xso: implement support for defaulting extracts
This commit is contained in:
Jonas Schäfer
parent
f318dd460d
commit
c7c180feb6
7 changed files with 388 additions and 31 deletions
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@ -19,8 +19,8 @@ use crate::scope::{AsItemsScope, FromEventsScope};
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use crate::types::{
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as_optional_xml_text_fn, as_xml_iter_fn, as_xml_text_fn, default_fn, extend_fn, from_events_fn,
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from_xml_builder_ty, from_xml_text_fn, into_iterator_into_iter_fn, into_iterator_item_ty,
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into_iterator_iter_ty, item_iter_ty, option_ty, ref_ty, string_ty, text_codec_decode_fn,
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text_codec_encode_fn, ty_from_ident,
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into_iterator_iter_ty, item_iter_ty, option_as_xml_ty, option_ty, ref_ty, string_ty,
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text_codec_decode_fn, text_codec_encode_fn, ty_from_ident,
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};
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/// Code slices necessary for declaring and initializing a temporary variable
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@ -306,6 +306,7 @@ impl FieldKind {
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XmlFieldMeta::Extract {
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span,
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default_,
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qname: QNameRef { namespace, name },
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amount,
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fields,
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@ -352,7 +353,7 @@ impl FieldKind {
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)?;
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Ok(Self::Child {
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default_: Flag::Absent,
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default_,
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amount,
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extract: Some(ExtractDef {
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xml_namespace,
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@ -565,12 +566,7 @@ impl FieldDef {
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&Visibility::Inherited,
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&from_xml_builder_ty_ident,
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&state_ty_ident,
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&Type::Tuple(TypeTuple {
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paren_token: token::Paren::default(),
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elems: [
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element_ty.clone(),
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].into_iter().collect(),
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})
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&parts.to_tuple_ty().into(),
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)?;
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let from_xml_builder_ty =
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ty_from_ident(from_xml_builder_ty_ident.clone()).into();
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@ -580,7 +576,31 @@ impl FieldDef {
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(
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extra_defs,
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matcher,
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quote! { #substate_result.0 },
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// This little ".into()" here goes a long way. It
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// relies on one of the most underrated trait
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// implementations in the standard library:
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// `impl From<T> for Option<T>`, which creates a
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// `Some(_)` from a `T`. Why is it so great?
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// Because there is also `impl From<Option<T>> for
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// Option<T>` (obviously), which is just a move.
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// So even without knowing the exact type of the
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// substate result and the field, we can make an
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// "downcast" to `Option<T>` if the field is of
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// type `Option<T>`, and it does the right thing
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// no matter whether the extracted field is of
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// type `Option<T>` or `T`.
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//
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// And then, type inferrence does the rest: There
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// is ambiguity there, of course, if we call
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// `.into()` on a value of type `Option<T>`:
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// Should Rust wrap it into another layer of
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// `Option`, or should it just move the value? The
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// answer lies in the type constraint imposed by
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// the place the value is *used*, which is
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// strictly bound by the field's type (so there
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// is, in fact, no ambiguity). So this works all
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// kinds of magic.
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quote! { #substate_result.0.into() },
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from_xml_builder_ty,
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)
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}
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@ -736,7 +756,7 @@ impl FieldDef {
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}
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};
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let (extra_defs, fetch, as_xml_iter, iter_ty) = match extract {
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let (extra_defs, init, iter_ty) = match extract {
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Some(ExtractDef {
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ref xml_namespace,
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ref xml_name,
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@ -776,21 +796,25 @@ impl FieldDef {
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.compile()
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.render(
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&Visibility::Inherited,
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&Type::Tuple(TypeTuple {
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paren_token: token::Paren::default(),
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elems: [ref_ty(item_ty.clone(), lifetime.clone())]
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.into_iter()
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.collect(),
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}),
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&parts.to_ref_tuple_ty(lifetime).into(),
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&state_ty_ident,
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lifetime,
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&item_iter_ty,
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)?;
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let item_iter_ty = option_as_xml_ty(item_iter_ty);
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(
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extra_defs,
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quote! { (&#bound_name,) },
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quote! { #item_iter_ty_ident::new },
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// Again we exploit the extreme usefulness of the
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// `impl From<T> for Option<T>`. We already wrote
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// extensively about that in the FromXml
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// implementation corresponding to this code
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// above, and we will not repeat it here.
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quote! {
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::xso::OptionAsXml::new(::core::option::Option::from(#bound_name).map(|#bound_name| {
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#item_iter_ty_ident::new((#bound_name,))
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}).transpose()?)
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},
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item_iter_ty,
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)
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}
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@ -800,8 +824,7 @@ impl FieldDef {
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(
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TokenStream::default(),
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quote! { #bound_name },
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quote! { #as_xml_iter },
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quote! { #as_xml_iter(#bound_name)? },
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item_iter,
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)
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}
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@ -810,12 +833,7 @@ impl FieldDef {
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match amount {
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AmountConstraint::FixedSingle(_) => Ok(FieldIteratorPart::Content {
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extra_defs,
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value: FieldTempInit {
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init: quote! {
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#as_xml_iter(#fetch)?
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},
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ty: iter_ty,
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},
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value: FieldTempInit { init, ty: iter_ty },
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generator: quote! {
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#bound_name.next().transpose()
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},
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@ -853,7 +871,10 @@ impl FieldDef {
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}
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}
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if let ::core::option::Option::Some(item) = #bound_name.0.next() {
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#bound_name.1 = ::core::option::Option::Some(#as_xml_iter({ let #bound_name = item; #fetch })?)
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#bound_name.1 = ::core::option::Option::Some({
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let #bound_name = item;
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#init
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});
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} else {
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break ::core::result::Result::Ok(::core::option::Option::None)
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}
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