Re: [PATCH v2] userdiff: add support for Swift

> Add a built-in userdiff driver for the Swift programming language so that
> diff hunk headers and word diffs work out of the box for ".swift" files.
>
> The funcname pattern is built for Swift's own declaration grammar: an
> optional run of attributes ("@objc", "@available(iOS 13, *)", ...),
> followed by an optional run of lowercase modifiers ("public", "static",
> "final", ...), followed by a declaration keyword (func, class, struct,
> enum, protocol, extension, actor, init, deinit, subscript). The keyword
> is followed by a boundary that allows whitespace, "(" (init/subscript),
> "?" or "!" (failable init), or "<" (generics), while still acting as a
> word boundary so e.g. "initialize(" does not match.
>
> The word regex recognizes Swift identifiers, hexadecimal, octal, binary,
> integer and floating-point literals, and the language's operators.
>
> Signed-off-by: Shlok Kulshreshtha <diy2903@gmail.com>
> ---
> v2, addressing Johannes Sixt's review of v1
> (<2a3a73c5-5e90-44a3-bf6a-6e98ce5e5a59@kdbg.org>).  Changes since v1:
>
>  - t4018/swift-{init,failable-init,generic-subscript}: "RIGHT" now
>    appears only once, on the declaration line, so the expected header is
>    unambiguous.
>  - word regex: dropped the redundant "?" after the single-character
>    operator class.  Single characters are already covered by the
>    "|[^[:space:]]" fallback that the PATTERNS macro appends, so only the
>    two-character forms need to be spelled out.
>
> (A couple of Hannes's other suggestions I kept as-is; I have explained
> the reasoning in a reply to his review.)