rhg: Colored output is not supported

rhg: Colored output is not supported

Fallback if it is requested explicitly.

The default is documented as use color "whenever it seems possible".
rhg proceeds without color in that case.

Differential Revision: https://phab.mercurial-scm.org/D11762

--- a/rust/rhg/src/main.rs	Tue Nov 09 19:09:57 2021 +0100
+++ b/rust/rhg/src/main.rs	Tue Nov 09 19:28:13 2021 +0100
@@ -28,7 +28,7 @@
     repo: Result<&Repo, &NoRepoInCwdError>,
     config: &Config,
 ) -> Result<(), CommandError> {
-    check_unsupported(config)?;
+    check_unsupported(config, ui)?;
 
     let app = App::new("rhg")
         .global_setting(AppSettings::AllowInvalidUtf8)
@@ -617,7 +617,10 @@
     }
 }
 
-fn check_unsupported(config: &Config) -> Result<(), CommandError> {
+fn check_unsupported(
+    config: &Config,
+    ui: &ui::Ui,
+) -> Result<(), CommandError> {
     check_extensions(config)?;
 
     if std::env::var_os("HG_PENDING").is_some() {
@@ -634,5 +637,11 @@
         Err(CommandError::unsupported("[decode] config"))?
     }
 
+    if let Some(color) = config.get(b"ui", b"color") {
+        if (color == b"always" || color == b"debug") && !ui.plain() {
+            Err(CommandError::unsupported("colored output"))?
+        }
+    }
+
     Ok(())
 }

--- a/tests/test-status-color.t	Tue Nov 09 19:09:57 2021 +0100
+++ b/tests/test-status-color.t	Tue Nov 09 19:28:13 2021 +0100
@@ -1,7 +1,3 @@
-TODO: fix rhg bugs that make this test fail when status is enabled
-  $ unset RHG_STATUS
-
-
   $ cat <<EOF >> $HGRCPATH
   > [ui]
   > color = always