Inconsistency Between Actual and Declared Type - Minor Break

[oleibman]

Fix #3711. User set a cell value to float (implicitly by default value binder), then used setDataType to change its type to string. This caused a problem for Xlsx Writer, which uses the string cell values as an index into a Shared String array. However, as the cell actually contained a floating point value, Php treated it as an integer index; such a treatment is both deprecated, and leads to invalid values in the spreadsheet.

The use case for setDataType is not strong. The user always has the option to use setValueExplicit if the type is important. Setting a type afterwards, i.e. irrespective of the value, seems like a peculiar action. Indeed, there are no tests whatever for such use in the unit test suite.

There are two possible approaches to fixing this problem. The first is to add casts to the 3 or 4 places in Writer Xlsx which might be affected by this problem (hoping that you've found them all and realizing that similar changes might be needed for other Writers). The second is to change setDataType to call setValueExplicit using the current value of the cell, thereby possibly changing the cell value. I have gone with the second option - it seems like a much more logical approach, and guarantees that the content of the cell will always be consistent with its declared type. It is, however, a breaking change; if, for example, you have a cell with a string or numeric value and specify boolean to setDataType, the cell's value will change to true or false with no way to get back to the original.

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?

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