bug#67677: 30.0.50; ERC 5.6: Use templates for formatting chat messages

[J.P.]

Tags: patch

The most valuable messages in a typical target buffer are those
featuring a leading display name, i.e., chat messages. While ERC's many
modules exert a good deal of influence over the fit and finish of an
inserted "speaker message," the fundamental layout is mostly set in
stone beforehand. This currently happens in a somewhat haphazard
fashion, with ERC cobbling together various ingredients that may or may
not factor into the finished article, which makes predicting and
influencing crucial aspects of the final look a somewhat shaky affair.

Longtime users are likely acquainted with ERC's notion of a "language
catalog." On the surface, these are just collections of variables
sharing a common "erc-message-<catalog>-<key>" naming scheme. Each
variable's value is a `format-spec' template befitting its key. Some
keys are just IRC commands, like `JOIN', while others describe the
context in which they're typically summoned.

The real benefit of these template catalogs is twofold:

  1. They're "declarative" in the sense that their form describes their
     purpose as a model preview of the result, in plain, quasi-literal
     terms (what you see is what you get).

  2. They're also an interface, with each collection of keys and their
     respective format strings and spec parameters forming a schema of
     sorts, making extensibility essentially ingrained.

The catch here is that ERC only currently uses these catalogs for select
informative messages but not actual chat content. The proposal is thus
to extend this catalog system to encompass speaker messages.

The approach I've chosen tries to strike a balance between code reuse
and extensibility and disregards seemingly vital distinctions, like
whether a message is being sent or received. Instead, it prefers to
organize things in terms of envelope semantics. Who is it from? How
should it be delivered? Etc. The answers become parameters that form the
various catalog keys, for example, "ctcp-action-statusmsg" or
"query-notice-input". Most of these combinations come prescribed by the
IRC protocol itself and by compatibility concerns. It's mostly just the
terminology and the ordering of the components that we're free to tinker
with.

So far, the most perceptible gains are maintenance oriented. But moving
toward user-facing extensibility is mainly a matter of nailing down the
core set of keys for the base speaker catalog and exposing custom
catalogs by promoting what's currently an internal variable to a user
option. At that point, the possibilities are many. For example, over the
years, folks have expressed a desire to have both "heading-style"
display names, which occupy their own line above a message body, and
"bracketless" display names. Both are easily doable with such a system
in place. (PoC available.)

I was originally hoping to tackle this feature in 5.7, but I think the
proposed approach is mature enough to refine and ship with this release.
A number of tangential and ancillary changes are included in this set as
soft dependencies, many as follow-ons to recently "closed" bugs. I will
address some of them separately, as needed, in their respective threads.

Thanks.


In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.38, cairo version 1.17.6) of 2023-12-06 built on localhost
Repository revision: d8a00879309a3bf62f6ffcae103aa3bdba776ee9
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Fedora Linux 37 (Workstation Edition)

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Load-path shadows:
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0001-5.6-Define-ERC-message-formatting-templates-with-def.patch
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0002-5.6-Sequester-some-special-variable-declarations-in-.patch
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0003-5.6-Double-hyphenate-internal-ERC-5.6-text-props.patch
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0004-5.6-Add-erc-spkr-text-property-to-chat-messages.patch
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0005-5.6-Add-utility-for-iterating-over-arrays-in-ERC.patch
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0006-5.6-Make-erc-input-s-refoldp-slot-conditionally-avai.patch
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0007-5.6-Add-erc-server-396-response-handler.patch
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0008-5.6-Clarify-warning-for-process-dependent-input-in-E.patch
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0009-5.6-Make-erc-get-user-mode-prefix-more-flexible.patch
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0010-5.6-Skip-erc-ignored-user-p-when-erc-ignore-list-is-.patch
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0011-5.6-Use-templates-for-formatting-chat-messages-in-ER.patch
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