Introduce specialised write for AnnotatedIOBuffer

src/io.jl

@@ -274,6 +274,20 @@ function show(io::IO, c::AnnotatedChar)
     end
 end
 
+function write(io::IO, aio::Base.AnnotatedIOBuffer)
+    if get(io, :color, false) == true
+        # This does introduce an overhead that technically
+        # could be avoided, but I'm not sure that it's currently
+        # worth the effort to implement an efficient version of
+        # writing from a AnnotatedIOBuffer with style.
+        # In the meantime, by converting to an `AnnotatedString` we can just
+        # reuse all the work done to make that work.
+        write(io, read(aio, AnnotatedString))
+    else
+        write(io, aio.io)
+    end
+end
+
 """
 A mapping between ANSI named colors and 8-bit colors for use in HTML
 representations.

test/runtests.jl

@@ -235,6 +235,17 @@ end
     @test normal == styled == "abcdef"
 end
 
+@testset "AnnotatedIOBuffer" begin
+    aio = Base.AnnotatedIOBuffer()
+    @test write(aio, styled"{red:hey} {blue:there}") == 9
+    buf = IOBuffer()
+    @test write(buf, seekstart(aio)) == 9
+    @test String(take!(buf)) == "hey there"
+    cbuf = IOContext(buf, :color => true)
+    @test write(cbuf, seekstart(aio)) == 29
+    @test String(take!(buf)) == "\e[31mhey\e[39m \e[34mthere\e[39m"
+end
+
 @testset "Legacy" begin
     @test StyledStrings.Legacy.legacy_color(:blue) == SimpleColor(:blue)
     @test StyledStrings.Legacy.legacy_color(:light_blue) == SimpleColor(:bright_blue)