Terminal escape sequence constants (#2461)

README.md

@@ -1877,6 +1877,30 @@ A number of constants are predefined:
 | `HEX`<sup>1.27.0</sup> | `"0123456789abcdef"` |
 | `HEXLOWER`<sup>1.27.0</sup> | `"0123456789abcdef"` |
 | `HEXUPPER`<sup>1.27.0</sup> | `"0123456789ABCDEF"` |
+| `CLEAR`<sup>master</sup> | `"\ec"` |
+| `NORMAL`<sup>master</sup> | `"\e[0m"` |
+| `BOLD`<sup>master</sup> | `"\e[1m"` |
+| `ITALIC`<sup>master</sup> | `"\e[3m"` |
+| `UNDERLINE`<sup>master</sup> | `"\e[4m"` |
+| `INVERT`<sup>master</sup> | `"\e[7m"` |
+| `HIDE`<sup>master</sup> | `"\e[8m"` |
+| `STRIKETHROUGH`<sup>master</sup> | `"\e[9m"` |
+| `BLACK`<sup>master</sup> | `"\e[30m"` |
+| `RED`<sup>master</sup> | `"\e[31m"` |
+| `GREEN`<sup>master</sup> | `"\e[32m"` |
+| `YELLOW`<sup>master</sup> | `"\e[33m"` |
+| `BLUE`<sup>master</sup> | `"\e[34m"` |
+| `MAGENTA`<sup>master</sup> | `"\e[35m"` |
+| `CYAN`<sup>master</sup> | `"\e[36m"` |
+| `WHITE`<sup>master</sup> | `"\e[37m"` |
+| `BG_BLACK`<sup>master</sup> | `"\e[40m"` |
+| `BG_RED`<sup>master</sup> | `"\e[41m"` |
+| `BG_GREEN`<sup>master</sup> | `"\e[42m"` |
+| `BG_YELLOW`<sup>master</sup> | `"\e[43m"` |
+| `BG_BLUE`<sup>master</sup> | `"\e[44m"` |
+| `BG_MAGENTA`<sup>master</sup> | `"\e[45m"` |
+| `BG_CYAN`<sup>master</sup> | `"\e[46m"` |
+| `BG_WHITE`<sup>master</sup> | `"\e[47m"` |
 
 ```just
 @foo:
@@ -1888,9 +1912,29 @@ $ just foo
 0123456789abcdef
 ```
 
+Constants starting with `\e` are
+[ANSI escape sequences](https://en.wikipedia.org/wiki/ANSI_escape_code).
+
+`CLEAR` clears the screen, similar to the `clear` command. The rest are of the
+form `\e[Nm`, where `N` is an integer, and set terminal display attributes.
+
+Terminal display attribute escape sequences can be combined, for example text
+weight `BOLD`, text style `STRIKETHROUGH`, foreground color `CYAN`, and
+background color `BG_BLUE`. They should be followed by `NORMAL`, to reset the
+terminal back to normal.
+
+Escape sequences should be quoted, since `[` is treated as a special character
+by some shells.
+
+```just
+@foo:
+  echo '{{BOLD + STRIKETHROUGH + CYAN + BG_BLUE}}Hi!{{NORMAL}}'
+```
+
 ### Attributes
 
-Recipes, `mod` statements, and aliases may be annotated with attributes that change their behavior.
+Recipes, `mod` statements, and aliases may be annotated with attributes that
+change their behavior.
 
 | Name | Type | Description |
 |------|------|-------------|

justfile

@@ -169,6 +169,10 @@ build-book:
   mdbook build book/en
   mdbook build book/zh
 
+[group: 'dev']
+print-readme-constants-table:
+  cargo test constants::tests::readme_table -- --nocapture
+
 # run all polyglot recipes
 [group: 'demo']
 polyglot: _python _js _perl _sh _ruby

src/constants.rs

@@ -1,15 +1,58 @@
 use super::*;
 
+const CONSTANTS: [(&str, &str, &str); 27] = [
+  ("HEX", "0123456789abcdef", "1.27.0"),
+  ("HEXLOWER", "0123456789abcdef", "1.27.0"),
+  ("HEXUPPER", "0123456789ABCDEF", "1.27.0"),
+  ("CLEAR", "\x1bc", "master"),
+  ("NORMAL", "\x1b[0m", "master"),
+  ("BOLD", "\x1b[1m", "master"),
+  ("ITALIC", "\x1b[3m", "master"),
+  ("UNDERLINE", "\x1b[4m", "master"),
+  ("INVERT", "\x1b[7m", "master"),
+  ("HIDE", "\x1b[8m", "master"),
+  ("STRIKETHROUGH", "\x1b[9m", "master"),
+  ("BLACK", "\x1b[30m", "master"),
+  ("RED", "\x1b[31m", "master"),
+  ("GREEN", "\x1b[32m", "master"),
+  ("YELLOW", "\x1b[33m", "master"),
+  ("BLUE", "\x1b[34m", "master"),
+  ("MAGENTA", "\x1b[35m", "master"),
+  ("CYAN", "\x1b[36m", "master"),
+  ("WHITE", "\x1b[37m", "master"),
+  ("BG_BLACK", "\x1b[40m", "master"),
+  ("BG_RED", "\x1b[41m", "master"),
+  ("BG_GREEN", "\x1b[42m", "master"),
+  ("BG_YELLOW", "\x1b[43m", "master"),
+  ("BG_BLUE", "\x1b[44m", "master"),
+  ("BG_MAGENTA", "\x1b[45m", "master"),
+  ("BG_CYAN", "\x1b[46m", "master"),
+  ("BG_WHITE", "\x1b[47m", "master"),
+];
+
 pub(crate) fn constants() -> &'static HashMap<&'static str, &'static str> {
-  static CONSTANTS: OnceLock<HashMap<&str, &str>> = OnceLock::new();
-
-  CONSTANTS.get_or_init(|| {
-    vec![
-      ("HEX", "0123456789abcdef"),
-      ("HEXLOWER", "0123456789abcdef"),
-      ("HEXUPPER", "0123456789ABCDEF"),
-    ]
-    .into_iter()
-    .collect()
+  static MAP: OnceLock<HashMap<&str, &str>> = OnceLock::new();
+  MAP.get_or_init(|| {
+    CONSTANTS
+      .into_iter()
+      .map(|(name, value, _version)| (name, value))
+      .collect()
   })
 }
+
+#[cfg(test)]
+mod tests {
+  use super::*;
+
+  #[test]
+  fn readme_table() {
+    println!("| Name | Value |");
+    println!("|------|-------------|");
+    for (name, value, version) in CONSTANTS {
+      println!(
+        "| `{name}`<sup>{version}</sup> | `\"{}\"` |",
+        value.replace('\x1b', "\\e")
+      );
+    }
+  }
+}