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xso-proc: Add n = 1 flag to element meta

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This allows exactly one arbitrary payload in any element, and is handled
after every other element with a more specific matcher has been parsed.

Both the #[xml(element(n = 1))] meta and its shortcut #[xml(element)]
are allowed and treated the exact same way.
This commit is contained in:
Emmanuel Gil Peyrot 2024-12-19 20:36:57 +01:00 • committed by Jonas Schäfer
commit c72cf3ddd1
7 changed files with 265 additions and 80 deletions
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26
xso/src/from_xml_doc.md
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@ -249,6 +249,20 @@ The following mapping types are defined:
| [`extract`](#extract-meta) | Map the field to contents of a child element of specified structure |
| [`text`](#text-meta) | Map the field to the text content of the struct's element |
#### Field order
Field order **matters**. The fields are parsed in the order they are declared
(for children, anyway). If multiple fields match a given child element, the
first field which matches will be taken. The only exception is
`#[xml(element(n = ..))]`, which is always processed last.
When XML is generated from a struct, the child elements are also generated
in the order of the fields. That means that passing an XML element through
FromXml and IntoXml may re-order some child elements.
Sorting order between elements which match the same field is generally
preserved, if the container preserves sort order on insertion.
### `attribute` meta
The `attribute` meta causes the field to be mapped to an XML attribute of the
@ -419,15 +433,13 @@ The following keys can be used inside the `#[xml(extract(..))]` meta:
| Key | Value type | Description |
| --- | --- | --- |
| `n` | `..` | Must be set to the value `..`. |
| `n` | `1` or `..` | If `1`, a single element is parsed. If `..`, a collection is parsed. Defaults to `1`. |
The `n` parameter will, in the future, support values other than `..`. In
order to provide a non-breaking path into that future, it must be set to the
value `..` right now, indicating that an arbitrary number of elements may be
collected by this meta.
When parsing a single child element (i.e. `n = 1` or no `n` value set at all),
the field's type must be a `minidom::Element`.
The field's type must be a collection of `minidom::Element`. It must thus
implement
When parsing a collection (with `n = ..`), the field's type must be a
collection of `minidom::Element`. It must thus implement
[`IntoIterator<Item = minidom::Element>`][`core::iter::IntoIterator`]. In
addition, the field's type must implement
[`Extend<minidom::Element>`][`core::iter::Extend`] to derive `FromXml` and the