From 9b463c5c7144d890bad3ed3c99e2c185799b8590 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Thu, 5 Aug 2021 11:50:18 -0700
Subject: [PATCH] Fix parsing of empty element `func` segments

This fixes an issue where `(elem func)` was parsed as `(elem funcref)`
which meant we couldn't distinguish the two nodes in the AST. The fix is
to force the usage of index-based elements if `func` is used.
---
 crates/wast/src/ast/table.rs | 8 ++++----
 tests/local/empty-elem.wast  | 6 ++++++
 2 files changed, 10 insertions(+), 4 deletions(-)
 create mode 100644 tests/local/empty-elem.wast

diff --git a/crates/wast/src/ast/table.rs b/crates/wast/src/ast/table.rs
index ef019d0f4d..0a5dcb2fd7 100644
--- a/crates/wast/src/ast/table.rs
+++ b/crates/wast/src/ast/table.rs
@@ -188,15 +188,15 @@ impl<'a> Parse<'a> for ElemPayload<'a> {
 
 impl<'a> ElemPayload<'a> {
     fn parse_tail(parser: Parser<'a>, ty: Option<ast::RefType<'a>>) -> Result<Self> {
-        let ty = match ty {
+        let (must_use_indices, ty) = match ty {
             None => {
                 parser.parse::<Option<kw::func>>()?;
-                ast::RefType::func()
+                (true, ast::RefType::func())
             }
-            Some(ty) => ty,
+            Some(ty) => (false, ty),
         };
         if let ast::HeapType::Func = ty.heap {
-            if parser.peek::<ast::IndexOrRef<kw::func>>() {
+            if must_use_indices || parser.peek::<ast::IndexOrRef<kw::func>>() {
                 let mut elems = Vec::new();
                 while !parser.is_empty() {
                     elems.push(parser.parse::<ast::IndexOrRef<_>>()?.0);
diff --git a/tests/local/empty-elem.wast b/tests/local/empty-elem.wast
new file mode 100644
index 0000000000..e30f9bd092
--- /dev/null
+++ b/tests/local/empty-elem.wast
@@ -0,0 +1,6 @@
+(module
+  (elem)
+  (elem func)
+  (elem funcref)
+  (elem declare func)
+  (elem declare funcref))