Tags: patch

I'm proposing we change the format (type) of the "tags" field in the
`erc-response' struct from

  (STRING . LIST)

where LIST contains at most one (possibly empty) string, to

  (SYMBOL . OPT-STRING)

where OPT-STRING, when non-nil, is a nonempty string. For ERC 5.5 and
Emacs 29, this change would merely manifest as a warning when first
encountered. In subsequent releases, it would still be reserved only for
users who opt in by activating optional modules. Rationale below.

Thanks,
J.P.


Imagined FAQ:

  Why bother?

    In the existing implementation, all code accessing a processed tag
    value must check that it's both non-nil and nonempty. This stands to
    become a common occurrence with the arrival of IRCv3 in future
    releases. The majority of instances will only contain one item (a
    timestamp) and will persist beyond the parsing stage as text
    properties in ERC buffers. And since we need to redo the parsing
    anyway to abide by all the escaping rules and other spec minutiae,
    we might as well make the processed goods as easy to manage as
    possible, no?

  Isn't this a breaking change?

    Yes. But I believe preserving backward compatibility (by adding an
    additional field and keeping the old one around) is less important
    in this case because the field currently goes unused in ERC's client
    code and is likely underused in user code (based on a cursory survey
    of Melpa packages, popular shared configs, and wiki snippets). While
    message tags *are* currently parsed when present, the field is only
    ever written to and never again accessed (on account of ERC's lack
    of general IRCv3 support). That said, the library function as well
    as the `erc-response' structure are indeed public (exported).

    There is also the matter of authoritative intent to consider. The
    doc string for the function `erc-parse-tags' describes its return
    type as being an alist of "(tag . value)". For anyone willing to
    entertain "value" as meaning "logical tag value," this change
    becomes a belated bug fix.

  Why now? Why not wait?

    It's true that the main benefit of doing this won't be felt for a
    couple more ERC releases. As stated above, the immediate effect of
    this change will merely be as a warning for any user code that
    depends on this field. This approach seems somewhat in keeping with
    the overall Emacs policy for function and variable deprecation.


In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
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