Inline and remove HumanReadableErrorType::new_emitter.

And likewise with `ColorConfig::suggests_using_colors`. They both have a
single call site. And note that `BufWriter::supports_color()` always
returns false, which enables a small bit of constant folding along the
way.

compiler/rustc_errors/src/emitter.rs

@@ -35,7 +35,7 @@ use std::io::prelude::*;
 use std::io::{self, IsTerminal};
 use std::iter;
 use std::path::Path;
-use termcolor::{Ansi, Buffer, BufferWriter, ColorChoice, ColorSpec, StandardStream};
+use termcolor::{Buffer, BufferWriter, ColorChoice, ColorSpec, StandardStream};
 use termcolor::{Color, WriteColor};
 
 /// Default column width, used in tests and when terminal dimensions cannot be determined.
@@ -58,18 +58,6 @@ impl HumanReadableErrorType {
             HumanReadableErrorType::AnnotateSnippet(cc) => (false, cc),
         }
     }
-    pub fn new_emitter(
-        self,
-        mut dst: Destination,
-        fallback_bundle: LazyFallbackBundle,
-    ) -> HumanEmitter {
-        let (short, color_config) = self.unzip();
-        let color = color_config.suggests_using_colors();
-        if !dst.supports_color() && color {
-            dst = Box::new(Ansi::new(dst));
-        }
-        HumanEmitter::new(dst, fallback_bundle).short_message(short)
-    }
 }
 
 #[derive(Clone, Copy, Debug)]
@@ -628,12 +616,6 @@ impl ColorConfig {
             ColorConfig::Auto => ColorChoice::Never,
         }
     }
-    fn suggests_using_colors(self) -> bool {
-        match self {
-            ColorConfig::Always | ColorConfig::Auto => true,
-            ColorConfig::Never => false,
-        }
-    }
 }
 
 /// Handles the writing of `HumanReadableErrorType::Default` and `HumanReadableErrorType::Short`

compiler/rustc_errors/src/json.rs

@@ -12,7 +12,10 @@
 use rustc_span::source_map::{FilePathMapping, SourceMap};
 use termcolor::{ColorSpec, WriteColor};
 
-use crate::emitter::{should_show_source_code, Emitter, HumanReadableErrorType};
+use crate::emitter::{
+    should_show_source_code, ColorConfig, Destination, Emitter, HumanEmitter,
+    HumanReadableErrorType,
+};
 use crate::registry::Registry;
 use crate::translation::{to_fluent_args, Translate};
 use crate::{
@@ -405,8 +408,17 @@ impl Diagnostic {
             .collect();
 
         let buf = BufWriter::default();
-        je.json_rendered
-            .new_emitter(Box::new(buf.clone()), je.fallback_bundle.clone())
+        let mut dst: Destination = Box::new(buf.clone());
+        let (short, color_config) = je.json_rendered.unzip();
+        let color = match color_config {
+            ColorConfig::Always | ColorConfig::Auto => true,
+            ColorConfig::Never => false,
+        };
+        if color {
+            dst = Box::new(termcolor::Ansi::new(dst));
+        }
+        HumanEmitter::new(dst, je.fallback_bundle.clone())
+            .short_message(short)
             .sm(Some(je.sm.clone()))
             .fluent_bundle(je.fluent_bundle.clone())
             .diagnostic_width(je.diagnostic_width)

compiler/rustc_errors/src/json/tests.rs

@@ -1,6 +1,5 @@
 use super::*;
 
-use crate::emitter::ColorConfig;
 use crate::DiagCtxt;
 use rustc_span::BytePos;