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node_modules/graphql/validation/rules/NoFragmentCycles.mjs

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+import { GraphQLError } from '../../error/GraphQLError';
+export function cycleErrorMessage(fragName, spreadNames) {
+  var via = spreadNames.length ? ' via ' + spreadNames.join(', ') : '';
+  return "Cannot spread fragment \"".concat(fragName, "\" within itself").concat(via, ".");
+}
+export function NoFragmentCycles(context) {
+  // Tracks already visited fragments to maintain O(N) and to ensure that cycles
+  // are not redundantly reported.
+  var visitedFrags = Object.create(null); // Array of AST nodes used to produce meaningful errors
+
+  var spreadPath = []; // Position in the spread path
+
+  var spreadPathIndexByName = Object.create(null);
+  return {
+    OperationDefinition: function OperationDefinition() {
+      return false;
+    },
+    FragmentDefinition: function FragmentDefinition(node) {
+      detectCycleRecursive(node);
+      return false;
+    }
+  }; // This does a straight-forward DFS to find cycles.
+  // It does not terminate when a cycle was found but continues to explore
+  // the graph to find all possible cycles.
+
+  function detectCycleRecursive(fragment) {
+    if (visitedFrags[fragment.name.value]) {
+      return;
+    }
+
+    var fragmentName = fragment.name.value;
+    visitedFrags[fragmentName] = true;
+    var spreadNodes = context.getFragmentSpreads(fragment.selectionSet);
+
+    if (spreadNodes.length === 0) {
+      return;
+    }
+
+    spreadPathIndexByName[fragmentName] = spreadPath.length;
+
+    for (var _i2 = 0; _i2 < spreadNodes.length; _i2++) {
+      var spreadNode = spreadNodes[_i2];
+      var spreadName = spreadNode.name.value;
+      var cycleIndex = spreadPathIndexByName[spreadName];
+      spreadPath.push(spreadNode);
+
+      if (cycleIndex === undefined) {
+        var spreadFragment = context.getFragment(spreadName);
+
+        if (spreadFragment) {
+          detectCycleRecursive(spreadFragment);
+        }
+      } else {
+        var cyclePath = spreadPath.slice(cycleIndex);
+        var fragmentNames = cyclePath.slice(0, -1).map(function (s) {
+          return s.name.value;
+        });
+        context.reportError(new GraphQLError(cycleErrorMessage(spreadName, fragmentNames), cyclePath));
+      }
+
+      spreadPath.pop();
+    }
+
+    spreadPathIndexByName[fragmentName] = undefined;
+  }
+}