use when input is tty. On *nix systems, sk runs the command with sh -c, so make  sure  that
@@ -468,6 +472,7 @@ pub struct SkimOptions {
     /// - **light**: 256-color light theme
     /// - **16**: Basic 16-color theme
     /// - **bw**: Minimal black & white theme (no colors, just styles)
+    /// - **none**: Minimal black & white theme (no colors, no styles). Default when NO_COLOR is set
     /// - **molokai**: Molokai-inspired 256-color theme
     ///
     /// ### Color Customization

skim/src/theme.rs

@@ -1,5 +1,5 @@
 //! Handle the color theme
-use std::sync::LazyLock;
+use std::{env, sync::LazyLock};
 
 use crate::options::SkimOptions;
 use skim_tuikit::prelude::*;
@@ -52,11 +52,14 @@ impl ColorTheme {
         if let Some(color) = options.color.clone() {
             ColorTheme::from_options(&color)
         } else {
-            ColorTheme::dark256()
+            match env::var_os("NO_COLOR") {
+                Some(no_color) if !no_color.is_empty() => ColorTheme::none(),
+                _ => ColorTheme::dark256(),
+            }
         }
     }
 
-    fn empty() -> Self {
+    fn none() -> Self {
         ColorTheme {
             fg:                   Color::Default,
             bg:                   Color::Default,
@@ -88,7 +91,7 @@ impl ColorTheme {
             matched_effect:       Effect::UNDERLINE,
             current_effect:       Effect::REVERSE,
             current_match_effect: Effect::UNDERLINE | Effect::REVERSE,
-            ..ColorTheme::empty()
+            ..ColorTheme::none()
         }
     }
 
@@ -107,7 +110,7 @@ impl ColorTheme {
             selected:         Color::MAGENTA,
             header:           Color::CYAN,
             border:           Color::LIGHT_BLACK,
-            ..ColorTheme::empty()
+            ..ColorTheme::none()
         }
     }
 
@@ -126,7 +129,7 @@ impl ColorTheme {
             selected:         Color::AnsiValue(168),
             header:           Color::AnsiValue(109),
             border:           Color::AnsiValue(59),
-            ..ColorTheme::empty()
+            ..ColorTheme::none()
         }
     }
 
@@ -145,7 +148,7 @@ impl ColorTheme {
             selected:         Color::AnsiValue(168),
             header:           Color::AnsiValue(109),
             border:           Color::AnsiValue(59),
-            ..ColorTheme::empty()
+            ..ColorTheme::none()
         }
     }
 
@@ -164,7 +167,7 @@ impl ColorTheme {
             selected:         Color::AnsiValue(168),
             header:           Color::AnsiValue(31),
             border:           Color::AnsiValue(145),
-            ..ColorTheme::empty()
+            ..ColorTheme::none()
         }
     }
 
@@ -179,7 +182,7 @@ impl ColorTheme {
                     "light"    => ColorTheme::light256(),
                     "16"       => ColorTheme::default16(),
                     "bw"       => ColorTheme::bw(),
-                    "empty"    => ColorTheme::empty(),
+                    "none" | "empty"    => ColorTheme::none(),
                     "dark" | "default" | _ => ColorTheme::dark256(),
                 };
                 continue;