Add a basic lookahead functionality

juniper/src/executor/mod.rs

@@ -19,6 +19,10 @@ use schema::model::{RootNode, SchemaType, TypeType};
 use types::base::GraphQLType;
 use types::name::Name;
 
+mod look_ahead;
+
+pub use self::look_ahead::{Applies, LookAheadArgument, LookAheadSelection, LookAheadValue, LookAheadMethods, ChildSelection};
+
 /// A type registry used to build schemas
 ///
 /// The registry gathers metadata for all types in a schema. It provides
@@ -51,6 +55,7 @@ where
     context: &'a CtxT,
     errors: &'a RwLock<Vec<ExecutionError>>,
     field_path: FieldPath<'a>,
+    type_name: &'a str,
 }
 
 /// Error type for errors that occur during query execution
@@ -319,6 +324,7 @@ impl<'a, CtxT> Executor<'a, CtxT> {
             context: ctx,
             errors: self.errors,
             field_path: self.field_path.clone(),
+            type_name: self.type_name,
         }
     }
 
@@ -345,6 +351,7 @@ impl<'a, CtxT> Executor<'a, CtxT> {
             context: self.context,
             errors: self.errors,
             field_path: FieldPath::Field(field_alias, location, &self.field_path),
+            type_name: self.type_name
         }
     }
 
@@ -366,6 +373,7 @@ impl<'a, CtxT> Executor<'a, CtxT> {
             context: self.context,
             errors: self.errors,
             field_path: self.field_path.clone(),
+            type_name: type_name.unwrap(),
         }
     }
 
@@ -421,6 +429,18 @@ impl<'a, CtxT> Executor<'a, CtxT> {
             error: error,
         });
     }
+
+    pub fn look_ahead(&self) -> LookAheadSelection {
+        LookAheadSelection{
+            name: self.type_name,
+            alias: None,
+            arguments: Vec::new(),
+            childs: self.current_selection_set.map(|s| s.iter().map(|s| ChildSelection {
+                inner: LookAheadSelection::build_from_selection(s, self.variables, self.fragments),
+                applies_for: Applies::All
+            }).collect()).unwrap_or_else(Vec::new)
+        }
+    }
 }
 
 impl<'a> FieldPath<'a> {
@@ -553,6 +573,7 @@ where
             context: context,
             errors: &errors,
             field_path: FieldPath::Root(op.start),
+            type_name: &op.item.name.map(|n| n.item).unwrap_or(""),
         };
 
         value = match op.item.operation_type {

juniper/src/lib.rs

@@ -153,6 +153,7 @@ use validation::{validate_input_values, visit_all_rules, ValidatorContext};
 pub use ast::{FromInputValue, InputValue, Selection, ToInputValue, Type};
 pub use executor::{Context, ExecutionError, ExecutionResult, Executor, FieldError, FieldResult,
                    FromContext, IntoResolvable, Registry, Variables};
+pub use executor::{Applies, LookAheadArgument, LookAheadSelection, LookAheadValue, LookAheadMethods};
 pub use schema::model::RootNode;
 pub use types::base::{Arguments, GraphQLType, TypeKind};
 pub use types::scalars::{EmptyMutation, ID};

juniper/src/value.rs

@@ -13,7 +13,7 @@ use parser::Spanning;
 /// values or variables. Also, lists and objects do not contain any location
 /// information since they are generated by resolving fields and values rather
 /// than parsing a source query.
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 #[allow(missing_docs)]
 pub enum Value {
     Null,