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// @flow strict
import { GraphQLError } from '../../error/GraphQLError';
import type { ASTVisitor } from '../../language/visitor';
import type { FragmentDefinitionNode } from '../../language/ast';
import type { ASTValidationContext } from '../ValidationContext';
export function NoFragmentCyclesRule(
context: ASTValidationContext,
): ASTVisitor {
// Tracks already visited fragments to maintain O(N) and to ensure that cycles
// are not redundantly reported.
const visitedFrags = Object.create(null);
// Array of AST nodes used to produce meaningful errors
const spreadPath = [];
// Position in the spread path
const spreadPathIndexByName = Object.create(null);
return {
OperationDefinition: () => false,
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: FragmentDefinitionNode): void {
if (visitedFrags[fragment.name.value]) {
return;
}
const fragmentName = fragment.name.value;
visitedFrags[fragmentName] = true;
const spreadNodes = context.getFragmentSpreads(fragment.selectionSet);
if (spreadNodes.length === 0) {
return;
}
spreadPathIndexByName[fragmentName] = spreadPath.length;
for (const spreadNode of spreadNodes) {
const spreadName = spreadNode.name.value;
const cycleIndex = spreadPathIndexByName[spreadName];
spreadPath.push(spreadNode);
if (cycleIndex === undefined) {
const spreadFragment = context.getFragment(spreadName);
if (spreadFragment) {
detectCycleRecursive(spreadFragment);
}
} else {
const cyclePath = spreadPath.slice(cycleIndex);
const viaPath = cyclePath
.slice(0, -1)
.map((s) => '"' + s.name.value + '"')
.join(', ');
context.reportError(
new GraphQLError(
`Cannot spread fragment "${spreadName}" within itself` +
(viaPath !== '' ? ` via ${viaPath}.` : '.'),
cyclePath,
),
);
}
spreadPath.pop();
}
spreadPathIndexByName[fragmentName] = undefined;
}
}
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