ffi: preserve uint8 semantics for bool fast calls

Normalize bool to kUint8 when creating Fast API metadata. This keeps
optimized calls consistent with generic FFI behavior, including numeric
return values and rejection of JavaScript Boolean values.

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

Author: trivikr

doc/contributing/ffi-fast-api-internals.md

@@ -200,15 +200,15 @@ surface. It models the ABI categories that the generated trampoline knows how to
 marshal directly:
 
 * `kVoid`
-* `kBool`
 * signed and unsigned 8-bit, 16-bit, 32-bit, and 64-bit integers
 * `kFloat32`
 * `kFloat64`
 * `kPointer`
 * `kBuffer`
 
 Public aliases are normalized in `FastScalarTypeFromName()` and
-`FastArgTypeFromName()`.
+`FastArgTypeFromName()`. In particular, `bool` is normalized to `kUint8` to
+match its documented 8-bit unsigned integer semantics.
 
 `pointer`, `ptr`, `string`, `str`, `buffer`, and `arraybuffer` all represent
 pointer-sized native values at the target ABI boundary. They differ in how

src/ffi/fast.cc

@@ -37,7 +37,7 @@ bool FastScalarTypeFromName(std::string_view type, FastFFIType* out) {
   if (type == "void") {
     *out = FastFFIType::kVoid;
   } else if (type == "bool") {
-    *out = FastFFIType::kBool;
+    *out = FastFFIType::kUint8;
   } else if (IsTypeName(type, {"i8", "int8"})) {
     *out = FastFFIType::kInt8;
   } else if (IsTypeName(type, {"u8", "uint8"})) {
@@ -96,8 +96,6 @@ CTypeInfo::Type ToV8Type(FastFFIType type, bool is_return) {
   switch (type) {
     case FastFFIType::kVoid:
       return CTypeInfo::Type::kVoid;
-    case FastFFIType::kBool:
-      return CTypeInfo::Type::kBool;
     case FastFFIType::kUint8:
       return CTypeInfo::Type::kUint32;
     case FastFFIType::kInt8:

src/ffi/fast.h

@@ -17,7 +17,6 @@ struct FFIFunction;
 
 enum class FastFFIType : uint8_t {
   kVoid,
-  kBool,
   kInt8,
   kUint8,
   kInt16,

src/ffi/platforms/arm64.cc

@@ -136,7 +136,6 @@ uint32_t UxthW(unsigned reg) {
 // to the ABI width expected by the native target before the final call.
 bool EmitNarrow(uint32_t** cursor, FastFFIType type, unsigned reg) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kUint8:
       *(*cursor)++ = UxtbW(reg);
       return true;

src/ffi/platforms/loong64.cc

@@ -19,7 +19,6 @@ bool IsFloatType(FastFFIType type) {
 
 bool IsNarrowType(FastFFIType type) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kInt8:
     case FastFFIType::kUint8:
     case FastFFIType::kInt16:

src/ffi/platforms/ppc64.cc

@@ -23,7 +23,6 @@ bool IsFloatType(FastFFIType type) {
 
 bool IsNarrowType(FastFFIType type) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kInt8:
     case FastFFIType::kUint8:
     case FastFFIType::kInt16:

src/ffi/platforms/riscv64.cc

@@ -19,7 +19,6 @@ bool IsFloatType(FastFFIType type) {
 
 bool IsNarrowType(FastFFIType type) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kInt8:
     case FastFFIType::kUint8:
     case FastFFIType::kInt16:

src/ffi/platforms/s390x.cc

@@ -19,7 +19,6 @@ bool IsFloatType(FastFFIType type) {
 
 bool IsNarrowType(FastFFIType type) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kInt8:
     case FastFFIType::kUint8:
     case FastFFIType::kInt16:

src/ffi/platforms/x64.cc

@@ -232,7 +232,6 @@ void EmitNarrowInstruction(uint8_t** cursor, uint8_t opcode, unsigned reg) {
 // consumes the declared low 8/16 bits.
 bool EmitNarrowReturn(uint8_t** cursor, FastFFIType type, unsigned reg) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kUint8:
       EmitNarrowInstruction(cursor, 0xb6, reg);
       return true;
@@ -252,7 +251,6 @@ bool EmitNarrowReturn(uint8_t** cursor, FastFFIType type, unsigned reg) {
 
 bool NeedsNarrow(FastFFIType type) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kUint8:
     case FastFFIType::kInt8:
     case FastFFIType::kUint16:
@@ -655,7 +653,6 @@ void EmitNarrowInstruction(uint8_t** cursor, uint8_t opcode, unsigned reg) {
 
 bool EmitNarrowReturn(uint8_t** cursor, FastFFIType type, unsigned reg) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kUint8:
       EmitNarrowInstruction(cursor, 0xb6, reg);
       return true;
@@ -675,7 +672,6 @@ bool EmitNarrowReturn(uint8_t** cursor, FastFFIType type, unsigned reg) {
 
 bool NeedsNarrow(FastFFIType type) {
   switch (type) {
-    case FastFFIType::kBool:
     case FastFFIType::kUint8:
     case FastFFIType::kInt8:
     case FastFFIType::kUint16:

test/ffi/test-ffi-calls.js

@@ -1,4 +1,4 @@
-// Flags: --experimental-ffi --expose-gc
+// Flags: --experimental-ffi --expose-gc --allow-natives-syntax
 'use strict';
 const common = require('../common');
 common.skipIfFFIMissing();
@@ -62,8 +62,16 @@ test('ffi bool signatures use uint8 values', () => {
       arguments: ['bool', 'bool'],
       return: 'bool',
     });
-    assert.strictEqual(boolAdder(1, 0), 1);
-    assert.throws(() => boolAdder(true, false), /Argument 0 must be a uint8/);
+    function callBoolAdder(a, b) {
+      return boolAdder(a, b);
+    }
+
+    eval('%PrepareFunctionForOptimization(callBoolAdder)');
+    assert.strictEqual(callBoolAdder(1, 0), 1);
+    eval('%OptimizeFunctionOnNextCall(callBoolAdder)');
+    assert.strictEqual(callBoolAdder(1, 0), 1);
+    assert.throws(
+      () => callBoolAdder(true, false), /Argument 0 must be a uint8/);
   } finally {
     lib.close();
   }