Implement automated marshalling for newtypes on primitives.

PiperOrigin-RevId: 296322954

3 files changed, 265 insertions, 89 deletions

diff --git a/tools/go_marshal/gomarshal/generator.go b/tools/go_marshal/gomarshal/generator.go
index 0fa868415..d365a1f3c 100644
--- a/tools/go_marshal/gomarshal/generator.go
+++ b/tools/go_marshal/gomarshal/generator.go
@@ -44,7 +44,8 @@ const (
 // All recievers are single letters, so we don't allow import aliases to be a
 // single letter.
 var badIdents = []string{
-	"addr", "blk", "buf", "dst", "dsts", "err", "hdr", "len", "ptr", "src", "srcs", "task", "val",
+	"addr", "blk", "buf", "dst", "dsts", "err", "hdr", "idx", "inner", "len",
+	"ptr", "src", "srcs", "task", "val",
 	// All single-letter identifiers.
 }
 
@@ -193,9 +194,9 @@ func (g *Generator) parse() ([]*ast.File, []*token.FileSet, error) {
 	return files, fsets, nil
 }
 
-// collectMarshallabeTypes walks the parsed AST and collects a list of type
+// collectMarshallableTypes walks the parsed AST and collects a list of type
 // declarations for which we need to generate the Marshallable interface.
-func (g *Generator) collectMarshallabeTypes(a *ast.File, f *token.FileSet) []*ast.TypeSpec {
+func (g *Generator) collectMarshallableTypes(a *ast.File, f *token.FileSet) []*ast.TypeSpec {
 	var types []*ast.TypeSpec
 	for _, decl := range a.Decls {
 		gdecl, ok := decl.(*ast.GenDecl)
@@ -222,14 +223,22 @@ func (g *Generator) collectMarshallabeTypes(a *ast.File, f *token.FileSet) []*as
 			continue
 		}
 		for _, spec := range gdecl.Specs {
-			// We already confirmed we're in a type declaration earlier.
+			// We already confirmed we're in a type declaration earlier, so this
+			// cast will succeed.
 			t := spec.(*ast.TypeSpec)
-			if _, ok := t.Type.(*ast.StructType); ok {
-				debugfAt(f.Position(t.Pos()), "Collected marshallable type %s.\n", t.Name.Name)
+			switch t.Type.(type) {
+			case *ast.StructType:
+				debugfAt(f.Position(t.Pos()), "Collected marshallable struct %s.\n", t.Name.Name)
+				types = append(types, t)
+				continue
+			case *ast.Ident: // Newtype on primitive.
+				debugfAt(f.Position(t.Pos()), "Collected marshallable newtype on primitive %s.\n", t.Name.Name)
 				types = append(types, t)
 				continue
 			}
-			debugf("Skipping declaration %v since it's not a struct declaration.\n", gdecl)
+			// A user specifically requested marshalling on this type, but we
+			// don't support it.
+			abortAt(f.Position(t.Pos()), fmt.Sprintf("Marshalling codegen was requested on type '%s', but go-marshal doesn't support this kind of declaration.\n", t.Name))
 		}
 	}
 	return types
@@ -269,12 +278,20 @@ func (g *Generator) collectImports(a *ast.File, f *token.FileSet) map[string]imp
 }
 
 func (g *Generator) generateOne(t *ast.TypeSpec, fset *token.FileSet) *interfaceGenerator {
-	// We're guaranteed to have only struct type specs by now. See
-	// Generator.collectMarshallabeTypes.
 	i := newInterfaceGenerator(t, fset)
-	i.validate()
-	i.emitMarshallable()
-	return i
+	switch ty := t.Type.(type) {
+	case *ast.StructType:
+		i.validateStruct()
+		i.emitMarshallableForStruct()
+		return i
+	case *ast.Ident:
+		i.validatePrimitiveNewtype(ty)
+		i.emitMarshallableForPrimitiveNewtype()
+		return i
+	default:
+		// This should've been filtered out by collectMarshallabeTypes.
+		panic(fmt.Sprintf("Unexpected type %+v", ty))
+	}
 }
 
 // generateOneTestSuite generates a test suite for the automatically generated
@@ -320,7 +337,7 @@ func (g *Generator) Run() error {
 	for i, a := range asts {
 		// Collect type declarations marked for code generation and generate
 		// Marshallable interfaces.
-		for _, t := range g.collectMarshallabeTypes(a, fsets[i]) {
+		for _, t := range g.collectMarshallableTypes(a, fsets[i]) {
 			impl := g.generateOne(t, fsets[i])
 			// Collect Marshallable types referenced by the generated code.
 			for ref, _ := range impl.ms {
diff --git a/tools/go_marshal/gomarshal/generator_interfaces.go b/tools/go_marshal/gomarshal/generator_interfaces.go
index 834c58cee..ea1af998e 100644
--- a/tools/go_marshal/gomarshal/generator_interfaces.go
+++ b/tools/go_marshal/gomarshal/generator_interfaces.go
@@ -55,9 +55,6 @@ func (g *interfaceGenerator) typeName() string {
 
 // newinterfaceGenerator creates a new interface generator.
 func newInterfaceGenerator(t *ast.TypeSpec, fset *token.FileSet) *interfaceGenerator {
-	if _, ok := t.Type.(*ast.StructType); !ok {
-		panic(fmt.Sprintf("Attempting to generate code for a not struct type %v", t))
-	}
 	g := &interfaceGenerator{
 		t:  t,
 		r:  receiverName(t),
@@ -103,9 +100,31 @@ func (g *interfaceGenerator) abortAt(p token.Pos, msg string) {
 	abortAt(g.f.Position(p), msg)
 }
 
-// validate ensures the type we're working with can be marshalled. These checks
-// are done ahead of time and in one place so we can make assumptions later.
-func (g *interfaceGenerator) validate() {
+func (g *interfaceGenerator) validatePrimitiveNewtype(t *ast.Ident) {
+	switch t.Name {
+	case "int8", "uint8", "byte", "int16", "uint16", "int32", "uint32", "int64", "uint64":
+		// These are the only primitive types we're allow. Below, we provide
+		// suggestions for some disallowed types and reject them, then attempt
+		// to marshal any remaining types by invoking the marshal.Marshallable
+		// interface on them. If these types don't actually implement
+		// marshal.Marshallable, compilation of the generated code will fail
+		// with an appropriate error message.
+		return
+	case "int":
+		g.abortAt(t.Pos(), "Type 'int' has ambiguous width, use int32 or int64")
+	case "uint":
+		g.abortAt(t.Pos(), "Type 'uint' has ambiguous width, use uint32 or uint64")
+	case "string":
+		g.abortAt(t.Pos(), "Type 'string' is dynamically-sized and cannot be marshalled, use a fixed size byte array '[...]byte' instead")
+	default:
+		debugfAt(g.f.Position(t.Pos()), fmt.Sprintf("Found derived type '%s', will attempt dispatch via marshal.Marshallable.\n", t.Name))
+	}
+}
+
+// validateStruct ensures the type we're working with can be marshalled. These
+// checks are done ahead of time and in one place so we can make assumptions
+// later.
+func (g *interfaceGenerator) validateStruct() {
 	g.forEachField(func(f *ast.Field) {
 		if len(f.Names) == 0 {
 			g.abortAt(f.Pos(), "Cannot marshal structs with embedded fields, give the field a name; use '_' for anonymous fields such as padding fields")
@@ -115,25 +134,7 @@ func (g *interfaceGenerator) validate() {
 	g.forEachField(func(f *ast.Field) {
 		fieldDispatcher{
 			primitive: func(_, t *ast.Ident) {
-				switch t.Name {
-				case "int8", "uint8", "byte", "int16", "uint16", "int32", "uint32", "int64", "uint64":
-					// These are the only primitive types we're allow. Below, we
-					// provide suggestions for some disallowed types and reject
-					// them, then attempt to marshal any remaining types by
-					// invoking the marshal.Marshallable interface on them. If
-					// these types don't actually implement
-					// marshal.Marshallable, compilation of the generated code
-					// will fail with an appropriate error message.
-					return
-				case "int":
-					g.abortAt(f.Pos(), "Type 'int' has ambiguous width, use int32 or int64")
-				case "uint":
-					g.abortAt(f.Pos(), "Type 'uint' has ambiguous width, use uint32 or uint64")
-				case "string":
-					g.abortAt(f.Pos(), "Type 'string' is dynamically-sized and cannot be marshalled, use a fixed size byte array '[...]byte' instead")
-				default:
-					debugfAt(g.f.Position(f.Pos()), fmt.Sprintf("Found derived type '%s', will attempt dispatch via marshal.Marshallable.\n", t.Name))
-				}
+				g.validatePrimitiveNewtype(t)
 			},
 			selector: func(_, _, _ *ast.Ident) {
 				// No validation to perform on selector fields. However this
@@ -190,7 +191,8 @@ func (g *interfaceGenerator) shiftDynamic(bufVar, name string) {
 	g.emit("%s = %s[%s.SizeBytes():]\n", bufVar, bufVar, name)
 }
 
-func (g *interfaceGenerator) marshalScalar(accessor, typ string, bufVar string) {
+// marshalStructFieldScalar writes a single scalar field from a struct to a byte slice.
+func (g *interfaceGenerator) marshalStructFieldScalar(accessor, typ, bufVar string) {
 	switch typ {
 	case "int8", "uint8", "byte":
 		g.emit("%s[0] = byte(%s)\n", bufVar, accessor)
@@ -213,43 +215,27 @@ func (g *interfaceGenerator) marshalScalar(accessor, typ string, bufVar string)
 	}
 }
 
-func (g *interfaceGenerator) unmarshalScalar(accessor, typ string, bufVar string) {
+// unmarshalStructFieldScalar reads a single scalar field from a struct, from a
+// byte slice.
+func (g *interfaceGenerator) unmarshalStructFieldScalar(accessor, typ, bufVar string) {
 	switch typ {
-	case "int8":
-		g.emit("%s = int8(%s[0])\n", accessor, bufVar)
-		g.shift(bufVar, 1)
-	case "uint8":
-		g.emit("%s = uint8(%s[0])\n", accessor, bufVar)
-		g.shift(bufVar, 1)
 	case "byte":
 		g.emit("%s = %s[0]\n", accessor, bufVar)
 		g.shift(bufVar, 1)
-
-	case "int16":
-		g.recordUsedImport("usermem")
-		g.emit("%s = int16(usermem.ByteOrder.Uint16(%s[:2]))\n", accessor, bufVar)
-		g.shift(bufVar, 2)
-	case "uint16":
+	case "int8", "uint8":
+		g.emit("%s = %s(%s[0])\n", accessor, typ, bufVar)
+		g.shift(bufVar, 1)
+	case "int16", "uint16":
 		g.recordUsedImport("usermem")
-		g.emit("%s = usermem.ByteOrder.Uint16(%s[:2])\n", accessor, bufVar)
+		g.emit("%s = %s(usermem.ByteOrder.Uint16(%s[:2]))\n", accessor, typ, bufVar)
 		g.shift(bufVar, 2)
-
-	case "int32":
-		g.recordUsedImport("usermem")
-		g.emit("%s = int32(usermem.ByteOrder.Uint32(%s[:4]))\n", accessor, bufVar)
-		g.shift(bufVar, 4)
-	case "uint32":
+	case "int32", "uint32":
 		g.recordUsedImport("usermem")
-		g.emit("%s = usermem.ByteOrder.Uint32(%s[:4])\n", accessor, bufVar)
+		g.emit("%s = %s(usermem.ByteOrder.Uint32(%s[:4]))\n", accessor, typ, bufVar)
 		g.shift(bufVar, 4)
-
-	case "int64":
-		g.recordUsedImport("usermem")
-		g.emit("%s = int64(usermem.ByteOrder.Uint64(%s[:8]))\n", accessor, bufVar)
-		g.shift(bufVar, 8)
-	case "uint64":
+	case "int64", "uint64":
 		g.recordUsedImport("usermem")
-		g.emit("%s = usermem.ByteOrder.Uint64(%s[:8])\n", accessor, bufVar)
+		g.emit("%s = %s(usermem.ByteOrder.Uint64(%s[:8]))\n", accessor, typ, bufVar)
 		g.shift(bufVar, 8)
 	default:
 		g.emit("%s.UnmarshalBytes(%s[:%s.SizeBytes()])\n", accessor, bufVar, accessor)
@@ -258,6 +244,49 @@ func (g *interfaceGenerator) unmarshalScalar(accessor, typ string, bufVar string
 	}
 }
 
+// marshalPrimitiveScalar writes a single primitive variable to a byte slice.
+func (g *interfaceGenerator) marshalPrimitiveScalar(accessor, typ, bufVar string) {
+	switch typ {
+	case "int8", "uint8", "byte":
+		g.emit("%s[0] = byte(*%s)\n", bufVar, accessor)
+	case "int16", "uint16":
+		g.recordUsedImport("usermem")
+		g.emit("usermem.ByteOrder.PutUint16(%s[:2], uint16(*%s))\n", bufVar, accessor)
+	case "int32", "uint32":
+		g.recordUsedImport("usermem")
+		g.emit("usermem.ByteOrder.PutUint32(%s[:4], uint32(*%s))\n", bufVar, accessor)
+	case "int64", "uint64":
+		g.recordUsedImport("usermem")
+		g.emit("usermem.ByteOrder.PutUint64(%s[:8], uint64(*%s))\n", bufVar, accessor)
+	default:
+		g.emit("inner := (*%s)(%s)\n", typ, accessor)
+		g.emit("inner.MarshalBytes(%s[:%s.SizeBytes()])\n", bufVar, accessor)
+	}
+}
+
+// unmarshalPrimitiveScalar read a single primitive variable from a byte slice.
+func (g *interfaceGenerator) unmarshalPrimitiveScalar(accessor, typ, bufVar, typeCast string) {
+	switch typ {
+	case "byte":
+		g.emit("*%s = %s(%s[0])\n", accessor, typeCast, bufVar)
+	case "int8", "uint8":
+		g.emit("*%s = %s(%s(%s[0]))\n", accessor, typeCast, typ, bufVar)
+	case "int16", "uint16":
+		g.recordUsedImport("usermem")
+		g.emit("*%s = %s(%s(usermem.ByteOrder.Uint16(%s[:2])))\n", accessor, typeCast, typ, bufVar)
+	case "int32", "uint32":
+		g.recordUsedImport("usermem")
+		g.emit("*%s = %s(%s(usermem.ByteOrder.Uint32(%s[:4])))\n", accessor, typeCast, typ, bufVar)
+
+	case "int64", "uint64":
+		g.recordUsedImport("usermem")
+		g.emit("*%s = %s(%s(usermem.ByteOrder.Uint64(%s[:8])))\n", accessor, typeCast, typ, bufVar)
+	default:
+		g.emit("inner := (*%s)(%s)\n", typ, accessor)
+		g.emit("inner.UnmarshalBytes(%s[:%s.SizeBytes()])\n", bufVar, accessor)
+	}
+}
+
 // areFieldsPackedExpression returns a go expression checking whether g.t's fields are
 // packed. Returns "", false if g.t has no fields that may be potentially
 // packed, otherwise returns <clause>, true, where <clause> is an expression
@@ -274,7 +303,7 @@ func (g *interfaceGenerator) areFieldsPackedExpression() (string, bool) {
 	return strings.Join(cs, " && "), true
 }
 
-func (g *interfaceGenerator) emitMarshallable() {
+func (g *interfaceGenerator) emitMarshallableForStruct() {
 	// Is g.t a packed struct without consideing field types?
 	thisPacked := true
 	g.forEachField(func(f *ast.Field) {
@@ -357,10 +386,10 @@ func (g *interfaceGenerator) emitMarshallable() {
 					}
 					return
 				}
-				g.marshalScalar(g.fieldAccessor(n), t.Name, "dst")
+				g.marshalStructFieldScalar(g.fieldAccessor(n), t.Name, "dst")
 			},
 			selector: func(n, tX, tSel *ast.Ident) {
-				g.marshalScalar(g.fieldAccessor(n), fmt.Sprintf("%s.%s", tX.Name, tSel.Name), "dst")
+				g.marshalStructFieldScalar(g.fieldAccessor(n), fmt.Sprintf("%s.%s", tX.Name, tSel.Name), "dst")
 			},
 			array: func(n, t *ast.Ident, size int) {
 				if n.Name == "_" {
@@ -377,9 +406,9 @@ func (g *interfaceGenerator) emitMarshallable() {
 					return
 				}
 
-				g.emit("for i := 0; i < %d; i++ {\n", size)
+				g.emit("for idx := 0; idx < %d; idx++ {\n", size)
 				g.inIndent(func() {
-					g.marshalScalar(fmt.Sprintf("%s[i]", g.fieldAccessor(n)), t.Name, "dst")
+					g.marshalStructFieldScalar(fmt.Sprintf("%s[idx]", g.fieldAccessor(n)), t.Name, "dst")
 				})
 				g.emit("}\n")
 			},
@@ -406,10 +435,10 @@ func (g *interfaceGenerator) emitMarshallable() {
 					}
 					return
 				}
-				g.unmarshalScalar(g.fieldAccessor(n), t.Name, "src")
+				g.unmarshalStructFieldScalar(g.fieldAccessor(n), t.Name, "src")
 			},
 			selector: func(n, tX, tSel *ast.Ident) {
-				g.unmarshalScalar(g.fieldAccessor(n), fmt.Sprintf("%s.%s", tX.Name, tSel.Name), "src")
+				g.unmarshalStructFieldScalar(g.fieldAccessor(n), fmt.Sprintf("%s.%s", tX.Name, tSel.Name), "src")
 			},
 			array: func(n, t *ast.Ident, size int) {
 				if n.Name == "_" {
@@ -426,9 +455,9 @@ func (g *interfaceGenerator) emitMarshallable() {
 					return
 				}
 
-				g.emit("for i := 0; i < %d; i++ {\n", size)
+				g.emit("for idx := 0; idx < %d; idx++ {\n", size)
 				g.inIndent(func() {
-					g.unmarshalScalar(fmt.Sprintf("%s[i]", g.fieldAccessor(n)), t.Name, "src")
+					g.unmarshalStructFieldScalar(fmt.Sprintf("%s[idx]", g.fieldAccessor(n)), t.Name, "src")
 				})
 				g.emit("}\n")
 			},
@@ -650,3 +679,144 @@ func (g *interfaceGenerator) emitMarshallable() {
 	})
 	g.emit("}\n\n")
 }
+
+// emitMarshallableForPrimitiveNewtype outputs code to implement the
+// marshal.Marshallable interface for a newtype on a primitive. Primitive
+// newtypes are always packed, so we can omit the various fallbacks required for
+// non-packed structs.
+func (g *interfaceGenerator) emitMarshallableForPrimitiveNewtype() {
+	g.recordUsedImport("io")
+	g.recordUsedImport("marshal")
+	g.recordUsedImport("reflect")
+	g.recordUsedImport("runtime")
+	g.recordUsedImport("safecopy")
+	g.recordUsedImport("unsafe")
+	g.recordUsedImport("usermem")
+
+	nt := g.t.Type.(*ast.Ident)
+
+	g.emit("// SizeBytes implements marshal.Marshallable.SizeBytes.\n")
+	g.emit("func (%s *%s) SizeBytes() int {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		if size, dynamic := g.scalarSize(nt); !dynamic {
+			g.emit("return %d\n", size)
+		} else {
+			g.emit("return (*%s)(nil).SizeBytes()\n", nt.Name)
+		}
+	})
+	g.emit("}\n\n")
+
+	g.emit("// MarshalBytes implements marshal.Marshallable.MarshalBytes.\n")
+	g.emit("func (%s *%s) MarshalBytes(dst []byte) {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.marshalPrimitiveScalar(g.r, nt.Name, "dst")
+	})
+	g.emit("}\n\n")
+
+	g.emit("// UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.\n")
+	g.emit("func (%s *%s) UnmarshalBytes(src []byte) {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.unmarshalPrimitiveScalar(g.r, nt.Name, "src", g.typeName())
+	})
+	g.emit("}\n\n")
+
+	g.emit("// Packed implements marshal.Marshallable.Packed.\n")
+	g.emit("func (%s *%s) Packed() bool {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.emit("// Scalar newtypes are always packed.\n")
+		g.emit("return true\n")
+	})
+	g.emit("}\n\n")
+
+	g.emit("// MarshalUnsafe implements marshal.Marshallable.MarshalUnsafe.\n")
+	g.emit("func (%s *%s) MarshalUnsafe(dst []byte) {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.emit("safecopy.CopyIn(dst, unsafe.Pointer(%s))\n", g.r)
+	})
+	g.emit("}\n\n")
+
+	g.emit("// UnmarshalUnsafe implements marshal.Marshallable.UnmarshalUnsafe.\n")
+	g.emit("func (%s *%s) UnmarshalUnsafe(src []byte) {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.emit("safecopy.CopyOut(unsafe.Pointer(%s), src)\n", g.r)
+	})
+	g.emit("}\n\n")
+
+	g.emit("// CopyOut implements marshal.Marshallable.CopyOut.\n")
+	g.emit("func (%s *%s) CopyOut(task marshal.Task, addr usermem.Addr) error {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		// Fast serialization.
+		g.emit("// Bypass escape analysis on %s. The no-op arithmetic operation on the\n", g.r)
+		g.emit("// pointer makes the compiler think val doesn't depend on %s.\n", g.r)
+		g.emit("// See src/runtime/stubs.go:noescape() in the golang toolchain.\n")
+		g.emit("ptr := unsafe.Pointer(%s)\n", g.r)
+		g.emit("val := uintptr(ptr)\n")
+		g.emit("val = val^0\n\n")
+
+		g.emit("// Construct a slice backed by %s's underlying memory.\n", g.r)
+		g.emit("var buf []byte\n")
+		g.emit("hdr := (*reflect.SliceHeader)(unsafe.Pointer(&buf))\n")
+		g.emit("hdr.Data = val\n")
+		g.emit("hdr.Len = %s.SizeBytes()\n", g.r)
+		g.emit("hdr.Cap = %s.SizeBytes()\n\n", g.r)
+
+		g.emit("_, err := task.CopyOutBytes(addr, buf)\n")
+		g.emit("// Since we bypassed the compiler's escape analysis, indicate that %s\n", g.r)
+		g.emit("// must live until after the CopyOutBytes.\n")
+		g.emit("runtime.KeepAlive(%s)\n", g.r)
+		g.emit("return err\n")
+	})
+	g.emit("}\n\n")
+
+	g.emit("// CopyIn implements marshal.Marshallable.CopyIn.\n")
+	g.emit("func (%s *%s) CopyIn(task marshal.Task, addr usermem.Addr) error {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.emit("// Bypass escape analysis on %s. The no-op arithmetic operation on the\n", g.r)
+		g.emit("// pointer makes the compiler think val doesn't depend on %s.\n", g.r)
+		g.emit("// See src/runtime/stubs.go:noescape() in the golang toolchain.\n")
+		g.emit("ptr := unsafe.Pointer(%s)\n", g.r)
+		g.emit("val := uintptr(ptr)\n")
+		g.emit("val = val^0\n\n")
+
+		g.emit("// Construct a slice backed by %s's underlying memory.\n", g.r)
+		g.emit("var buf []byte\n")
+		g.emit("hdr := (*reflect.SliceHeader)(unsafe.Pointer(&buf))\n")
+		g.emit("hdr.Data = val\n")
+		g.emit("hdr.Len = %s.SizeBytes()\n", g.r)
+		g.emit("hdr.Cap = %s.SizeBytes()\n\n", g.r)
+
+		g.emit("_, err := task.CopyInBytes(addr, buf)\n")
+		g.emit("// Since we bypassed the compiler's escape analysis, indicate that %s\n", g.r)
+		g.emit("// must live until after the CopyInBytes.\n")
+		g.emit("runtime.KeepAlive(%s)\n", g.r)
+		g.emit("return err\n")
+	})
+	g.emit("}\n\n")
+
+	g.emit("// WriteTo implements io.WriterTo.WriteTo.\n")
+	g.emit("func (%s *%s) WriteTo(w io.Writer) (int64, error) {\n", g.r, g.typeName())
+	g.inIndent(func() {
+		g.emit("// Bypass escape analysis on %s. The no-op arithmetic operation on the\n", g.r)
+		g.emit("// pointer makes the compiler think val doesn't depend on %s.\n", g.r)
+		g.emit("// See src/runtime/stubs.go:noescape() in the golang toolchain.\n")
+		g.emit("ptr := unsafe.Pointer(%s)\n", g.r)
+		g.emit("val := uintptr(ptr)\n")
+		g.emit("val = val^0\n\n")
+
+		g.emit("// Construct a slice backed by %s's underlying memory.\n", g.r)
+		g.emit("var buf []byte\n")
+		g.emit("hdr := (*reflect.SliceHeader)(unsafe.Pointer(&buf))\n")
+		g.emit("hdr.Data = val\n")
+		g.emit("hdr.Len = %s.SizeBytes()\n", g.r)
+		g.emit("hdr.Cap = %s.SizeBytes()\n\n", g.r)
+
+		g.emit("len, err := w.Write(buf)\n")
+		g.emit("// Since we bypassed the compiler's escape analysis, indicate that %s\n", g.r)
+		g.emit("// must live until after the Write.\n")
+		g.emit("runtime.KeepAlive(%s)\n", g.r)
+		g.emit("return int64(len), err\n")
+
+	})
+	g.emit("}\n\n")
+
+}
diff --git a/tools/go_marshal/gomarshal/generator_tests.go b/tools/go_marshal/gomarshal/generator_tests.go
index 2326e7a07..8ba47eb67 100644
--- a/tools/go_marshal/gomarshal/generator_tests.go
+++ b/tools/go_marshal/gomarshal/generator_tests.go
@@ -49,9 +49,6 @@ type testGenerator struct {
 }
 
 func newTestGenerator(t *ast.TypeSpec) *testGenerator {
-	if _, ok := t.Type.(*ast.StructType); !ok {
-		panic(fmt.Sprintf("Attempting to generate code for a not struct type %v", t))
-	}
 	g := &testGenerator{
 		t:       t,
 		r:       receiverName(t),
@@ -69,14 +66,6 @@ func (g *testGenerator) typeName() string {
 	return g.t.Name.Name
 }
 
-func (g *testGenerator) forEachField(fn func(f *ast.Field)) {
-	// This is guaranteed to succeed because g.t is always a struct.
-	st := g.t.Type.(*ast.StructType)
-	for _, field := range st.Fields.List {
-		fn(field)
-	}
-}
-
 func (g *testGenerator) testFuncName(base string) string {
 	return fmt.Sprintf("%s%s", base, strings.Title(g.t.Name.Name))
 }
@@ -89,7 +78,7 @@ func (g *testGenerator) inTestFunction(name string, body func()) {
 
 func (g *testGenerator) emitTestNonZeroSize() {
 	g.inTestFunction("TestSizeNonZero", func() {
-		g.emit("x := &%s{}\n", g.typeName())
+		g.emit("var x %v\n", g.typeName())
 		g.emit("if x.SizeBytes() == 0 {\n")
 		g.inIndent(func() {
 			g.emit("t.Fatal(\"Marshallable.SizeBytes() should not return zero\")\n")
@@ -100,7 +89,7 @@ func (g *testGenerator) emitTestNonZeroSize() {
 
 func (g *testGenerator) emitTestSuspectAlignment() {
 	g.inTestFunction("TestSuspectAlignment", func() {
-		g.emit("x := %s{}\n", g.typeName())
+		g.emit("var x %v\n", g.typeName())
 		g.emit("analysis.AlignmentCheck(t, reflect.TypeOf(x))\n")
 	})
 }