Fix #322.

parser/src/graphql.pest

@@ -47,8 +47,8 @@ object_type = {
 implements_interfaces = { "implements" ~ "&"? ~ name ~ ("&" ~ name)* }
 
 interface_type = {
-	string? ~ "interface" ~ name ~ const_directives? ~ fields_definition?
-	| extend ~ "interface" ~ name ~ (const_directives? ~ fields_definition | const_directives)
+	string? ~ "interface" ~ name ~ implements_interfaces? ~ const_directives? ~ fields_definition?
+	| extend ~ "interface" ~ name ~ implements_interfaces? ~ (const_directives? ~ fields_definition | const_directives)
 }
 
 fields_definition = { "{" ~ field_definition+ ~ "}" }

parser/src/parse/service.rs

@@ -149,12 +149,26 @@ fn parse_type_definition(
             )
         }
         Rule::interface_type => {
+            let implements = parse_if_rule(&mut pairs, Rule::implements_interfaces, |pair| {
+                debug_assert_eq!(pair.as_rule(), Rule::implements_interfaces);
+
+                pair.into_inner()
+                    .map(|pair| parse_name(pair, pc))
+                    .collect::<Result<_>>()
+            })?;
+
             let directives = parse_opt_const_directives(&mut pairs, pc)?;
             let fields = parse_if_rule(&mut pairs, Rule::fields_definition, |pair| {
                 parse_fields_definition(pair, pc)
             })?
             .unwrap_or_default();
-            (directives, TypeKind::Interface(InterfaceType { fields }))
+            (
+                directives,
+                TypeKind::Interface(InterfaceType {
+                    implements: implements.unwrap_or_default(),
+                    fields,
+                }),
+            )
         }
         Rule::union_type => {
             let directives = parse_opt_const_directives(&mut pairs, pc)?;

parser/src/types/service.rs

@@ -112,6 +112,8 @@ pub struct FieldDefinition {
 /// [Reference](https://spec.graphql.org/June2018/#InterfaceType).
 #[derive(Debug, Clone)]
 pub struct InterfaceType {
+    /// The interfaces implemented by the interface.
+    pub implements: Vec<Positioned<Name>>,
     /// The fields of the interface type.
     pub fields: Vec<Positioned<FieldDefinition>>,
 }

parser/tests/services/implements.graphql

@@ -1,3 +1,7 @@
 type Type1 implements IOne
 
 type Type1 implements IOne & ITwo
+
+interface Type1 implements IOne
+
+interface Type1 implements IOne & ITwo