Add JSONMarshal to go sdk

This is not as useful for Go as it is for other languages, but it's
consistent and it saves an Apply call.

Ideally we would handle nested Output types during marshalling, but to
do that correctly we need some way to get access to
per-call-to-JSONMarshal flags to note if we see any unknowns, or
secrets.

Go just (AFAIK) have any way to support doing that.

So we do the next best thing which is we at least error that nested
Outputs can't be marshalled. Note that the `Output` interface doesn't
embed the `Marshal` interface because there _may_ be users who have
wrote their own `Output` types and that would be a breaking change.

changelog/pending/20221209--sdk-go--add-jsonmarshal-to-go-sdk.yaml

@@ -0,0 +1,4 @@
+changes:
+- type: feat
+  scope: sdk/go
+  description: Add JSONMarshal to go sdk.

sdk/go/pulumi/generate/templates/types_builtins.go.template

@@ -19,6 +19,7 @@ package pulumi
 
 import (
 	"context"
+	"fmt"
 	"reflect"
 )
 
@@ -55,6 +56,7 @@ func {{.Name}}FromPtr(v *{{.ElemElementType}}) {{.Name}}Input {
 }
 {{end}}
 {{if .DefineInputMethods}}
+
 // ElementType returns the element type of this Input ({{.ElementType}}).
 func ({{.InputType}}) ElementType() reflect.Type {
 	return {{.Name | Unexported}}Type
@@ -92,6 +94,10 @@ func (in {{.InputType}}) To{{.Name}}PtrOutputWithContext(ctx context.Context) {{
 // {{.Name}}Output is an Output that returns {{.ElementType}} values.
 type {{.Name}}Output struct { *OutputState }
 
+func ({{.Name}}Output) MarshalJSON() ([]byte, error) {
+	return nil, fmt.Errorf("Outputs can not be marshaled to JSON")
+}
+
 // ElementType returns the element type of this Output ({{.ElementType}}).
 func ({{.Name}}Output) ElementType() reflect.Type {
 	return {{.Name | Unexported}}Type

sdk/go/pulumi/types.go

@@ -17,6 +17,7 @@ package pulumi
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"reflect"
@@ -602,6 +603,18 @@ func AllWithContext(ctx context.Context, inputs ...interface{}) ArrayOutput {
 	return ToOutputWithContext(ctx, inputs).(ArrayOutput)
 }
 
+// JSONMarshal uses "encoding/json".Marshal to serialize the given Output value into a JSON string.
+func JSONMarshal(ctx context.Context, v interface{}) StringOutput {
+	o := ToOutputWithContext(ctx, v)
+	return o.ApplyTWithContext(ctx, func(_ context.Context, v interface{}) (string, error) {
+		json, err := json.Marshal(v)
+		if err != nil {
+			return "", err
+		}
+		return string(json), nil
+	}).(StringOutput)
+}
+
 func gatherJoins(v interface{}) workGroups {
 	if v == nil {
 		return nil
@@ -1065,6 +1078,10 @@ func anyWithContext(ctx context.Context, join *workGroup, v interface{}) AnyOutp
 
 type AnyOutput struct{ *OutputState }
 
+func (AnyOutput) MarshalJSON() ([]byte, error) {
+	return nil, fmt.Errorf("Outputs can not be marshaled to JSON")
+}
+
 func (AnyOutput) ElementType() reflect.Type {
 	return anyType
 }
@@ -1129,6 +1146,10 @@ func convert(v interface{}, to reflect.Type) interface{} {
 // TODO: ResourceOutput and the init() should probably be code generated.
 type ResourceOutput struct{ *OutputState }
 
+func (ResourceOutput) MarshalJSON() ([]byte, error) {
+	return nil, fmt.Errorf("Outputs can not be marshaled to JSON")
+}
+
 // ElementType returns the element type of this Output (Resource).
 func (ResourceOutput) ElementType() reflect.Type {
 	return reflect.TypeOf((*Resource)(nil)).Elem()
@@ -1192,6 +1213,10 @@ func (in ResourceArray) ToResourceArrayOutputWithContext(ctx context.Context) Re
 // ResourceArrayOutput is an Output that returns []Resource values.
 type ResourceArrayOutput struct{ *OutputState }
 
+func (ResourceArrayOutput) MarshalJSON() ([]byte, error) {
+	return nil, fmt.Errorf("Outputs can not be marshaled to JSON")
+}
+
 // ElementType returns the element type of this Output ([]Resource).
 func (ResourceArrayOutput) ElementType() reflect.Type {
 	return resourceArrayType