PowerPoint2007 Reader : Read a slide number and a date with their styling

[dkulyk]

Description

Depends on #914 — it rewrites the body of the same loop. The first two commits are that PR (and @Wilkolicious's #871 under it); only the last one belongs to this review.

What is wrong

a:fld is a run whose text the application recomputes: the number of the slide it ended up on, the date the file is opened on. The Writer emits one for every sldNum or dt placeholder (AbstractSlide.php:326), but the Reader walked (a:r|a:br) only, so the element was skipped and everything inside it with it.

The shape survives the round trip — the placeholder is restored from p:ph further up, and the Writer re-derives the field from it — so a deck keeps its numbering. What it loses is how that number looks. Measured on a sldNum placeholder styled Georgia 18pt bold red:

	before	after
placeholder read back	sldNum	sldNum
runs in the paragraph	0	1
a:fld on re-save	present, no a:rPr at all	full a:rPr

dt behaves identically.

The change

CT_TextField holds the same a:rPr and a:t as CT_RegularTextRun, so the element is read by the branch that already reads a run — the XPath and the condition, nothing else. Both field types are covered at once, the kind being an attribute rather than a separate element.

One deliberate consequence

A shape that is not a placeholder but holds a field — page <slidenum> of 12 in a plain text box — now reads its stand-in text as an ordinary run, where it used to be dropped. The text of the file is kept rather than lost, but a field is not expressible in the model, so re-saving that shape freezes it into dead text.

Both outcomes are wrong; I think keeping the text is the better of the two, and it is easy to reverse if you disagree. What actually closes it is a field element of its own next to Run and BreakElement, which is a larger change and a separate PR. For reference, that is how LibreOffice models it — class TextField final : public TextRun, and both its OOXML and its ODF exporters decide per run rather than per shape.

Checklist:

• My CI is 🟢
• I have covered by unit tests my new code (check build/coverage for coverage report)

  PowerPoint2007Test::testFieldKeepsItsStyle, over both field types; the fixture is the library's own output, so nothing binary is added. Each half of the fix was checked by breaking it — without a:fld in the XPath, and without it in the condition — and both cases fail with actual size 0.

• I have updated the documentation to describe the changes

  Reader behaviour; no documented API changed. docs/usage/slides/layout.md already describes the fields, from ODPresentation Writer : Write the number of a slide and its date as fields #913.

• I have updated the changelog

[coveralls]

coverage: 92.159%. remained the same — sapientpro:fix/reader-field into PHPOffice:master