Fix span reported with "duplicate import" errors.

When the imported item was an interface by package path, the span of the import
was for the local identifier and not for the package path.

Fixes #15.

Author: peterhuene

crates/wac-parser/src/resolution.rs

@@ -646,6 +646,9 @@ pub enum Error {
         /// The span where the error occurred.
         #[label("previous {kind} here")]
         previous: SourceSpan,
+        /// The help of the error.
+        #[help]
+        help: Option<String>,
     },
     /// An invalid extern name was encountered.
     #[error("{kind} name `{name}` is not valid")]

crates/wac-parser/src/resolution/ast.rs

@@ -208,17 +208,20 @@ impl<'a> AstResolver<'a> {
             "resolving import statement for id `{id}`",
             id = stmt.id.string
         );
-        let kind = match &stmt.ty {
-            ast::ImportType::Package(p) => self.resolve_package_export(state, p)?,
-            ast::ImportType::Func(ty) => ItemKind::Func(self.func_type(
-                state,
-                &ty.params,
-                &ty.results,
-                FuncKind::Free,
-                None,
-            )?),
-            ast::ImportType::Interface(i) => self.inline_interface(state, i)?,
-            ast::ImportType::Ident(id) => state.local_item(id)?.1.kind(),
+        let (kind, span) = match &stmt.ty {
+            ast::ImportType::Package(p) => (self.resolve_package_export(state, p)?, p.span),
+            ast::ImportType::Func(ty) => (
+                ItemKind::Func(self.func_type(
+                    state,
+                    &ty.params,
+                    &ty.results,
+                    FuncKind::Free,
+                    None,
+                )?),
+                stmt.id.span,
+            ),
+            ast::ImportType::Interface(i) => (self.inline_interface(state, i)?, stmt.id.span),
+            ast::ImportType::Ident(id) => (state.local_item(id)?.1.kind(), stmt.id.span),
         };
 
         // Promote function types, instance types, and component types to functions, instances, and components
@@ -230,17 +233,18 @@ impl<'a> AstResolver<'a> {
         };
 
         let (name, span) = if let Some(name) = stmt.name {
+            // Override the span to the `as` clause string
             (name.value, name.span)
         } else {
             // If the item is an instance with an id, use the id
             if let ItemKind::Instance(id) = kind {
                 if let Some(id) = &self.definitions.interfaces[id].id {
-                    (id.as_str(), stmt.id.span)
+                    (id.as_str(), span)
                 } else {
-                    (stmt.id.string, stmt.id.span)
+                    (stmt.id.string, span)
                 }
             } else {
-                (stmt.id.string, stmt.id.span)
+                (stmt.id.string, span)
             }
         };
 
@@ -275,12 +279,16 @@ impl<'a> AstResolver<'a> {
                         });
                     }
 
-                    // TODO: should use prev_span with this error
                     return Err(Error::DuplicateExternName {
                         name: name.to_owned(),
                         kind: ExternKind::Import,
                         span,
                         previous: existing.span,
+                        help: if stmt.name.is_some() {
+                            None
+                        } else {
+                            Some("consider using an `as` clause to use a different name".into())
+                        },
                     });
                 }
                 _ => unreachable!(),
@@ -412,6 +420,11 @@ impl<'a> AstResolver<'a> {
                 kind: ExternKind::Export,
                 span,
                 previous: existing.span,
+                help: if stmt.name.is_some() {
+                    None
+                } else {
+                    Some("consider using an `as` clause to use a different name".into())
+                },
             });
         }
 

crates/wac-parser/tests/resolution/fail/import-id-span.wac

@@ -0,0 +1,5 @@
+package test:comp;
+
+import env-foo: wasi:cli/environment;
+
+import env-bar: wasi:cli/environment;

crates/wac-parser/tests/resolution/fail/import-id-span.wac.result

@@ -0,0 +1,14 @@
+failed to resolve document
+
+  × duplicate import `wasi:cli/environment`
+   ╭─[tests/resolution/fail/import-id-span.wac:5:17]
+ 2 │ 
+ 3 │ import env-foo: wasi:cli/environment;
+   ·                 ──────────┬─────────
+   ·                           ╰── previous import here
+ 4 │ 
+ 5 │ import env-bar: wasi:cli/environment;
+   ·                 ──────────┬─────────
+   ·                           ╰── duplicate import name `wasi:cli/environment`
+   ╰────
+  help: consider using an `as` clause to use a different name

crates/wac-parser/tests/resolution/fail/import-id-span/wasi/cli/package.wit

@@ -0,0 +1,4 @@
+package wasi:cli;
+
+interface environment {
+}

crates/wac-parser/tests/resolution/fail/windows-file.wac.result

@@ -10,3 +10,4 @@ failed to resolve document
    ·        ┬
    ·        ╰── duplicate import name `x`
    ╰────
+  help: consider using an `as` clause to use a different name