use less IOBuffer internals

stdlib/REPL/src/LineEdit.jl

@@ -1297,7 +1297,7 @@ _edit_indent(buf::IOBuffer, b::Int, num::Int) =
  num >= 0 ? edit_splice!(buf, b => b, ' '^num, rigid_mark=false) :
  edit_splice!(buf, b => (b - num))
 
-function mode_idx(hist #=::REPLHistoryProvider =#, mode::TextInterface)
+function mode_idx(hist::HistoryProvider, mode::TextInterface)
  c = :julia
  for (k,v) in hist.mode_mapping
  isequal(v, mode) && (c = k)
@@ -1323,29 +1323,25 @@ function edit_input(s)
  filename *= ".sh"
  end
  buf = buffer(s)
- data = buf.data
  pos = position(buf)
- size0 = buf.size
- resize!(data, buf.size) # to not write garbage into filename
- line = 1 + count(==(_newline), view(data, 1:pos))
+ str = String(take!(buf))
+ line = 1 + count(==(_newline), view(str, 1:pos))
  ct0 = open(filename, "w") do io
- write(io, data)
+ write(io, str)
  ctime(io)
  end
  InteractiveUtils.edit(filename, line)
- n, ct = open(filename) do io
- readbytes!(io, empty!(buf.data), typemax(Int)),
+ str_mod, ct = open(filename) do io
+ readchomp(io),
  ctime(io)
  end
  rm(filename)
- @assert n == length(buf.data)
- buf.size = n
- buf.ptr = n+1
  if ct0 != ct # something was changed, run the input
+ write(buf, str_mod)
  commit_line(s)
  :done
  else # no change, the edit session probably unsuccessful
- @assert n == size0
+ write(buf, str)
  seek(buf, pos) # restore state from before edit
  refresh_line(s)
  end