Allow import/export overlap in wit-parser (#1400)

Updates to WebAssembly/component-model#259 by relaxing some checks here
and there.

Closes #1396

Author: alexcrichton

crates/wit-parser/src/ast/resolve.rs

@@ -591,11 +591,12 @@ impl<'a> Resolver<'a> {
 
         let mut export_spans = Vec::new();
         let mut import_spans = Vec::new();
-        let mut used_names = HashMap::new();
+        let mut import_names = HashMap::new();
+        let mut export_names = HashMap::new();
         for (name, (item, span)) in self.type_lookup.iter() {
             match *item {
                 TypeOrItem::Type(id) => {
-                    let prev = used_names.insert(*name, "import");
+                    let prev = import_names.insert(*name, "import");
                     if let Some(prev) = prev {
                         return Err(Error {
                             span: *span,
@@ -617,20 +618,22 @@ impl<'a> Resolver<'a> {
         let mut imported_interfaces = HashSet::new();
         let mut exported_interfaces = HashSet::new();
         for item in world.items.iter() {
-            let (docs, kind, desc, spans, interfaces) = match item {
+            let (docs, kind, desc, spans, interfaces, names) = match item {
                 ast::WorldItem::Import(import) => (
                     &import.docs,
                     &import.kind,
                     "import",
                     &mut import_spans,
                     &mut imported_interfaces,
+                    &mut import_names,
                 ),
                 ast::WorldItem::Export(export) => (
                     &export.docs,
                     &export.kind,
                     "export",
                     &mut export_spans,
                     &mut exported_interfaces,
+                    &mut export_names,
                 ),
 
                 ast::WorldItem::Type(ast::TypeDef {
@@ -659,7 +662,7 @@ impl<'a> Resolver<'a> {
             };
             let key = match kind {
                 ast::ExternKind::Interface(name, _) | ast::ExternKind::Func(name, _) => {
-                    let prev = used_names.insert(name.name, desc);
+                    let prev = names.insert(name.name, desc);
                     if let Some(prev) = prev {
                         return Err(Error {
                             span: kind.span(),

crates/wit-parser/src/resolve.rs

@@ -1463,14 +1463,6 @@ impl Remap {
                     span,
                 })
             }
-
-            // check if this type has name conflict with any of the exported item.
-            if world.exports.contains_key(&WorldKey::Name(name.clone())) {
-                bail!(Error {
-                    msg: format!("import type `{name}` conflicts with prior export of interface",),
-                    span,
-                })
-            }
         }
 
         for (name, func, span) in import_funcs {
@@ -1485,40 +1477,20 @@ impl Remap {
                     span,
                 })
             }
-
-            // check if this function has name conflict with any of the exported item.
-            if world.exports.contains_key(&WorldKey::Name(name.clone())) {
-                bail!(Error {
-                    msg: format!(
-                        "import of function `{name}` conflicts with prior export of interface",
-                    ),
-                    span,
-                })
-            }
         }
 
         for (name, func, span) in export_funcs {
             let prev = world
                 .exports
                 .insert(WorldKey::Name(name.clone()), WorldItem::Function(func));
-            if prev.is_some() || world.imports.contains_key(&WorldKey::Name(name.clone())) {
+            if prev.is_some() {
                 bail!(Error {
                     msg: format!(
                         "export of function `{name}` shadows previously exported interface"
                     ),
                     span,
                 })
             }
-
-            // check if this function has name conflict with any of the import item.
-            if world.imports.contains_key(&WorldKey::Name(name.clone())) {
-                bail!(Error {
-                    msg: format!(
-                        "export of function `{name}` conflicts with prior import of interface",
-                    ),
-                    span,
-                })
-            }
         }
 
         // After all that sort functions in exports to come before interfaces in

crates/wit-parser/tests/ui/parse-fail/import-export-overlap1.wit renamed to crates/wit-parser/tests/ui/import-export-overlap1.wit

@@ -0,0 +1,39 @@
+{
+  "worlds": [
+    {
+      "name": "foo",
+      "imports": {
+        "a": {
+          "function": {
+            "name": "a",
+            "kind": "freestanding",
+            "params": [],
+            "results": []
+          }
+        }
+      },
+      "exports": {
+        "a": {
+          "function": {
+            "name": "a",
+            "kind": "freestanding",
+            "params": [],
+            "results": []
+          }
+        }
+      },
+      "package": 0
+    }
+  ],
+  "interfaces": [],
+  "types": [],
+  "packages": [
+    {
+      "name": "foo:foo",
+      "interfaces": {},
+      "worlds": {
+        "foo": 0
+      }
+    }
+  ]
+}

crates/wit-parser/tests/ui/import-export-overlap1.wit.json

@@ -0,0 +1,41 @@
+{
+  "worlds": [
+    {
+      "name": "foo",
+      "imports": {
+        "a": {
+          "function": {
+            "name": "a",
+            "kind": "freestanding",
+            "params": [],
+            "results": []
+          }
+        }
+      },
+      "exports": {
+        "a": {
+          "interface": 0
+        }
+      },
+      "package": 0
+    }
+  ],
+  "interfaces": [
+    {
+      "name": null,
+      "types": {},
+      "functions": {},
+      "package": 0
+    }
+  ],
+  "types": [],
+  "packages": [
+    {
+      "name": "foo:foo",
+      "interfaces": {},
+      "worlds": {
+        "foo": 0
+      }
+    }
+  ]
+}

crates/wit-parser/tests/ui/parse-fail/import-export-overlap2.wit renamed to crates/wit-parser/tests/ui/import-export-overlap2.wit

@@ -0,0 +1,6 @@
+package demo:greeter;
+
+world greeter {
+    import greet: func() -> string;
+    export greet: func() -> string;
+}