[BUG] Spurious error generated for faulty `for` statement

[soraros]

Bug description

As title. Couldn't think of a better one, sorry.

Steps to reproduce

fn f():
  for i in range(a):
    ...

Error message looks like the following:

workspaces/ubuntu/bug.mojo:2:18: error: use of unknown declaration 'a', 'fn' declarations require explicit variable declarations
  for i in range(a):
                 ^
/workspaces/ubuntu/bug.mojo:2:20: error: unexpected token in expression
  for i in range(a):
                   ^
/workspaces/ubuntu/bug.mojo:2:20: error: statements must start at the beginning of a line
  for i in range(a):
                   ^
/home/vscode/.modular/pkg/packages.modular.com_mojo/bin/mojo: error: failed to parse the provided Mojo

The error "unexpected token" can be really confusing because it appears to indicate that there is a syntax error.

System information

Mojo 24.2 on Docker, Intel Mac