Attribute substitution silently fails or crashes inside for loops

[eggdropsoap]

This haml template demonstrates various ways attribute substitution fails inside for loops:

.attributes-work-outside-loops
  %a(href="#{links[1].url}" title="#{links[1].title}")= links[1].title
  %a(href="#{links[2].url}" title="#{links[2].title}")= links[2].title
-# -# uncomment for crash
-# .accessing-tables-in-attributes-throws-error-in-loops
-#   - for i,link in pairs(links) do
-#     %a(href="#{link.url}" title="#{link.title}")= link.title
.simple-attributes-in-loops-dont-error-but-dont-replace-either-but-DO-work-outside-attributes
  - for i,link in pairs(links) do
    %a(href="#{i}" title="#{i}")= i
.this-workaround-for-loops-is-self-defeating
  - for i,link in pairs(links) do
    = "<a href='" .. link.url .. "' title='" .. link.title .. "'>" .. link.title .. "</a>"
.this-workaround-might-clobber-things
  - for i,link in pairs(links) do
    - locals["i"] = i
    - locals["link"] = link
    %a(href="#{link.url}" title="#{link.title}")= link.title

When stored in bug.haml and used in this Lua:

haml = require "haml"

haml_options = {format = "html5"}
engine = haml.new(haml_options)

links = {}
links[1] = {}
links[1].url = "http://example.com"
links[1].title = "Example dot com"
links[2] = {}
links[2].url = "http://example.com"
links[2].title = "Also example dot com"

locals = {links}
template = "bug.haml"
rendered = engine:render_file(template,locals)
print (rendered)

it produces this output:

<div class='attributes-work-outside-loops'>
  <a href='http://example.com' title='Example dot com'>Example dot com</a>
  <a href='http://example.com' title='Also example dot com'>Also example dot com</a>
</div>
<div class='simple-attributes-in-loops-dont-error-but-dont-replace-either-but-DO-work-outside-attributes'>
  <a href='#{i}' title='#{i}'>1</a>
  <a href='#{i}' title='#{i}'>2</a>
</div>
<div class='this-workaround-for-loops-is-self-defeating'>
  <a href='http://example.com' title='Example dot com'>Example dot com</a>
  <a href='http://example.com' title='Also example dot com'>Also example dot com</a>
</div>
<div class='this-workaround-might-clobber-things'>
  <a href='http://example.com' title='Example dot com'>Example dot com</a>
  <a href='http://example.com' title='Also example dot com'>Also example dot com</a>
</div>

When the "crash" loop in the haml is uncommented, Lua 5.1.5 produces this error:

/home/redacted/local/bin/lua: /home/redacted/local/share/lua/5.1/haml/renderer.lua:139: 
Error in bug.haml at line 7 (offset 278): attempt to index global 'link' (a nil value)
stack traceback:
    [C]: in function 'error'
    /home/redacted/local/share/lua/5.1/haml/renderer.lua:139: in function 'render'
    /home/redacted/local/share/lua/5.1/haml.lua:67: in function </home/redacted/local/share/lua/5.1/haml.lua:64>
    (tail call): ?
    ./demo.lua:21: in main chunk
    [C]: ?