How is the variable scoping for macros determined?

Question

Take the following example macro, defined in macro.el.

(defmacro some-macro (&rest body)
  `(let ((some-variable 1))
     ,@body))

And take the following function, defined in a different file, function.el.

(defun some-function ()
  (some-macro (do-something)))

When function.el is byte-compiled, will some-variable be bound under lexical or dynamic binding?

I understand this depends on whether the file uses -*- lexical-binding: t; -*-, so my question specifically regards the following situations:

1. If function.el uses lexical binding, but macro.el doesn't.
2. If macro.el uses lexical binding, but function.el doesn't.

Does it make a difference if some-var has been declared global (with a defvar) inside function.el? If it does, I'm specifically interested in the case where it hasn't.

Answer 1

The kind of scoping active for the (let ((some-variable ..)) ...) in your example, is the one active at the site of the macro call (i.e. the one that applies to some-function).

A macro can know which kind of scoping will be used for the code it returns by checking the value of the lexical-binding variable.