[Bug]: json-schema emitter fails on @extension value referencing an enum

[copland]

Describe the bug

When using an enum to define appropriate values for a given @extension, @typespec/json-schema fails with TypeError: Converting circular structure to JSON.

This example is sufficient to trigger the issue (same content as playground link):

import "@typespec/json-schema";

using JsonSchema;

@jsonSchema
namespace Schemas;

const MetadataTag = "x-metadata";

enum MetadataValue {
  Foo: "foo",
  Bar: "bar"
}

@extension(MetadataTag, MetadataValue.Foo)
model Car {
  /** Kind of car */
  kind: "ev" | "ice";

  /** Brand of the car */
  brand: string;

  /** Model of the car */
  `model`: string;
}

Running this locally you see:

> tsp compile .

TypeSpec compiler v0.67.2

✔ Compiling
× Running @typespec/json-schema...
Emitter "@typespec/json-schema" crashed! This is a bug.
Please file an issue at https://github.com/microsoft/typespec/issues

TypeError: Converting circular structure to JSON
    --> starting at object with constructor 'Object'
    |     property 'id' -> object with constructor 'Object'
    --- property 'parent' closes the circle
    at JSON.stringify (<anonymous>)
    at #serializeSourceFileContent (file:///..path../node_modules/@typespec/json-schema/dist/src/json-schema-emitter.js:564:25)
    at JsonSchemaEmitter.sourceFile (file:///..path../node_modules/@typespec/json-schema/dist/src/json-schema-emitter.js:534:55)
    at Object.emitSourceFile (file:///..path../node_modules/@typespec/asset-emitter/dist/src/asset-emitter.js:347:38)
    at JsonSchemaEmitter.writeOutput (file:///..path../node_modules/@typespec/json-schema/dist/src/json-schema-emitter.js:517:54)
    at async Object.$onEmit [as emitFunction] (file:///..path../node_modules/@typespec/json-schema/dist/src/on-emit.js:19:5)
    at async runEmitter (file:///..path../node_modules/@typespec/compiler/dist/src/core/program.js:668:9)
    at async file:///..path../node_modules/@typespec/compiler/dist/src/core/program.js:647:9
    at async trackAction (file:///..path../node_modules/@typespec/compiler/dist/src/core/logger/console-sink.js:121:24)
    at async emit (file:///..path../node_modules/@typespec/compiler/dist/src/core/program.js:646:5)

--------------------------------------------------
Library Version                0.67.1
TypeSpec Compiler Version      0.67.2
--------------------------------------------------

It is possible to work around this by changing the enum to a set of const values:

const MetadataTag = "x-metadata";

const Foo = "foo";
const Bar = "bar";

@extension(MetadataTag, Foo)
model Car { ... }

Reproduction

Playground Link

NOTE: The playground link fails a bit differently (with a call stack error rather than a type error)

Checklist

• Follow our Code of Conduct
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.

[timotheeguerin]

Doesn't seem to be only json schema, openapi3 also crash playground

First of all it shouldn't obviously not crash, so we at least need to handle this gracefully.

Now for the enum part I think this means we need to resolve what is the value of the enum that you want which is maybe a specific case of this design issue #1720
The main issue is that the enum is more than the value that it might match and just blindly serializing it might result in information loss. For teh json schema and openapi3 case in @extension it is probably what you want so we could also consider a targeted fix.