Improve visitability of lookahead types. (#431)

I've added methods which allow Juniper users to visit all nodes of a lookahead tree so that they can be used for query generation.

juniper/CHANGELOG.md

@@ -1,10 +1,11 @@
 # master
 
-- Add ability to parse 'subscription'
+- Improve lookahead visitability.
+- Add ability to parse 'subscription'.
 
 # [[0.13.1] 2019-07-29](https://github.com/graphql-rust/juniper/releases/tag/juniper-0.13.1)
 
-- Fix a regression when using lookaheads with fragments containing nested types [#404](https://github.com/graphql-rust/juniper/pull/404)	
+- Fix a regression when using lookaheads with fragments containing nested types [#404](https://github.com/graphql-rust/juniper/pull/404)
 
 - Allow `mut` arguments for resolver functions in `#[object]` macros [#402](https://github.com/graphql-rust/juniper/pull/402)
 
@@ -15,7 +16,7 @@
 See [#345](https://github.com/graphql-rust/juniper/pull/345).
 
 The newtype pattern can now be used with the `GraphQLScalarValue` custom derive
-to easily implement custom scalar values that just wrap another scalar, 
+to easily implement custom scalar values that just wrap another scalar,
 similar to serdes `#[serde(transparent)]` functionality.
 
 Example:
@@ -34,7 +35,7 @@ struct UserId(i32);
 
 ### object macro
 
-The `graphql_object!` macro is deprecated and will be removed in the future. 
+The `graphql_object!` macro is deprecated and will be removed in the future.
 It is replaced by the new [object](https://docs.rs/juniper/latest/juniper/macro.object.html) procedural macro.
 
 [#333](https://github.com/graphql-rust/juniper/pull/333)
@@ -53,7 +54,7 @@ This should not have any impact on your code, since juniper already was 2018 com
 - The `GraphQLType` impl for () was removed to improve compile time safefty. [#355](https://github.com/graphql-rust/juniper/pull/355)
 - The `ScalarValue` custom derive has been renamed to `GraphQLScalarValue`.
 - Added built-in support for the canonical schema introspection query via
-  `juniper::introspect()`. 
+  `juniper::introspect()`.
   [#307](https://github.com/graphql-rust/juniper/issues/307)
 - Fix introspection query validity
   The DirectiveLocation::InlineFragment had an invalid literal value,

juniper/src/executor/look_ahead.rs

@@ -88,6 +88,11 @@ where
         }
     }
 
+    /// The argument's name
+    pub fn name(&'a self) -> &str {
+        &self.name
+    }
+
     /// The value of the argument
     pub fn value(&'a self) -> &LookAheadValue<'a, S> {
         &self.value
@@ -347,6 +352,12 @@ pub trait LookAheadMethods<S> {
         self.select_child(name).is_some()
     }
 
+    /// Does the current node have any arguments?
+    fn has_arguments(&self) -> bool;
+
+    /// Does the current node have any children?
+    fn has_children(&self) -> bool;
+
     /// Get the top level arguments for the current selection
     fn arguments(&self) -> &[LookAheadArgument<S>];
 
@@ -354,6 +365,9 @@ pub trait LookAheadMethods<S> {
     fn argument(&self, name: &str) -> Option<&LookAheadArgument<S>> {
         self.arguments().iter().find(|a| a.name == name)
     }
+
+    /// Get the top level children for the current selection
+    fn child_names(&self) -> Vec<&str>;
 }
 
 impl<'a, S> LookAheadMethods<S> for ConcreteLookAheadSelection<'a, S> {
@@ -368,6 +382,21 @@ impl<'a, S> LookAheadMethods<S> for ConcreteLookAheadSelection<'a, S> {
     fn arguments(&self) -> &[LookAheadArgument<S>] {
         &self.arguments
     }
+
+    fn child_names(&self) -> Vec<&str> {
+        self.children
+            .iter()
+            .map(|c| c.alias.unwrap_or(c.name))
+            .collect()
+    }
+
+    fn has_arguments(&self) -> bool {
+        !self.arguments.is_empty()
+    }
+
+    fn has_children(&self) -> bool {
+        !self.children.is_empty()
+    }
 }
 
 impl<'a, S> LookAheadMethods<S> for LookAheadSelection<'a, S> {
@@ -385,6 +414,21 @@ impl<'a, S> LookAheadMethods<S> for LookAheadSelection<'a, S> {
     fn arguments(&self) -> &[LookAheadArgument<S>] {
         &self.arguments
     }
+
+    fn child_names(&self) -> Vec<&str> {
+        self.children
+            .iter()
+            .map(|c| c.inner.alias.unwrap_or(c.inner.name))
+            .collect()
+    }
+
+    fn has_arguments(&self) -> bool {
+        !self.arguments.is_empty()
+    }
+
+    fn has_children(&self) -> bool {
+        !self.children.is_empty()
+    }
 }
 
 #[cfg(test)]
@@ -1399,4 +1443,59 @@ fragment heroFriendNames on Hero {
             panic!("No Operation found");
         }
     }
+
+    #[test]
+    fn check_visitability() {
+        let docs = parse_document_source::<DefaultScalarValue>(
+            "
+query Hero {
+    hero(episode: EMPIRE) {
+        name
+        friends {
+            name
+        }
+    }
+}
+            ",
+        )
+        .unwrap();
+        let fragments = extract_fragments(&docs);
+
+        if let crate::ast::Definition::Operation(ref op) = docs[0] {
+            let vars = Variables::default();
+            let look_ahead = LookAheadSelection::build_from_selection(
+                &op.item.selection_set[0],
+                &vars,
+                &fragments,
+            )
+            .unwrap();
+
+            assert_eq!(look_ahead.field_name(), "hero");
+
+            assert!(look_ahead.has_arguments());
+            let args = look_ahead.arguments();
+            assert_eq!(args[0].name(), "episode");
+            assert_eq!(args[0].value(), &LookAheadValue::Enum("EMPIRE"));
+
+            assert!(look_ahead.has_children());
+            assert_eq!(look_ahead.child_names(), vec!["name", "friends"]);
+
+            let child0 = look_ahead.select_child("name").unwrap();
+            assert_eq!(child0.field_name(), "name");
+            assert!(!child0.has_arguments());
+            assert!(!child0.has_children());
+
+            let child1 = look_ahead.select_child("friends").unwrap();
+            assert_eq!(child1.field_name(), "friends");
+            assert!(!child1.has_arguments());
+            assert!(child1.has_children());
+            assert_eq!(child1.child_names(), vec!["name"]);
+
+            let child2 = child1.select_child("name").unwrap();
+            assert!(!child2.has_arguments());
+            assert!(!child2.has_children());
+        } else {
+            panic!("No Operation found");
+        }
+    }
 }