illformed AST for errorneous tuple syntax in for-loop variables

[alaviss]

Example

iterator iter(): (int, int) = yield (1, 0)

iterator other(): int =
  for (i,) in iter():
    yield i

Actual Output

test.nim(4, 7) Error: illformed AST: (i)

Expected Output

An error that the (i, _) form should be used or something similar. Accepting this is also an option.

[zerbina]

Given that:

• the grammar and parser consider for (x) in ... to be valid
• the language supports single-element tuples

I'd say that for (x) in ... and - by extension - var (x) = 0 should be allowed.

The provided example must not compile, however, as iter returns a binary tuple, which cannot be unpacked with the (x) syntax.