Inability to override built-in scalars with `mapSchema`

[mderriey]

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---

Describe the bug

@graphql-tools/utils allowed to override built-in scalars with mapSchema until #5294.

We caught that thanks to our tests when we updated to the latest version.

I'm a bit surprised that this behavioural breaking change got flagged as a patch change in the release notes (https://the-guild.dev/graphql/tools/changelogs/utils).

To Reproduce Steps to reproduce the behavior:

export function overrideIDScalar(schema: GraphQLSchema): GraphQLSchema {
  return mapSchema(schema, {
    [MapperKind.SCALAR_TYPE]: (type) => {
      if (type.name === 'ID') {
        return customIDScalar
      }
      return type
    },
  })
}

Expected behavior

The ID built-in scalar in the executable schema points to the custom scalar.

Environment:

• OS: Windows for local dev, Linux when deployed
• @graphql-tools/utils: 10.11.0
• NodeJS: 22.14.0

Additional context

I'm not expecting that the library will revert to the original behaviour, but an issue will hopefully help others in the same situation.

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🔗 Similar Issues

Related Issues

• ardatan/graphql-tools#6711
• ardatan/graphql-tools#6983
• ardatan/graphql-tools#7682
• ardatan/graphql-tools#7052
• ardatan/graphql-tools#7011

🔗 Related PRs

#7012 - fix(mergeDeep): handle undefined sources correctly [merged]
#7210 - preserve resolvers should use the resolved typename [merged]
#7225 - Support 'extend schema' syntax and add 'link' to the list of builtins [merged]
#7588 - feat(executor): add schema coordinate to graphql errors [merged]
#7683 - Revert "fix(utils/astFromSchema): support GraphQLSchema instances without operation types defined" [merged]

👤 Suggested Assignees

• ardatan
• jdolle
• ksullivanmcc
• elrumordelaluz
• klippx

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[ardatan]

Builtin scalars are added and handled by graphql-js itself. mapSchema is never intended to modify GraphQLID exported from graphql-js. Overriding it can cause an unexpected behavior which we don't want to handle with this utility.