track adt variant and field names do not conflict

The intent of this change is to add a check for adts that enum variant
names are unique, and that struct and enum field names are unique
(within a given enum variant).

Author: shua

crates/formality-check/src/adts.rs

@@ -1,3 +1,6 @@
+use std::collections::HashSet;
+
+use anyhow::bail;
 use formality_prove::Env;
 use formality_rust::grammar::{Adt, AdtBoundData, Field, Variant};
 use formality_types::grammar::Fallible;
@@ -15,10 +18,17 @@ impl super::Check<'_> {
 
         self.prove_where_clauses_well_formed(&env, &where_clauses, &where_clauses)?;
 
-        // FIXME: check names are unique or integers from 0..n
-
-        for Variant { name: _, fields } in &variants {
-            for Field { name: _, ty } in fields {
+        // names is used to check that there are no name conflicts
+        let mut names = HashSet::new();
+        for Variant { name, fields } in &variants {
+            if !names.insert((name, None)) {
+                bail!("variant \"{name:?}\" defined multiple times");
+            }
+            let vname = name;
+            for Field { name, ty } in fields {
+                if !names.insert((vname, Some(name))) {
+                    bail!("field \"{name:?}\" of variant \"{vname:?}\" defined multiple times");
+                }
                 self.prove_goal(&env, &where_clauses, ty.well_formed())?;
             }
         }

src/test/mod.rs

@@ -133,3 +133,39 @@ fn basic_where_clauses_fail() {
                                    expression evaluated to an empty collection: `decls.trait_invariants()`"#]]
     )
 }
+
+#[test]
+fn basic_adt_variant_dup() {
+    crate::assert_err!(
+        [
+            crate Foo {
+                enum Bar {
+                    Baz{},
+                    Baz{},
+                }
+            }
+        ]
+
+        [ /* TODO */ ]
+
+        expect_test::expect![[r#"variant "Baz" defined multiple times"#]]
+    )
+}
+
+#[test]
+fn basic_adt_field_dup() {
+    crate::assert_err!(
+        [
+            crate Foo {
+                struct Bar {
+                    baz: (),
+                    baz: (),
+                }
+            }
+        ]
+
+        [ /* TODO */ ]
+
+        expect_test::expect![[r#"field "baz" of variant "struct" defined multiple times"#]]
+    )
+}