Tidy up name suggestions

Breaks up the long, vertical method chain into some separate
definitions, and tweaks the field names in the related messages for
clarity.

Author: brendanzab

fathom/src/surface/elaboration.rs

@@ -1330,20 +1330,16 @@ impl<'arena> Context<'arena> {
                     return (core::Term::Prim(file_range.into(), prim), r#type.clone());
                 }
 
-                let candidates = self
-                    .local_env
-                    .names
-                    .iter()
-                    .flatten()
-                    .copied()
-                    .chain(self.item_env.names.iter().copied());
-                let suggestion = suggest_name(*name, candidates);
-
                 self.push_message(Message::UnboundName {
                     range: file_range,
                     name: *name,
-                    suggestion,
+                    suggested_name: {
+                        let item_names = self.item_env.names.iter().copied();
+                        let local_names = self.local_env.names.iter().flatten().copied();
+                        suggest_name(*name, item_names.chain(local_names))
+                    },
                 });
+
                 self.synth_reported_error(*range)
             }
             Term::Hole(_, name) => {
@@ -1660,7 +1656,7 @@ impl<'arena> Context<'arena> {
                         head_type: self.pretty_value(&head_type),
                         label_range: self.file_range(*label_range),
                         label: *proj_label,
-                        suggestion: suggest_name(*proj_label, labels.iter().map(|(_, l)| *l)),
+                        suggested_label: suggest_name(*proj_label, labels.iter().map(|(_, l)| *l)),
                     });
                     return self.synth_reported_error(*range);
                 }

fathom/src/surface/elaboration/reporting.rs

@@ -15,7 +15,7 @@ pub enum Message {
     UnboundName {
         range: FileRange,
         name: Symbol,
-        suggestion: Option<Symbol>,
+        suggested_name: Option<Symbol>,
     },
     RefutablePattern {
         pattern_range: FileRange,
@@ -47,7 +47,7 @@ pub enum Message {
         head_type: String,
         label_range: FileRange,
         label: Symbol,
-        suggestion: Option<Symbol>,
+        suggested_label: Option<Symbol>,
     },
     MismatchedFieldLabels {
         range: FileRange,
@@ -148,21 +148,16 @@ impl Message {
             Message::UnboundName {
                 range,
                 name,
-                suggestion,
+                suggested_name,
             } => {
                 let name = name.resolve();
 
-                let mut diagnostic = Diagnostic::error()
+                Diagnostic::error()
                     .with_message(format!("cannot find `{name}` in scope"))
-                    .with_labels(vec![primary_label(range).with_message("unbound name")]);
-
-                if let Some(suggestion) = suggestion {
-                    diagnostic = diagnostic.with_notes(vec![format!(
-                        "help: did you mean `{}`?",
-                        suggestion.resolve()
-                    )])
-                }
-                diagnostic
+                    .with_labels(vec![primary_label(range).with_message("unbound name")])
+                    .with_notes(suggested_name.map_or(Vec::new(), |name| {
+                        vec![format!("help: did you mean `{}`?", name.resolve())]
+                    }))
             }
             Message::RefutablePattern { pattern_range } => Diagnostic::error()
                 .with_message("refutable patterns found in binding")
@@ -219,24 +214,20 @@ impl Message {
                 head_type,
                 label_range,
                 label,
-                suggestion,
+                suggested_label,
             } => {
                 let label = label.resolve();
 
-                let mut diagnostic = Diagnostic::error()
+                Diagnostic::error()
                     .with_message(format!("cannot find `{label}` in expression"))
                     .with_labels(vec![
                         primary_label(label_range).with_message("unknown label"),
                         secondary_label(head_range)
                             .with_message(format!("expression of type {head_type}")),
-                    ]);
-                if let Some(suggestion) = suggestion {
-                    diagnostic = diagnostic.with_notes(vec![format!(
-                        "help: did you mean `{}`?",
-                        suggestion.resolve()
-                    )]);
-                }
-                diagnostic
+                    ])
+                    .with_notes(suggested_label.map_or(Vec::new(), |label| {
+                        vec![format!("help: did you mean `{}`?", label.resolve())]
+                    }))
             }
             Message::MismatchedFieldLabels {
                 range,