Re: mandoc: -Tlint: spurious warning about empty IP macro

[G. Branden Robinson]

Hi Alex,

At 2022-11-10T00:31:27+0100, Alejandro Colomar wrote:
> mandoc: man2/mount_setattr.2:644:2: WARNING: skipping paragraph macro:
> IP empty

I suspect this warning did not anticipate that a paragraphing macro
might be used solely for its spacing function, which is not redundant
with an adjacent paragraphing macro if (1) the amount of inter-pargraph
space has been changed (`PD`) or (2) the relative inset distance has
been changes (`RS`, `RE`).  In your exhibit (below), you do both.

> Unless I'm very confused, that macro is necessary there.  First let's
> see that part of the rendered page (using groff 1.23.0):
> 
>        •  The   underlying  filesystem  must  support  ID‐mapped
>           mounts.  Currently, the following filesystems  support
>           ID‐mapped mounts:
> 
>           •  xfs(5) (since Linux 5.12)
>           •  ext4(5) (since Linux 5.12)
>           •  FAT (since Linux 5.12)
>           [...]
> 
> That code is from when I made lists consistent, a few weeks ago.  The
> code is:
> 
> .IP \(bu
> The underlying filesystem must support ID-mapped mounts.
> Currently, the following filesystems support ID-mapped mounts:
> .\" fs_flags = FS_ALLOW_IDMAP in kernel sources
> .IP
> .RS
> .PD 0
> .IP \(bu 3
> .BR xfs (5)
> (since Linux 5.12)
> .IP \(bu
> .BR ext4 (5)
> (since Linux 5.12)
> .IP \(bu
> .B FAT
> (since Linux 5.12)
> 
> If I remove that .IP, the blank line between the inner list and the
> outer list vanishes.

Yes.  Almost any paragraphing macro would do the same here.  Have you
tried simply 'P'?  Maybe mandoc(1) recognizes that as idiomatic for its
spacing function.

In the event you end up needing to retreat to raw roff for this, I would
replace the "empty" `IP` call with a simple `sp` request.

> Not that I think, let's try mandoc(1):
> 
>        •  The underlying filesystem must support ID-mapped mounts.
>           Currently, the following filesystems support ID-mapped
>           mounts:
>           •  xfs(5) (since Linux 5.12)
>           •  ext4(5) (since Linux 5.12)
>           •  FAT (since Linux 5.12)
> 
> Hmm, the warning seems legit for mandoc(1): it's actually ignoring it.
> But that seems like a bug in mandoc(1) to me.

Indeed, I am not sure I agree with mandoc(1)'s rendering of this input.

In groff man(7), we could solve this gracefully--that is, without
messing with `PD`--with new list management macros `LS` and `LE`; it
composes in obvious ways with paragraphing macros before and after, and
with relative insets.  This is cleaner, in my opinion, than mdoc(7)'s
'-compact' and '-offset' options to its `Bl` macro.  This has come up
before[1].  Maybe I'll take another run at the icy wall of conservatism
that greets all such things after groff 1.23 is finalized.

Regards,
Branden

[1] https://lists.gnu.org/archive/html/groff/2022-05/msg00025.html

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