Initialisation

Added the packages and files for the backend server

node_modules/graphql/validation/rules/OverlappingFieldsCanBeMergedRule.js

@@ -0,0 +1,820 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true,
+});
+exports.OverlappingFieldsCanBeMergedRule = OverlappingFieldsCanBeMergedRule;
+
+var _inspect = require('../../jsutils/inspect.js');
+
+var _GraphQLError = require('../../error/GraphQLError.js');
+
+var _kinds = require('../../language/kinds.js');
+
+var _printer = require('../../language/printer.js');
+
+var _definition = require('../../type/definition.js');
+
+var _sortValueNode = require('../../utilities/sortValueNode.js');
+
+var _typeFromAST = require('../../utilities/typeFromAST.js');
+
+function reasonMessage(reason) {
+  if (Array.isArray(reason)) {
+    return reason
+      .map(
+        ([responseName, subReason]) =>
+          `subfields "${responseName}" conflict because ` +
+          reasonMessage(subReason),
+      )
+      .join(' and ');
+  }
+
+  return reason;
+}
+/**
+ * Overlapping fields can be merged
+ *
+ * A selection set is only valid if all fields (including spreading any
+ * fragments) either correspond to distinct response names or can be merged
+ * without ambiguity.
+ *
+ * See https://spec.graphql.org/draft/#sec-Field-Selection-Merging
+ */
+
+function OverlappingFieldsCanBeMergedRule(context) {
+  // A memoization for when two fragments are compared "between" each other for
+  // conflicts. Two fragments may be compared many times, so memoizing this can
+  // dramatically improve the performance of this validator.
+  const comparedFragmentPairs = new PairSet(); // A cache for the "field map" and list of fragment names found in any given
+  // selection set. Selection sets may be asked for this information multiple
+  // times, so this improves the performance of this validator.
+
+  const cachedFieldsAndFragmentNames = new Map();
+  return {
+    SelectionSet(selectionSet) {
+      const conflicts = findConflictsWithinSelectionSet(
+        context,
+        cachedFieldsAndFragmentNames,
+        comparedFragmentPairs,
+        context.getParentType(),
+        selectionSet,
+      );
+
+      for (const [[responseName, reason], fields1, fields2] of conflicts) {
+        const reasonMsg = reasonMessage(reason);
+        context.reportError(
+          new _GraphQLError.GraphQLError(
+            `Fields "${responseName}" conflict because ${reasonMsg}. Use different aliases on the fields to fetch both if this was intentional.`,
+            {
+              nodes: fields1.concat(fields2),
+            },
+          ),
+        );
+      }
+    },
+  };
+}
+
+/**
+ * Algorithm:
+ *
+ * Conflicts occur when two fields exist in a query which will produce the same
+ * response name, but represent differing values, thus creating a conflict.
+ * The algorithm below finds all conflicts via making a series of comparisons
+ * between fields. In order to compare as few fields as possible, this makes
+ * a series of comparisons "within" sets of fields and "between" sets of fields.
+ *
+ * Given any selection set, a collection produces both a set of fields by
+ * also including all inline fragments, as well as a list of fragments
+ * referenced by fragment spreads.
+ *
+ * A) Each selection set represented in the document first compares "within" its
+ * collected set of fields, finding any conflicts between every pair of
+ * overlapping fields.
+ * Note: This is the *only time* that a the fields "within" a set are compared
+ * to each other. After this only fields "between" sets are compared.
+ *
+ * B) Also, if any fragment is referenced in a selection set, then a
+ * comparison is made "between" the original set of fields and the
+ * referenced fragment.
+ *
+ * C) Also, if multiple fragments are referenced, then comparisons
+ * are made "between" each referenced fragment.
+ *
+ * D) When comparing "between" a set of fields and a referenced fragment, first
+ * a comparison is made between each field in the original set of fields and
+ * each field in the the referenced set of fields.
+ *
+ * E) Also, if any fragment is referenced in the referenced selection set,
+ * then a comparison is made "between" the original set of fields and the
+ * referenced fragment (recursively referring to step D).
+ *
+ * F) When comparing "between" two fragments, first a comparison is made between
+ * each field in the first referenced set of fields and each field in the the
+ * second referenced set of fields.
+ *
+ * G) Also, any fragments referenced by the first must be compared to the
+ * second, and any fragments referenced by the second must be compared to the
+ * first (recursively referring to step F).
+ *
+ * H) When comparing two fields, if both have selection sets, then a comparison
+ * is made "between" both selection sets, first comparing the set of fields in
+ * the first selection set with the set of fields in the second.
+ *
+ * I) Also, if any fragment is referenced in either selection set, then a
+ * comparison is made "between" the other set of fields and the
+ * referenced fragment.
+ *
+ * J) Also, if two fragments are referenced in both selection sets, then a
+ * comparison is made "between" the two fragments.
+ *
+ */
+// Find all conflicts found "within" a selection set, including those found
+// via spreading in fragments. Called when visiting each SelectionSet in the
+// GraphQL Document.
+function findConflictsWithinSelectionSet(
+  context,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  parentType,
+  selectionSet,
+) {
+  const conflicts = [];
+  const [fieldMap, fragmentNames] = getFieldsAndFragmentNames(
+    context,
+    cachedFieldsAndFragmentNames,
+    parentType,
+    selectionSet,
+  ); // (A) Find find all conflicts "within" the fields of this selection set.
+  // Note: this is the *only place* `collectConflictsWithin` is called.
+
+  collectConflictsWithin(
+    context,
+    conflicts,
+    cachedFieldsAndFragmentNames,
+    comparedFragmentPairs,
+    fieldMap,
+  );
+
+  if (fragmentNames.length !== 0) {
+    // (B) Then collect conflicts between these fields and those represented by
+    // each spread fragment name found.
+    for (let i = 0; i < fragmentNames.length; i++) {
+      collectConflictsBetweenFieldsAndFragment(
+        context,
+        conflicts,
+        cachedFieldsAndFragmentNames,
+        comparedFragmentPairs,
+        false,
+        fieldMap,
+        fragmentNames[i],
+      ); // (C) Then compare this fragment with all other fragments found in this
+      // selection set to collect conflicts between fragments spread together.
+      // This compares each item in the list of fragment names to every other
+      // item in that same list (except for itself).
+
+      for (let j = i + 1; j < fragmentNames.length; j++) {
+        collectConflictsBetweenFragments(
+          context,
+          conflicts,
+          cachedFieldsAndFragmentNames,
+          comparedFragmentPairs,
+          false,
+          fragmentNames[i],
+          fragmentNames[j],
+        );
+      }
+    }
+  }
+
+  return conflicts;
+} // Collect all conflicts found between a set of fields and a fragment reference
+// including via spreading in any nested fragments.
+
+function collectConflictsBetweenFieldsAndFragment(
+  context,
+  conflicts,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  areMutuallyExclusive,
+  fieldMap,
+  fragmentName,
+) {
+  const fragment = context.getFragment(fragmentName);
+
+  if (!fragment) {
+    return;
+  }
+
+  const [fieldMap2, referencedFragmentNames] =
+    getReferencedFieldsAndFragmentNames(
+      context,
+      cachedFieldsAndFragmentNames,
+      fragment,
+    ); // Do not compare a fragment's fieldMap to itself.
+
+  if (fieldMap === fieldMap2) {
+    return;
+  } // (D) First collect any conflicts between the provided collection of fields
+  // and the collection of fields represented by the given fragment.
+
+  collectConflictsBetween(
+    context,
+    conflicts,
+    cachedFieldsAndFragmentNames,
+    comparedFragmentPairs,
+    areMutuallyExclusive,
+    fieldMap,
+    fieldMap2,
+  ); // (E) Then collect any conflicts between the provided collection of fields
+  // and any fragment names found in the given fragment.
+
+  for (const referencedFragmentName of referencedFragmentNames) {
+    // Memoize so two fragments are not compared for conflicts more than once.
+    if (
+      comparedFragmentPairs.has(
+        referencedFragmentName,
+        fragmentName,
+        areMutuallyExclusive,
+      )
+    ) {
+      continue;
+    }
+
+    comparedFragmentPairs.add(
+      referencedFragmentName,
+      fragmentName,
+      areMutuallyExclusive,
+    );
+    collectConflictsBetweenFieldsAndFragment(
+      context,
+      conflicts,
+      cachedFieldsAndFragmentNames,
+      comparedFragmentPairs,
+      areMutuallyExclusive,
+      fieldMap,
+      referencedFragmentName,
+    );
+  }
+} // Collect all conflicts found between two fragments, including via spreading in
+// any nested fragments.
+
+function collectConflictsBetweenFragments(
+  context,
+  conflicts,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  areMutuallyExclusive,
+  fragmentName1,
+  fragmentName2,
+) {
+  // No need to compare a fragment to itself.
+  if (fragmentName1 === fragmentName2) {
+    return;
+  } // Memoize so two fragments are not compared for conflicts more than once.
+
+  if (
+    comparedFragmentPairs.has(
+      fragmentName1,
+      fragmentName2,
+      areMutuallyExclusive,
+    )
+  ) {
+    return;
+  }
+
+  comparedFragmentPairs.add(fragmentName1, fragmentName2, areMutuallyExclusive);
+  const fragment1 = context.getFragment(fragmentName1);
+  const fragment2 = context.getFragment(fragmentName2);
+
+  if (!fragment1 || !fragment2) {
+    return;
+  }
+
+  const [fieldMap1, referencedFragmentNames1] =
+    getReferencedFieldsAndFragmentNames(
+      context,
+      cachedFieldsAndFragmentNames,
+      fragment1,
+    );
+  const [fieldMap2, referencedFragmentNames2] =
+    getReferencedFieldsAndFragmentNames(
+      context,
+      cachedFieldsAndFragmentNames,
+      fragment2,
+    ); // (F) First, collect all conflicts between these two collections of fields
+  // (not including any nested fragments).
+
+  collectConflictsBetween(
+    context,
+    conflicts,
+    cachedFieldsAndFragmentNames,
+    comparedFragmentPairs,
+    areMutuallyExclusive,
+    fieldMap1,
+    fieldMap2,
+  ); // (G) Then collect conflicts between the first fragment and any nested
+  // fragments spread in the second fragment.
+
+  for (const referencedFragmentName2 of referencedFragmentNames2) {
+    collectConflictsBetweenFragments(
+      context,
+      conflicts,
+      cachedFieldsAndFragmentNames,
+      comparedFragmentPairs,
+      areMutuallyExclusive,
+      fragmentName1,
+      referencedFragmentName2,
+    );
+  } // (G) Then collect conflicts between the second fragment and any nested
+  // fragments spread in the first fragment.
+
+  for (const referencedFragmentName1 of referencedFragmentNames1) {
+    collectConflictsBetweenFragments(
+      context,
+      conflicts,
+      cachedFieldsAndFragmentNames,
+      comparedFragmentPairs,
+      areMutuallyExclusive,
+      referencedFragmentName1,
+      fragmentName2,
+    );
+  }
+} // Find all conflicts found between two selection sets, including those found
+// via spreading in fragments. Called when determining if conflicts exist
+// between the sub-fields of two overlapping fields.
+
+function findConflictsBetweenSubSelectionSets(
+  context,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  areMutuallyExclusive,
+  parentType1,
+  selectionSet1,
+  parentType2,
+  selectionSet2,
+) {
+  const conflicts = [];
+  const [fieldMap1, fragmentNames1] = getFieldsAndFragmentNames(
+    context,
+    cachedFieldsAndFragmentNames,
+    parentType1,
+    selectionSet1,
+  );
+  const [fieldMap2, fragmentNames2] = getFieldsAndFragmentNames(
+    context,
+    cachedFieldsAndFragmentNames,
+    parentType2,
+    selectionSet2,
+  ); // (H) First, collect all conflicts between these two collections of field.
+
+  collectConflictsBetween(
+    context,
+    conflicts,
+    cachedFieldsAndFragmentNames,
+    comparedFragmentPairs,
+    areMutuallyExclusive,
+    fieldMap1,
+    fieldMap2,
+  ); // (I) Then collect conflicts between the first collection of fields and
+  // those referenced by each fragment name associated with the second.
+
+  for (const fragmentName2 of fragmentNames2) {
+    collectConflictsBetweenFieldsAndFragment(
+      context,
+      conflicts,
+      cachedFieldsAndFragmentNames,
+      comparedFragmentPairs,
+      areMutuallyExclusive,
+      fieldMap1,
+      fragmentName2,
+    );
+  } // (I) Then collect conflicts between the second collection of fields and
+  // those referenced by each fragment name associated with the first.
+
+  for (const fragmentName1 of fragmentNames1) {
+    collectConflictsBetweenFieldsAndFragment(
+      context,
+      conflicts,
+      cachedFieldsAndFragmentNames,
+      comparedFragmentPairs,
+      areMutuallyExclusive,
+      fieldMap2,
+      fragmentName1,
+    );
+  } // (J) Also collect conflicts between any fragment names by the first and
+  // fragment names by the second. This compares each item in the first set of
+  // names to each item in the second set of names.
+
+  for (const fragmentName1 of fragmentNames1) {
+    for (const fragmentName2 of fragmentNames2) {
+      collectConflictsBetweenFragments(
+        context,
+        conflicts,
+        cachedFieldsAndFragmentNames,
+        comparedFragmentPairs,
+        areMutuallyExclusive,
+        fragmentName1,
+        fragmentName2,
+      );
+    }
+  }
+
+  return conflicts;
+} // Collect all Conflicts "within" one collection of fields.
+
+function collectConflictsWithin(
+  context,
+  conflicts,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  fieldMap,
+) {
+  // A field map is a keyed collection, where each key represents a response
+  // name and the value at that key is a list of all fields which provide that
+  // response name. For every response name, if there are multiple fields, they
+  // must be compared to find a potential conflict.
+  for (const [responseName, fields] of Object.entries(fieldMap)) {
+    // This compares every field in the list to every other field in this list
+    // (except to itself). If the list only has one item, nothing needs to
+    // be compared.
+    if (fields.length > 1) {
+      for (let i = 0; i < fields.length; i++) {
+        for (let j = i + 1; j < fields.length; j++) {
+          const conflict = findConflict(
+            context,
+            cachedFieldsAndFragmentNames,
+            comparedFragmentPairs,
+            false, // within one collection is never mutually exclusive
+            responseName,
+            fields[i],
+            fields[j],
+          );
+
+          if (conflict) {
+            conflicts.push(conflict);
+          }
+        }
+      }
+    }
+  }
+} // Collect all Conflicts between two collections of fields. This is similar to,
+// but different from the `collectConflictsWithin` function above. This check
+// assumes that `collectConflictsWithin` has already been called on each
+// provided collection of fields. This is true because this validator traverses
+// each individual selection set.
+
+function collectConflictsBetween(
+  context,
+  conflicts,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  parentFieldsAreMutuallyExclusive,
+  fieldMap1,
+  fieldMap2,
+) {
+  // A field map is a keyed collection, where each key represents a response
+  // name and the value at that key is a list of all fields which provide that
+  // response name. For any response name which appears in both provided field
+  // maps, each field from the first field map must be compared to every field
+  // in the second field map to find potential conflicts.
+  for (const [responseName, fields1] of Object.entries(fieldMap1)) {
+    const fields2 = fieldMap2[responseName];
+
+    if (fields2) {
+      for (const field1 of fields1) {
+        for (const field2 of fields2) {
+          const conflict = findConflict(
+            context,
+            cachedFieldsAndFragmentNames,
+            comparedFragmentPairs,
+            parentFieldsAreMutuallyExclusive,
+            responseName,
+            field1,
+            field2,
+          );
+
+          if (conflict) {
+            conflicts.push(conflict);
+          }
+        }
+      }
+    }
+  }
+} // Determines if there is a conflict between two particular fields, including
+// comparing their sub-fields.
+
+function findConflict(
+  context,
+  cachedFieldsAndFragmentNames,
+  comparedFragmentPairs,
+  parentFieldsAreMutuallyExclusive,
+  responseName,
+  field1,
+  field2,
+) {
+  const [parentType1, node1, def1] = field1;
+  const [parentType2, node2, def2] = field2; // If it is known that two fields could not possibly apply at the same
+  // time, due to the parent types, then it is safe to permit them to diverge
+  // in aliased field or arguments used as they will not present any ambiguity
+  // by differing.
+  // It is known that two parent types could never overlap if they are
+  // different Object types. Interface or Union types might overlap - if not
+  // in the current state of the schema, then perhaps in some future version,
+  // thus may not safely diverge.
+
+  const areMutuallyExclusive =
+    parentFieldsAreMutuallyExclusive ||
+    (parentType1 !== parentType2 &&
+      (0, _definition.isObjectType)(parentType1) &&
+      (0, _definition.isObjectType)(parentType2));
+
+  if (!areMutuallyExclusive) {
+    // Two aliases must refer to the same field.
+    const name1 = node1.name.value;
+    const name2 = node2.name.value;
+
+    if (name1 !== name2) {
+      return [
+        [responseName, `"${name1}" and "${name2}" are different fields`],
+        [node1],
+        [node2],
+      ];
+    } // Two field calls must have the same arguments.
+
+    if (!sameArguments(node1, node2)) {
+      return [
+        [responseName, 'they have differing arguments'],
+        [node1],
+        [node2],
+      ];
+    }
+  } // The return type for each field.
+
+  const type1 = def1 === null || def1 === void 0 ? void 0 : def1.type;
+  const type2 = def2 === null || def2 === void 0 ? void 0 : def2.type;
+
+  if (type1 && type2 && doTypesConflict(type1, type2)) {
+    return [
+      [
+        responseName,
+        `they return conflicting types "${(0, _inspect.inspect)(
+          type1,
+        )}" and "${(0, _inspect.inspect)(type2)}"`,
+      ],
+      [node1],
+      [node2],
+    ];
+  } // Collect and compare sub-fields. Use the same "visited fragment names" list
+  // for both collections so fields in a fragment reference are never
+  // compared to themselves.
+
+  const selectionSet1 = node1.selectionSet;
+  const selectionSet2 = node2.selectionSet;
+
+  if (selectionSet1 && selectionSet2) {
+    const conflicts = findConflictsBetweenSubSelectionSets(
+      context,
+      cachedFieldsAndFragmentNames,
+      comparedFragmentPairs,
+      areMutuallyExclusive,
+      (0, _definition.getNamedType)(type1),
+      selectionSet1,
+      (0, _definition.getNamedType)(type2),
+      selectionSet2,
+    );
+    return subfieldConflicts(conflicts, responseName, node1, node2);
+  }
+}
+
+function sameArguments(node1, node2) {
+  const args1 = node1.arguments;
+  const args2 = node2.arguments;
+
+  if (args1 === undefined || args1.length === 0) {
+    return args2 === undefined || args2.length === 0;
+  }
+
+  if (args2 === undefined || args2.length === 0) {
+    return false;
+  }
+  /* c8 ignore next */
+
+  if (args1.length !== args2.length) {
+    /* c8 ignore next */
+    return false;
+    /* c8 ignore next */
+  }
+
+  const values2 = new Map(args2.map(({ name, value }) => [name.value, value]));
+  return args1.every((arg1) => {
+    const value1 = arg1.value;
+    const value2 = values2.get(arg1.name.value);
+
+    if (value2 === undefined) {
+      return false;
+    }
+
+    return stringifyValue(value1) === stringifyValue(value2);
+  });
+}
+
+function stringifyValue(value) {
+  return (0, _printer.print)((0, _sortValueNode.sortValueNode)(value));
+} // Two types conflict if both types could not apply to a value simultaneously.
+// Composite types are ignored as their individual field types will be compared
+// later recursively. However List and Non-Null types must match.
+
+function doTypesConflict(type1, type2) {
+  if ((0, _definition.isListType)(type1)) {
+    return (0, _definition.isListType)(type2)
+      ? doTypesConflict(type1.ofType, type2.ofType)
+      : true;
+  }
+
+  if ((0, _definition.isListType)(type2)) {
+    return true;
+  }
+
+  if ((0, _definition.isNonNullType)(type1)) {
+    return (0, _definition.isNonNullType)(type2)
+      ? doTypesConflict(type1.ofType, type2.ofType)
+      : true;
+  }
+
+  if ((0, _definition.isNonNullType)(type2)) {
+    return true;
+  }
+
+  if (
+    (0, _definition.isLeafType)(type1) ||
+    (0, _definition.isLeafType)(type2)
+  ) {
+    return type1 !== type2;
+  }
+
+  return false;
+} // Given a selection set, return the collection of fields (a mapping of response
+// name to field nodes and definitions) as well as a list of fragment names
+// referenced via fragment spreads.
+
+function getFieldsAndFragmentNames(
+  context,
+  cachedFieldsAndFragmentNames,
+  parentType,
+  selectionSet,
+) {
+  const cached = cachedFieldsAndFragmentNames.get(selectionSet);
+
+  if (cached) {
+    return cached;
+  }
+
+  const nodeAndDefs = Object.create(null);
+  const fragmentNames = Object.create(null);
+
+  _collectFieldsAndFragmentNames(
+    context,
+    parentType,
+    selectionSet,
+    nodeAndDefs,
+    fragmentNames,
+  );
+
+  const result = [nodeAndDefs, Object.keys(fragmentNames)];
+  cachedFieldsAndFragmentNames.set(selectionSet, result);
+  return result;
+} // Given a reference to a fragment, return the represented collection of fields
+// as well as a list of nested fragment names referenced via fragment spreads.
+
+function getReferencedFieldsAndFragmentNames(
+  context,
+  cachedFieldsAndFragmentNames,
+  fragment,
+) {
+  // Short-circuit building a type from the node if possible.
+  const cached = cachedFieldsAndFragmentNames.get(fragment.selectionSet);
+
+  if (cached) {
+    return cached;
+  }
+
+  const fragmentType = (0, _typeFromAST.typeFromAST)(
+    context.getSchema(),
+    fragment.typeCondition,
+  );
+  return getFieldsAndFragmentNames(
+    context,
+    cachedFieldsAndFragmentNames,
+    fragmentType,
+    fragment.selectionSet,
+  );
+}
+
+function _collectFieldsAndFragmentNames(
+  context,
+  parentType,
+  selectionSet,
+  nodeAndDefs,
+  fragmentNames,
+) {
+  for (const selection of selectionSet.selections) {
+    switch (selection.kind) {
+      case _kinds.Kind.FIELD: {
+        const fieldName = selection.name.value;
+        let fieldDef;
+
+        if (
+          (0, _definition.isObjectType)(parentType) ||
+          (0, _definition.isInterfaceType)(parentType)
+        ) {
+          fieldDef = parentType.getFields()[fieldName];
+        }
+
+        const responseName = selection.alias
+          ? selection.alias.value
+          : fieldName;
+
+        if (!nodeAndDefs[responseName]) {
+          nodeAndDefs[responseName] = [];
+        }
+
+        nodeAndDefs[responseName].push([parentType, selection, fieldDef]);
+        break;
+      }
+
+      case _kinds.Kind.FRAGMENT_SPREAD:
+        fragmentNames[selection.name.value] = true;
+        break;
+
+      case _kinds.Kind.INLINE_FRAGMENT: {
+        const typeCondition = selection.typeCondition;
+        const inlineFragmentType = typeCondition
+          ? (0, _typeFromAST.typeFromAST)(context.getSchema(), typeCondition)
+          : parentType;
+
+        _collectFieldsAndFragmentNames(
+          context,
+          inlineFragmentType,
+          selection.selectionSet,
+          nodeAndDefs,
+          fragmentNames,
+        );
+
+        break;
+      }
+    }
+  }
+} // Given a series of Conflicts which occurred between two sub-fields, generate
+// a single Conflict.
+
+function subfieldConflicts(conflicts, responseName, node1, node2) {
+  if (conflicts.length > 0) {
+    return [
+      [responseName, conflicts.map(([reason]) => reason)],
+      [node1, ...conflicts.map(([, fields1]) => fields1).flat()],
+      [node2, ...conflicts.map(([, , fields2]) => fields2).flat()],
+    ];
+  }
+}
+/**
+ * A way to keep track of pairs of things when the ordering of the pair does not matter.
+ */
+
+class PairSet {
+  constructor() {
+    this._data = new Map();
+  }
+
+  has(a, b, areMutuallyExclusive) {
+    var _this$_data$get;
+
+    const [key1, key2] = a < b ? [a, b] : [b, a];
+    const result =
+      (_this$_data$get = this._data.get(key1)) === null ||
+      _this$_data$get === void 0
+        ? void 0
+        : _this$_data$get.get(key2);
+
+    if (result === undefined) {
+      return false;
+    } // areMutuallyExclusive being false is a superset of being true, hence if
+    // we want to know if this PairSet "has" these two with no exclusivity,
+    // we have to ensure it was added as such.
+
+    return areMutuallyExclusive ? true : areMutuallyExclusive === result;
+  }
+
+  add(a, b, areMutuallyExclusive) {
+    const [key1, key2] = a < b ? [a, b] : [b, a];
+
+    const map = this._data.get(key1);
+
+    if (map === undefined) {
+      this._data.set(key1, new Map([[key2, areMutuallyExclusive]]));
+    } else {
+      map.set(key2, areMutuallyExclusive);
+    }
+  }
+}