Do not render ascii colors to buffers

Author: oli-obk

src/librustc/session/mod.rs

@@ -1050,8 +1050,8 @@ fn default_emitter(
                     dst,
                     Some(source_map.clone()),
                     short,
-                    false,
-                    color_config.suggests_using_colors(),
+                    false, // no teach messages when writing to a buffer
+                    false, // no colors when writing to a buffer
                 ),
             };
             Box::new(emitter.ui_testing(sopts.debugging_opts.ui_testing))

src/librustc_errors/emitter.rs

@@ -146,7 +146,7 @@ impl ColorConfig {
             ColorConfig::Auto => ColorChoice::Never,
         }
     }
-    pub fn suggests_using_colors(self) -> bool {
+    fn suggests_using_colors(self) -> bool {
         match self {
             | ColorConfig::Always
             | ColorConfig::Auto