Re: Proposed feature: die on compile with undefined functions

On Thu, Jan 29, 2026 at 12:18 PM demerphq <[email protected]> wrote:
>
> On Thu, 29 Jan 2026, 11:52 Philippe Bruhat (BooK), <[email protected]> wrote:
>>
>> On Wed, Jan 28, 2026 at 11:59:47AM -0600, David Condon wrote:
>> >
>> > *1. Here is a problem*
>> > Scripts that have undeclared subroutines will run, even though the
>> > subroutines are not declared/loaded/whatever:
>> >
>> > There are no syntax changes.  The only change is that undefined subroutines
>> > would be treated the same way that undefined scalars are treated.
>>
>> s/undefined scalares/undeclared scalars/
>>
>> > I want perl to check for the undefined function max before running the
>> > script, similarly to the way that this 1-line script:
>>
>> > *4. Here are potential problems*
>> >
>> > I am unaware of any.  I just want something that will happen anyway to
>> > happen sooner to save time.  This change *shouldn't *be buggy.
>>
>> The problem is see is that it's extremely hard to detect if a function
>
>
> Indeed, "halting problem" hard.
>
>> will be defined by the time Perl tries to call it:
>>
>>     use v5.42;
>>     require List::Util;
>>     List::Util->import("max");
>>     say max( 1..10, -1..7);
>>
>> All of those lines happens at run time, and max is available by the time
>> it's called. At the end of compilation, though, max is not defined
>
>
> And while a super strict mode could require forward declarations for this exact case there are others where we document that forward references to fully qualified subs should  work.

I may be naive here but the argument that symbols can be created at
runtime applies to variables too doesn't it?

 » perl -E'eval q[our $x = 1]; say $x'
1

» perl -M5.40.0 -E'eval q[our $x = 1]; say $x'
Global symbol "$x" requires explicit package name (did you forget to
declare "my $x"?) at -e line 1.
Execution of -e aborted due to compilation errors.

» perl -M5.40.0 -E'BEGIN { eval q[our $x = 1]; } say $x'
Variable "$x" is not imported at -e line 1.
Global symbol "$x" requires explicit package name (did you forget to
declare "my $x"?) at -e line 1.
Execution of -e aborted due to compilation errors.

» perl -M5.40.0 -E'BEGIN { eval q[our $x = 1]; } say $main::x'
1

» perl -M5.40.0 -E'eval q[our $x = 1]; say $main::x'
Name "main::x" used only once: possible typo at -e line 1.
1

-Chris