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node_modules/graphql/validation/rules/NoUnusedVariables.js.flow

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+// @flow strict
+
+import { GraphQLError } from '../../error/GraphQLError';
+import { type ASTVisitor } from '../../language/visitor';
+
+import { type ValidationContext } from '../ValidationContext';
+
+export function unusedVariableMessage(
+  varName: string,
+  opName: ?string,
+): string {
+  return opName
+    ? `Variable "$${varName}" is never used in operation "${opName}".`
+    : `Variable "$${varName}" is never used.`;
+}
+
+/**
+ * No unused variables
+ *
+ * A GraphQL operation is only valid if all variables defined by an operation
+ * are used, either directly or within a spread fragment.
+ */
+export function NoUnusedVariables(context: ValidationContext): ASTVisitor {
+  let variableDefs = [];
+
+  return {
+    OperationDefinition: {
+      enter() {
+        variableDefs = [];
+      },
+      leave(operation) {
+        const variableNameUsed = Object.create(null);
+        const usages = context.getRecursiveVariableUsages(operation);
+        const opName = operation.name ? operation.name.value : null;
+
+        for (const { node } of usages) {
+          variableNameUsed[node.name.value] = true;
+        }
+
+        for (const variableDef of variableDefs) {
+          const variableName = variableDef.variable.name.value;
+          if (variableNameUsed[variableName] !== true) {
+            context.reportError(
+              new GraphQLError(
+                unusedVariableMessage(variableName, opName),
+                variableDef,
+              ),
+            );
+          }
+        }
+      },
+    },
+    VariableDefinition(def) {
+      variableDefs.push(def);
+    },
+  };
+}