bug#74145: 31.0.50; Default lexical-binding to t

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Hi Stefan,

>> @@ -392,7 +392,7 @@ Void Variables
>>  to evaluate the variable signals a @code{void-variable} error, instead
>>  of returning a value.
>>
>> -  Under the optional lexical scoping rule, the value cell only holds
>> +  Under the optional lexical scoping rule, the value cell holds only
>>  the variable's global value---the value outside of any lexical binding
>>  construct.  When a variable is lexically bound, the local value is
>>  determined by the lexical environment; hence, variables can have local
>
> I think this section might need more work.  It's a bit confusing to talk
> about "default dynamic scoping" and "optional lexical scoping" now.
> Shouldn't we talk about "normal variables with lexical scoping" and
> "special variables with dynamic scoping" or something along those lines?

Very good point, will take a closer look.

>> +                    (lexical-binding (default-toplevel-value 'lexical-binding)))
> Why not just use `t` here instead of its `default-toplevel-value`?

I "fixed" the code such that the default is set at exactly one place,
i.e. in `syms_of_lread`, but indeed it's not indispensable.

It's not super important, but it seemed cleaner.
It also makes it easy for users to "go back" to the nil default,
e.g. for testing purposes, or as a quick fix until you can track down
the `.el` files that need to be adjusted.


        Stefan