wit, wit/bindgen: represent error-context as a primitive type

Mirrors bytecodealliance/wasm-tools#2060

Author: ydnar

wit/bindgen/generator.go

@@ -659,8 +659,6 @@ func (g *generator) typeDefRep(file *gen.File, dir wit.Direction, t *wit.TypeDef
 		return g.ownRep(file, dir, kind)
 	case *wit.Borrow:
 		return g.borrowRep(file, dir, kind)
-	case *wit.ErrorContext:
-		return g.errorContextRep(file, dir, kind)
 	case *wit.Stream:
 		return g.streamRep(file, dir, kind)
 	case *wit.Future:
@@ -691,13 +689,13 @@ func (g *generator) typeRep(file *gen.File, dir wit.Direction, t wit.Type) strin
 		// TODO: add wit.Type.BuiltIn() method?
 		return g.typeDefRep(file, dir, t, "")
 	case wit.Primitive:
-		return g.primitiveRep(t)
+		return g.primitiveRep(file, t)
 	default:
 		panic(fmt.Sprintf("BUG: unknown wit.Type %T", t)) // should never reach here
 	}
 }
 
-func (g *generator) primitiveRep(p wit.Primitive) string {
+func (g *generator) primitiveRep(file *gen.File, p wit.Primitive) string {
 	switch p := p.(type) {
 	case wit.Bool:
 		return "bool"
@@ -725,6 +723,8 @@ func (g *generator) primitiveRep(p wit.Primitive) string {
 		return "rune"
 	case wit.String:
 		return "string"
+	case wit.ErrorContext:
+		return file.Import(g.opts.cmPackage) + ".ErrorContext"
 	default:
 		panic(fmt.Sprintf("BUG: unknown wit.Primitive %T", p)) // should never reach here
 	}
@@ -1005,10 +1005,6 @@ func (g *generator) borrowRep(file *gen.File, dir wit.Direction, b *wit.Borrow)
 	}
 }
 
-func (g *generator) errorContextRep(file *gen.File, dir wit.Direction, e *wit.ErrorContext) string {
-	return file.Import(g.opts.cmPackage) + ".ErrorContext"
-}
-
 func (g *generator) streamRep(file *gen.File, dir wit.Direction, s *wit.Stream) string {
 	var b strings.Builder
 	stringio.Write(&b, file.Import(g.opts.cmPackage), ".Stream[", g.typeRep(file, dir, s.Type), "]")
@@ -1050,7 +1046,7 @@ func (g *generator) typeDefShape(file *gen.File, dir wit.Direction, t *wit.TypeD
 			return g.typeRep(file, dir, t)
 		}
 	case *wit.Enum, *wit.Flags, *wit.List,
-		*wit.Resource, *wit.Own, *wit.Borrow, *wit.ErrorContext, *wit.Stream, *wit.Future:
+		*wit.Resource, *wit.Own, *wit.Borrow, *wit.Stream, *wit.Future:
 		// Certain types do not need custom type shapes:
 		// own, borrow, error-context, stream, future, enum, flags, and list
 		return g.typeRep(file, dir, t)
@@ -1120,8 +1116,7 @@ func (g *generator) lowerTypeDef(file *gen.File, dir wit.Direction, t *wit.TypeD
 		return g.lowerOption(file, dir, t, input)
 	case *wit.List:
 		return g.cmCall(file, "LowerList", input)
-	case *wit.Resource, *wit.Own, *wit.Borrow,
-		*wit.ErrorContext, *wit.Stream, *wit.Future:
+	case *wit.Resource, *wit.Own, *wit.Borrow, *wit.Stream, *wit.Future:
 		return g.cmCall(file, "Reinterpret["+g.typeRep(file, dir, flat[0])+"]", input)
 	default:
 		panic(fmt.Sprintf("BUG: unknown wit.TypeDef %T", kind)) // should never reach here
@@ -1275,6 +1270,8 @@ func (g *generator) lowerPrimitive(file *gen.File, dir wit.Direction, p wit.Prim
 	switch p := p.(type) {
 	case wit.String:
 		return g.cmCall(file, "LowerString", input)
+	case wit.ErrorContext:
+		return g.cmCall(file, "Reinterpret["+g.typeRep(file, dir, flat[0])+"]", input)
 	default:
 		return g.cast(file, dir, p, flat[0], input)
 	}
@@ -1334,8 +1331,7 @@ func (g *generator) liftTypeDef(file *gen.File, dir wit.Direction, t *wit.TypeDe
 		return g.liftOption(file, dir, t, input)
 	case *wit.List:
 		return g.cmCall(file, "LiftList["+g.typeRep(file, dir, t)+"]", input)
-	case *wit.Resource, *wit.Own, *wit.Borrow,
-		*wit.ErrorContext, *wit.Stream, *wit.Future:
+	case *wit.Resource, *wit.Own, *wit.Borrow, *wit.Stream, *wit.Future:
 		return g.cmCall(file, "Reinterpret["+g.typeRep(file, dir, t)+"]", input)
 	default:
 		panic(fmt.Sprintf("BUG: unknown wit.TypeDef %T", kind)) // should never reach here
@@ -1485,6 +1481,8 @@ func (g *generator) liftPrimitive(file *gen.File, dir wit.Direction, t wit.Type,
 	switch p.(type) {
 	case wit.String:
 		return g.cmCall(file, "LiftString["+g.typeRep(file, dir, t)+"]", input)
+	case wit.ErrorContext:
+		return g.cmCall(file, "Reinterpret["+g.typeRep(file, dir, t)+"]", input)
 	default:
 		return g.cast(file, dir, flat[0], t, input)
 	}

wit/codec.go

@@ -326,7 +326,7 @@ func (c *typeDefKindCodec) DecodeString(s string) error {
 		*c.v = &Resource{}
 	case "errorcontext", // https://github.com/bytecodealliance/wasm-tools/pull/1964
 		"error-context":
-		*c.v = &ErrorContext{}
+		*c.v = ErrorContext{}
 	}
 	return nil
 }
@@ -577,6 +577,12 @@ func (f *Function) DecodeField(dec codec.Decoder, name string) error {
 		return dec.Decode(&f.Kind)
 	case "params":
 		return codec.DecodeSlice(dec, &f.Params)
+	case "result":
+		// Multiple function results were removed in this PR:
+		// https://github.com/bytecodealliance/wasm-tools/pull/2050/files
+		// For now, this package preserves the underlying ability to support > 1 result.
+		f.Results = []Param{{}}
+		return dec.Decode(&f.Results[0].Type)
 	case "results":
 		return codec.DecodeSlice(dec, &f.Results)
 	case "stability":

wit/error.go

@@ -71,6 +71,8 @@ func ParseType(s string) (Type, error) {
 		return Char{}, nil
 	case "string":
 		return String{}, nil
+	case "error-context":
+		return &ErrorContext{}, nil
 	}
 	return nil, fmt.Errorf("unknown primitive type %q", s)
 }
@@ -79,12 +81,15 @@ func ParseType(s string) (Type, error) {
 //
 // [primitive types]: https://component-model.bytecodealliance.org/design/wit.html#primitive-types
 type primitive interface {
-	bool | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | float32 | float64 | char | string
+	bool | int8 | uint8 | int16 | uint16 | int32 | uint32 | int64 | uint64 | float32 | float64 | char | string | errorContext
 }
 
 // char is defined because [rune] is an alias of [int32]
 type char rune
 
+// errorContext is defined because WIT error-context is a primitive type in the Component Model.
+type errorContext uint32
+
 // Primitive is the interface implemented by WIT [primitive types].
 // It also conforms to the [Node], [ABI], [Type], and [TypeDefKind] interfaces.
 //
@@ -144,7 +149,7 @@ func (_primitive[T]) hasPointer() bool {
 func (_primitive[T]) Flat() []Type {
 	var v T
 	switch any(v).(type) {
-	case bool, int8, uint8, int16, uint16, int32, uint32, char:
+	case bool, int8, uint8, int16, uint16, int32, uint32, char, errorContext:
 		return []Type{U32{}}
 	case int64, uint64:
 		return []Type{U64{}}
@@ -263,3 +268,9 @@ type Char struct{ _primitive[char] }
 // [primitive type]: https://component-model.bytecodealliance.org/design/wit.html#primitive-types
 // [string]: https://pkg.go.dev/builtin#string
 type String struct{ _primitive[string] }
+
+// ErrorContext represents a WIT [error-context] type.
+// It implements the [Node], [ABI], and [TypeDefKind] interfaces.
+//
+// [resource type]: https://github.com/WebAssembly/component-model/blob/main/design/mvp/Explainer.md#error-context-type
+type ErrorContext struct{ _primitive[errorContext] }

wit/type.go

@@ -693,12 +693,12 @@ func (b *Borrow) WIT(ctx Node, name string) string {
 }
 
 // WITKind returns the WIT kind.
-func (*ErrorContext) WITKind() string { return "error-context" }
+func (ErrorContext) WITKind() string { return "error-context" }
 
 // WIT returns the [WIT] text format for [ErrorContext] r.
 //
 // [WIT]: https://github.com/WebAssembly/component-model/blob/main/design/mvp/WIT.md
-func (*ErrorContext) WIT(_ Node, name string) string {
+func (ErrorContext) WIT(_ Node, name string) string {
 	var b strings.Builder
 	if name != "" {
 		b.WriteString("type ")
@@ -962,9 +962,12 @@ func (s *Stream) WIT(_ Node, name string) string {
 		b.WriteString(escape(name))
 		b.WriteString(" = ")
 	}
-	b.WriteString("stream<")
-	b.WriteString(s.Type.WIT(s, ""))
-	b.WriteRune('>')
+	b.WriteString("stream")
+	if s.Type != nil {
+		b.WriteRune('<')
+		b.WriteString(s.Type.WIT(s, ""))
+		b.WriteRune('>')
+	}
 	return b.String()
 }
 
@@ -1001,6 +1004,8 @@ func (_primitive[T]) WITKind() string {
 		return "char"
 	case string:
 		return "string"
+	case errorContext:
+		return "error-context"
 	default:
 		panic(fmt.Sprintf("BUG: unknown primitive type %T", v)) // should never reach here
 	}