fix color preference parsing from env

lib/std/zig.zig

@@ -2,6 +2,9 @@
 //! source lives here. These APIs are provided as-is and have absolutely no API
 //! guarantees whatsoever.
 
+const builtin = @import("builtin");
+const native_os = builtin.os.tag;
+
 pub const ErrorBundle = @import("zig/ErrorBundle.zig");
 pub const Server = @import("zig/Server.zig");
 pub const Client = @import("zig/Client.zig");
@@ -45,6 +48,20 @@ pub const Color = enum {
     /// Assume stderr is a terminal.
     on,
 
+    pub fn getEnv(arena: std.mem.Allocator) !Color {
+        // Disable color on WASI per https://github.com/WebAssembly/WASI/issues/162
+        if (native_os == .wasi) return .off;
+        // https://no-color.org/
+        // Command-line software which adds ANSI color to its output by default should check for
+        // a NO_COLOR environment variable that, when present and not an empty string (regardless
+        // of its value), prevents the addition of ANSI color.
+        if (try EnvVar.NO_COLOR.get(arena)) |no_color| {
+            if (no_color.len != 0) return .off;
+        }
+        // There is no specification for CLICOLOR_FORCE, so we will just check if it is set.
+        return if (EnvVar.CLICOLOR_FORCE.isSet()) .on else .auto;
+    }
+
     pub fn get_tty_conf(color: Color) std.io.tty.Config {
         return switch (color) {
             .auto => std.io.tty.detectConfig(std.io.getStdErr()),

src/main.zig

@@ -992,16 +992,9 @@ fn buildOutputType(
     };
     defer create_module.link_inputs.deinit(gpa);
 
-    // before arg parsing, check for the NO_COLOR and CLICOLOR_FORCE environment variables
-    // if set, default the color setting to .off or .on, respectively
-    // explicit --color arguments will still override this setting.
-    // Disable color on WASI per https://github.com/WebAssembly/WASI/issues/162
-    var color: Color = if (native_os == .wasi or EnvVar.NO_COLOR.isSet())
-        .off
-    else if (EnvVar.CLICOLOR_FORCE.isSet())
-        .on
-    else
-        .auto;
+    // Detect color preferences using environment variables.
+    // Explicit --color arguments will still override this setting.
+    var color: Color = try .getEnv(arena);
     var n_jobs: ?u32 = null;
 
     switch (arg_mode) {