From e24f935f489a32439ab811cedf58bce2f73246ea Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Wed, 12 Nov 2025 14:54:25 -0800
Subject: [PATCH] [Custom Descriptors] Exact imports require CD

Validate that exact function imports require custom descriptors. An
alternative approach (that we may switch to in the future if necessary)
would be to always allow exact imports, but then strip them out in the
binary writer when custom descriptors are not enabled. For now take the
more explicit what-you-see-is-what-you-get approach.
---
 src/wasm/wasm-validator.cpp           | 7 ++++++-
 test/lit/validation/exact-import.wast | 9 +++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 test/lit/validation/exact-import.wast

diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 94d3b137699..0a1df50dbb9 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -4159,7 +4159,12 @@ void FunctionValidator::visitFunction(Function* curr) {
                curr->name,
                "all used types should be allowed");
 
-  if (!curr->imported()) {
+  if (curr->imported()) {
+    shouldBeTrue(
+      curr->type.isInexact() || getModule()->features.hasCustomDescriptors(),
+      curr->name,
+      "exact imports require custom descriptors [--enable-custom-descriptors]");
+  } else {
     shouldBeTrue(
       curr->type.isExact(), curr->name, "defined function should be exact");
   }
diff --git a/test/lit/validation/exact-import.wast b/test/lit/validation/exact-import.wast
new file mode 100644
index 00000000000..318d397cfcb
--- /dev/null
+++ b/test/lit/validation/exact-import.wast
@@ -0,0 +1,9 @@
+;; Test that exact imports require custom descriptors.
+
+;; RUN: not wasm-opt %s -all --disable-custom-descriptors 2>&1 | filecheck %s
+
+;; CHECK: exact imports require custom descriptors [--enable-custom-descriptors]
+
+(module
+  (import "" "" (func $f (exact)))
+)