disallow post-return functions for async lifts (#1976)

I can't find where in the spec this is disallowed, but Luke agreed that it
_should_ be disallowed, so we'll update the spec to make that explicit.  Indeed,
we hope to deprecate post-return functions for both sync and async lifts in
favor of `task.return`.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Author: dicej

crates/wasmparser/src/validator/component.rs

@@ -2045,6 +2045,13 @@ impl ComponentState {
             bail!(offset, "cannot specify callback without lifting async")
         }
 
+        if post_return.is_some() && async_ {
+            bail!(
+                offset,
+                "cannot specify post-return function when lifting async"
+            )
+        }
+
         if info.requires_memory && memory.is_none() {
             return Err(BinaryReaderError::new(
                 "canonical option `memory` is required",

tests/local/component-model-async/lift.wast

@@ -10,6 +10,22 @@
   )
 )
 
+;; async lift; no callback; with post-return
+(assert_invalid
+  (component
+    (core module $m
+      (func (export "foo") (param i32) unreachable)
+      (func (export "post-return-foo") unreachable)
+    )
+    (core instance $i (instantiate $m))
+
+    (func (export "foo") (param "p1" u32) (result u32)
+      (canon lift (core func $i "foo") async (post-return (func $i "post-return-foo")))
+    )
+  )
+  "cannot specify post-return function when lifting async"
+)
+
 ;; async lift; with callback
 (component
   (core module $m
@@ -39,6 +55,23 @@
   "canonical option `callback` uses a core function with an incorrect signature"
 )
 
+;; async lift; with callback and post-return
+(assert_invalid
+  (component
+    (core module $m
+      (func (export "callback") (param i32 i32 i32 i32) (result i32) unreachable)
+      (func (export "foo") (param i32) (result i32) unreachable)
+      (func (export "post-return-foo") (param i32) unreachable)
+    )
+    (core instance $i (instantiate $m))
+
+    (func (export "foo") (param "p1" u32) (result u32)
+      (canon lift (core func $i "foo") async (callback (func $i "callback")) (post-return (func $i "post-return-foo")))
+    )
+  )
+  "cannot specify post-return function when lifting async"
+)
+
 ;; async lift; with incorrectly-typed core function
 (assert_invalid
   (component

tests/snapshots/local/component-model-async/lift.wast.json

@@ -8,37 +8,51 @@
       "module_type": "binary"
     },
     {
-      "type": "module",
-      "line": 14,
+      "type": "assert_invalid",
+      "line": 15,
       "filename": "lift.1.wasm",
-      "module_type": "binary"
+      "module_type": "binary",
+      "text": "cannot specify post-return function when lifting async"
     },
     {
-      "type": "assert_invalid",
-      "line": 28,
+      "type": "module",
+      "line": 30,
       "filename": "lift.2.wasm",
-      "module_type": "binary",
-      "text": "canonical option `callback` uses a core function with an incorrect signature"
+      "module_type": "binary"
     },
     {
       "type": "assert_invalid",
       "line": 44,
       "filename": "lift.3.wasm",
       "module_type": "binary",
-      "text": "lowered parameter types `[I32]` do not match parameter types `[I32, I32]` of core function 0"
+      "text": "canonical option `callback` uses a core function with an incorrect signature"
     },
     {
       "type": "assert_invalid",
       "line": 60,
       "filename": "lift.4.wasm",
       "module_type": "binary",
-      "text": "core instance 0 has no export named `callback`"
+      "text": "cannot specify post-return function when lifting async"
     },
     {
       "type": "assert_invalid",
-      "line": 75,
+      "line": 77,
       "filename": "lift.5.wasm",
       "module_type": "binary",
+      "text": "lowered parameter types `[I32]` do not match parameter types `[I32, I32]` of core function 0"
+    },
+    {
+      "type": "assert_invalid",
+      "line": 93,
+      "filename": "lift.6.wasm",
+      "module_type": "binary",
+      "text": "core instance 0 has no export named `callback`"
+    },
+    {
+      "type": "assert_invalid",
+      "line": 108,
+      "filename": "lift.7.wasm",
+      "module_type": "binary",
       "text": "cannot specify callback without lifting async"
     }
   ]