"Cannot infer argument types" for foreach over byLine

[Meta via Digitalmars-d-learn]

import std.stdio;

void main()
{
    foreach (i, line; file.byLine())
    {
        writeln(line);
    }
}
This code gives me the error:

Error: cannot infer argument types, expected 1 argument, not 2

This is a very obtuse compiler message considering how simple the 
code is; I know it's got something to do with the foreach 
statement and what byLine() returns, but I can't seem to get it 
to compile without removing `i`.