Several blank lines in multi-line scalar values collapsed to one

[Witiko]

See peposso#13:

The following two YAML documents will produce the same output when passed to tinyyaml.parse().

first_input = [[
abstract: |
  This is *the abstract*.
  It consists of two paragraphs.
]]

second_input = [[
abstract: |
  This is *the abstract*.

  It consists of two paragraphs.
]]

tinyyaml = require("tinyyaml")
for k, v in pairs(tinyyaml.parse(first_input)) do
  print(k, v)
end
for k, v in pairs(tinyyaml.parse(second_input)) do
  print(k, v)
end

Executing the above code in Lua 5.2.4 and in Lua 5.3 gives me the following results:

abstract        This is *the abstract*.
It consists of two paragraphs.

abstract        This is *the abstract*.
It consists of two paragraphs.

Here is the expected output:

abstract        This is *the abstract*.
It consists of two paragraphs.

abstract        This is *the abstract*.

It consists of two paragraphs.

The following seems to be the cause:

lua-tinyyaml/tinyyaml.lua

Line 358 in fe0e8e5

if s[i] == '' then

This behavior is contrary to the YAML spec (emphasis mine):

The literal style is denoted by the “|” indicator. It is the simplest, most restricted, and most readable scalar style. [...] Inside literal scalars, all (indented) characters are considered to be content, including white space characters. Note that all line break characters are normalized. In addition, empty lines are not folded, though final line breaks and trailing empty lines are chomped.

— YAML Ain’t Markup Language (YAML™) Version 1.2, 3rd Edition, Patched at 2009-10-01, Section 8.1.2. Literal Style

[spacewander]

The empty lines are removed from the beginning...

lua-tinyyaml/tinyyaml.lua

Line 719 in 264cead

lines = select(lines, function(s) return not isemptyline(s) end)

[Witiko]

@spacewander You are right. Is this intentional, or should I take a stab at fixing it? In my application, blank lines are meaningful.

[spacewander]

I think the author missed this corner case.

[kalekje]

Upvoting this! Noticed the same issue.

[Witiko]

@spacewander @kalekje I propose a fix in #11.