Styles extension for ODT in pandoc reader

[bkmks]

Pandoc’s docx reader has +styles extension. This is a feature request asking for the same in the odt reader—a parity request. Right now the pandoc writer allows writing customs styles to odt but we can't round trip making it an asymmetric feature...

The reason this becomes crucial is that except Microsoft Office, all other programs struggle to maintain fidelity in rendering docx. Whereas that's not so with odt which is cleaner by design.

It would be great if Pandoc being free and open source could support other open source initiatives.

[jgm]

I am in favor of supporting this. The description of the styles extension is:

When converting from docx, add custom-styles attributes
for all docx styles, regardless of whether pandoc understands
the meanings of these styles. Because attributes cannot be
added directly to paragraphs or text in the pandoc AST,
paragraph styles will cause Divs to be created and character
styles will cause Spans to be created to hold the attributes.
(Table styles will be added to the Table elements directly.)
This extension can be used with docx custom styles.

We'd have to exclude automatic styles. There might be other differences in how styles work that we need to think about.

[bkmks]

pandoc-odt-styles-v2.patch
Great. I used Claude Sonnet 5.5 to come up with a prototype patch. Please find it attached and here is what Claude has to say:
What it does

Extension registered: Ext_styles is now allowed for odt and fodt. The earlier patch (built with Chatgpt) missed this, so -f odt+styles would still have been rejected.
Named styles, not automatic ones: LibreOffice records direct formatting as automatic styles like P1 and T3, which point to the real style as their parent. The style reader now remembers which styles are automatic and their style:display-name. A new lookupNamedStyleName follows an automatic style to its first named parent. It uses the display name, so you get Heading 1 rather than Heading_20_1.
Paragraphs: a paragraph gets a Div with custom-style, as the docx reader does. Paragraphs in Standard are left alone.
Spans: a span gets a custom-style Span only if it resolves to a named style. A span with only direct formatting stays plain text.
Headings: a heading gets a custom-style attribute only when its style differs from the standard one for its level. This is simpler than the docx reader, which adds the other styles as classes.
Image and table captions: table-caption paragraphs and text-box paragraphs are deliberately not wrapped. The earlier patch would have broken image captions and table-caption attachment. I only found this by reading the 3.13 code.
Tests and docs: it adds a hand-written flat ODT fixture, test/odt/fodt/styles.fodt, with tests for the extension on and off, plus the MANUAL.txt changes.

What I checked

Syntax: all changed Haskell files parse without errors. This is syntax only, not types.
Extension-off expectation: I repackaged the fixture as an .odt and ran stock Pandoc 3.9 on it. The structure matches styles-off.native, so existing behaviour is unchanged. The 3.9 build I could install lacks fodt, so I used odt for this.

What I couldn’t check

Type errors: I have no Haskell toolchain, so a compile may turn up errors. Please run cabal build and then cabal test --test-options='-p ODT'.
The “extension on” expectation: styles.native is derived by hand from the code. If it differs, check whether the code or my expectation is wrong before regenerating it.

Known trade-offs

Consecutive Preformatted Text paragraphs are no longer merged into one code block when the extension is on, because each sits in its own Div.
A list item whose paragraph has a non-default style becomes a loose list, since the paragraph is wrapped in a Div. The docx reader behaves the same way.
Table styles are not recorded.

If the build reports errors, paste them here and I’ll fix them. Before filing upstream, search the tracker for an existing issue and mention that the patch is tested only against these fixtures.

[jgm]

see PR #12065 Please review and test.

[bkmks]

Is it possible to give me a windows build for this for testing?

[jgm]

When this workflow finishes https://github.com/jgm/pandoc/actions/runs/42396487879 there should be an artifact there.

[bkmks]

Tested the build from this PR on Windows with a real ODT document. -f odt+styles gives custom-style Divs and Spans with the correct style names, including for paragraphs that also have direct formatting. Without +styles the output is unchanged. Works for my use case (Lua filters matching on custom-style). Happy for it to be merged. Haven't test in on tables though.