add no_unused_variables and mark missing defer ones

src/validate/rules/mod.rs

@@ -1,10 +1,14 @@
 use crate::visit::ComposedVisitor;
 
+// Missing schemaless rules
+// https://github.com/graphql/graphql-js/blob/main/src/validation/rules/DeferStreamDirectiveLabelRule.ts
+// https://github.com/graphql/graphql-js/blob/main/src/validation/rules/DeferStreamDirectiveOnValidOperationsRule.ts
 mod known_fragment_names;
 mod lone_anonymous_operation;
 mod no_fragment_cycles;
 mod no_undefined_variables;
 mod no_unused_fragments;
+mod no_unused_variables;
 mod unique_argument_names;
 mod unique_fragment_names;
 mod unique_operation_names;
@@ -16,6 +20,7 @@ pub use lone_anonymous_operation::*;
 pub use no_fragment_cycles::*;
 pub use no_undefined_variables::*;
 pub use no_unused_fragments::*;
+pub use no_unused_variables::*;
 pub use unique_argument_names::*;
 pub use unique_fragment_names::*;
 pub use unique_operation_names::*;
@@ -51,7 +56,7 @@ pub type DefaultRules<'a> = ComposedVisitor<
                 'a,
                 ValidationContext<'a>,
                 NoFragmentCycles<'a>,
-                NoUndefinedVariables<'a>,
+                ComposedVisitor<'a, ValidationContext<'a>, NoUndefinedVariables<'a>, NoUnusedVariables<'a>>
             >,
         >,
     >,

src/validate/rules/no_unused_variables.rs

@@ -0,0 +1,75 @@
+use super::super::{ValidationContext, ValidationRule};
+use crate::{ast::*, visit::*};
+
+/// Validate that a document uses all the variables it defines at least once.
+///
+/// See [`ValidationRule`]
+/// [Reference](https://spec.graphql.org/draft/#sec-All-Variables-Used)
+#[derive(Default)]
+pub struct NoUnusedVariables<'a> {
+    variables: Vec<&'a str>,
+    used_variables: Vec<&'a str>,
+}
+
+impl<'a> ValidationRule<'a> for NoUnusedVariables<'a> {}
+
+impl<'a> Visitor<'a, ValidationContext<'a>> for NoUnusedVariables<'a> {
+    fn enter_operation(
+        &mut self,
+        _ctx: &mut ValidationContext<'a>,
+        operation: &'a OperationDefinition<'a>,
+        _info: &VisitInfo
+    ) -> VisitFlow {
+        operation.variable_definitions.children.iter().for_each(|def| {
+            self.variables.push(def.variable.name);
+        });
+        VisitFlow::Next
+    }
+
+    fn enter_field(&mut self, _ctx: &mut ValidationContext<'a>, field: &'a Field<'a>, _info: &VisitInfo) -> VisitFlow {
+        field.arguments.children.iter().for_each(|arg| {
+            if let Value::Variable(var) = arg.value {
+                self.used_variables.push(var.name);
+            }
+        });
+        VisitFlow::Next
+    }
+
+    fn leave_document(
+        &mut self,
+        ctx: &mut ValidationContext<'a>,
+        _document: &'a Document<'a>,
+        _info: &VisitInfo
+    ) -> VisitFlow {
+        self.variables.iter().for_each(|defined_variable| {
+            if !self.used_variables.contains(defined_variable) {
+                ctx.add_error("All defined variables must be at least used once");
+            }
+        });
+        VisitFlow::Next
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn used_all_variables() {
+        let ctx = ASTContext::new();
+        let document =
+            Document::parse(&ctx, "query ($x: Int!) { todos(from: $x) { id } }").unwrap();
+        NoUnusedVariables::validate(&ctx, document).unwrap();
+    }
+
+    #[test]
+    fn has_unused_variable() {
+        let ctx = ASTContext::new();
+        let document = Document::parse(
+            &ctx,
+            "query ($x: Int!, $unused: String!) { todos(from: $x) { id } }",
+        )
+        .unwrap();
+        NoUnusedVariables::validate(&ctx, document).unwrap_err();
+    }
+}