Re: Make all Perl warnings fatal

Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:

> On 2023-Aug-10, Peter Eisentraut wrote:
>
>> I wanted to figure put if we can catch these more reliably, in the style of
>> -Werror. AFAICT, there is no way to automatically turn all warnings into
>> fatal errors. But there is a way to do it per script, by replacing
>>
>> use warnings;
>>
>> by
>>
>> use warnings FATAL => 'all';
>>
>> See attached patch to try it out.
>
> BTW in case we do find that there's some unforeseen problem and we want
> to roll back, it would be great to have a way to disable this without
> having to edit every single Perl file again later. However, I didn't
> find a way to do it -- I thought about creating a separate PgWarnings.pm
> file that would do the "use warnings FATAL => 'all'" dance and which
> every other Perl file would use or include; but couldn't make it work.
> Maybe some Perl expert knows a good answer to this.

Like most pragmas (all-lower-case module names), `warnings` affects the
currently-compiling lexical scope, so to have a module like PgWarnings
inject it into the module that uses it, you'd call warnings->import in
its import method (which gets called when the `use PgWarnings;``
statement is compiled, e.g.:

package PgWarnings;

sub import {
warnings->import(FATAL => 'all');
}

I wouldn't bother with a whole module just for that, but if we have a
group of pragmas or modules we always want to enable/import and have the
ability to change this set without having to edit all the files, it's
quite common to have a ProjectName::Policy module that does that. For
example, to exclude warnings that are unsafe, pointless, or impossible
to fatalise (c.f. https://metacpan.org/pod/strictures#CATEGORY-SELECTIONS):

package PostgreSQL::Policy;

sub import {
strict->import;
warnings->import(
FATAL => 'all',
NONFATAL => qw(exec internal malloc recursion),
);
warnings->uniport(qw(once));
}

Now that we require Perl 5.14, we might want to consider enabling its
feature bundle as well, with:

feature->import(':5.14')

Although the only features of note that adds are:

- say: the `say` function, like `print` but appends a newline

- state: `state` variables, like `my` but only initialised the first
time the function they're in is called, and the value persists
between calls (like function-scoped `static` variables in C)

- unicode_strings: use unicode semantics for characters in the
128-255 range, regardless of internal representation

> Maybe the BEGIN block of each file can `eval` a new PgWarnings.pm that
> emits the "use warnings" line?

That's ugly as sin, and thankfully not necessary.

-ilmari