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</pre><pre class="rust"><code><span class="kw">use </span>std::collections::HashSet;
<span class="kw">use </span>syn;
<span class="kw">use </span>syn::punctuated::{Pair, Punctuated};
<span class="kw">use </span>internals::ast::{Container, Data};
<span class="kw">use </span>internals::{attr, ungroup};
<span class="kw">use </span>proc_macro2::Span;
<span class="comment">// Remove the default from every type parameter because in the generated impls
// they look like associated types: &quot;error: associated type bindings are not
// allowed here&quot;.
</span><span class="kw">pub fn </span>without_defaults(generics: <span class="kw-2">&amp;</span>syn::Generics) -&gt; syn::Generics {
syn::Generics {
params: generics
.params
.iter()
.map(|param| <span class="kw">match </span>param {
syn::GenericParam::Type(param) =&gt; syn::GenericParam::Type(syn::TypeParam {
eq_token: <span class="prelude-val">None</span>,
default: <span class="prelude-val">None</span>,
..param.clone()
}),
<span class="kw">_ </span>=&gt; param.clone(),
})
.collect(),
..generics.clone()
}
}
<span class="kw">pub fn </span>with_where_predicates(
generics: <span class="kw-2">&amp;</span>syn::Generics,
predicates: <span class="kw-2">&amp;</span>[syn::WherePredicate],
) -&gt; syn::Generics {
<span class="kw">let </span><span class="kw-2">mut </span>generics = generics.clone();
generics
.make_where_clause()
.predicates
.extend(predicates.iter().cloned());
generics
}
<span class="kw">pub fn </span>with_where_predicates_from_fields(
cont: <span class="kw-2">&amp;</span>Container,
generics: <span class="kw-2">&amp;</span>syn::Generics,
from_field: <span class="kw">fn</span>(<span class="kw-2">&amp;</span>attr::Field) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span>[syn::WherePredicate]&gt;,
) -&gt; syn::Generics {
<span class="kw">let </span>predicates = cont
.data
.all_fields()
.filter_map(|field| from_field(<span class="kw-2">&amp;</span>field.attrs))
.flat_map(&lt;[syn::WherePredicate]&gt;::to_vec);
<span class="kw">let </span><span class="kw-2">mut </span>generics = generics.clone();
generics.make_where_clause().predicates.extend(predicates);
generics
}
<span class="kw">pub fn </span>with_where_predicates_from_variants(
cont: <span class="kw-2">&amp;</span>Container,
generics: <span class="kw-2">&amp;</span>syn::Generics,
from_variant: <span class="kw">fn</span>(<span class="kw-2">&amp;</span>attr::Variant) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span>[syn::WherePredicate]&gt;,
) -&gt; syn::Generics {
<span class="kw">let </span>variants = <span class="kw">match </span><span class="kw-2">&amp;</span>cont.data {
Data::Enum(variants) =&gt; variants,
Data::Struct(<span class="kw">_</span>, <span class="kw">_</span>) =&gt; {
<span class="kw">return </span>generics.clone();
}
};
<span class="kw">let </span>predicates = variants
.iter()
.filter_map(|variant| from_variant(<span class="kw-2">&amp;</span>variant.attrs))
.flat_map(&lt;[syn::WherePredicate]&gt;::to_vec);
<span class="kw">let </span><span class="kw-2">mut </span>generics = generics.clone();
generics.make_where_clause().predicates.extend(predicates);
generics
}
<span class="comment">// Puts the given bound on any generic type parameters that are used in fields
// for which filter returns true.
//
// For example, the following struct needs the bound `A: Serialize, B:
// Serialize`.
//
// struct S&lt;&#39;b, A, B: &#39;b, C&gt; {
// a: A,
// b: Option&lt;&amp;&#39;b B&gt;
// #[serde(skip_serializing)]
// c: C,
// }
</span><span class="kw">pub fn </span>with_bound(
cont: <span class="kw-2">&amp;</span>Container,
generics: <span class="kw-2">&amp;</span>syn::Generics,
filter: <span class="kw">fn</span>(<span class="kw-2">&amp;</span>attr::Field, <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span>attr::Variant&gt;) -&gt; bool,
bound: <span class="kw-2">&amp;</span>syn::Path,
) -&gt; syn::Generics {
<span class="kw">struct </span>FindTyParams&lt;<span class="lifetime">&#39;ast</span>&gt; {
<span class="comment">// Set of all generic type parameters on the current struct (A, B, C in
// the example). Initialized up front.
</span>all_type_params: HashSet&lt;syn::Ident&gt;,
<span class="comment">// Set of generic type parameters used in fields for which filter
// returns true (A and B in the example). Filled in as the visitor sees
// them.
</span>relevant_type_params: HashSet&lt;syn::Ident&gt;,
<span class="comment">// Fields whose type is an associated type of one of the generic type
// parameters.
</span>associated_type_usage: Vec&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::TypePath&gt;,
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;ast</span>&gt; FindTyParams&lt;<span class="lifetime">&#39;ast</span>&gt; {
<span class="kw">fn </span>visit_field(<span class="kw-2">&amp;mut </span><span class="self">self</span>, field: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::Field) {
<span class="kw">if let </span>syn::Type::Path(ty) = ungroup(<span class="kw-2">&amp;</span>field.ty) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(Pair::Punctuated(t, <span class="kw">_</span>)) = ty.path.segments.pairs().next() {
<span class="kw">if </span><span class="self">self</span>.all_type_params.contains(<span class="kw-2">&amp;</span>t.ident) {
<span class="self">self</span>.associated_type_usage.push(ty);
}
}
}
<span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>field.ty);
}
<span class="kw">fn </span>visit_path(<span class="kw-2">&amp;mut </span><span class="self">self</span>, path: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::Path) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(seg) = path.segments.last() {
<span class="kw">if </span>seg.ident == <span class="string">&quot;PhantomData&quot; </span>{
<span class="comment">// Hardcoded exception, because PhantomData&lt;T&gt; implements
// Serialize and Deserialize whether or not T implements it.
</span><span class="kw">return</span>;
}
}
<span class="kw">if </span>path.leading_colon.is_none() &amp;&amp; path.segments.len() == <span class="number">1 </span>{
<span class="kw">let </span>id = <span class="kw-2">&amp;</span>path.segments[<span class="number">0</span>].ident;
<span class="kw">if </span><span class="self">self</span>.all_type_params.contains(id) {
<span class="self">self</span>.relevant_type_params.insert(id.clone());
}
}
<span class="kw">for </span>segment <span class="kw">in </span><span class="kw-2">&amp;</span>path.segments {
<span class="self">self</span>.visit_path_segment(segment);
}
}
<span class="comment">// Everything below is simply traversing the syntax tree.
</span><span class="kw">fn </span>visit_type(<span class="kw-2">&amp;mut </span><span class="self">self</span>, ty: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::Type) {
<span class="kw">match </span>ty {
syn::Type::Array(ty) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>ty.elem),
syn::Type::BareFn(ty) =&gt; {
<span class="kw">for </span>arg <span class="kw">in </span><span class="kw-2">&amp;</span>ty.inputs {
<span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>arg.ty);
}
<span class="self">self</span>.visit_return_type(<span class="kw-2">&amp;</span>ty.output);
}
syn::Type::Group(ty) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>ty.elem),
syn::Type::ImplTrait(ty) =&gt; {
<span class="kw">for </span>bound <span class="kw">in </span><span class="kw-2">&amp;</span>ty.bounds {
<span class="self">self</span>.visit_type_param_bound(bound);
}
}
syn::Type::Macro(ty) =&gt; <span class="self">self</span>.visit_macro(<span class="kw-2">&amp;</span>ty.mac),
syn::Type::Paren(ty) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>ty.elem),
syn::Type::Path(ty) =&gt; {
<span class="kw">if let </span><span class="prelude-val">Some</span>(qself) = <span class="kw-2">&amp;</span>ty.qself {
<span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>qself.ty);
}
<span class="self">self</span>.visit_path(<span class="kw-2">&amp;</span>ty.path);
}
syn::Type::Ptr(ty) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>ty.elem),
syn::Type::Reference(ty) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>ty.elem),
syn::Type::Slice(ty) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>ty.elem),
syn::Type::TraitObject(ty) =&gt; {
<span class="kw">for </span>bound <span class="kw">in </span><span class="kw-2">&amp;</span>ty.bounds {
<span class="self">self</span>.visit_type_param_bound(bound);
}
}
syn::Type::Tuple(ty) =&gt; {
<span class="kw">for </span>elem <span class="kw">in </span><span class="kw-2">&amp;</span>ty.elems {
<span class="self">self</span>.visit_type(elem);
}
}
syn::Type::Infer(<span class="kw">_</span>) | syn::Type::Never(<span class="kw">_</span>) | syn::Type::Verbatim(<span class="kw">_</span>) =&gt; {}
<span class="attribute">#[cfg_attr(all(test, exhaustive), deny(non_exhaustive_omitted_patterns))]
</span><span class="kw">_ </span>=&gt; {}
}
}
<span class="kw">fn </span>visit_path_segment(<span class="kw-2">&amp;mut </span><span class="self">self</span>, segment: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::PathSegment) {
<span class="self">self</span>.visit_path_arguments(<span class="kw-2">&amp;</span>segment.arguments);
}
<span class="kw">fn </span>visit_path_arguments(<span class="kw-2">&amp;mut </span><span class="self">self</span>, arguments: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::PathArguments) {
<span class="kw">match </span>arguments {
syn::PathArguments::None =&gt; {}
syn::PathArguments::AngleBracketed(arguments) =&gt; {
<span class="kw">for </span>arg <span class="kw">in </span><span class="kw-2">&amp;</span>arguments.args {
<span class="kw">match </span>arg {
syn::GenericArgument::Type(arg) =&gt; <span class="self">self</span>.visit_type(arg),
syn::GenericArgument::AssocType(arg) =&gt; <span class="self">self</span>.visit_type(<span class="kw-2">&amp;</span>arg.ty),
syn::GenericArgument::Lifetime(<span class="kw">_</span>)
| syn::GenericArgument::Const(<span class="kw">_</span>)
| syn::GenericArgument::AssocConst(<span class="kw">_</span>)
| syn::GenericArgument::Constraint(<span class="kw">_</span>) =&gt; {}
<span class="attribute">#[cfg_attr(
all(test, exhaustive),
deny(non_exhaustive_omitted_patterns)
)]
</span><span class="kw">_ </span>=&gt; {}
}
}
}
syn::PathArguments::Parenthesized(arguments) =&gt; {
<span class="kw">for </span>argument <span class="kw">in </span><span class="kw-2">&amp;</span>arguments.inputs {
<span class="self">self</span>.visit_type(argument);
}
<span class="self">self</span>.visit_return_type(<span class="kw-2">&amp;</span>arguments.output);
}
}
}
<span class="kw">fn </span>visit_return_type(<span class="kw-2">&amp;mut </span><span class="self">self</span>, return_type: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::ReturnType) {
<span class="kw">match </span>return_type {
syn::ReturnType::Default =&gt; {}
syn::ReturnType::Type(<span class="kw">_</span>, output) =&gt; <span class="self">self</span>.visit_type(output),
}
}
<span class="kw">fn </span>visit_type_param_bound(<span class="kw-2">&amp;mut </span><span class="self">self</span>, bound: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::TypeParamBound) {
<span class="kw">match </span>bound {
syn::TypeParamBound::Trait(bound) =&gt; <span class="self">self</span>.visit_path(<span class="kw-2">&amp;</span>bound.path),
syn::TypeParamBound::Lifetime(<span class="kw">_</span>) | syn::TypeParamBound::Verbatim(<span class="kw">_</span>) =&gt; {}
<span class="attribute">#[cfg_attr(all(test, exhaustive), deny(non_exhaustive_omitted_patterns))]
</span><span class="kw">_ </span>=&gt; {}
}
}
<span class="comment">// Type parameter should not be considered used by a macro path.
//
// struct TypeMacro&lt;T&gt; {
// mac: T!(),
// marker: PhantomData&lt;T&gt;,
// }
</span><span class="kw">fn </span>visit_macro(<span class="kw-2">&amp;mut </span><span class="self">self</span>, _mac: <span class="kw-2">&amp;</span><span class="lifetime">&#39;ast </span>syn::Macro) {}
}
<span class="kw">let </span>all_type_params = generics
.type_params()
.map(|param| param.ident.clone())
.collect();
<span class="kw">let </span><span class="kw-2">mut </span>visitor = FindTyParams {
all_type_params,
relevant_type_params: HashSet::new(),
associated_type_usage: Vec::new(),
};
<span class="kw">match </span><span class="kw-2">&amp;</span>cont.data {
Data::Enum(variants) =&gt; {
<span class="kw">for </span>variant <span class="kw">in </span>variants.iter() {
<span class="kw">let </span>relevant_fields = variant
.fields
.iter()
.filter(|field| filter(<span class="kw-2">&amp;</span>field.attrs, <span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span>variant.attrs)));
<span class="kw">for </span>field <span class="kw">in </span>relevant_fields {
visitor.visit_field(field.original);
}
}
}
Data::Struct(<span class="kw">_</span>, fields) =&gt; {
<span class="kw">for </span>field <span class="kw">in </span>fields.iter().filter(|field| filter(<span class="kw-2">&amp;</span>field.attrs, <span class="prelude-val">None</span>)) {
visitor.visit_field(field.original);
}
}
}
<span class="kw">let </span>relevant_type_params = visitor.relevant_type_params;
<span class="kw">let </span>associated_type_usage = visitor.associated_type_usage;
<span class="kw">let </span>new_predicates = generics
.type_params()
.map(|param| param.ident.clone())
.filter(|id| relevant_type_params.contains(id))
.map(|id| syn::TypePath {
qself: <span class="prelude-val">None</span>,
path: id.into(),
})
.chain(associated_type_usage.into_iter().cloned())
.map(|bounded_ty| {
syn::WherePredicate::Type(syn::PredicateType {
lifetimes: <span class="prelude-val">None</span>,
<span class="comment">// the type parameter that is being bounded e.g. T
</span>bounded_ty: syn::Type::Path(bounded_ty),
colon_token: &lt;<span class="macro">Token!</span>[:]&gt;::default(),
<span class="comment">// the bound e.g. Serialize
</span>bounds: <span class="macro">vec!</span>[syn::TypeParamBound::Trait(syn::TraitBound {
paren_token: <span class="prelude-val">None</span>,
modifier: syn::TraitBoundModifier::None,
lifetimes: <span class="prelude-val">None</span>,
path: bound.clone(),
})]
.into_iter()
.collect(),
})
});
<span class="kw">let </span><span class="kw-2">mut </span>generics = generics.clone();
generics
.make_where_clause()
.predicates
.extend(new_predicates);
generics
}
<span class="kw">pub fn </span>with_self_bound(
cont: <span class="kw-2">&amp;</span>Container,
generics: <span class="kw-2">&amp;</span>syn::Generics,
bound: <span class="kw-2">&amp;</span>syn::Path,
) -&gt; syn::Generics {
<span class="kw">let </span><span class="kw-2">mut </span>generics = generics.clone();
generics
.make_where_clause()
.predicates
.push(syn::WherePredicate::Type(syn::PredicateType {
lifetimes: <span class="prelude-val">None</span>,
<span class="comment">// the type that is being bounded e.g. MyStruct&lt;&#39;a, T&gt;
</span>bounded_ty: type_of_item(cont),
colon_token: &lt;<span class="macro">Token!</span>[:]&gt;::default(),
<span class="comment">// the bound e.g. Default
</span>bounds: <span class="macro">vec!</span>[syn::TypeParamBound::Trait(syn::TraitBound {
paren_token: <span class="prelude-val">None</span>,
modifier: syn::TraitBoundModifier::None,
lifetimes: <span class="prelude-val">None</span>,
path: bound.clone(),
})]
.into_iter()
.collect(),
}));
generics
}
<span class="kw">pub fn </span>with_lifetime_bound(generics: <span class="kw-2">&amp;</span>syn::Generics, lifetime: <span class="kw-2">&amp;</span>str) -&gt; syn::Generics {
<span class="kw">let </span>bound = syn::Lifetime::new(lifetime, Span::call_site());
<span class="kw">let </span>def = syn::LifetimeParam {
attrs: Vec::new(),
lifetime: bound.clone(),
colon_token: <span class="prelude-val">None</span>,
bounds: Punctuated::new(),
};
<span class="kw">let </span>params = <span class="prelude-val">Some</span>(syn::GenericParam::Lifetime(def))
.into_iter()
.chain(generics.params.iter().cloned().map(|<span class="kw-2">mut </span>param| {
<span class="kw">match </span><span class="kw-2">&amp;mut </span>param {
syn::GenericParam::Lifetime(param) =&gt; {
param.bounds.push(bound.clone());
}
syn::GenericParam::Type(param) =&gt; {
param
.bounds
.push(syn::TypeParamBound::Lifetime(bound.clone()));
}
syn::GenericParam::Const(<span class="kw">_</span>) =&gt; {}
}
param
}))
.collect();
syn::Generics {
params,
..generics.clone()
}
}
<span class="kw">fn </span>type_of_item(cont: <span class="kw-2">&amp;</span>Container) -&gt; syn::Type {
syn::Type::Path(syn::TypePath {
qself: <span class="prelude-val">None</span>,
path: syn::Path {
leading_colon: <span class="prelude-val">None</span>,
segments: <span class="macro">vec!</span>[syn::PathSegment {
ident: cont.ident.clone(),
arguments: syn::PathArguments::AngleBracketed(
syn::AngleBracketedGenericArguments {
colon2_token: <span class="prelude-val">None</span>,
lt_token: &lt;<span class="macro">Token!</span>[&lt;]&gt;::default(),
args: cont
.generics
.params
.iter()
.map(|param| <span class="kw">match </span>param {
syn::GenericParam::Type(param) =&gt; {
syn::GenericArgument::Type(syn::Type::Path(syn::TypePath {
qself: <span class="prelude-val">None</span>,
path: param.ident.clone().into(),
}))
}
syn::GenericParam::Lifetime(param) =&gt; {
syn::GenericArgument::Lifetime(param.lifetime.clone())
}
syn::GenericParam::Const(<span class="kw">_</span>) =&gt; {
<span class="macro">panic!</span>(<span class="string">&quot;Serde does not support const generics yet&quot;</span>);
}
})
.collect(),
gt_token: &lt;<span class="macro">Token!</span>[&gt;]&gt;::default(),
},
),
}]
.into_iter()
.collect(),
},
})
}
</code></pre></div>
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