Allow escaped | chars in tables

Markdown tables might require literal `|` to be written within a
cell, such as when writing the function `|`. This allows `|`
to be escaped using a `\`.

base/markdown/GitHub/table.jl

@@ -8,10 +8,10 @@ end
 function parserow(stream::IO)
  withstream(stream) do
  line = readline(stream) |> chomp
- row = split(line, "|")
+ row = split(line, r"(?<!\\)\|")
  length(row) == 1 && return
  row[1] == "" && shift!(row)
- map!(strip, row)
+ map!(x -> strip(replace(x, "\\|", "|")), row)
  row[end] == "" && pop!(row)
  return row
  end
@@ -103,7 +103,9 @@ _dash(width, align) =
  throw(ArgumentError("Invalid alignment $align"))
 
 function plain(io::IO, md::Table)
- cells = mapmap(plaininline, md.rows)
+ cells = mapmap(md.rows) do each
+ replace(plaininline(each), "|", "\\|")
+ end
  padcells!(cells, md.align, len = length, min = 3)
  for i = indices(cells,1)
  print(io, "| ")

test/markdown.jl

@@ -362,6 +362,15 @@ let text =
  table = Markdown.parse(text)
  @test text == Markdown.plain(table)
 end
+let text =
+ """
+ | a | b |
+ |:-------- | ---:|
+ | `x \\| y` | 2 |
+ """,
+ table = Markdown.parse(text)
+ @test text == Markdown.plain(table)
+end
 
 # LaTeX extension