I started typing up some of my thoughts on this into a proposal:
https://docs.google.com/document/d/1qvCH9aHwCzp5qtKTna4jJXuloNU0b96gAxAHSKPuXpU/edit?usp=sharing

(anyone with the link can comment on but not edit the document)

I haven't gotten very far but I thought I would throw it out here for early
review/feedback.
I think if we can agree on some of the basics, we can work towards it
incrementally.
I think it wouldn't be too hard to come up with a spec for rule storage
that could both capture the current possible rules in KiCad 5, and also the
new things we want to make available in 6.

-Jon

On Sat, Apr 14, 2018 at 11:04 AM, Wayne Stambaugh <stambau...@gmail.com>
wrote:

> On 04/14/2018 10:46 AM, Jeff Young wrote:
> > I still don’t think I’d put netclass dimensions in the schematic.
> >  However, I do completely agree with putting the netclass *set* (and net
> > membership) in the schematic.
>
> I see netclasses as just another constraint.  I use the same netclasses
> over and over again in my projects so having a way to make them easily
> shareable between projects would be useful to me.  I'm not sure a
> separate method to handle netclasses versus all other constraints makes
> sense.  I do agree that it should be possible to defined them in the
> schematic editor.  I would think a properly designed constraint editor
> would work equally well in both the schematic and board editors as well
> as stand alone.  Given what I have learned about the board file design,
> saving the netclasses and other constraints in the schematic file
> doesn't make sense.  This will need to be defined before I can begin
> writing the new schematic file format.
>
> >
> > For that kind of stuff we could start leaning more heavily on the
> > project file, or we could use inter-app communication as we do for the
> > netlist.
>
> I would consider inter-app communication a given regardless of where we
> store this information.  What form the inter-app communication takes is
> certainly open for discussion.  It could be using our kiway messaging or
> it could be a file watcher that updates the constraints when the
> constraint file is edited.
>
> >
> > From first blush I’d prefer the later (as it makes stand-alone files
> > more viable).  But, like I said, first blush….
> >
> >
> >> On 14 Apr 2018, at 15:37, Jon Evans <j...@craftyjon.com
> >> <mailto:j...@craftyjon.com>> wrote:
> >>
> >> It's also a somewhat common workflow for design rules to be driven
> >> from the schematic (rather than created as part of board layout).
> >> Having a separate file for design rules isn't the only way to do that,
> >> but I just wanted to mention that use case so that it is also
> >> considered. In that workflow, you need a way to define design rules
> >> before there is even a PCB design started.
> >>
> >> On Sat, Apr 14, 2018, 10:29 Wayne Stambaugh <stambau...@gmail.com
> >> <mailto:stambau...@gmail.com>> wrote:
> >>
> >>     It makes sense to me to have importing and exporting constraints
> >>     as part
> >>     of the design.  I would also add copying a default constraints file
> as
> >>     part of the new project and new project by template commands.  I
> think
> >>     that pretty much covers all of the bases.
> >>
> >>     On 04/14/2018 10:23 AM, Jeff Young wrote:
> >>     > Good point.  A lot of the constraints are defined by the fab
> >>     house rather than the particular board design.
> >>     >
> >>     > FrameMaker had a “Use Formats From” feature which imported page
> >>     layouts, paragraph formats, variable definitions, etc. from
> >>     another document.  Our customers liked that a lot better than
> >>     having to manage yet another file.
> >>     >
> >>     >> On 14 Apr 2018, at 15:14, Wayne Stambaugh <stambau...@gmail.com
> >>     <mailto:stambau...@gmail.com>> wrote:
> >>     >>
> >>     >> We definitely should define this before we get too far down the
> >>     road.  I
> >>     >> would rather not store layout constraints in the board file if
> >>     at all
> >>     >> possible.  I think this was somewhat shortsighted when I
> originally
> >>     >> wrote the current board file format.  I would rather the
> >>     constraints be
> >>     >> written either to a separate file or into the configuration
> >>     file so they
> >>     >> can easily be reused between projects.  I find that I reuse the
> >>     same
> >>     >> constraints from project to project so being able to easily
> >>     reuse them
> >>     >> without having to reenter them every new project or modify the
> >>     board
> >>     >> file with a text editor would be rather handy.  This would also
> >>     have a
> >>     >> nice side effect of the board file format not changing every
> >>     time we
> >>     >> want to add a new constraint.
> >>     >>
> >>     >> Wayne
> >>     >>
> >>     >> On 04/14/2018 09:37 AM, Jon Evans wrote:
> >>     >>> I see what you are saying, but I also think that if there's
> >>     any chance
> >>     >>> we will be able to define a spec/format for design rules this
> >>     cycle, we
> >>     >>> can avoid the need for multiple (potentially incompatible)
> >>     changes to
> >>     >>> the way rules are stored during the development cycle.
> >>     >>>
> >>     >>> On Sat, Apr 14, 2018, 09:25 Jeff Young <j...@rokeby.ie
> >>     <mailto:j...@rokeby.ie>
> >>     >>> <mailto:j...@rokeby.ie <mailto:j...@rokeby.ie>>> wrote:
> >>     >>>
> >>     >>>    Hi Jon,
> >>     >>>
> >>     >>>    I agree we should have that conversation, but I also don’t
> >>     want to
> >>     >>>    fall into the trap of doing nothing until you can do
> >>     everything.
> >>     >>>
> >>     >>>    We don’t store even the single set of differential pair
> >>     dimensions
> >>     >>>    in the board right now.
> >>     >>>
> >>     >>>    Cheers,
> >>     >>>    Jeff.
> >>     >>>
> >>     >>>
> >>     >>>>    On 14 Apr 2018, at 14:12, Jon Evans <j...@craftyjon.com
> >>     <mailto:j...@craftyjon.com>
> >>     >>>>    <mailto:j...@craftyjon.com <mailto:j...@craftyjon.com>>>
> wrote:
> >>     >>>>
> >>     >>>>    I'm not exactly sure what you're planning, but I think
> >>     before you
> >>     >>>>    go too far down this road we should have a conversation /
> >>     plan for
> >>     >>>>    how we actually want DRC to work architecturally.
> >>     >>>>
> >>     >>>>    There are definitely lots of reasons to have multiple diff
> >>     pair
> >>     >>>>    rules per board, and also have those rules only apply to
> >>     certain
> >>     >>>>    areas of the board.
> >>     >>>>
> >>     >>>>    There might not be a specific feature request for this
> >>     because it
> >>     >>>>    is part of a request for a net class system and rule by
> >>     area system.
> >>     >>>>
> >>     >>>>    The ideal DRC system, in my mind at least, has a split
> >>     between the
> >>     >>>>    "what objects does this rule apply to" part and the "what
> >>     is this
> >>     >>>>    rule and what are its limits" part. That makes it very
> >>     flexible
> >>     >>>>    and easy to expand.
> >>     >>>>
> >>     >>>>    It would be nice to be able to build a rule kind of like a
> >>     >>>>    database query like:
> >>     >>>>
> >>     >>>>    "If something is part of a diff pair AND "is part of net
> class
> >>     >>>>    'USB'" AND is within the polygon 'FlexArea'"
> >>     >>>>
> >>     >>>>    Then once you have a selector that applies to the objects
> you
> >>     >>>>    want, you can apply whatever rule is relevant (trace widths,
> >>     >>>>    spacing, what vias are allowed, how close copper pours can
> >>     come,
> >>     >>>>    and 100 other things if you like)
> >>     >>>>
> >>     >>>>    (the above selector happens to rely on two features that
> KiCad
> >>     >>>>    doesn't have yet, but could have for V6: net classes and
> >>     named areas)
> >>     >>>>
> >>     >>>>    These selectors would be cascading, like CSS, so you could
> >>     define
> >>     >>>>    a base set of rules that apply to everything, and more
> >>     specific
> >>     >>>>    rules that override things defined in the general rules.
> >>     >>>>
> >>     >>>>    Not a super trivial bit of code to write, but an important
> >>     one in
> >>     >>>>    my mind since it's the only way to offer the flexibility
> >>     of rules
> >>     >>>>    that people who are used to tools like
> >>     Altium/Cadence/Mentor are
> >>     >>>>    used to.
> >>     >>>>
> >>     >>>>    -Jon
> >>     >>>>
> >>     >>>>
> >>     >>>>    On Sat, Apr 14, 2018, 08:57 Jeff Young <j...@rokeby.ie
> >>     <mailto:j...@rokeby.ie>
> >>     >>>>    <mailto:j...@rokeby.ie <mailto:j...@rokeby.ie>>> wrote:
> >>     >>>>
> >>     >>>>        I was looking into moving the solder mask and paste
> >>     >>>>        dimensions, courtyard rules, and differential pairs
> >>     dimensions
> >>     >>>>        to the board for 6.0.  It seemed like having multiple
> >>     sets of
> >>     >>>>        differential pair dimensions (like we do for tracks
> >>     and vias)
> >>     >>>>        would be good, yet there are no feature requests for
> >>     this.
> >>     >>>>        Are differential pairs specific enough that there is
> >>     usually
> >>     >>>>        only one spec per board?
> >>     >>>>
> >>     >>>>        Thanks,
> >>     >>>>        Jeff.
> >>     >>>>        _______________________________________________
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> >>     >>>
> >>     >>>
> >>     >>>
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