Hi Italo, IMO RFC7950 Section 11 makes the second case NBC (and I remember it being confirmed on this list in the past). It may not turn out to be impactful depending on the client design (and if only XML is used) but officially it is NBC. The type of the leaf is changing from whatever foo is, to type ‘union’. (even changes from uint8 to uint16 are NBC).
Some of those sections of 7950 are really focussed on XML encoding. But YANG is intended to work with other encodings (and some of those may not encode foo in and out of a union in the same way). Jason From: Italo Busi <[email protected]> Sent: Thursday, January 18, 2024 3:19 PM To: Jason Sterne (Nokia) <[email protected]>; Reshad Rahman <[email protected]>; Jan Lindblad <[email protected]> Cc: [email protected] Subject: RE: [netmod] Is changing the type with union a BC change? Hi Reshad, Jason, Jan, Thanks for your replies I have found these pieces of text in sections 9.12 and 11 which might be interpreted as stating that the changes to the union are BC: When generating an XML encoding, a value is encoded according to the rules of the member type to which the value belongs. When interpreting an XML encoding, a value is validated consecutively against each member type, in the order they are specified in the "type" statement, until a match is found. The type that matched will be the type of the value for the node that was validated, and the encoding is interpreted according to the rules for that type. <…> The lexical representation of a union is a value that corresponds to the representation of any one of the member types. <…> The canonical form of a union value is the same as the canonical form of the member type of the value. <…> o A "type" statement may be replaced with another "type" statement that does not change the syntax or semantics of the type. For example, an inline type definition may be replaced with a typedef, but an int8 type cannot be replaced by an int16, since the syntax would change. Given these definitions I am wondering whether having a different encoding between the union and its member types is a valid encoding according to RFC7950 If this is the case, my feeling is that both examples can be considered BC changes at least when the base types are the same (e.g., type foo, bar and baz are all strings) Italo From: Jason Sterne (Nokia) <[email protected]<mailto:[email protected]>> Sent: giovedì 18 gennaio 2024 19:33 To: Reshad Rahman <[email protected]<mailto:[email protected]>>; Jan Lindblad <[email protected]<mailto:[email protected]>>; Italo Busi <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> Subject: RE: [netmod] Is changing the type with union a BC change? It was subtle and I can’t remember the exact reasoning (or section of RFC7950) but I think Martin pointed it out. Basically: adding another member to a union that already has members of that same type doesn’t change the possible encodings or storage types. But adding a new member with a new/different type (that wasn’t part of the union previously) suddenly introduces the possibility of a new type for that leaf. So it kinda falls under “don’t change the base type(s)”. From: Reshad Rahman <[email protected]<mailto:[email protected]>> Sent: Thursday, January 18, 2024 10:59 AM To: Jan Lindblad <[email protected]<mailto:[email protected]>>; Italo Busi <[email protected]<mailto:[email protected]>>; Jason Sterne (Nokia) <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> Subject: Re: [netmod] Is changing the type with union a BC change? You don't often get email from [email protected]<mailto:[email protected]>. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification> CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information. Hi Jason, I agree for the second case, and IIRC we did discuss that in the yang-module-versioning context. But the first case, I don't understand why it's NBC if there's a new type. Encodings of the OLD types wouldn't change? Regards, Reshad. On Thursday, January 18, 2024, 09:36:46 AM EST, Jason Sterne (Nokia) <[email protected]<mailto:[email protected]>> wrote: Hi guys, The second case is NBC. I remember wondering the same thing myself but the type in OLD is foo which the type in NEW is union. That is NBC (and in some encodings outside of XML, sending that leaf with type foo vs type union, member foo would be different). OLD type foo; NEW type union { type foo; type bar } The first case is NBC if the addition of the new member adds a new type to the list of members. So it depends on the underlying types of foo, bar and baz. If they were all strings, for example, then it is BC. But if foo and bar are “int” and then “baz” is a string, then adding that new member type into the union is NBC. Jason From: netmod <[email protected]<mailto:[email protected]>> On Behalf Of Jan Lindblad Sent: Thursday, January 18, 2024 5:13 AM To: Italo Busi <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> Subject: Re: [netmod] Is changing the type with union a BC change? CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information. Italo, Yes, this too would be BC according to the rules. There may be some situations where this kind of change might be disruptive in the real world, however, for example if you did this to a list key. Best Regards, /jan Thanks Jan Following the same logic, also the following change can be considered BC: OLD type foo; NEW type union { type foo; type bar } Is my understanding correct? Thanks again Italo From: Jan Lindblad <[email protected]<mailto:[email protected]>> Sent: giovedì 18 gennaio 2024 10:33 To: Italo Busi <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> Subject: Re: [netmod] Is changing the type with union a BC change? Italo, Yes, in my judgement this change should be considered BC according to YANG rules. Note that the BC concept is a sort of *agreement* between client and server implementors that determines what kind of changes a) are allowed + b) have to be tolerated. Even when things are BC, that does not guarantee that things will always keep interoperating properly. Best Regards, /jan On 17 Jan 2024, at 23:22, Italo Busi <[email protected]<mailto:[email protected]>> wrote: I have some questions/doubts about whether changing a type with union is a BC or NBC change For example, is the following change a BC or NBC change? OLD type union { type foo; type bar } NEW type union { type foo; type bar; type baz } Section 11 of RFC7950 is silent on this case although this change is expanding the allowed value space and therefore it looks like a BC change Thanks, Italo _______________________________________________ netmod mailing list [email protected]<mailto:[email protected]> https://www.ietf.org/mailman/listinfo/netmod _______________________________________________ netmod mailing list [email protected]<mailto:[email protected]> https://www.ietf.org/mailman/listinfo/netmod
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