Possible fix for issue #3337

[fdjohnston]

Using the FunctionPrefix::addFunctionPrefixStripEquals appears to fix the issue by adding the _xlfn prefix to functions in array formulas.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Addresses issue #3337.

I didn't write any unit tests since I wasn't sure how to test the underlying XML output by the writer. Happy to take a crack at it if you have any tips.

[oleibman]

Take a look at the test member Writer\Xlsx\ConditionalTest. Those tests make assertions about the generated Xml (without even having to write to an output file).

[fdjohnston]

Thanks for the recommendation. I started with a couple simple cases. These can be expanded upon if necessary, though based on @MarkBaker comments back in issue #3337 it sounds like this is all getting overhauled in the next major version of PhpSpreadsheet anyway.

[MarkBaker]

based on @MarkBaker comments back in issue #3337 it sounds like this is all getting overhauled in the next major version of PhpSpreadsheet anyway.

That doesn't change the need to write the function prefix though

[fdjohnston]

Totally agree. Was just suggestion that a couple of simpler tests is probably adequate.

[fdjohnston]

But of course that's up to you. Happy to add others if you feel it's necessary.