This is a quick post that want to describe a curious thing discovered 3 days ago. A partner contacted me on a social network (yes, I answer also on my socials but please don’t abuse on questions here, I have an email address…) and said me that he had problems on deploying an update of a per-tenant extension (big extension) to a SaaS tenant (the extension was previously working).
The error that occours when publishing the extension was the following:
Unable to cast object of type 'Microsoft.Dynamics.Nav.CodeAnalysis.Symbols.ExtendedErrorTypeSymbol' to type 'Microsoft.Dynamics.Nav.CodeAnalysis.Symbols.FieldSymbol'.
Nothing more…
My first question to the partner was: do you have errors on your code? Answer: NO. And do you have warnings? CodeAnalysis reminds me to something related to code compiling… Answer: YES, a lot of warnings, but we don’t care about them now.
Oh wait… you cannot forgot warnings without a check. So, we started checking the big list of warnings and I’ve discovered the following situation: in this extension (different developers works on the code), the partner creates a tableextension object for the Vendor table for adding a big set of fields.
Then, in the new extension’s update, they modify the property of one of these fields in the following way (they forgot that the field was added in the tableextension object itself):
As you can see, the field here is modified before its declaration. The AL language signals you that this is a warning:
But unfortunately this is signaled only as a warning, not as an error. If you forgot to fix this warning and you deploy this extension to your SaaS tenant, you receive the above error message (that it’s not so intuitive for the developers I think). In my opinion, this warning should be converted as an error immediately.
Please always check warnings in your code! A clean code should not have any warnings. The only admitted warnings where you can delay the fixes are the warnings related to Microsoft’s obsoletes things, where you have a time window to adapt your code to the new Microsoft’s refactored things. But at the end your extensions should always be “warning free”.
Stefano Demiliani 
Too bad there are already 20 million useless and ridiculous warnings and more being constantly created by microsoft. No one is going to take them seriously as long as most of them are totally nonsense, and as long as ms keeps making breaking changes. There’s no way to maintain a codebase without these “warnings”, as long as we work full week keeping the code working in response to constant changes in the platform.
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