Support a single Resource per MeterProvider in the SDK (#2120)

* Remove resource from export.Record

* fix bridge/opencensus

* partial fixes in exporters/otlp/otlpmetric

* Use go-cmp to simplify exporter_test

* OTLP http/grpc

* prometheus

* fix stdout (pending PR 2015)

* oc bridge cleanups

* Lint and changelog

* pr num

* cleanup

* revert

* fix multiple

* always merge the environment

* lint

* precommit

* qualify package names in changelog

sdk/metric/controller/basic/controller.go

@@ -59,6 +59,7 @@ type Controller struct {
 	accumulator  *sdk.Accumulator
 	provider     *registry.MeterProvider
 	checkpointer export.Checkpointer
+	resource     *resource.Resource
 	exporter     export.Exporter
 	wg           sync.WaitGroup
 	stopCh       chan struct{}
@@ -88,16 +89,19 @@ func New(checkpointer export.Checkpointer, opts ...Option) *Controller {
 	}
 	if c.Resource == nil {
 		c.Resource = resource.Default()
+	} else {
+		var err error
+		c.Resource, err = resource.Merge(resource.Environment(), c.Resource)
+		if err != nil {
+			otel.Handle(err)
+		}
 	}
-
-	impl := sdk.NewAccumulator(
-		checkpointer,
-		c.Resource,
-	)
+	impl := sdk.NewAccumulator(checkpointer)
 	return &Controller{
 		provider:     registry.NewMeterProvider(impl),
 		accumulator:  impl,
 		checkpointer: checkpointer,
+		resource:     c.Resource,
 		exporter:     c.Exporter,
 		stopCh:       nil,
 		clock:        controllerTime.RealClock{},
@@ -121,6 +125,12 @@ func (c *Controller) MeterProvider() metric.MeterProvider {
 	return c.provider
 }
 
+// Resource returns the *resource.Resource associated with this
+// controller.
+func (c *Controller) Resource() *resource.Resource {
+	return c.resource
+}
+
 // Start begins a ticker that periodically collects and exports
 // metrics with the configured interval.  This is required for calling
 // a configured Exporter (see WithExporter) and is otherwise optional
@@ -257,7 +267,7 @@ func (c *Controller) export(ctx context.Context) error {
 		defer cancel()
 	}
 
-	return c.exporter.Export(ctx, ckpt)
+	return c.exporter.Export(ctx, c.resource, ckpt)
 }
 
 // ForEach gives the caller read-locked access to the current