Suggest a similar name when reporting UnboundName or UnknownField

Co-authored-by: Brendan Zabarauskas <[email protected]>

Author: Kmeakin

Cargo.lock

@@ -24,6 +24,7 @@ codespan-reporting = "0.11.1"
 fxhash = "0.2"
 itertools = "0.10"
 lalrpop-util = "0.19.5"
+levenshtein = "1.0.5"
 logos = "0.12"
 pretty = "0.11.2"
 rpds = "0.12.0"

fathom/Cargo.toml

@@ -286,6 +286,18 @@ pub struct Context<'interner, 'arena> {
     messages: Vec<Message>,
 }
 
+fn suggest_name(
+    interner: &StringInterner,
+    name: StringId,
+    candidates: impl Iterator<Item = StringId>,
+) -> Option<StringId> {
+    let name = interner.resolve(name).unwrap();
+    candidates.min_by_key(|candidate| {
+        let candidate = interner.resolve(*candidate).unwrap();
+        levenshtein::levenshtein(name, candidate)
+    })
+}
+
 impl<'interner, 'arena> Context<'interner, 'arena> {
     /// Construct a new elaboration context, backed by the supplied arena.
     pub fn new(
@@ -1338,9 +1350,19 @@ impl<'interner, 'arena> Context<'interner, '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(&self.interner.borrow(), *name, candidates);
+
                 self.push_message(Message::UnboundName {
                     range: file_range,
                     name: *name,
+                    suggestion,
                 });
                 self.synth_reported_error(*range)
             }
@@ -1654,11 +1676,17 @@ impl<'interner, 'arena> Context<'interner, 'arena> {
                     }
 
                     let head_type = self.pretty_print_value(&head_type);
+                    let suggestion = suggest_name(
+                        &self.interner.borrow(),
+                        *proj_label,
+                        labels.iter().map(|(_, label)| *label),
+                    );
                     self.push_message(Message::UnknownField {
                         head_range: self.file_range(head_range),
                         head_type,
                         label_range: self.file_range(*label_range),
                         label: *proj_label,
+                        suggestion,
                     });
                     return self.synth_reported_error(*range);
                 }

fathom/src/surface/elaboration.rs

@@ -16,6 +16,7 @@ pub enum Message {
     UnboundName {
         range: FileRange,
         name: StringId,
+        suggestion: Option<StringId>,
     },
     RefutablePattern {
         pattern_range: FileRange,
@@ -47,6 +48,7 @@ pub enum Message {
         head_type: String,
         label_range: FileRange,
         label: StringId,
+        suggestion: Option<StringId>,
     },
     MismatchedFieldLabels {
         range: FileRange,
@@ -144,14 +146,25 @@ impl Message {
         let secondary_label = |range: &FileRange| Label::secondary(range.file_id(), *range);
 
         match self {
-            Message::UnboundName { range, name } => {
+            Message::UnboundName {
+                range,
+                name,
+                suggestion,
+            } => {
                 let interner = interner.borrow();
                 let name = interner.resolve(*name).unwrap();
 
-                Diagnostic::error()
+                let mut diagnostic = Diagnostic::error()
                     .with_message(format!("cannot find `{name}` in scope"))
-                    .with_labels(vec![primary_label(range).with_message("unbound name")])
-                // TODO: list suggestions
+                    .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 `{}`?",
+                        interner.resolve(*suggestion).unwrap()
+                    )])
+                }
+                diagnostic
             }
             Message::RefutablePattern { pattern_range } => Diagnostic::error()
                 .with_message("refutable patterns found in binding")
@@ -208,18 +221,25 @@ impl Message {
                 head_type,
                 label_range,
                 label,
+                suggestion,
             } => {
                 let interner = interner.borrow();
                 let label = interner.resolve(*label).unwrap();
 
-                Diagnostic::error()
+                let mut diagnostic = 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}")),
-                    ])
-                // TODO: list suggestions
+                    ]);
+                if let Some(suggestion) = suggestion {
+                    diagnostic = diagnostic.with_notes(vec![format!(
+                        "help: did you mean `{}`?",
+                        interner.resolve(*suggestion).unwrap()
+                    )]);
+                }
+                diagnostic
             }
             Message::MismatchedFieldLabels {
                 range,

fathom/src/surface/elaboration/reporting.rs

@@ -14,5 +14,7 @@ error: cannot find `a` in scope
   │
 3 │ fun A => fun (a : Type) => a : fun (A : Type) -> A -> A
   │                            ^ unbound name
+  │
+  = help: did you mean `A`?
 
 '''

tests/fail/elaboration/unification/mismatch/fun-literal-param-ann.snap

@@ -7,5 +7,7 @@ error: cannot find `goodbye` in expression
   │ -------------- ^^^^^^^ unknown label
   │ │               
   │ expression of type { hello : () }
+  │
+  = help: did you mean `goodbye`?
 
 '''

tests/fail/elaboration/unknown-field/record-literal.snap

@@ -7,5 +7,7 @@ error: cannot find `foo` in expression
   │ ---- ^^^ unknown label
   │ │     
   │ expression of type Type
+  │
+  = help: did you mean `foo`?
 
 '''

tests/fail/elaboration/unknown-field/type.snap

@@ -7,5 +7,7 @@ error: cannot find `goodbye` in expression
   │ -- ^^^^^^^ unknown label
   │ │   
   │ expression of type ()
+  │
+  = help: did you mean `goodbye`?
 
 '''