Tolerate Configure panics if one provider errors out (#2931)

Minimally scoped panic recovery to address the scenario found in
pulumi/pulumi-gcp#3007

GCP expects failure in Configure for SDKv2 to be final. When our code
attempts to call Configure for PF after that failure, it results in a
panic.

I do not know if fail-on-first-error is the desired behavior as it seems
preferable to collect all the errors to show to the user if possible.
Therefore this PR is scoped to tolerate panics if there have been
preceding errors.

pkg/x/muxer/muxer.go

@@ -302,7 +302,20 @@ func (m *muxer) Configure(ctx context.Context, req *pulumirpc.ConfigureRequest)
 
 	for _, s := range m.servers {
 		req := proto.Clone(req).(*pulumirpc.ConfigureRequest)
-		r, err := s.Configure(ctx, req)
+
+		var r *pulumirpc.ConfigureResponse
+		var err error
+
+		if errs.Len() > 0 {
+			var panicked bool
+			r, panicked, err = panicRecoveringConfigure(ctx, s, req)
+			if panicked {
+				continue
+			}
+		} else {
+			r, err = s.Configure(ctx, req)
+		}
+
 		if err != nil {
 			errs.Errors = append(errs.Errors, err)
 			continue
@@ -317,6 +330,20 @@ func (m *muxer) Configure(ctx context.Context, req *pulumirpc.ConfigureRequest)
 	return response, m.muxedErrors(errs)
 }
 
+func panicRecoveringConfigure(
+	ctx context.Context,
+	s server,
+	req *pulumirpc.ConfigureRequest,
+) (response *pulumirpc.ConfigureResponse, panicked bool, finalError error) {
+	defer func() {
+		if p := recover(); p != nil {
+			panicked = true
+		}
+	}()
+	r, err := s.Configure(ctx, req)
+	return r, false, err
+}
+
 type resourceRequest interface {
 	GetUrn() string
 }

pkg/x/muxer/muxer_test.go

@@ -224,6 +224,46 @@ func TestConfigureInSequence(t *testing.T) {
 	}
 }
 
+// Some providers such as pulumi-gcp will panic in PluginFramework Configure if SDKv2 Configure has
+// produced errors. That is they do not expect both being called in the error case. This test checks
+// that such panics are ignored and processed as expected.
+func TestConfigureIgnorePanics(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+
+	m := &muxer{
+		host: &host{},
+		servers: []server{
+			configureReturnsErrors{},
+			configurePanics{},
+		},
+	}
+	_, err := m.Configure(ctx, &pulumirpc.ConfigureRequest{})
+	require.Error(t, err)
+}
+
+type configureReturnsErrors struct {
+	pulumirpc.UnimplementedResourceProviderServer
+}
+
+func (x configureReturnsErrors) Configure(
+	ctx context.Context,
+	req *pulumirpc.ConfigureRequest,
+) (*pulumirpc.ConfigureResponse, error) {
+	return nil, fmt.Errorf("Required configuration values have not been set")
+}
+
+type configurePanics struct {
+	pulumirpc.UnimplementedResourceProviderServer
+}
+
+func (x configurePanics) Configure(
+	ctx context.Context,
+	req *pulumirpc.ConfigureRequest,
+) (*pulumirpc.ConfigureResponse, error) {
+	panic("Configure panics unexpectedly")
+}
+
 type configure struct {
 	pulumirpc.UnimplementedResourceProviderServer
 	t       *testing.T