Move eachregion(::AnnotatedString) implementation to Base (#57912)

Excising part of #56194 on the
way to reviving that PR.

(cherry picked from commit a5e0eab)

Author: topolarity

base/strings/annotated.jl

@@ -460,201 +460,109 @@ function annotated_chartransform(f::Function, str::AnnotatedString, state=nothin
     AnnotatedString(String(take!(outstr)), annots)
 end
 
-## AnnotatedIOBuffer
-
-struct AnnotatedIOBuffer <: AbstractPipe
-    io::IOBuffer
-    annotations::Vector{RegionAnnotation}
-end
-
-AnnotatedIOBuffer(io::IOBuffer) = AnnotatedIOBuffer(io, Vector{RegionAnnotation}())
-AnnotatedIOBuffer() = AnnotatedIOBuffer(IOBuffer())
-
-function show(io::IO, aio::AnnotatedIOBuffer)
-    show(io, AnnotatedIOBuffer)
-    size = filesize(aio.io)
-    print(io, '(', size, " byte", ifelse(size == 1, "", "s"), ", ",
-          length(aio.annotations), " annotation", ifelse(length(aio.annotations) == 1, "", "s"), ")")
+struct RegionIterator{S <: AbstractString}
+    str::S
+    regions::Vector{UnitRange{Int}}
+    annotations::Vector{Vector{Annotation}}
 end
 
-pipe_reader(io::AnnotatedIOBuffer) = io.io
-pipe_writer(io::AnnotatedIOBuffer) = io.io
-
-# Useful `IOBuffer` methods that we don't get from `AbstractPipe`
-position(io::AnnotatedIOBuffer) = position(io.io)
-seek(io::AnnotatedIOBuffer, n::Integer) = (seek(io.io, n); io)
-seekend(io::AnnotatedIOBuffer) = (seekend(io.io); io)
-skip(io::AnnotatedIOBuffer, n::Integer) = (skip(io.io, n); io)
-copy(io::AnnotatedIOBuffer) = AnnotatedIOBuffer(copy(io.io), copy(io.annotations))
-
-annotations(io::AnnotatedIOBuffer) = io.annotations
-
-annotate!(io::AnnotatedIOBuffer, range::UnitRange{Int}, label::Symbol, @nospecialize(val::Any)) =
-    (_annotate!(io.annotations, range, label, val); io)
-
-function write(io::AnnotatedIOBuffer, astr::Union{AnnotatedString, SubString{<:AnnotatedString}})
-    astr = AnnotatedString(astr)
-    offset = position(io.io)
-    eof(io) || _clear_annotations_in_region!(io.annotations, offset+1:offset+ncodeunits(astr))
-    _insert_annotations!(io, astr.annotations)
-    write(io.io, String(astr))
-end
+Base.length(si::RegionIterator) = length(si.regions)
 
-write(io::AnnotatedIOBuffer, c::AnnotatedChar) =
-    write(io, AnnotatedString(string(c), [(region=1:ncodeunits(c), a...) for a in c.annotations]))
-write(io::AnnotatedIOBuffer, x::AbstractString) = write(io.io, x)
-write(io::AnnotatedIOBuffer, s::Union{SubString{String}, String}) = write(io.io, s)
-write(io::AnnotatedIOBuffer, b::UInt8) = write(io.io, b)
-
-function write(dest::AnnotatedIOBuffer, src::AnnotatedIOBuffer)
-    destpos = position(dest)
-    isappending = eof(dest)
-    srcpos = position(src)
-    nb = write(dest.io, src.io)
-    isappending || _clear_annotations_in_region!(dest.annotations, destpos:destpos+nb)
-    srcannots = [setindex(annot, max(1 + srcpos, first(annot.region)):last(annot.region), :region)
-                 for annot in src.annotations if first(annot.region) >= srcpos]
-    _insert_annotations!(dest, srcannots, destpos - srcpos)
-    nb
+Base.@propagate_inbounds function Base.iterate(si::RegionIterator, i::Integer=1)
+    if i <= length(si.regions)
+        @inbounds ((SubString(si.str, si.regions[i]), si.annotations[i]), i+1)
+    end
 end
 
-# So that read/writes with `IOContext` (and any similar `AbstractPipe` wrappers)
-# work as expected.
-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
+Base.eltype(::RegionIterator{S}) where { S <: AbstractString} =
+    Tuple{SubString{S}, Vector{Annotation}}
 
 """
-    _clear_annotations_in_region!(annotations::Vector{$RegionAnnotation}, span::UnitRange{Int})
+    eachregion(s::AnnotatedString{S})
+    eachregion(s::SubString{AnnotatedString{S}})
 
-Erase the presence of `annotations` within a certain `span`.
+Identify the contiguous substrings of `s` with a constant annotations, and return
+an iterator which provides each substring and the applicable annotations as a
+`Tuple{SubString{S}, Vector{$Annotation}}`.
 
-This operates by removing all elements of `annotations` that are entirely
-contained in `span`, truncating ranges that partially overlap, and splitting
-annotations that subsume `span` to just exist either side of `span`.
+# Examples
+
+```jldoctest; setup=:(using Base: AnnotatedString, eachregion)
+julia> collect(eachregion(AnnotatedString(
+           "hey there", [(1:3, :face, :bold),
+                         (5:9, :face, :italic)])))
+3-element Vector{Tuple{SubString{String}, Vector{$Annotation}}}:
+ ("hey", [$Annotation((:face, :bold))])
+ (" ", [])
+ ("there", [$Annotation((:face, :italic))])
+```
 """
-function _clear_annotations_in_region!(annotations::Vector{RegionAnnotation}, span::UnitRange{Int})
-    # Clear out any overlapping pre-existing annotations.
-    filter!(ann -> first(ann.region) < first(span) || last(ann.region) > last(span), annotations)
-    extras = Tuple{Int, RegionAnnotation}[]
-    for i in eachindex(annotations)
-        annot = annotations[i]
-        region = annot.region
-        # Test for partial overlap
-        if first(region) <= first(span) <= last(region) || first(region) <= last(span) <= last(region)
-            annotations[i] =
-                setindex(annot,
-                         if first(region) < first(span)
-                             first(region):first(span)-1
-                         else
-                             last(span)+1:last(region)
-                         end,
-                         :region)
-            # If `span` fits exactly within `region`, then we've only copied over
-            # the beginning overhang, but also need to conserve the end overhang.
-            if first(region) < first(span) && last(span) < last(region)
-                push!(extras, (i, setindex(annot, last(span)+1:last(region), :region)))
-            end
+function eachregion(s::AnnotatedString, subregion::UnitRange{Int}=firstindex(s):lastindex(s))
+    isempty(s) || isempty(subregion) &&
+        return RegionIterator(s.string, UnitRange{Int}[], Vector{Annotation}[])
+    events = annotation_events(s, subregion)
+    isempty(events) && return RegionIterator(s.string, [subregion], [Annotation[]])
+    annotvals = Annotation[
+        (; label, value) for (; label, value) in annotations(s)]
+    regions = Vector{UnitRange{Int}}()
+    annots = Vector{Vector{Annotation}}()
+    pos = first(events).pos
+    if pos > first(subregion)
+        push!(regions, thisind(s, first(subregion)):prevind(s, pos))
+        push!(annots, [])
+    end
+    activelist = Int[]
+    for event in events
+        if event.pos != pos
+            push!(regions, pos:prevind(s, event.pos))
+            push!(annots, annotvals[activelist])
+            pos = event.pos
+        end
+        if event.active
+            insert!(activelist, searchsortedfirst(activelist, event.index), event.index)
+        else
+            deleteat!(activelist, searchsortedfirst(activelist, event.index))
         end
     end
-    # Insert any extra entries in the appropriate position
-    for (offset, (i, entry)) in enumerate(extras)
-        insert!(annotations, i + offset, entry)
+    if last(events).pos < nextind(s, last(subregion))
+        push!(regions, last(events).pos:thisind(s, last(subregion)))
+        push!(annots, [])
     end
-    annotations
+    RegionIterator(s.string, regions, annots)
 end
 
-"""
-    _insert_annotations!(io::AnnotatedIOBuffer, annotations::Vector{$RegionAnnotation}, offset::Int = position(io))
+function eachregion(s::SubString{<:AnnotatedString}, pos::UnitRange{Int}=firstindex(s):lastindex(s))
+    if isempty(s)
+        RegionIterator(s.string, Vector{UnitRange{Int}}(), Vector{Vector{Annotation}}())
+    else
+        eachregion(s.string, first(pos)+s.offset:last(pos)+s.offset)
+    end
+end
 
-Register new `annotations` in `io`, applying an `offset` to their regions.
+"""
+    annotation_events(string::AbstractString, annots::Vector{$RegionAnnotation}, subregion::UnitRange{Int})
+    annotation_events(string::AnnotatedString, subregion::UnitRange{Int})
 
-The largely consists of simply shifting the regions of `annotations` by `offset`
-and pushing them onto `io`'s annotations. However, when it is possible to merge
-the new annotations with recent annotations in accordance with the semantics
-outlined in [`AnnotatedString`](@ref), we do so. More specifically, when there
-is a run of the most recent annotations that are also present as the first
-`annotations`, with the same value and adjacent regions, the new annotations are
-merged into the existing recent annotations by simply extending their range.
+Find all annotation "change events" that occur within a `subregion` of `annots`,
+with respect to `string`. When `string` is styled, `annots` is inferred.
 
-This is implemented so that one can say write an `AnnotatedString` to an
-`AnnotatedIOBuffer` one character at a time without needlessly producing a
-new annotation for each character.
+Each change event is given in the form of a `@NamedTuple{pos::Int, active::Bool,
+index::Int}` where `pos` is the position of the event, `active` is a boolean
+indicating whether the annotation is being activated or deactivated, and `index`
+is the index of the annotation in question.
 """
-function _insert_annotations!(io::AnnotatedIOBuffer, annotations::Vector{RegionAnnotation}, offset::Int = position(io))
-    run = 0
-    if !isempty(io.annotations) && last(last(io.annotations).region) == offset
-        for i in reverse(axes(annotations, 1))
-            annot = annotations[i]
-            first(annot.region) == 1 || continue
-            i <= length(io.annotations) || continue
-            if annot.label == last(io.annotations).label && annot.value == last(io.annotations).value
-                valid_run = true
-                for runlen in 1:i
-                    new = annotations[begin+runlen-1]
-                    old = io.annotations[end-i+runlen]
-                    if last(old.region) != offset || first(new.region) != 1 || old.label != new.label || old.value != new.value
-                        valid_run = false
-                        break
-                    end
-                end
-                if valid_run
-                    run = i
-                    break
-                end
-            end
+function annotation_events(s::AbstractString, annots::Vector{RegionAnnotation}, subregion::UnitRange{Int})
+    events = Vector{NamedTuple{(:pos, :active, :index), Tuple{Int, Bool, Int}}}() # Position, Active?, Annotation index
+    for (i, (; region)) in enumerate(annots)
+        if !isempty(intersect(subregion, region))
+            start, stop = max(first(subregion), first(region)), min(last(subregion), last(region))
+            start <= stop || continue # Currently can't handle empty regions
+            push!(events, (pos=thisind(s, start), active=true, index=i))
+            push!(events, (pos=nextind(s, stop), active=false, index=i))
         end
     end
-    for runindex in 0:run-1
-        old_index = lastindex(io.annotations) - run + 1 + runindex
-        old = io.annotations[old_index]
-        new = annotations[begin+runindex]
-        io.annotations[old_index] = setindex(old, first(old.region):last(new.region)+offset, :region)
-    end
-    for index in run+1:lastindex(annotations)
-        annot = annotations[index]
-        start, stop = first(annot.region), last(annot.region)
-        push!(io.annotations, setindex(annotations[index], start+offset:stop+offset, :region))
-    end
+    sort(events, by=e -> e.pos)
 end
 
-function read(io::AnnotatedIOBuffer, ::Type{AnnotatedString{T}}) where {T <: AbstractString}
-    if (start = position(io)) == 0
-        AnnotatedString(read(io.io, T), copy(io.annotations))
-    else
-        annots = [setindex(annot, UnitRange{Int}(max(1, first(annot.region) - start), last(annot.region)-start), :region)
-                  for annot in io.annotations if last(annot.region) > start]
-        AnnotatedString(read(io.io, T), annots)
-    end
-end
-read(io::AnnotatedIOBuffer, ::Type{AnnotatedString{AbstractString}}) = read(io, AnnotatedString{String})
-read(io::AnnotatedIOBuffer, ::Type{AnnotatedString}) = read(io, AnnotatedString{String})
-
-function read(io::AnnotatedIOBuffer, ::Type{AnnotatedChar{T}}) where {T <: AbstractChar}
-    pos = position(io)
-    char = read(io.io, T)
-    annots = [NamedTuple{(:label, :value)}(annot) for annot in io.annotations if pos+1 in annot.region]
-    AnnotatedChar(char, annots)
-end
-read(io::AnnotatedIOBuffer, ::Type{AnnotatedChar{AbstractChar}}) = read(io, AnnotatedChar{Char})
-read(io::AnnotatedIOBuffer, ::Type{AnnotatedChar}) = read(io, AnnotatedChar{Char})
-
-function truncate(io::AnnotatedIOBuffer, size::Integer)
-    truncate(io.io, size)
-    filter!(ann -> first(ann.region) <= size, io.annotations)
-    map!(ann -> setindex(ann, first(ann.region):min(size, last(ann.region)), :region),
-         io.annotations, io.annotations)
-    io
-end
+annotation_events(s::AnnotatedString, subregion::UnitRange{Int}) =
+    annotation_events(s.string, annotations(s), subregion)