rustdoc: Properly detect syntactically invalid doctests (to fix a regression)

compiler/rustc_attr_parsing/src/attributes/mod.rs

@@ -232,7 +232,7 @@ pub(crate) enum AttributeOrder {
  ///
  /// Attributes are processed from bottom to top, so this raises a warning/error on all the attributes
  /// further above the lowest one:
- /// ```
+ /// ```ignore (illustrative)
  /// #[stable(since="1.0")] //~ WARNING duplicated attribute
  /// #[stable(since="2.0")]
  /// ```
@@ -243,7 +243,7 @@ pub(crate) enum AttributeOrder {
  ///
  /// Attributes are processed from bottom to top, so this raises a warning/error on all the attributes
  /// below the highest one:
- /// ```
+ /// ```ignore (illustrative)
  /// #[path="foo.rs"]
  /// #[path="bar.rs"] //~ WARNING duplicated attribute
  /// ```

compiler/rustc_errors/src/emitter.rs

@@ -205,11 +205,6 @@ pub trait Emitter {
  true
  }
 
- /// Checks if we can use colors in the current output stream.
- fn supports_color(&self) -> bool {
- false
- }
-
  fn source_map(&self) -> Option<&SourceMap>;
 
  fn translator(&self) -> &Translator;