Function descriptions

DuckDB's C extension API has no way to set a function's description or examples: duckdb_scalar_function_set_name, _set_return_type, _set_varargs, _set_volatile … and that is it. There is no _set_description and no _add_example. So the Added Functions table on a community extension's page (the list of extensions) would be a bare list of names without help from somewhere else.

That text sits next to the function it describes, on the #[duck_*] attribute (here: the two places in functions/aggregate_html/html_returns.rs and html_prices.rs):

#[duck_aggregate_function(
    description = "Renders one quantstats HTML report per symbol from a long table of periodic returns",
    comment = "Groups by symbol internally, so the SQL needs no GROUP BY …",
    examples = ["SELECT unnest(qs_html_reports(…)) FROM daily_returns", "…"]
)]

The chain from that attribute to the published table:

All three keys are optional (example for one, examples for several; the two are mutually exclusive) and take no part in registration — the macro only records them, along with the registered name, in an inventory entry. To export:

just docs_csv                                           # -> target/function_descriptions.csv
cargo run --bin duckfn -- function_descriptions --all    # -> target/function_descriptions_all.csv
                                                         #    (includes undocumented functions, as a checklist)

No extension is loaded, the catalog is never queried and DuckDB need not be around: this reads what the macros recorded at compile time, and the path is always the project's target/. The #[path = "../extension/mod.rs"] mod extension; in src/bin/duckfn.rs is essential — inventory's static constructors only fire for object files that are really linked into the final binary, so switching to use duckfn_quantstats::… would make the CSV come out empty, silently.

Three rules apply to the text itself: several examples are joined with "; " and lose their trailing semicolons on export; line breaks collapse to a single space (the generated page is a Markdown table, where a newline inside a cell ends the row); commas, quotes and non-ASCII text pass through unchanged. So write one full statement per entry. The text is English because it is pasted onto that page as it is.

When the extension goes to the community repository, drop this CSV at extensions/duckfn_quantstats/docs/function_descriptions.csv in community-extensions (its generate_md.sh LEFT JOINs it on function_name to override the function tables). No copy needs to live in this repository — regenerate it after changing the code. See Community extensions.