upgrade to HTML::TreeBuilder 5 to get weak references

[simbabque]

This might break people's code on really old Perls.

Closes #251

[coveralls]

Pull Request Test Coverage Report for Build 223

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 18 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 92.711%

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Files with Coverage Reduction	New Missed Lines	%
lib/WWW/Mechanize.pm	18	92.28%

Totals
Change from base Build 222:	0.02%
Covered Lines:	725
Relevant Lines:	782

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💛 - Coveralls

[skaji]

Why do you skip checking version and importing -weak if exists $INC{'HTML::TreeBuilder'}?

[simbabque]

I am checking the version, but it has to be done after the require call. It's easy to do it with use, but the code we have here explicitly loads the module at run-time. In the require perldoc it explains

If the VERSION argument is present between Module and LIST, then the use will call the VERSION method in class Module with the given version as an argument:

use Module 12.34;

is equivalent to:

BEGIN { require Module; Module->VERSION(12.34) }

I put the %INC lookup in because without it, it will do the version check and import call every single time this method is called. I would have liked to tie it to require, but it always returns true even if the module has already been loaded. Under the hood it also checks in %INC as far as I understand, so doing that myself before attempting the version check and import seemed like the right thing to do.

I'm happy to add a test that proves this works.

[oalders]

This might break people's code on really old Perls.

Could you elaborate?

[simbabque]

This might break people's code on really old Perls.

Could you elaborate?

Sure. In https://metacpan.org/pod/HTML::Element#Weak-References it says

Because HTML::Element stores a reference to the parent element, Perl's reference-count garbage collection doesn't work properly with HTML::Element trees. Starting with version 5.00, HTML::Element uses weak references (if available) to prevent that problem. Weak references were introduced in Perl 5.6.0, but you also need a version of Scalar::Util that provides the weaken function.

I merely paraphrased this. 5.6.0 is Old of course, and I did not check if Mech can work there at all. But I thought I'd at least mention it in the commit. I did change the minimum version of Scalar::List::Util from any to the earliest that brings weaken, as far as I could tell. The history is a bit strange as there are no version numbers that far back.

Anyway, I believe we are not going to seriously break anyone's code. It is just a backwards compatibility change that should probably be mentioned.

[simbabque]

It's also interesting that the travis builds failed because of perltidy. What happened there?

[oalders]

It's also interesting that the travis builds failed because of perltidy. What happened there?

We need to add a test dep on Perl::Tidy

[oalders]

Anyway, I believe we are not going to seriously break anyone's code. It is just a backwards compatibility change that should probably be mentioned.

Thanks for bringing that up. With this module, I don't think we care about going back that far. With some of the other modules in this org, we might be more conservative, but that's seriously old.

[oalders]

@skaji are you happy with this pull request?

[skaji]

@oalders Yes, I am.
@simbabque Thanks for this PR.

[oalders]

Thanks @simbabque and @skaji!