Improve some names.

Lots of vectors of messages called `message` or `msg`. This commit
pluralizes them.

Note that `emit_message_default` and `emit_messages_default` both
already existed, and both process a vector, so I renamed the former
`emit_messages_default_inner` because it's called by the latter.

compiler/rustc_errors/src/emitter.rs

@@ -350,7 +350,7 @@ pub trait Emitter: Translate {
 
                 children.push(SubDiagnostic {
                     level: Level::Note,
-                    message: vec![(DiagnosticMessage::from(msg), Style::NoStyle)],
+                    messages: vec![(DiagnosticMessage::from(msg), Style::NoStyle)],
                     span: MultiSpan::new(),
                     render_span: None,
                 });
@@ -533,7 +533,7 @@ impl Emitter for EmitterWriter {
 
         self.emit_messages_default(
             &diag.level,
-            &diag.message,
+            &diag.messages,
             &fluent_args,
             &diag.code,
             &primary_span,
@@ -1228,10 +1228,10 @@ impl EmitterWriter {
 
     /// Adds a left margin to every line but the first, given a padding length and the label being
     /// displayed, keeping the provided highlighting.
-    fn msg_to_buffer(
+    fn msgs_to_buffer(
         &self,
         buffer: &mut StyledBuffer,
-        msg: &[(DiagnosticMessage, Style)],
+        msgs: &[(DiagnosticMessage, Style)],
         args: &FluentArgs<'_>,
         padding: usize,
         label: &str,
@@ -1267,7 +1267,7 @@ impl EmitterWriter {
 
         // Provided the following diagnostic message:
         //
-        //     let msg = vec![
+        //     let msgs = vec![
         //       ("
         //       ("highlighted multiline\nstring to\nsee how it ", Style::NoStyle),
         //       ("looks", Style::Highlight),
@@ -1284,7 +1284,7 @@ impl EmitterWriter {
         //                see how it *looks* with
         //                very *weird* formats
         //                see?
-        for (text, style) in msg.iter() {
+        for (text, style) in msgs.iter() {
             let text = self.translate_message(text, args).map_err(Report::new).unwrap();
             let text = &normalize_whitespace(&text);
             let lines = text.split('\n').collect::<Vec<_>>();
@@ -1303,10 +1303,10 @@ impl EmitterWriter {
     }
 
     #[instrument(level = "trace", skip(self, args), ret)]
-    fn emit_message_default(
+    fn emit_messages_default_inner(
         &mut self,
         msp: &MultiSpan,
-        msg: &[(DiagnosticMessage, Style)],
+        msgs: &[(DiagnosticMessage, Style)],
         args: &FluentArgs<'_>,
         code: &Option<DiagnosticId>,
         level: &Level,
@@ -1327,7 +1327,7 @@ impl EmitterWriter {
                 buffer.append(0, level.to_str(), Style::MainHeaderMsg);
                 buffer.append(0, ": ", Style::NoStyle);
             }
-            self.msg_to_buffer(&mut buffer, msg, args, max_line_num_len, "note", None);
+            self.msgs_to_buffer(&mut buffer, msgs, args, max_line_num_len, "note", None);
         } else {
             let mut label_width = 0;
             // The failure note level itself does not provide any useful diagnostic information
@@ -1360,7 +1360,7 @@ impl EmitterWriter {
                 buffer.append(0, ": ", header_style);
                 label_width += 2;
             }
-            for (text, _) in msg.iter() {
+            for (text, _) in msgs.iter() {
                 let text = self.translate_message(text, args).map_err(Report::new).unwrap();
                 // Account for newlines to align output to its label.
                 for (line, text) in normalize_whitespace(&text).lines().enumerate() {
@@ -1747,7 +1747,7 @@ impl EmitterWriter {
         buffer.append(0, level.to_str(), Style::Level(*level));
         buffer.append(0, ": ", Style::HeaderMsg);
 
-        self.msg_to_buffer(
+        self.msgs_to_buffer(
             &mut buffer,
             &[(suggestion.msg.to_owned(), Style::NoStyle)],
             args,
@@ -2074,7 +2074,7 @@ impl EmitterWriter {
     fn emit_messages_default(
         &mut self,
         level: &Level,
-        message: &[(DiagnosticMessage, Style)],
+        messages: &[(DiagnosticMessage, Style)],
         args: &FluentArgs<'_>,
         code: &Option<DiagnosticId>,
         span: &MultiSpan,
@@ -2089,9 +2089,9 @@ impl EmitterWriter {
             num_decimal_digits(n)
         };
 
-        match self.emit_message_default(
+        match self.emit_messages_default_inner(
             span,
-            message,
+            messages,
             args,
             code,
             level,
@@ -2119,9 +2119,9 @@ impl EmitterWriter {
                 if !self.short_message {
                     for child in children {
                         let span = child.render_span.as_ref().unwrap_or(&child.span);
-                        if let Err(err) = self.emit_message_default(
+                        if let Err(err) = self.emit_messages_default_inner(
                             span,
-                            &child.message,
+                            &child.messages,
                             args,
                             &None,
                             &child.level,
@@ -2138,7 +2138,7 @@ impl EmitterWriter {
                                 // do not display this suggestion, it is meant only for tools
                             }
                             SuggestionStyle::HideCodeAlways => {
-                                if let Err(e) = self.emit_message_default(
+                                if let Err(e) = self.emit_messages_default_inner(
                                     &MultiSpan::new(),
                                     &[(sugg.msg.to_owned(), Style::HeaderMsg)],
                                     args,