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 </pre><pre class="rust"><code><span class="kw">use </span>internals::ast::{Container, Data, Field, Style};
 <span class="kw">use </span>internals::attr::{Identifier, TagType};
 <span class="kw">use </span>internals::{ungroup, Ctxt, Derive};
 <span class="kw">use </span>syn::{Member, Type};

 <span class="comment">// Cross-cutting checks that require looking at more than a single attrs object.
 // Simpler checks should happen when parsing and building the attrs.
 </span><span class="kw">pub fn </span>check(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;mut </span>Container, derive: Derive) {
     check_remote_generic(cx, cont);
     check_getter(cx, cont);
     check_flatten(cx, cont);
     check_identifier(cx, cont);
     check_variant_skip_attrs(cx, cont);
     check_internal_tag_field_name_conflict(cx, cont);
     check_adjacent_tag_conflict(cx, cont);
     check_transparent(cx, cont, derive);
     check_from_and_try_from(cx, cont);
 }

 <span class="comment">// Remote derive definition type must have either all of the generics of the
 // remote type:
 //
 //     #[serde(remote = &quot;Generic&quot;)]
 //     struct Generic&lt;T&gt; {…}
 //
 // or none of them, i.e. defining impls for one concrete instantiation of the
 // remote type only:
 //
 //     #[serde(remote = &quot;Generic&lt;T&gt;&quot;)]
 //     struct ConcreteDef {…}
 //
 </span><span class="kw">fn </span>check_remote_generic(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <span class="kw">if let </span><span class="prelude-val">Some</span>(remote) = cont.attrs.remote() {
         <span class="kw">let </span>local_has_generic = !cont.generics.params.is_empty();
         <span class="kw">let </span>remote_has_generic = !remote.segments.last().unwrap().arguments.is_none();
         <span class="kw">if </span>local_has_generic &amp;&amp; remote_has_generic {
             cx.error_spanned_by(remote, <span class="string">&quot;remove generic parameters from this path&quot;</span>);
         }
     }
 }

 <span class="comment">// Getters are only allowed inside structs (not enums) with the `remote`
 // attribute.
 </span><span class="kw">fn </span>check_getter(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <span class="kw">match </span>cont.data {
         Data::Enum(<span class="kw">_</span>) =&gt; {
             <span class="kw">if </span>cont.data.has_getter() {
                 cx.error_spanned_by(
                     cont.original,
                     <span class="string">&quot;#[serde(getter = \&quot;...\&quot;)] is not allowed in an enum&quot;</span>,
                 );
             }
         }
         Data::Struct(<span class="kw">_</span>, <span class="kw">_</span>) =&gt; {
             <span class="kw">if </span>cont.data.has_getter() &amp;&amp; cont.attrs.remote().is_none() {
                 cx.error_spanned_by(
                     cont.original,
                     <span class="string">&quot;#[serde(getter = \&quot;...\&quot;)] can only be used in structs that have #[serde(remote = \&quot;...\&quot;)]&quot;</span>,
                 );
             }
         }
     }
 }

 <span class="comment">// Flattening has some restrictions we can test.
 </span><span class="kw">fn </span>check_flatten(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <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 {
                 <span class="kw">for </span>field <span class="kw">in </span><span class="kw-2">&amp;</span>variant.fields {
                     check_flatten_field(cx, variant.style, field);
                 }
             }
         }
         Data::Struct(style, fields) =&gt; {
             <span class="kw">for </span>field <span class="kw">in </span>fields {
                 check_flatten_field(cx, <span class="kw-2">*</span>style, field);
             }
         }
     }
 }

 <span class="kw">fn </span>check_flatten_field(cx: <span class="kw-2">&amp;</span>Ctxt, style: Style, field: <span class="kw-2">&amp;</span>Field) {
     <span class="kw">if </span>!field.attrs.flatten() {
         <span class="kw">return</span>;
     }
     <span class="kw">match </span>style {
         Style::Tuple =&gt; {
             cx.error_spanned_by(
                 field.original,
                 <span class="string">&quot;#[serde(flatten)] cannot be used on tuple structs&quot;</span>,
             );
         }
         Style::Newtype =&gt; {
             cx.error_spanned_by(
                 field.original,
                 <span class="string">&quot;#[serde(flatten)] cannot be used on newtype structs&quot;</span>,
             );
         }
         <span class="kw">_ </span>=&gt; {}
     }
 }

 <span class="comment">// The `other` attribute must be used at most once and it must be the last
 // variant of an enum.
 //
 // Inside a `variant_identifier` all variants must be unit variants. Inside a
 // `field_identifier` all but possibly one variant must be unit variants. The
 // last variant may be a newtype variant which is an implicit &quot;other&quot; case.
 </span><span class="kw">fn </span>check_identifier(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <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>;
         }
     };

     <span class="kw">for </span>(i, variant) <span class="kw">in </span>variants.iter().enumerate() {
         <span class="kw">match </span>(
             variant.style,
             cont.attrs.identifier(),
             variant.attrs.other(),
             cont.attrs.tag(),
         ) {
             <span class="comment">// The `other` attribute may not be used in a variant_identifier.
             </span>(<span class="kw">_</span>, Identifier::Variant, <span class="bool-val">true</span>, <span class="kw">_</span>) =&gt; {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="string">&quot;#[serde(other)] may not be used on a variant identifier&quot;</span>,
                 );
             }

             <span class="comment">// Variant with `other` attribute cannot appear in untagged enum
             </span>(<span class="kw">_</span>, Identifier::No, <span class="bool-val">true</span>, <span class="kw-2">&amp;</span>TagType::None) =&gt; {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="string">&quot;#[serde(other)] cannot appear on untagged enum&quot;</span>,
                 );
             }

             <span class="comment">// Variant with `other` attribute must be the last one.
             </span>(Style::Unit, Identifier::Field, <span class="bool-val">true</span>, <span class="kw">_</span>) | (Style::Unit, Identifier::No, <span class="bool-val">true</span>, <span class="kw">_</span>) =&gt; {
                 <span class="kw">if </span>i &lt; variants.len() - <span class="number">1 </span>{
                     cx.error_spanned_by(
                         variant.original,
                         <span class="string">&quot;#[serde(other)] must be on the last variant&quot;</span>,
                     );
                 }
             }

             <span class="comment">// Variant with `other` attribute must be a unit variant.
             </span>(<span class="kw">_</span>, Identifier::Field, <span class="bool-val">true</span>, <span class="kw">_</span>) | (<span class="kw">_</span>, Identifier::No, <span class="bool-val">true</span>, <span class="kw">_</span>) =&gt; {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="string">&quot;#[serde(other)] must be on a unit variant&quot;</span>,
                 );
             }

             <span class="comment">// Any sort of variant is allowed if this is not an identifier.
             </span>(<span class="kw">_</span>, Identifier::No, <span class="bool-val">false</span>, <span class="kw">_</span>) =&gt; {}

             <span class="comment">// Unit variant without `other` attribute is always fine.
             </span>(Style::Unit, <span class="kw">_</span>, <span class="bool-val">false</span>, <span class="kw">_</span>) =&gt; {}

             <span class="comment">// The last field is allowed to be a newtype catch-all.
             </span>(Style::Newtype, Identifier::Field, <span class="bool-val">false</span>, <span class="kw">_</span>) =&gt; {
                 <span class="kw">if </span>i &lt; variants.len() - <span class="number">1 </span>{
                     cx.error_spanned_by(
                         variant.original,
                         <span class="macro">format!</span>(<span class="string">&quot;`{}` must be the last variant&quot;</span>, variant.ident),
                     );
                 }
             }

             (<span class="kw">_</span>, Identifier::Field, <span class="bool-val">false</span>, <span class="kw">_</span>) =&gt; {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="string">&quot;#[serde(field_identifier)] may only contain unit variants&quot;</span>,
                 );
             }

             (<span class="kw">_</span>, Identifier::Variant, <span class="bool-val">false</span>, <span class="kw">_</span>) =&gt; {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="string">&quot;#[serde(variant_identifier)] may only contain unit variants&quot;</span>,
                 );
             }
         }
     }
 }

 <span class="comment">// Skip-(de)serializing attributes are not allowed on variants marked
 // (de)serialize_with.
 </span><span class="kw">fn </span>check_variant_skip_attrs(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <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>;
         }
     };

     <span class="kw">for </span>variant <span class="kw">in </span>variants.iter() {
         <span class="kw">if </span>variant.attrs.serialize_with().is_some() {
             <span class="kw">if </span>variant.attrs.skip_serializing() {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="macro">format!</span>(
                         <span class="string">&quot;variant `{}` cannot have both #[serde(serialize_with)] and #[serde(skip_serializing)]&quot;</span>,
                         variant.ident
                     ),
                 );
             }

             <span class="kw">for </span>field <span class="kw">in </span><span class="kw-2">&amp;</span>variant.fields {
                 <span class="kw">let </span>member = member_message(<span class="kw-2">&amp;</span>field.member);

                 <span class="kw">if </span>field.attrs.skip_serializing() {
                     cx.error_spanned_by(
                         variant.original,
                         <span class="macro">format!</span>(
                             <span class="string">&quot;variant `{}` cannot have both #[serde(serialize_with)] and a field {} marked with #[serde(skip_serializing)]&quot;</span>,
                             variant.ident, member
                         ),
                     );
                 }

                 <span class="kw">if </span>field.attrs.skip_serializing_if().is_some() {
                     cx.error_spanned_by(
                         variant.original,
                         <span class="macro">format!</span>(
                             <span class="string">&quot;variant `{}` cannot have both #[serde(serialize_with)] and a field {} marked with #[serde(skip_serializing_if)]&quot;</span>,
                             variant.ident, member
                         ),
                     );
                 }
             }
         }

         <span class="kw">if </span>variant.attrs.deserialize_with().is_some() {
             <span class="kw">if </span>variant.attrs.skip_deserializing() {
                 cx.error_spanned_by(
                     variant.original,
                     <span class="macro">format!</span>(
                         <span class="string">&quot;variant `{}` cannot have both #[serde(deserialize_with)] and #[serde(skip_deserializing)]&quot;</span>,
                         variant.ident
                     ),
                 );
             }

             <span class="kw">for </span>field <span class="kw">in </span><span class="kw-2">&amp;</span>variant.fields {
                 <span class="kw">if </span>field.attrs.skip_deserializing() {
                     <span class="kw">let </span>member = member_message(<span class="kw-2">&amp;</span>field.member);

                     cx.error_spanned_by(
                         variant.original,
                         <span class="macro">format!</span>(
                             <span class="string">&quot;variant `{}` cannot have both #[serde(deserialize_with)] and a field {} marked with #[serde(skip_deserializing)]&quot;</span>,
                             variant.ident, member
                         ),
                     );
                 }
             }
         }
     }
 }

 <span class="comment">// The tag of an internally-tagged struct variant must not be the same as either
 // one of its fields, as this would result in duplicate keys in the serialized
 // output and/or ambiguity in the to-be-deserialized input.
 </span><span class="kw">fn </span>check_internal_tag_field_name_conflict(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <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>,
     };

     <span class="kw">let </span>tag = <span class="kw">match </span>cont.attrs.tag() {
         TagType::Internal { tag } =&gt; tag.as_str(),
         TagType::External | TagType::Adjacent { .. } | TagType::None =&gt; <span class="kw">return</span>,
     };

     <span class="kw">let </span>diagnose_conflict = || {
         cx.error_spanned_by(
             cont.original,
             <span class="macro">format!</span>(<span class="string">&quot;variant field name `{}` conflicts with internal tag&quot;</span>, tag),
         );
     };

     <span class="kw">for </span>variant <span class="kw">in </span>variants {
         <span class="kw">match </span>variant.style {
             Style::Struct =&gt; {
                 <span class="kw">for </span>field <span class="kw">in </span><span class="kw-2">&amp;</span>variant.fields {
                     <span class="kw">let </span>check_ser = !field.attrs.skip_serializing();
                     <span class="kw">let </span>check_de = !field.attrs.skip_deserializing();
                     <span class="kw">let </span>name = field.attrs.name();
                     <span class="kw">let </span>ser_name = name.serialize_name();

                     <span class="kw">if </span>check_ser &amp;&amp; ser_name == tag {
                         diagnose_conflict();
                         <span class="kw">return</span>;
                     }

                     <span class="kw">for </span>de_name <span class="kw">in </span>field.attrs.aliases() {
                         <span class="kw">if </span>check_de &amp;&amp; de_name == tag {
                             diagnose_conflict();
                             <span class="kw">return</span>;
                         }
                     }
                 }
             }
             Style::Unit | Style::Newtype | Style::Tuple =&gt; {}
         }
     }
 }

 <span class="comment">// In the case of adjacently-tagged enums, the type and the contents tag must
 // differ, for the same reason.
 </span><span class="kw">fn </span>check_adjacent_tag_conflict(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;</span>Container) {
     <span class="kw">let </span>(type_tag, content_tag) = <span class="kw">match </span>cont.attrs.tag() {
         TagType::Adjacent { tag, content } =&gt; (tag, content),
         TagType::Internal { .. } | TagType::External | TagType::None =&gt; <span class="kw">return</span>,
     };

     <span class="kw">if </span>type_tag == content_tag {
         cx.error_spanned_by(
             cont.original,
             <span class="macro">format!</span>(
                 <span class="string">&quot;enum tags `{}` for type and content conflict with each other&quot;</span>,
                 type_tag
             ),
         );
     }
 }

 <span class="comment">// Enums and unit structs cannot be transparent.
 </span><span class="kw">fn </span>check_transparent(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;mut </span>Container, derive: Derive) {
     <span class="kw">if </span>!cont.attrs.transparent() {
         <span class="kw">return</span>;
     }

     <span class="kw">if </span>cont.attrs.type_from().is_some() {
         cx.error_spanned_by(
             cont.original,
             <span class="string">&quot;#[serde(transparent)] is not allowed with #[serde(from = \&quot;...\&quot;)]&quot;</span>,
         );
     }

     <span class="kw">if </span>cont.attrs.type_try_from().is_some() {
         cx.error_spanned_by(
             cont.original,
             <span class="string">&quot;#[serde(transparent)] is not allowed with #[serde(try_from = \&quot;...\&quot;)]&quot;</span>,
         );
     }

     <span class="kw">if </span>cont.attrs.type_into().is_some() {
         cx.error_spanned_by(
             cont.original,
             <span class="string">&quot;#[serde(transparent)] is not allowed with #[serde(into = \&quot;...\&quot;)]&quot;</span>,
         );
     }

     <span class="kw">let </span>fields = <span class="kw">match </span><span class="kw-2">&amp;mut </span>cont.data {
         Data::Enum(<span class="kw">_</span>) =&gt; {
             cx.error_spanned_by(
                 cont.original,
                 <span class="string">&quot;#[serde(transparent)] is not allowed on an enum&quot;</span>,
             );
             <span class="kw">return</span>;
         }
         Data::Struct(Style::Unit, <span class="kw">_</span>) =&gt; {
             cx.error_spanned_by(
                 cont.original,
                 <span class="string">&quot;#[serde(transparent)] is not allowed on a unit struct&quot;</span>,
             );
             <span class="kw">return</span>;
         }
         Data::Struct(<span class="kw">_</span>, fields) =&gt; fields,
     };

     <span class="kw">let </span><span class="kw-2">mut </span>transparent_field = <span class="prelude-val">None</span>;

     <span class="kw">for </span>field <span class="kw">in </span>fields {
         <span class="kw">if </span>allow_transparent(field, derive) {
             <span class="kw">if </span>transparent_field.is_some() {
                 cx.error_spanned_by(
                     cont.original,
                     <span class="string">&quot;#[serde(transparent)] requires struct to have at most one transparent field&quot;</span>,
                 );
                 <span class="kw">return</span>;
             }
             transparent_field = <span class="prelude-val">Some</span>(field);
         }
     }

     <span class="kw">match </span>transparent_field {
         <span class="prelude-val">Some</span>(transparent_field) =&gt; transparent_field.attrs.mark_transparent(),
         <span class="prelude-val">None </span>=&gt; <span class="kw">match </span>derive {
             Derive::Serialize =&gt; {
                 cx.error_spanned_by(
                     cont.original,
                     <span class="string">&quot;#[serde(transparent)] requires at least one field that is not skipped&quot;</span>,
                 );
             }
             Derive::Deserialize =&gt; {
                 cx.error_spanned_by(
                     cont.original,
                     <span class="string">&quot;#[serde(transparent)] requires at least one field that is neither skipped nor has a default&quot;</span>,
                 );
             }
         },
     }
 }

 <span class="kw">fn </span>member_message(member: <span class="kw-2">&amp;</span>Member) -&gt; String {
     <span class="kw">match </span>member {
         Member::Named(ident) =&gt; <span class="macro">format!</span>(<span class="string">&quot;`{}`&quot;</span>, ident),
         Member::Unnamed(i) =&gt; <span class="macro">format!</span>(<span class="string">&quot;#{}&quot;</span>, i.index),
     }
 }

 <span class="kw">fn </span>allow_transparent(field: <span class="kw-2">&amp;</span>Field, derive: Derive) -&gt; bool {
     <span class="kw">if let </span>Type::Path(ty) = ungroup(field.ty) {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(seg) = ty.path.segments.last() {
             <span class="kw">if </span>seg.ident == <span class="string">&quot;PhantomData&quot; </span>{
                 <span class="kw">return </span><span class="bool-val">false</span>;
             }
         }
     }

     <span class="kw">match </span>derive {
         Derive::Serialize =&gt; !field.attrs.skip_serializing(),
         Derive::Deserialize =&gt; !field.attrs.skip_deserializing() &amp;&amp; field.attrs.default().is_none(),
     }
 }

 <span class="kw">fn </span>check_from_and_try_from(cx: <span class="kw-2">&amp;</span>Ctxt, cont: <span class="kw-2">&amp;mut </span>Container) {
     <span class="kw">if </span>cont.attrs.type_from().is_some() &amp;&amp; cont.attrs.type_try_from().is_some() {
         cx.error_spanned_by(
             cont.original,
             <span class="string">&quot;#[serde(from = \&quot;...\&quot;)] and #[serde(try_from = \&quot;...\&quot;)] conflict with each other&quot;</span>,
         );
     }
 }
 </code></pre></div>
 </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="serde_derive" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>