bug#64272: 28.1; lisp_file_lexically_bound_p behavior mismatches file local variables

[LdBeth <andpuke@foxmail.com>]

>>>>> In <83mt0ny47z.fsf@gnu.org> 
>>>>>	Eli Zaretskii <eliz@gnu.org> wrote:

Eli> I'm not sure we want to support this outside of a Lisp comment.
Eli> Stefan, WDYT?  Could false positives cause harm?
 
Stefan> I'd much rather we try and stay as close as possible to the behavior of
Stefan> `hack-local-variables-prop-line`

Eli> The fact that most -*- lines are in comments is because they are in
Eli> program source files, so we need to hide them from the compiler or the
Eli> interpreter.

Eli> Am I missing something?

Ok I find the reason the `lisp_file_lexically_bound_p' would give
up if the first line isn't a comment is, it said:

 Return true if the lisp code read using READCHARFUN defines a non-nil
 `lexical-binding' file variable.  After returning, the stream is
 positioned following the first line, if it is a comment or #! line,
 otherwise nothing is read.

So this function assumes the first line is discarded if file local
variables would have been read.

If first line is lisp code, and we want to keep the similar
behavior of `hack-local-variables-prop-line`, there needs a mean
to buffer the content of the first line. (Or reset file position
but I don't think there is a way to do that without
substantially change lread.c)

But it would be easier to only handle the extra whitespace at
beginning of file.

---
ldb