Check for sortedness must not use ==

[a-ludi]

Checking sortedness according to a given predicate must not use == operator
because it may not be in accordance with the predicate.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21810	minor	Check for sortedness in merge must not use ==

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7928"

[RazvanN7]

Hi @a-ludi , thanks for your PR! In case this is your first PR to phobos: welcome to the Dlang community!

Generally, changes that are accepted into the standard library need to be accompanied by a strong justification.

Can you please provide a case where the current code does not work correctly? The unittest you added passes
even without your changes so it is hard to understand why this PR is needed. Note that equality is tested there
because the default predicate is a < b and alongside a > b, these are the most common predicates. This is
much faster than having to call binaryFun directly.

[RazvanN7]

Provide a justification for this PR.

[a-ludi]

Oh, I am sorry, that the unit test is a bad example. I did not really check it. I am going to write one that really shows the trouble.

The theoretical justification is simply that == and the predicate may yield different results which is unacceptable IMHO.

[a-ludi]

I updated the unit test accordingly. Note, that the behavior only occurs when compiling with -debug.

[RazvanN7]

Thanks!

[thewilsonator]

Issue number?

[a-ludi]

I have not created an issue. Should I do so?

[RazvanN7]

It would be great if you could create the issue and link it to this PR.

[RazvanN7]

ping @a-ludi

[a-ludi]

Filed as issue 21810.

[thewilsonator]

Please retitle the commit message to say "Fix issue 21810: issue description goes here"

[RazvanN7]

Please add a commit that contains the message "Fix Issue 21810 - .." so that the bot picks it up.

[RazvanN7]

For some reason, buildkite is always failing druntime with this PR. As far as I could tell the error seems unrelated. @thewilsonator any ideas?

[RazvanN7]

Unfortunately, the message must contain "Fix", not "Fixed".

[a-ludi]

For some reason, buildkite is always failing druntime with this PR. As far as I could tell the error seems unrelated. @thewilsonator any ideas?

Should I try rebasing the current master branch?

[a-ludi]

CircleCI failed because it could not pull docker images. Maybe a restart will fix it.

[thewilsonator]

Should I try rebasing the current master branch?

yes

[RazvanN7]

yes, please rebase.

[a-ludi]

The rebase changed the actual error encountered in buildkite but the pipeline still fails.