Report defaultValue in introspection as a GraphQL literal

[xperiandri]

Introspection reported the defaultValue of an argument or an input object field serialized to JSON with the schema's JsonOptions, while the spec defines it as "a GraphQL-formatted string" (§4.2.3). JSON is a valid GraphQL literal only by chance: an enum value became its .NET value, such as {"Case":"Local"} for an F# union case, the keys of an input object were quoted, and the output coercion of a scalar was skipped. Clients that build a schema from introspection, like graphql-js buildClientSchema used by graphql-codegen, parse every defaultValue and failed with Syntax Error: Expected Name, found String "Case".

Fixes #623. Builds on #628, which this PR targets; it recognizes skippable values through the type checks of #628. Every commit builds on its own, so the PR is meant to be merged with rebase.

Changes

• The new internal ValueLiterals module of FSharp.Data.GraphQL.Shared prints a value by its input type, like astFromValue and print of graphql-js, and Schema reports default values with it:
  • an enum value as the name of its EnumValue, e.g. LOCAL;
  • a scalar value as its output coercion serializes it: numbers, booleans and escaped strings directly, and any other type, like a date, a GUID or a URI, the way the schema's JsonOptions serialize it;
  • a list with every item printed by the item type, e.g. [LOCAL, REMOTE];
  • an input object with the GraphQL names of its fields, read through the properties the fields bind to, leaving skipped SkippableInput fields out, e.g. {userId: "1", attendanceMode: REMOTE};
  • an option or voption unwrapped, and a missing one as null.
• A default value without a GraphQL literal (a value outside of its enum, NaN or an infinity, a value its scalar cannot or refuses to serialize, an input object without a property for one of its fields) is no longer reported, and its input stays nullable. Printing never throws: the introspected schema backs the validation of every request, so one bad default value would fail them all.
• Document.ToQueryString printed a string value between quotes as it was, so a string with a quote, a backslash or a control character produced an invalid document. The string printer moves from ValueLiterals to AstExtensions as appendStringValue, and both use it.

Notes

• The format follows print of graphql-js 16: {a: 1} and [1, 2], without the inner spaces ToQueryString puts in.
• An ID is always printed as a string, while graphql-js prints an ID that looks like an integer as an Int; both are valid ID input.
• Besides the control characters, strings escape U+2028 and U+2029, which the parser of this library does not accept unescaped in a string.
• Booleans, integers and plain strings print as before, so the introspection snapshots of the integration tests do not change; the integration tests were not run.

Verification

• FSharp.Data.GraphQL.Tests: 786 passed, 5 skipped, 0 failed, including the new ValueLiteralsTests, two introspection tests with the repro of Introspection emits JSON-serialized value as defaultValue instead of a GraphQL literal (breaks enum defaults) #623 and a ToQueryString test with characters to escape
• Release build of FSharp.Data.GraphQL.slnx with SDK 10.0.401: 0 warnings, 0 errors; the first commit alone builds too

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟡 Changes recommended

Recursive defaults can overflow the stack, and enum matching uses equality semantics inconsistent with runtime serialization.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Guard recursive input traversal against cycles and excessive depth · New
• Use consistent equality semantics for reference-valued enum mappings · New

What changed in this PR

Fixes #623 by formatting introspection default values as valid GraphQL literals rather than JSON.

Changes:

• Adds type-aware literal formatting for scalars, enums, lists, and input objects.
• Integrates formatting into schema introspection and fixes option-array unwrapping.
• Adds regression and unit coverage plus release notes.

File	Description
src/​FSharp.Data.GraphQL.Shared/​ValueLiterals.fs	Implements GraphQL literal formatting.
src/​FSharp.Data.GraphQL.Shared/​Helpers/​Reflection.fs	Corrects option type detection.
src/​FSharp.Data.GraphQL.Shared/​FSharp.Data.GraphQL.Shared.fsproj	Includes the new module.
src/​FSharp.Data.GraphQL.Server/​Schema.fs	Uses literals for introspection defaults.
tests/​FSharp.Data.GraphQL.Tests/​ValueLiteralsTests.fs	Tests literal formatting behavior.
tests/​FSharp.Data.GraphQL.Tests/​IntrospectionTests.fs	Adds introspection regressions.
tests/​FSharp.Data.GraphQL.Tests/​FSharp.Data.GraphQL.Tests.fsproj	Includes the new tests.
RELEASE_NOTES.md	Documents both fixes.

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Test Results

    9 files      9 suites   14m 47s ⏱️
  899 tests   894 ✅  5 💤 0 ❌
2 697 runs  2 682 ✅ 15 💤 0 ❌

Results for commit d3a9152.

♻️ This comment has been updated with latest results.