ffi: evaluate function signatures once

Function signatures were read by the native implementation and then
read again while creating JavaScript wrappers. Accessors, proxies,
or mutations could therefore produce different native and JavaScript
signatures.

Build wrappers from signature metadata captured by native code instead.

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
Assisted-by: openai:gpt-5.6-sol

Author: trivikr

lib/ffi.js

@@ -80,8 +80,10 @@ function makeSignature(argumentTypes, returnType) {
   };
 }
 
-function wrapFFIFunction(rawFn, argumentTypes, returnType, owner) {
-  if (argumentTypes === undefined && rawFn !== undefined && rawFn !== null) {
+function wrapFFIFunction(rawFn, owner) {
+  let argumentTypes;
+  let returnType;
+  if (rawFn !== undefined && rawFn !== null) {
     const sbArguments = rawFn[kSbArguments];
     argumentTypes = sbArguments ?? rawFn[kFastArguments];
     if (sbArguments !== undefined) {
@@ -103,7 +105,7 @@ const rawGetFunctions = DynamicLibrary.prototype.getFunctions;
 
 DynamicLibrary.prototype.getFunction = function getFunction(name, signature) {
   const raw = FunctionPrototypeCall(rawGetFunction, this, name, signature);
-  return wrapFFIFunction(raw, signature.arguments, signature.return, this);
+  return wrapFFIFunction(raw, this);
 };
 
 DynamicLibrary.prototype.getFunctions = function getFunctions(definitions) {
@@ -115,13 +117,7 @@ DynamicLibrary.prototype.getFunctions = function getFunctions(definitions) {
   const out = { __proto__: null };
   for (let i = 0; i < keys.length; i++) {
     const name = keys[i];
-    if (definitions === undefined) {
-      out[name] = wrapFFIFunction(raw[name], undefined, undefined, this);
-    } else {
-      const signature = definitions[name];
-      out[name] = wrapFFIFunction(
-        raw[name], signature.arguments, signature.return, this);
-    }
+    out[name] = wrapFFIFunction(raw[name], this);
   }
   return out;
 };
@@ -145,7 +141,7 @@ DynamicLibrary.prototype.getFunctions = function getFunctions(definitions) {
       const keys = ObjectKeys(raw);
       for (let i = 0; i < keys.length; i++) {
         const name = keys[i];
-        wrapped[name] = wrapFFIFunction(raw[name], undefined, undefined, this);
+        wrapped[name] = wrapFFIFunction(raw[name], this);
       }
       return wrapped;
     },

test/ffi/test-ffi-dynamic-library.js

@@ -103,6 +103,60 @@ test('DynamicLibrary exposes functions and symbols', () => {
   }
 });
 
+test('DynamicLibrary evaluates function signatures once', () => {
+  function makeChangingSignature() {
+    const reads = { arguments: 0, return: 0 };
+    return {
+      reads,
+      signature: {
+        get arguments() {
+          reads.arguments++;
+          return reads.arguments === 1 ?
+            Array(8).fill('i32') : ['i32'];
+        },
+        get return() {
+          reads.return++;
+          return 'i32';
+        },
+      },
+    };
+  }
+
+  {
+    const lib = new ffi.DynamicLibrary(libraryPath);
+    const { reads, signature } = makeChangingSignature();
+
+    try {
+      const fn = lib.getFunction('sum_8_i32', signature);
+      assert.strictEqual(fn(1, 2, 3, 4, 5, 6, 7, 8), 36);
+      assert.deepStrictEqual(reads, { arguments: 1, return: 1 });
+    } finally {
+      lib.close();
+    }
+  }
+
+  {
+    const lib = new ffi.DynamicLibrary(libraryPath);
+    const { reads, signature } = makeChangingSignature();
+    let definitionReads = 0;
+    const definitions = {
+      get sum_8_i32() {
+        definitionReads++;
+        return signature;
+      },
+    };
+
+    try {
+      const { sum_8_i32: fn } = lib.getFunctions(definitions);
+      assert.strictEqual(fn(1, 2, 3, 4, 5, 6, 7, 8), 36);
+      assert.strictEqual(definitionReads, 1);
+      assert.deepStrictEqual(reads, { arguments: 1, return: 1 });
+    } finally {
+      lib.close();
+    }
+  }
+});
+
 test('getFunction caches signatures consistently', () => {
   const lib = new ffi.DynamicLibrary(libraryPath);