Fix the ability of websockets to get errors

Because DispatchOperation creates tempResponseContext,
which is passed into Exec, which is then used in _Subscription to
generate the next function. Inside the various subscription functions
when generating next the context was captured there.

Which means later when the returned function from DispatchOperation is
called. The responseContext which accumulates the errors is the
tempResponseContext which we no longer have access to to read the errors
out of it.

Instead add a context to next() so that it can be passed through and
accumulated the errors as expected.

Added a unit test for this as well.

codegen/directives.gotpl

@@ -70,7 +70,7 @@ func (ec *executionContext) _mutationMiddleware(ctx context.Context, obj *ast.Op
 {{ end }}
 
 {{ if .Directives.LocationDirectives "SUBSCRIPTION" }}
-func (ec *executionContext) _subscriptionMiddleware(ctx context.Context, obj *ast.OperationDefinition, next func(ctx context.Context) (interface{}, error)) func() graphql.Marshaler {
+func (ec *executionContext) _subscriptionMiddleware(ctx context.Context, obj *ast.OperationDefinition, next func(ctx context.Context) (interface{}, error)) func(ctx context.Context) graphql.Marshaler {
 	for _, d := range obj.Directives {
 		switch d.Name {
 		{{- range $directive := .Directives.LocationDirectives "SUBSCRIPTION" }}
@@ -80,7 +80,7 @@ func (ec *executionContext) _subscriptionMiddleware(ctx context.Context, obj *as
 				args, err := ec.{{ $directive.ArgsFunc }}(ctx,rawArgs)
 				if err != nil {
 					ec.Error(ctx, err)
-					return func() graphql.Marshaler {
+					return func(ctx context.Context) graphql.Marshaler {
 						return graphql.Null
 					}
 				}
@@ -98,15 +98,15 @@ func (ec *executionContext) _subscriptionMiddleware(ctx context.Context, obj *as
 	tmp, err := next(ctx)
 	if err != nil {
 		ec.Error(ctx, err)
-		return func() graphql.Marshaler {
+		return func(ctx context.Context) graphql.Marshaler {
 			return graphql.Null
 		}
 	}
-	if data, ok := tmp.(func() graphql.Marshaler); ok {
+	if data, ok := tmp.(func(ctx context.Context) graphql.Marshaler); ok {
 		return data
 	}
 	ec.Errorf(ctx, `unexpected type %T from directive, should be graphql.Marshaler`, tmp)
-	return func() graphql.Marshaler {
+	return func(ctx context.Context) graphql.Marshaler {
 		return graphql.Null
 	}
 }

codegen/field.gotpl

@@ -1,6 +1,6 @@
 {{- range $object := .Objects }}{{- range $field := $object.Fields }}
 
-func (ec *executionContext) _{{$object.Name}}_{{$field.Name}}(ctx context.Context, field graphql.CollectedField{{ if not $object.Root }}, obj {{$object.Reference | ref}}{{end}}) (ret {{ if $object.Stream }}func(){{ end }}graphql.Marshaler) {
+func (ec *executionContext) _{{$object.Name}}_{{$field.Name}}(ctx context.Context, field graphql.CollectedField{{ if not $object.Root }}, obj {{$object.Reference | ref}}{{end}}) (ret {{ if $object.Stream }}func(ctx context.Context){{ end }}graphql.Marshaler) {
 	{{- $null := "graphql.Null" }}
 	{{- if $object.Stream }}
 		{{- $null = "nil" }}
@@ -38,7 +38,7 @@ func (ec *executionContext) _{{$object.Name}}_{{$field.Name}}(ctx context.Contex
 		return {{ $null }}
 	}
 	{{- if $object.Stream }}
-		return func() graphql.Marshaler {
+		return func(ctx context.Context) graphql.Marshaler {
 			res, ok := <-resTmp.(<-chan {{$field.TypeReference.GO | ref}})
 			if !ok {
 				return nil

codegen/generated!.gotpl

@@ -190,7 +190,7 @@
 			var buf bytes.Buffer
 			return func(ctx context.Context) *graphql.Response {
 				buf.Reset()
-				data := next()
+				data := next(ctx)
 
 				if data == nil {
 					return nil

codegen/object.gotpl

@@ -3,7 +3,7 @@
 var {{ $object.Name|lcFirst}}Implementors = {{$object.Implementors}}
 
 {{- if .Stream }}
-func (ec *executionContext) _{{$object.Name}}(ctx context.Context, sel ast.SelectionSet) func() graphql.Marshaler {
+func (ec *executionContext) _{{$object.Name}}(ctx context.Context, sel ast.SelectionSet) func(ctx context.Context) graphql.Marshaler {
 	fields := graphql.CollectFields(ec.OperationContext, sel, {{$object.Name|lcFirst}}Implementors)
 	ctx = graphql.WithFieldContext(ctx, &graphql.FieldContext{
 		Object: {{$object.Name|quote}},

codegen/root_.gotpl

@@ -157,7 +157,7 @@ func (e *executableSchema) Exec(ctx context.Context) graphql.ResponseHandler {
 		var buf bytes.Buffer
 		return func(ctx context.Context) *graphql.Response {
 			buf.Reset()
-			data := next()
+			data := next(ctx)
 
 			if data == nil {
 				return nil

codegen/testserver/followschema/nulls.graphql

@@ -6,6 +6,10 @@ extend type Query {
     valid: String!
 }
 
+extend type Subscription {
+	errorRequired: Error!
+}
+
 type Errors {
     a: Error!
     b: Error!

codegen/testserver/followschema/resolver.go

@@ -372,6 +372,10 @@ func (r *subscriptionResolver) Issue896b(ctx context.Context) (<-chan []*CheckIs
 	panic("not implemented")
 }
 
+func (r *subscriptionResolver) ErrorRequired(ctx context.Context) (<-chan *Error, error) {
+	panic("not implemented")
+}
+
 func (r *userResolver) Friends(ctx context.Context, obj *User) ([]*User, error) {
 	panic("not implemented")
 }