validate circular default values#4253
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jbellenger wants to merge 4 commits intographql-java:masterfrom
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validate circular default values#4253jbellenger wants to merge 4 commits intographql-java:masterfrom
jbellenger wants to merge 4 commits intographql-java:masterfrom
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Feb 19, 2026
A recent change to use the IR value generator to produce default values for arbitrary schemas exposed a class of issues related to cyclic input values.
For example, consider this sdl:
```graphql
input A { b: B = {} }
input B { a: A = {} }
```
The spec considers this configuration invalid (see [InputObjectDefaultValueHasCycle](https://spec.graphql.org/draft/#sec-Input-Object-Default-Value-Has-Cycle)), because the coerced default value for `A.b` is an infinitely large object `{a: {b: {a: ...}}}`.
The change introduced in #998226 allowed generating more edge-casey default values in a schema, including invalid types like what's described above.
To make things slightly worse, these invalid schemas were only detected at execution time via a StackOverflow in graphql-java. I've put up a PR for graphql-java to reject these kinds of invalid schemas during the validation phase, which we should get the next time we update:
graphql-java/graphql-java#4253
This PR updates the IR value generator to not generate values like the above. It uses strongly-connected component analysis to generate explicit values for fields where required. This allows us to keep generating interesting edge cases that we can use for testing.
Github-Change-Id: 999823
GitOrigin-RevId: 7e54ef25732b5bb8245d1a86cd828b6fc9d3edda
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Input object fields can define default values in ways that form cycles. For example in this schema:
types A and B form a cycle with their default values, such that the coerced default value of
A.bis an infinitely nested ObjectValue like{a: {b: {a: {...}}}Today, this sdl can be parsed into a GraphQLSchema object, though a StackOverflow will be thrown during execution if the system encounters a value for one of these types.
The spec added an InputObjectDefaultValueHasCycle algorithm to handle this case. This PR implements this algorithm as a
NoDefaultValueCircularRefsvalidator which allows these cyclic schemas to be rejected during validation.This behavior matches graphql-js v17, which added a similar validation in this pr