Merge pull request #349 from bytecodealliance/ydnar/issue344

cm: do not use bool discriminant in variant, result, and option types

Author: ydnar

Makefile

@@ -22,7 +22,6 @@ generated: clean json
 clean:
 	rm -rf ./generated/*
 	rm -f internal/wasmtools/wasm-tools.wasm
-	rm -f internal/wasmtools/wasm-tools.wasm.gz
 
 # tests/generated writes generated Go code to the tests directory
 .PHONY: tests/generated

cm/CHANGELOG.md

@@ -8,6 +8,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 - Mutating methods `SetOK` and `SetErr` on `result` types (`Result[Shape, OK, Err]`).
 
+### Changed
+
+- Breaking: `BoolResult` is now represented as a `uint8` rather than a `bool`. This fixes an issue with TinyGo where `bool` values are treated distinctly from `uint8`. See [#344](https://github.com/bytecodealliance/go-modules/issues/344) for more information.
+
+### Fixed
+
+- [#344](https://github.com/bytecodealliance/go-modules/issues/344): the memory representation of `option` and `result` now use `uint8` instead of `bool` for the discriminator. LLVM optimizes `bool` values into a single bit, which breaks WIT variants where the associated types share memory.
+
 ## [v0.2.2] — 2025-03-16
 
 ### Fixed

cm/option.go

@@ -18,30 +18,30 @@ func None[T any]() Option[T] {
 func Some[T any](v T) Option[T] {
 	return Option[T]{
 		option: option[T]{
-			isSome: true,
+			isSome: 1,
 			some:   v,
 		},
 	}
 }
 
 // option represents the internal representation of a Component Model option type.
-// The first byte is a bool representing none or some,
+// The first byte is a byte representing the none or some case,
 // followed by storage for the associated type T.
 type option[T any] struct {
 	_      HostLayout
-	isSome bool
+	isSome uint8
 	some   T
 }
 
 // None returns true if o represents the none case.
 func (o *option[T]) None() bool {
-	return !o.isSome
+	return o.isSome == 0
 }
 
 // Some returns a non-nil *T if o represents the some case,
 // or nil if o represents the none case.
 func (o *option[T]) Some() *T {
-	if o.isSome {
+	if o.isSome == 1 {
 		return &o.some
 	}
 	return nil
@@ -51,7 +51,7 @@ func (o *option[T]) Some() *T {
 // or the zero value of T if o represents the none case.
 // This does not have a pointer receiver, so it can be chained.
 func (o option[T]) Value() T {
-	if !o.isSome {
+	if o.isSome == 0 {
 		var zero T
 		return zero
 	}

cm/result.go

@@ -4,15 +4,15 @@ import "unsafe"
 
 const (
 	// ResultOK represents the OK case of a result.
-	ResultOK = false
+	ResultOK = 0
 
 	// ResultErr represents the error case of a result.
-	ResultErr = true
+	ResultErr = 1
 )
 
 // BoolResult represents a result with no OK or error type.
 // False represents the OK case and true represents the error case.
-type BoolResult bool
+type BoolResult uint8
 
 // Result represents a result sized to hold the Shape type.
 // The size of the Shape type must be greater than or equal to the size of OK and Err types.
@@ -33,7 +33,7 @@ type AnyResult[Shape, OK, Err any] interface {
 // result represents the internal representation of a Component Model result type.
 type result[Shape, OK, Err any] struct {
 	_     HostLayout
-	isErr bool
+	isErr uint8
 	_     [0]OK
 	_     [0]Err
 	data  Shape // [unsafe.Sizeof(*(*Shape)(unsafe.Pointer(nil)))]byte
@@ -76,20 +76,20 @@ func (r *result[Shape, OK, Err]) SetErr(err Err) {
 // IsOK returns true if r represents the OK case.
 func (r *result[Shape, OK, Err]) IsOK() bool {
 	r.validate()
-	return !r.isErr
+	return r.isErr == ResultOK
 }
 
 // IsErr returns true if r represents the error case.
 func (r *result[Shape, OK, Err]) IsErr() bool {
 	r.validate()
-	return r.isErr
+	return r.isErr == ResultErr
 }
 
 // OK returns a non-nil *OK pointer if r represents the OK case.
 // If r represents an error, then it returns nil.
 func (r *result[Shape, OK, Err]) OK() *OK {
 	r.validate()
-	if r.isErr {
+	if r.isErr == ResultErr {
 		return nil
 	}
 	return (*OK)(unsafe.Pointer(&r.data))
@@ -99,7 +99,7 @@ func (r *result[Shape, OK, Err]) OK() *OK {
 // If r represents the OK case, then it returns nil.
 func (r *result[Shape, OK, Err]) Err() *Err {
 	r.validate()
-	if !r.isErr {
+	if r.isErr == ResultOK {
 		return nil
 	}
 	return (*Err)(unsafe.Pointer(&r.data))
@@ -109,7 +109,7 @@ func (r *result[Shape, OK, Err]) Err() *Err {
 // or (zero value of OK, Err, true) if r represents the error case.
 // This does not have a pointer receiver, so it can be chained.
 func (r result[Shape, OK, Err]) Result() (ok OK, err Err, isErr bool) {
-	if r.isErr {
+	if r.isErr == ResultErr {
 		return ok, *(*Err)(unsafe.Pointer(&r.data)), true
 	}
 	return *(*OK)(unsafe.Pointer(&r.data)), err, false

cm/result_test.go

@@ -87,7 +87,7 @@ func TestResultLayout(t *testing.T) {
 		size   uintptr
 		offset uintptr
 	}{
-		{"result", BoolResult(false), 1, 0},
+		{"result", BoolResult(0), 1, 0},
 		{"ok", BoolResult(ResultOK), 1, 0},
 		{"err", BoolResult(ResultErr), 1, 0},
 
@@ -350,3 +350,40 @@ func TestIssue284NotTinyGo(t *testing.T) {
 		}
 	}
 }
+
+func TestIssue344Option(t *testing.T) {
+	type T Result[Option[uint64], uint64, Option[uint64]]
+
+	want := uint64(2)
+	v := T(OK[Result[Option[uint64], uint64, Option[uint64]]](want))
+	got := *v.OK()
+
+	if got != want {
+		t.Errorf("*v.OK(): %v, expected %v", got, want)
+	}
+}
+
+func TestIssue344Result(t *testing.T) {
+	type R Result[uint64, uint64, bool]
+	type T Result[R, uint64, R]
+
+	want := uint64(2)
+	v := T(OK[T](want))
+	got := *v.OK()
+
+	if got != want {
+		t.Errorf("*v.OK(): %v, expected %v", got, want)
+	}
+}
+
+func TestIssue344BoolResult(t *testing.T) {
+	type T Result[BoolResult, uint8, BoolResult]
+
+	want := uint8(2)
+	v := T(OK[T](want))
+	got := *v.OK()
+
+	if got != want {
+		t.Errorf("*v.OK(): %v, expected %v", got, want)
+	}
+}

testdata/issues/issue344.wit

@@ -0,0 +1,15 @@
+package issues:issue344;
+
+world w {
+    import i;
+}
+
+interface i {
+	type a = result<u64, tuple<option<u64>>>;
+	type b = result<u64, tuple<result<u64, bool>>>;
+	type c = result<result, u8>;
+
+	fa: func() -> a;
+	fb: func() -> b;
+	fc: func() -> c;
+}

testdata/issues/issue344.wit.json

@@ -0,0 +1,145 @@
+{
+  "worlds": [
+    {
+      "name": "w",
+      "imports": {
+        "interface-0": {
+          "interface": {
+            "id": 0
+          }
+        }
+      },
+      "exports": {},
+      "package": 0
+    }
+  ],
+  "interfaces": [
+    {
+      "name": "i",
+      "types": {
+        "a": 2,
+        "b": 5,
+        "c": 7
+      },
+      "functions": {
+        "fa": {
+          "name": "fa",
+          "kind": "freestanding",
+          "params": [],
+          "result": 2
+        },
+        "fb": {
+          "name": "fb",
+          "kind": "freestanding",
+          "params": [],
+          "result": 5
+        },
+        "fc": {
+          "name": "fc",
+          "kind": "freestanding",
+          "params": [],
+          "result": 7
+        }
+      },
+      "package": 0
+    }
+  ],
+  "types": [
+    {
+      "name": null,
+      "kind": {
+        "option": "u64"
+      },
+      "owner": null
+    },
+    {
+      "name": null,
+      "kind": {
+        "tuple": {
+          "types": [
+            0
+          ]
+        }
+      },
+      "owner": null
+    },
+    {
+      "name": "a",
+      "kind": {
+        "result": {
+          "ok": "u64",
+          "err": 1
+        }
+      },
+      "owner": {
+        "interface": 0
+      }
+    },
+    {
+      "name": null,
+      "kind": {
+        "result": {
+          "ok": "u64",
+          "err": "bool"
+        }
+      },
+      "owner": null
+    },
+    {
+      "name": null,
+      "kind": {
+        "tuple": {
+          "types": [
+            3
+          ]
+        }
+      },
+      "owner": null
+    },
+    {
+      "name": "b",
+      "kind": {
+        "result": {
+          "ok": "u64",
+          "err": 4
+        }
+      },
+      "owner": {
+        "interface": 0
+      }
+    },
+    {
+      "name": null,
+      "kind": {
+        "result": {
+          "ok": null,
+          "err": null
+        }
+      },
+      "owner": null
+    },
+    {
+      "name": "c",
+      "kind": {
+        "result": {
+          "ok": 6,
+          "err": "u8"
+        }
+      },
+      "owner": {
+        "interface": 0
+      }
+    }
+  ],
+  "packages": [
+    {
+      "name": "issues:issue344",
+      "interfaces": {
+        "i": 0
+      },
+      "worlds": {
+        "w": 0
+      }
+    }
+  ]
+}

testdata/issues/issue344.wit.json.golden.wit

@@ -0,0 +1,14 @@
+package issues:issue344;
+
+interface i {
+	type a = result<u64, tuple<option<u64>>>;
+	type b = result<u64, tuple<result<u64, bool>>>;
+	type c = result<result, u8>;
+	fa: func() -> a;
+	fb: func() -> b;
+	fc: func() -> c;
+}
+
+world w {
+	import i;
+}