Reworked Error message in newParam() in services.go

[gunadhya]

References to other Issues or PRs

Fixes #1863

Have you read the Contributing Guidelines?

Yes

Brief description of what is fixed or changed

Changes to error format

Before:

grpc-gateway/internal/descriptor/services.go

Line 251 in 26104fd

return Parameter{}, fmt.Errorf("aggregate type %s in parameter of %s.%s: %s", target.Type, meth.Service.GetName(), meth.GetName(), path)

After:

return Parameter{}, fmt.Errorf("%s.%s: %s is a protobuf message type. Protobuf message types cannot be used as path parameters, use a scalar value type (such as string) instead", meth.Service.GetName(), meth.GetName(), path)

Other comments

[johanbrandhorst]

Thanks for this PR, do you think you could add a test which triggers this error? You can look at

grpc-gateway/internal/descriptor/services_test.go

Line 558 in 4bfe484

func TestExtractServicesWithPathParam(t *testing.T) {

for an example of a test that uses a path parameter.

[johanbrandhorst]

Thanks for your contribution!