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Add read/write specialisation for IOContext{AnnIO} #53715

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Add specialised AnnotatedString pipe read/writes
Ensure that when an AnnotatedIOBuffer is wrapped in an IOContext (or
similar AnnotatedPipe-based construct), that writes of annotated
strings/chars and reading out an AnnotatedString is unimpeded by the
IOContext wrapping.

Without these specialisations, the generic pipe_reader/pipe_writer
fallbacks will directly access the underlying IOBuffer and annotations
will be lost.

There are a number of scenarios in which one might want to combine an
AnnotatedIOBuffer and IOContext (for example setting the compact
property). Losing annotations in such scenarios is highly undesirable.
It is of particular note that this can arise in situations where you
can't unwrap the IOContext as needed, for example when passing IO to a
function you do not control (which is currently extremely hard to work
around).

Getting this right is a little difficult, and a few approaches have been
tried. Initially, I added IOContext{AnnotatedIOBuffer} specialisations
to show.jl, but arguably it's a bit of a code smell to specialise in
this way (and Jameson wasn't happy with it, with concerns that it could
be tricked by IOContext{Any}).

    # So that read/writes with `IOContext` (and any similar `AbstractPipe` wrappers)
    # work as expected.
    write(io::IOContext{AnnotatedIOBuffer}, s::Union{AnnotatedString, SubString{<:AnnotatedString}}) =
        write(io.io, s)
    write(io::AnnotatedIOBuffer, c::AnnotatedChar) = write(io.io, c)

Then I tried making it so that IOContext writes dispatched on the
wrapped IO type, but of course that broke cases like IOContext{IOBuffer}
with :color=>true.

    # So that read/writes with `IOContext` (and any similar `AbstractPipe` wrappers)
    # work as expected.
    write(io::AbstractPipe, s::Union{AnnotatedString, SubString{<:AnnotatedString}}) =
        write(pipe_writer(io), s)
    write(io::AbstractPipe, c::AnnotatedChar) = write(pipe_writer(io), c)

Finally, we have the current AbstractPipe + Annotated type
specialisation, which IOContext is just an instance of. To avoid
behaving too broadly, we need to confirm that the underlying IO is
actually an AnnotatedIOBuffer. I'm still not happy with this, only idea
I've had other than implementing IOContext{AnnotatedIOBuffer} methods
that actually seems viable, and I've had trouble soliciting help from
other people brainstorming here.

If somebody can implement something cleaner here in the future, I'd be
thrilled.
tecosaur committed May 2, 2024
commit 9fdb4dbfc49114dc8773ec92c3ceaaaa9a42be49
18 changes: 18 additions & 0 deletions base/strings/annotated.jl
Original file line number Diff line number Diff line change
@@ -500,6 +500,24 @@ function write(dest::AnnotatedIOBuffer, src::AnnotatedIOBuffer)
nb
end

# So that read/writes with `IOContext` (and any similar `AbstractPipe` wrappers)
# work as expected.
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Still trying to wrap my brain around this:

  • by default, unsafe_write(io::AbstractPipe, ...) for simply redispatches to unsafe_write(pipe_writer(io)::IO, ...)
  • by default, all write(io, ...) methods in the end go through unsafe_write(io, ...)
  • so naively write(pipe_writer(io), s) seems pointless
  • but then there are custom write methods ... such as your write(io::AnnotatedIOBuffer, astr::Union{AnnotatedString, SubString{<:AnnotatedString}}) method...

And now we have a problem if AbstractPipe type, such as IOContext, wraps an AnnotatedIOBuffer: instead of dispatching from write(io, ...) to unsafe_write(io, ...) you need it to go through pipe_writer(io) so that the annotations can be handled by that.

What if there is a sandwich of three AbstractPipe types, say an IOContext outermost, then some other AbstractPipe type, then the AnnotatedIOBuffer -- it wouldn't work out then either, right?

This then makes me wonder: why not "simply" something like

write(io::AbstractPipe, s::AnnotatedString) = write(pipe_writer(io), s)

I bet you considered this and ruled it out for some reason, but I didn't see it in the PR discussion.

None of this is meant as fundamental objection to this PR, but I feel at least this comment should be a bit more elaborate (which, if you happen to agree with this POV, could certainly wait for a future PR -- I don't mind to hold this one up). I'd love to be helpful and suggest something, but for that I'd first have to really understand it, hence my questions :-).

function write(io::AbstractPipe, s::Union{AnnotatedString, SubString{<:AnnotatedString}})
if pipe_writer(io) isa AnnotatedIOBuffer
write(pipe_writer(io), s)
else
invoke(write, Tuple{IO, typeof(s)}, io, s)
end::Int
end
# Can't be part of the `Union` above because it introduces method ambiguities
function write(io::AbstractPipe, c::AnnotatedChar)
if pipe_writer(io) isa AnnotatedIOBuffer
write(pipe_writer(io), c)
else
invoke(write, Tuple{IO, typeof(c)}, io, c)
end::Int
end
Comment on lines +505 to +519
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The following is a 100% optional suggestion that is ultimately a matter of taste

As you are most likely aware, you could avoid the code duplication by using @eval, i.e.

Suggested change
function write(io::AbstractPipe, s::Union{AnnotatedString, SubString{<:AnnotatedString}})
if pipe_writer(io) isa AnnotatedIOBuffer
write(pipe_writer(io), s)
else
invoke(write, Tuple{IO, typeof(s)}, io, s)
end::Int
end
# Can't be part of the `Union` above because it introduces method ambiguities
function write(io::AbstractPipe, c::AnnotatedChar)
if pipe_writer(io) isa AnnotatedIOBuffer
write(pipe_writer(io), c)
else
invoke(write, Tuple{IO, typeof(c)}, io, c)
end::Int
end
# (can't do this via a single method with a 'Union' argument due to method ambiguities)
for T in (AnnotatedChar, AnnotatedString, SubString{<:AnnotatedString}) do
@eval function write(io::AbstractPipe, arg::$T)
if pipe_writer(io) isa AnnotatedIOBuffer
write(pipe_writer(io), arg)
else
invoke(write, Tuple{IO, typeof(arg)}, io, arg)
end::Int
end
end


"""
_clear_annotations_in_region!(annotations::Vector{Tuple{UnitRange{Int}, Pair{Symbol, Any}}}, span::UnitRange{Int})

7 changes: 7 additions & 0 deletions test/strings/annotated.jl
Original file line number Diff line number Diff line change
@@ -209,4 +209,11 @@ end
@test write(aio2, Base.AnnotatedChar('c', [:b => 2, :c => 3, :d => 4])) == 1
@test Base.annotations(aio2) == [(1:2, :a => 1), (1:3, :b => 2), (3:3, :c => 3), (3:3, :d => 4)]
end
# Working through an IOContext
aio = Base.AnnotatedIOBuffer()
wrapio = IOContext(aio)
@test write(wrapio, Base.AnnotatedString("hey", [(1:3, :x => 1)])) == 3
@test write(wrapio, Base.AnnotatedChar('a', [:y => 2])) == 1
@test read(seekstart(aio), Base.AnnotatedString) ==
Base.AnnotatedString("heya", [(1:3, :x => 1), (4:4, :y => 2)])
end