From 73dfe3b423ec13c67d5802debfb61070e955d6a6 Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Mon, 19 Aug 2024 11:56:36 -0700
Subject: [PATCH] Print explicit typeuses for non-MVP function types

We previously printed explicit typeuses (e.g. `(type $f)`) in function
signatures when GC was enabled. But even when GC is not enabled,
function types may use non-MVP features that require the explicit
typeuse to be printed. Fix the printer to always print the explicit type
use for such types.

Fixes #6850.
---
 src/passes/Print.cpp                       | 13 +++++-
 test/lit/basic/print-explicit-typeuse.wast | 51 ++++++++++++++++++++++
 2 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 test/lit/basic/print-explicit-typeuse.wast

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 3abe1f73821..6350347c46d 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -2804,13 +2804,21 @@ bool PrintSExpression::maybePrintUnreachableOrNullReplacement(Expression* curr,
   return maybePrintUnreachableReplacement(curr, type);
 }
 
+static bool requiresExplicitFuncType(HeapType type) {
+  // When the `(type $f)` in a function's typeuse is omitted, the typeuse
+  // matches or declares an MVP function type. When the intended type is not an
+  // MVP function type, we therefore need the explicit `(type $f)`.
+  return type.isOpen() || type.isShared() || type.getRecGroup().size() > 1;
+}
+
 void PrintSExpression::handleSignature(HeapType curr, Name name) {
   Signature sig = curr.getSignature();
   o << "(func";
   if (name.is()) {
     o << ' ';
     name.print(o);
-    if (currModule && currModule->features.hasGC()) {
+    if ((currModule && currModule->features.hasGC()) ||
+        requiresExplicitFuncType(curr)) {
       o << " (type ";
       printHeapType(curr) << ')';
     }
@@ -2947,7 +2955,8 @@ void PrintSExpression::visitDefinedFunction(Function* curr) {
   o << '(';
   printMajor(o, "func ");
   curr->name.print(o);
-  if (currModule && currModule->features.hasGC()) {
+  if ((currModule && currModule->features.hasGC()) ||
+      requiresExplicitFuncType(curr->type)) {
     o << " (type ";
     printHeapType(curr->type) << ')';
   }
diff --git a/test/lit/basic/print-explicit-typeuse.wast b/test/lit/basic/print-explicit-typeuse.wast
new file mode 100644
index 00000000000..d299a3eb430
--- /dev/null
+++ b/test/lit/basic/print-explicit-typeuse.wast
@@ -0,0 +1,51 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+;; RUN: wasm-opt %s --no-validation -S -o - | filecheck %s
+
+;; Check that we print explicit type uses for function signatures when the
+;; function type uses non-MVP features, whether or not those features are
+;; actually enabled.
+
+(module
+  ;; CHECK:      (type $mvp (func))
+  (type $mvp (func))
+  ;; CHECK:      (type $open (sub (func)))
+  (type $open (sub (func)))
+  ;; CHECK:      (type $shared (shared (func)))
+  (type $shared (shared (func)))
+  (rec
+    ;; CHECK:      (rec
+    ;; CHECK-NEXT:  (type $rec (func))
+    (type $rec (func))
+    ;; CHECK:       (type $other (struct))
+    (type $other (struct))
+  )
+
+  ;; CHECK:      (import "" "" (func $mvp-import))
+  (import "" "" (func $mvp-import))
+
+  ;; CHECK:      (import "" "" (func $open-import (type $open)))
+  (import "" "" (func $open-import (type $open)))
+
+  ;; CHECK:      (import "" "" (func $shared-import (type $shared)))
+  (import "" "" (func $shared-import (type $shared)))
+
+  ;; CHECK:      (import "" "" (func $rec-import (type $rec)))
+  (import "" "" (func $rec-import (type $rec)))
+
+  ;; CHECK:      (func $mvp
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $mvp (type $mvp))
+  ;; CHECK:      (func $open (type $open)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $open (type $open))
+  ;; CHECK:      (func $shared (type $shared)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $shared (type $shared))
+  ;; CHECK:      (func $rec (type $rec)
+  ;; CHECK-NEXT:  (nop)
+  ;; CHECK-NEXT: )
+  (func $rec (type $rec))
+)