Crash when specifying parameter names in `metamethod __index` function

[13k]

Using tl stable 0.15.2.

When specifying parameter names in __index signature, tl crashes:

local record R
  metamethod __index: function(self: R, key: string): any
end

function R:brackets()
  print(self["x"])
end

function R:dot()
  print(self.x)
end

> tl check meta-index.tl
.../lua: .../share/lua/5.4/tl.lua:7528: attempt to index a nil value (field 'e1')
stack traceback:
        .../share/lua/5.4/tl.lua:7528: in upvalue 'check_call'
        .../share/lua/5.4/tl.lua:7580: in upvalue 'type_check_function_call'
        .../share/lua/5.4/tl.lua:7919: in upvalue 'check_metamethod'
        .../share/lua/5.4/tl.lua:8008: in upvalue 'type_check_index'
        .../share/lua/5.4/tl.lua:9839: in local 'cbkind_after'
        .../share/lua/5.4/tl.lua:3610: in upvalue 'recurse'
        .../share/lua/5.4/tl.lua:3418: in local 'fn'
        .../share/lua/5.4/tl.lua:3602: in upvalue 'recurse'
        .../share/lua/5.4/tl.lua:3460: in local 'fn'
        .../share/lua/5.4/tl.lua:3602: in upvalue 'recurse'
        .../share/lua/5.4/tl.lua:3418: in local 'fn'
        .../share/lua/5.4/tl.lua:3602: in upvalue 'recurse'
        .../share/lua/5.4/tl.lua:3533: in local 'fn'
        .../share/lua/5.4/tl.lua:3602: in upvalue 'recurse'
        .../share/lua/5.4/tl.lua:3418: in local 'fn'
        .../share/lua/5.4/tl.lua:3602: in function <.../share/lua/5.4/tl.lua:3580>
        (...tail calls...)
        .../share/lua/5.4/tl.lua:10310: in function 'tl.type_check'
        .../share/lua/5.4/tl.lua:10716: in function 'tl.process_string'
        (...tail calls...)
        .../lib/luarocks/rocks-5.4/tl/0.15.2-1/bin/tl:1181: in field '?'
        .../lib/luarocks/rocks-5.4/tl/0.15.2-1/bin/tl:1410: in main chunk
        [C]: in ?

After removing the parameter names:

local record R
  metamethod __index: function(R, string): any
end

function R:brackets()
  print(self["x"])
end

function R:dot()
  print(self.x)
end

> tl check meta-index.tl
========================================
Type checked meta-index.tl
0 errors detected
...

Also doesn't matter if using dot-notation or brackets for field access. When using one or the other, or both, crash still happens.

[hishamhm]

@13k Thank you for the report and testcase!