Auto merge of #78548 - camelid:driver-tty, r=oli-obk

driver: Only output ANSI logging if connected to a terminal

Fixes #78435.

See #78435 for more.

Cc `@RalfJung` `@oli-obk`

compiler/rustc_driver/src/lib.rs

@@ -1284,11 +1284,30 @@ pub fn init_env_logger(env: &str) {
         Ok(s) if s.is_empty() => return,
         Ok(_) => {}
     }
+    let color_logs = match std::env::var(String::from(env) + "_COLOR") {
+        Ok(value) => match value.as_ref() {
+            "always" => true,
+            "never" => false,
+            "auto" => stdout_isatty(),
+            _ => early_error(
+                ErrorOutputType::default(),
+                &format!(
+                    "invalid log color value '{}': expected one of always, never, or auto",
+                    value
+                ),
+            ),
+        },
+        Err(std::env::VarError::NotPresent) => stdout_isatty(),
+        Err(std::env::VarError::NotUnicode(_value)) => early_error(
+            ErrorOutputType::default(),
+            "non-Unicode log color value: expected one of always, never, or auto",
+        ),
+    };
     let filter = tracing_subscriber::EnvFilter::from_env(env);
     let layer = tracing_tree::HierarchicalLayer::default()
         .with_writer(io::stderr)
         .with_indent_lines(true)
-        .with_ansi(true)
+        .with_ansi(color_logs)
         .with_targets(true)
         .with_wraparound(10)
         .with_verbose_exit(true)
@@ -1314,7 +1333,7 @@ pub fn main() -> ! {
                 arg.into_string().unwrap_or_else(|arg| {
                     early_error(
                         ErrorOutputType::default(),
-                        &format!("Argument {} is not valid Unicode: {:?}", i, arg),
+                        &format!("argument {} is not valid Unicode: {:?}", i, arg),
                     )
                 })
             })