* Font Themes
It isn't a feature of Excel that I've made any use of, but PR #3476 added better Theme support for colors, and it is relatively easy to add Theme support for Fonts on top of that.
Excel assigns two theme fonts to its spreadsheets, one for Headings (major), and one for Body (minor). If the body theme is Calibri, when you choose a font for a cell in Excel, you can choose 'Calibri (Body)' from the Theme Fonts section at the top of the Font dropdown, or 'Calibri' from the 'All Fonts' section. If you choose the former, the cell will be automatically restyled if you change the Theme Fonts (via Page Layout, Themes, Fonts). The relationship to the theme fonts is recorded in the XML via a `scheme` tag (descending from `font`) whose `val` attribute can be either `major` or `minor`. Accordingly, this PR, in addition to defining the Theme Font properties, adds a `scheme` property, with getter and setter, to Style/Font.
The main benefit of this PR is that you can now load and save a spreadsheet preserving the connections to the Theme Fonts, without having to take any additional action.
A secondary benefit arises from the following difference. Empty cells in Excel will use the spreadsheet's default font name when they are filled in; but, in Google Sheets, they will use the Theme Minor Font name. By setting the `scheme` property in the default style, the resulting spreadsheet will behave the same in both Excel and Google.
I will note that Excel's font themes specify a Latin font, an East Asian font, a Complex Scripts font, and a set of font substitutions for various languages. PhpSpreadsheet will preserve all of these, and allow them to be changed. However, although it is easy to imagine how the non-Latin options might work, I have not yet been able to come up with an example where Excel uses any of them. In particular, if I use a theme font which does not support language X, and I use Language X in a cell bound to the theme, Excel will use a substitution font which does support it, but the font which it uses does not seem to be chosen from the alternatives supplied in the theme.
* Scrutinizer
The sun rises in the east, and Scrutinizer issues more false positives.
* Font and Effects Support for Chart Data Labels and Axis
Addresses some remaining issues with 32readwriteLineChart5 (see issue #1797). Font size is covered. So are effects, although the results are a bit odd. For the new spreadsheet 32readwriteLineChart6, the Axis labels have a yellow-ish glow, but reading and writing the spreadsheet in PhpSpreadsheet gives them a purple-ish glow. Nevertheless, the new test shows that the output file uses schemeClr accent4, as does the input file. So the effect is handled correctly, but it seems there is likely to be a difference between theme colors (Writer/Xlsx/Theme appears to write hard-coded color schemes, and, in any case, Reader/Xlsx does not appear to handle schemeClr). Fixing that will be a great deal more difficult, with a large chance of regression, and will need to happen in a separate PR (one that I am not currently investigating, but I will open a new issue). Effects using srgbClr (and probably sysclr) should be okay.
* Better Theme Support
When reading Xlsx, the theme colors will now also be used for writing. This means that a file can be loaded and saved and its chart colors will now be preserved. If the spreadsheet is created new, Excel 2007-2010 colors are used. The writer is currently hard-coded to use them, so this avoids making this a breaking change. The theme colors can be explicitly changed if desired, and Excel 2013+ colors can be introduced very easily.
```php
$spreadsheet->getTheme()
->setThemeColorName(Theme::COLOR_SCHEME_2013_PLUS_NAME);
```
Likewise, if the old behavior of changing to the 2007-2010 scheme rather than using the input values is desired, that is easy to achieve after the load has taken place.
```php
$spreadsheet->getTheme()
->setThemeColorName(Theme::COLOR_SCHEME_2007_2010_NAME);
```
The new Theme class introduced by this change can easily be extended to include Fonts and Effects. Unlike Colors, I am unsure what the practical effects of changing those to, say, the 2013+ defaults would be.
* Scrutinizer
Use an alias in a use statement.
* Update Change Log
Due to potential behavior change.
Fix#3453. User sets a valid formula (e.g. `=SUM(Sheet2!B1:Sheet2!B3)`), and then does something to invalidate the formula (e.g. delete Sheet2). Excel changes the formula to `SUM(#REF!:#REF!)` when the spreadsheet is saved; apparently someone thought this was a good idea. But PhpSpreadsheet (a) used to throw an Exception when it evaluated the formula, and (b) now gives a result of `0` when evaluating the formula. Neither is ideal. It would be better to propagate the `#REF!` error.
It is likely that more tests are needed, which is why I will keep this in draft status for a bit.
MarkBaker
dependabot[bot]
oleibman
Esteban Gehring