Fix 'canon lower' validation rule inconsistency

design/mvp/CanonicalABI.md

@@ -3795,7 +3795,7 @@ validation is performed where `$callee` has type `$ft`:
 * requires options [based on `lower(param)`](#canonopt-validation) for all parameters in `ft`
 * requires options [based on `lift(result)`](#canonopt-validation) if `ft` has a result
 * if `len(flatten_types(ft.param_types())) > max_flat_params`, `memory` is required
-* if `len(flatten_types(ft.result_type())) > max_flat_results`, `realloc` is required
+* if `len(flatten_types(ft.result_type())) > max_flat_results`, `memory` is required
 * 🔀 if `async` is specified, `memory` must be present
 
 When instantiating a component instance, the runtime calls `Store.lower` (defined

test/validation/abi.wast

@@ -0,0 +1,31 @@
+(assert_invalid
+  (component
+    (import "foo" (func $foo (result (tuple u64 u64 u64 u64 u64 u64 u64 u64))))
+    (canon lower (func $foo) (core func $foo'))
+  )
+  "canonical option `memory` is required"
+)
+(assert_invalid
+  (component
+    (import "foo" (func $foo (result (tuple u64 u64 u64 u64 u64 u64 u64 u64))))
+    (core module $M
+      (func (export "realloc") (param i32 i32 i32 i32) (result i32) unreachable)
+    )
+    (core instance $i (instantiate $M))
+    (canon lower (func $foo) (realloc (func $i "realloc")) (core func $foo'))
+  )
+  "canonical option `realloc` requires `memory` to also be specified"
+)
+(component
+  (component
+    (import "foo" (func $foo (result (tuple u64 u64 u64 u64 u64 u64 u64 u64))))
+    (core module $M
+      (memory (export "mem") 1)
+      (func (export "realloc") (param i32 i32 i32 i32) (result i32) unreachable)
+    )
+    (core instance $i (instantiate $M))
+    (canon lower (func $foo) (memory $i "mem") (core func $foo1))
+    ;; realloc superfluous but allowed:
+    (canon lower (func $foo) (memory $i "mem") (realloc (func $i "realloc")) (core func $foo2))
+  )
+)