Alfredo writes (below for full thread)
That is a deceptively simple question you ask there :-) I don't
have a strong view myself, but I can offer the perspective of
somebody who was been for a long time on the "other side of the
trenches" (i.e. working Haskell programmer, not necessarily
working GHC programmer):
* Blog post: yes, it's true that is a snapshot, and it's true
that is not under GHC's gitlab umbrella, so I wouldn't treat it
as a reliable source of documentation (for the reasons you also
explain) but it's surely a good testament that "at this point in
time, for this particular GHC commit, things were this way);
* The wiki page: in the past, when I wanted to learn more about
some GHC feature, Google would point me to the relevant Wiki page
on the GHC repo describing such a feature, but I have to say I
have almost always dismissed it, because everybody knows
Wikis are seldomly up-to-date :) In order for a Wiki page to work
we would have to at least add a banner at the top that states
this can be trusted as a reliable source of information, and
offer in the main section the current, up-to-date design. We can
still offer the historical breakdown of the designs in later
sections, as it's still valuable info to keep;
* GHC notes: I have always considered GHC notes a double-edge
sword -- from one side they are immensely useful when navigating
the source code, but these won't be rendered in the Hackage's
haddocks, and this is not helpful for GHC-the-library users
willing to understand how to use (or which is the semantic of) a
particular type (sure, one can click "Show Source" on Hackage but
it's an annoying extra step to do just to hunt for notes). We
already have Notes for this work in strategic places -- even
better, we have proper Haddock comments for things like "Severity
vs DiagnosticReason" , e.g.
https://gitlab.haskell.org/ghc/ghc/-/blob/master/compiler/GHC/Types/Error.hs#L279
<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fblob%2Fmaster%2Fcompiler%2FGHC%2FTypes%2FError.hs%23L279&data=04%7C01%7Csimonpj%40microsoft.com%7Cdb46814133bc4404b6d308d9685a487e%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637655559255320972%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=WU2dKu2Q%2FFdwntJ2h%2F6zO1Ic01c9o0VhZc5JrE0AurY%3D&reserved=0>
.
Yes Haddock doesn’t understand Notes but that’s a deficiency in
Haddock! There so much in GHC that simply does not fit well with
the Haddocks attached to a particular data decl or function. We
need Notes to explain how all the moving parts fit together, and
to point to them.
Even better, we have proper Haddock comments for things like
"Severity vs DiagnosticReason"
But I don’t think this is better – I think it is significantly
worse! In the case you cite, the Haddock is about
DiagnosticReason, and mentions Severity only incidentally. I bet
that the Haddock for Severity doesn’t refer to this. Nor is
there a clear “Note [Severity vs DiagnosticReason]” title that
bits of code across GHC can refer to by saying “See Note
[Severity vs DiagnosticReason]”. It’s far less satisfactory (to
me) than a single Note that
* covers just *one topic* (the difference between Severity and
DiagnosticReason, rather than fully describing either
* can be *pointed to* symmetrically from both Severity and
DiagnosticReason
* can be *pointed to* by many other bits of code
The way it is better is that today’s Haddock doesn’t understand
Notes. But we could fix that if we were minded to.
Returning to how to document the error-message architecture, if
you’d prefer to use a Note than a wiki page, that’s fine. But
please write that Overview Note that explains all the pieces,
points to them one by one. And then copiously refer to that Note
from all those places, so people will update it.
_Hopefully as the time goes by the new design will "spread"
across all the different peers working on GHC, and it will become
"second nature"._
I really don’t think that will happen unless there is a Note that
explains what the new design is! Lacking this explicit design,
everyone will infer their own mental model of how it all works
from sundry scattered clues – and those mental models will
differ. So instead of one thing “spreading” a dozen subtly
different things will spread. And then the next one, confused by
these slightly different clues, will be even less coherent.
Let’s have one, fully-explicit version of The Plan that we
constantly refer to.
cc’ing ghc-devs because we must constantly question and refine
how we describe and document GHC.
Simon
PS: I am leaving Microsoft at the end of November 2021, at which
point simo...@microsoft.com <mailto:simo...@microsoft.com> will
cease to work. Use simon.peytonjo...@gmail.com
<mailto:simon.peytonjo...@gmail.com> instead. (For now, it just
forwards to simo...@microsoft.com.)
*From:*Alfredo Di Napoli <alfredo.dinap...@gmail.com>
<mailto:alfredo.dinap...@gmail.com>
*Sent:* 26 August 2021 07:25
*To:* Simon Peyton Jones <simo...@microsoft.com>
<mailto:simo...@microsoft.com>
*Cc:* r...@richarde.dev
*Subject:* Re: [Haskell Community] [Links] [Well-Typed Blog] The
new GHC diagnostic infrastructure
Hello Simon!
On Wed, 25 Aug 2021 at 13:36, Simon Peyton Jones
<simo...@microsoft.com> wrote:
Alfredo
Thanks for all the work you are doing on GHC’s error message
infrastructure. Your blog post gives a great overview.
Thanks, and I am glad you enjoyed it :)
As you know I’m very keen for GHC to have a Note or wiki page
that gives a solid, up-to-date overview of all the moving
parts. (NOT the design alternatives, nor the time sequence;
just the outcome.) This is incredibly useful for our future
selves; and it helps ensure that people understand (say) the
difference between Severity and DiagnosticReason, and use
them correctly.
So the question is: where is the canonical overview? It could be
* Your blog post below. But that is a snapshot… you aren’t
going to go back to edit it as the design evolves. And
it’s not in the repo.
* The wiki page:
https://gitlab.haskell.org/ghc/ghc/-/wikis/Errors-as-(structured)-values
<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fwikis%2FErrors-as-(structured)-values&data=04%7C01%7Csimonpj%40microsoft.com%7Cdb46814133bc4404b6d308d9685a487e%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637655559255310976%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=A%2FyWqfqPWPYUk3EpaorYP29JvLIhgcdSdcYceFIKvhc%3D&reserved=0>.
But it’s hard to keep up to date (it was last edited 3
months ago).
* Note(s) in the code. We seem to use this increasingly,
and it has the great merit of being part of the source
code itself. But then we need clear pointer to the
canonical overview Notes, and need to make sure they are
up to date.
I’m not advocating any particular path here… just wanting to
be sure that we end up with a good overview somewhere! What
is your view?
_TL;DR Probably a combo of a well-written (and up-to-date Wiki)
plus some carefully added Notes (and Haddock comments) in GHC
might do the trick._
That is a deceptively simple question you ask there :-) I don't
have a strong view myself, but I can offer the perspective of
somebody who was been for a long time on the "other side of the
trenches" (i.e. working Haskell programmer, not necessarily
working GHC programmer):
* Blog post: yes, it's true that is a snapshot, and it's true
that is not under GHC's gitlab umbrella, so I wouldn't treat it
as a reliable source of documentation (for the reasons you also
explain) but it's surely a good testament that "at this point in
time, for this particular GHC commit, things were this way);
* The wiki page: in the past, when I wanted to learn more about
some GHC feature, Google would point me to the relevant Wiki page
on the GHC repo describing such a feature, but I have to say I
have almost always dismissed it, because everybody knows
Wikis are seldomly up-to-date :) In order for a Wiki page to work
we would have to at least add a banner at the top that states
this can be trusted as a reliable source of information, and
offer in the main section the current, up-to-date design. We can
still offer the historical breakdown of the designs in later
sections, as it's still valuable info to keep;
* GHC notes: I have always considered GHC notes a double-edge
sword -- from one side they are immensely useful when navigating
the source code, but these won't be rendered in the Hackage's
haddocks, and this is not helpful for GHC-the-library users
willing to understand how to use (or which is the semantic of) a
particular type (sure, one can click "Show Source" on Hackage but
it's an annoying extra step to do just to hunt for notes). We
already have Notes for this work in strategic places -- even
better, we have proper Haddock comments for things like "Severity
vs DiagnosticReason" , e.g.
https://gitlab.haskell.org/ghc/ghc/-/blob/master/compiler/GHC/Types/Error.hs#L279
<https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2F-%2Fblob%2Fmaster%2Fcompiler%2FGHC%2FTypes%2FError.hs%23L279&data=04%7C01%7Csimonpj%40microsoft.com%7Cdb46814133bc4404b6d308d9685a487e%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637655559255320972%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=WU2dKu2Q%2FFdwntJ2h%2F6zO1Ic01c9o0VhZc5JrE0AurY%3D&reserved=0>
.
_So, in practical terms, I suggest we (I) give the Wiki a little
overhaul to add at the top the current design (or anything not
captured directly in GHC's source code) and I will keep an eye on
the GHC notes and Haddock comments to see if there is anything
worth adding. Hopefully as the time goes by the new design will
"spread" across all the different peers working on GHC, and it
will become "second nature"._
Hope it helps, and sorry for the long ramble!
Alfredo
Thanks
Simon
*From:*Alfredo Di Napoli via Haskell Community
<discou...@haskell.org>
*Sent:* 23 August 2021 11:26
*To:* Simon Peyton Jones <simo...@microsoft.com>
*Subject:* [Haskell Community] [Links] [Well-Typed Blog] The
new GHC diagnostic infrastructure
Image removed by sender.
*adinapoli*
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August 23
Image removed by sender.*well-typed.com*
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*Error! Filename not specified.*
The new GHC diagnostic infrastructure - Well-Typed: The
Haskell Consultants
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