Add a --color flag (#3060)

Co-authored-by: Laurenz <laurmaedje@gmail.com>

crates/typst-cli/src/args.rs

@@ -2,7 +2,7 @@ use std::fmt::{self, Display, Formatter};
 use std::path::PathBuf;
 
 use clap::builder::ValueParser;
-use clap::{ArgAction, Args, Parser, Subcommand, ValueEnum};
+use clap::{ArgAction, Args, ColorChoice, Parser, Subcommand, ValueEnum};
 use semver::Version;
 
 /// The character typically used to separate path components
@@ -17,6 +17,18 @@ pub struct CliArguments {
     #[command(subcommand)]
     pub command: Command,
 
+    /// Set when to use color.
+    /// auto = use color if a capable terminal is detected
+    #[clap(
+        long,
+        value_name = "WHEN",
+        require_equals = true,
+        num_args = 0..=1,
+        default_value = "auto",
+        default_missing_value = "always",
+    )]
+    pub color: ColorChoice,
+
     /// Path to a custom CA certificate to use when making network requests.
     #[clap(long = "cert", env = "TYPST_CERT")]
     pub cert: Option<PathBuf>,

crates/typst-cli/src/main.rs

@@ -68,10 +68,16 @@ fn print_error(msg: &str) -> io::Result<()> {
 
 /// Get stderr with color support if desirable.
 fn color_stream() -> termcolor::StandardStream {
-    termcolor::StandardStream::stderr(if std::io::stderr().is_terminal() {
-        ColorChoice::Auto
-    } else {
-        ColorChoice::Never
+    termcolor::StandardStream::stderr(match ARGS.color {
+        clap::ColorChoice::Auto => {
+            if std::io::stderr().is_terminal() {
+                ColorChoice::Auto
+            } else {
+                ColorChoice::Never
+            }
+        }
+        clap::ColorChoice::Always => ColorChoice::Always,
+        clap::ColorChoice::Never => ColorChoice::Never,
     })
 }