bug#47080: 28.0.50; Spurious variable left uninitialized compiler warning

[Stefan Monnier]

Lars Ingebrigtsen [2021-03-12 01:23:01] wrote:
> Michael Heerdegen <michael_heerdegen@web.de> writes:
>> Compiling gives me:
>> | compile-test.el:6:1: Warning: Variable `file' left uninitialized
>> | compile-test.el:6:1: Warning: Variable `file' left uninitialized
>
> This is perhaps the same problem that's causing this warning on the
> current Emacs trunk?

Indeed.

> In toplevel form:
> progmodes/sh-script.el:1050:1: Warning: Variable `syntax' left uninitialized

I just fixed this one.

> I was just looking at this, and it looks like a spurious warning, if I
> read the syntax-propertize-rules correctly.

The warning complains when you initially bind a lexical var to nil
(either by not giving a value or by giving an explicit nil) and then
never set it to any other value.

Indeed, it's a useless binding: you could just use nil instead wherever
you use that var, so the warning is working as intended.  And indeed, it
found a few places where we bound a var to nil and then just
returned its value (and it's thanks to this warning that I discovered
that those var needed to be declared as dynamically scoped).

But the above `pcase` and `syntax-propertize-rules` show that it can be
quite inconvenient.  I can probably fix `pcase` to work around the
issue, but ... it's probably better to tone down the warning so it's
only issued if the nil binding is implicit rather than explicit.


        Stefan