librustc_errors: Add some more documentation

src/librustc/session/config.rs

@@ -227,13 +227,17 @@ impl OutputType {
     }
 }
 
+/// The type of diagnostics output to generate
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum ErrorOutputType {
+    /// Output meant for the consumption of humans.
     HumanReadable(HumanReadableErrorType),
+    /// Output that's consumed by other tools such as `rustfix` or the `RLS`.
     Json {
-        /// Render the json in a human readable way (with indents and newlines)
+        /// Render the JSON in a human readable way (with indents and newlines)
         pretty: bool,
-        /// The way the `rendered` field is created
+        /// The JSON output includes a `rendered` field that includes the rendered
+        /// human output.
         json_rendered: HumanReadableErrorType,
     },
 }

src/librustc_errors/diagnostic_builder.rs

@@ -348,7 +348,7 @@ impl<'a> DiagnosticBuilder<'a> {
 
     /// Convenience function for internal use, clients should use one of the
     /// struct_* methods on Handler.
-    pub fn new_with_code(handler: &'a Handler,
+    pub(crate) fn new_with_code(handler: &'a Handler,
                          level: Level,
                          code: Option<DiagnosticId>,
                          message: &str)

src/librustc_errors/emitter.rs

@@ -1,3 +1,12 @@
+//! The current rustc diagnostics emitter.
+//!
+//! An `Emitter` takes care of generating the output from a `DiagnosticBuilder` struct.
+//!
+//! There are various `Emitter` implementations that generate different output formats such as
+//! JSON and human readable output.
+//!
+//! The output types are defined in `librustc::session::config::ErrorOutputType`.
+
 use Destination::*;
 
 use syntax_pos::{SourceFile, Span, MultiSpan};

src/librustc_errors/lib.rs

@@ -1,3 +1,7 @@
+//! Diagnostics creation and emission for rustc
+//!
+//! This module contains the code for creating and emitting diagnostics.
+
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![allow(unused_attributes)]