Dne 13. 09. 23 v 16:06 Jernej Tuljak napsal(a):
On 13/09/2023 14:26, Jan Lindblad (jlindbla) wrote:
Jernej,
Hat off for the tools (and tool vendors!) that assist authors to stay
true to YANG RFC sections 10 and 11 also. Well done. :-)
I intentionally used "compiler" rather than "toolchain", "IDE" or
something more open ended, because a compiler is what I have and can
speak for.
Even so, I have a hard time thinking the customers of even the best
YANG IDEs would be interested to pay the effort for distinguishing
between YANG 1.1 and YANG 1.2 solely on the proposed RFC wording
difference. Since a BC verification capability apparently already
exists in some IDEs, I think it would make sense for their vendors to
turn the checks it into a warnings (if they aren't already),
regardless of which yang-version statement is found in the module header.
This might mean a non-zero implementation effort for a few YANG
toolchain implementors. While this is a good point, it does not really
sway my opinion about what the pragmatic choice for IETF is. Or
Jernej, do you think the users of those good IDEs would prefer a new
YANG version? If so, why?
If you are asking whether I'd like to see a new version of YANG for the
sole purpose of changing those MUST and MUST NOTs - no, I would not.
However, a change like this mandates a yang-version bump, IMHO.
Right, so we have two ugly options, but bumping YANG version really
makes no sense, so breaking those few tools that check update rules
looks like a better choice to me.
We have already seen cases that the update rules prevented fixing
problems in YANG modules in a straightforward way, and
backward-compatible fixes negatively affected module readability. This
is inevitable until the ecosystem of YANG modules stabilizes. That's why
I think changing update rules from MUST to SHOULD is appropriate - it
should have been so from the beginning.
Lada
Jernej
Best Regards,
/jan
On 13 Sep 2023, at 10:57, Jernej Tuljak <jernej.tul...@mg-soft.si> wrote:
On 12/09/2023 14:43, Jan Lindblad (jlindbla) wrote:
Jürgen, all,
I see the irony in changing the YANG RFC(s) without updating the
YANG language version number, but digging a bit deeper, I think the
question is not as clear-cut as it might seem at first.
Altering the contents of the backwards-compatibility section of RFC
6020 (sec 10) and RFC 7950 (sec 11) clearly implies changes in YANG
module authors' behavior.
Speaking as a YANG compiler implementor, however, I don't see any
changes that have to made to the compiler because of this RFC
change. There are no new keywords, none are removed. There is no
change in the meaning of existing keywords. There is no difference
in the output the compiler needs to generate.
So while there are changes to the YANG *standard* (meaning RFCs)
there is no actual change to the YANG *language*. If we require
user's to mark their modules with version 1.2 (or 2.0), from the
compiler's pov, that would just be an alias for YANG 1.1. It means a
fair amount of trouble to update all the tools out there to accept
"yang-version 1.2" but do nothing new. It also adds a burden to YANG
module implementors, since they would have to go through all YANG
1.1 modules and mark them 1.2, for no change in meaning. For
organizations with some modules still on YANG 1.0, the bar is even
higher.
I think the most pragmatic approach in this case would be to change
the RFC text in the backwards-compatibility sections and not update
the yang-version number as long as no change is required in the
compilers. If anyone can point to actual things the compiler needs
to do differently, I'd be interested to hear.
You will first have to define what a YANG compiler is before you can
make such assumptions. YANG code validation rules may be implemented
in several ways, depending on what the tool that utilizes them is
used for. I choose to call that a "validation engine" - "compiler"
implies translation into a lower level language in my world and not
all tools require that. I know of at least one tool that utilizes a
validation engine that performs the checks in Updating a Module
sections of RFC 6020 and RFC 7950, when requested. And I would expect
a YANG authoring tool to do the same if it claims full RFC
compliance. Those are not optional guidelines intended just for
humans. It is true that some of the rules can only be reliably
checked by a human, but not all (or even most) of them. Point being -
there are implementations out there that rely on the text of this
Section to remain unchanged. I would imagine that they represent a
drop in the sea compared to implementations that have chosen to
completely ignore the spec (forking YANG into YANG' in the process),
but they do exist.
I disagree that changing those sections does not change the language.
Of course it does. It makes combinations of language constructs, that
were previously not allowed, valid. This is no different to
prescribing a mandatory-to-implement YANG extension.
File versioning is baked into YANG, a peculiarity of the language.
There are many more such peculiarities. I'd like to know what other
backward incompatible changes to the spec I can expect to occur in
the future because there's now a precedent for it.
Jernej
Best Regards,
/jan
On 12 Sep 2023, at 07:55, Jürgen Schönwälder
<jschoenwaelder@constructor.university> wrote:
I disagree with the poll. There are important teachnigal differences
behind the two options that this polls tries to hide.
Updating YANG 1 and YANG 1.1 means creating YANG 1' and YANG
1.1'. There is no way that a new versioning approach will be
understood by existing YANG tooling. That's an illusion.
/js
On Mon, Sep 11, 2023 at 10:39:39PM +0000, Kent Watsen wrote:
WG,
Please help the YANG-versioning effort move forward by
participating in the following poll:
- https://notes.ietf.org/netmod-2023-sept-poll (Datatracker
login required)
Kent and Lou
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