fix(schema-compat): escape discriminator key in generated discriminatedUnion

[greymoth-jp]

Problem

@mastra/schema-compat's jsonSchemaToZod builds a Zod schema as a source string that is later evaluated at runtime with Function(). When it detects a discriminated union (an anyOf of objects that share a const property), it inserts the discriminator property name into the generated z.discriminatedUnion(...) call directly:

parsed = `z.discriminatedUnion("${discriminator}", [${schema.anyOf...}])`;

Every other string this generator emits is serialized with JSON.stringify (object keys, .describe(...), .default(...)), but the discriminator key is interpolated raw. A JSON Schema property name may legally contain a double quote, so a name such as ty"pe produces:

z.discriminatedUnion("ty"pe", [z.object({ "ty\"pe": z.literal("cat"), ... }), ...])

The object key is escaped correctly ("ty\"pe"), but the discriminatedUnion argument is not, so the generated string throws SyntaxError: missing ) after argument list when it is evaluated. This is the same kind of runtime Function() failure that was fixed for parseOneOf in #11610.

Solution

Serialize the discriminator key with JSON.stringify, the same helper already used for the object keys it refers to:

parsed = `z.discriminatedUnion(${JSON.stringify(discriminator)}, [${schema.anyOf...}])`;

For any ordinary property name this is byte-identical to the previous output, since JSON.stringify("type") === '"type"', so existing schemas generate exactly the same code.

Verification

I added a test in the DiscriminatedUnion Detection block that uses a discriminator name containing a double quote, evaluates the generated string with Function() the way the output is consumed, and asserts it no longer throws and parses a matching value.

• Before the change the new test fails: the generated code throws a SyntaxError when evaluated.
• After the change it passes.
• The existing discriminated-union tests are unaffected, because the generated code for their normal property names is identical.

ELI5

This change fixes a bug where a special character in a schema property name could break generated code. Now the property name is safely escaped before being put into the code, so schemas with quotes in their discriminator key work correctly.

Changes

• Fixed jsonSchemaToZod to serialize discriminated-union keys with JSON.stringify, matching other generated strings.
• Added a test that uses a discriminator name containing a double quote and verifies the generated code runs and parses successfully.
• Added a changeset entry documenting the patch release for @mastra/schema-compat.

Why

• Prevents runtime SyntaxError when JSON Schema discriminator keys contain double quotes.
• Keeps normal output unchanged for standard property names.

[changeset-bot]

🦋 Changeset detected

Latest commit: 8d6f680

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 29 packages

Name	Type
@mastra/schema-compat	Patch
mastracode	Patch
@mastra/agent-builder	Patch
@mastra/core	Patch
@mastra/editor	Patch
@mastra/memory	Patch
@internal/playground	Patch
@mastra/server	Patch
@mastra/voice-google-gemini-live	Patch
@mastra/voice-openai-realtime	Patch
@mastra/voice-xai-realtime	Patch
@mastra/client-js	Patch
@mastra/mcp-docs-server	Patch
@mastra/opencode	Patch
@mastra/longmemeval	Patch
@mastra/express	Patch
@mastra/fastify	Patch
@mastra/hono	Patch
@mastra/koa	Patch
@mastra/nestjs	Patch
mastra	Patch
@mastra/deployer-cloud	Patch
@mastra/react	Patch
@mastra/playground-ui	Patch
@mastra/deployer	Patch
create-mastra	Patch
@mastra/next	Patch
@mastra/tanstack-start	Patch
@mastra/temporal	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[vercel]

@greymoth-jp is attempting to deploy a commit to the Mastra Team on Vercel.

A member of the Team first needs to authorize it.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 9d8c002f-ef34-448e-85e5-9b84f73ae190

📥 Commits

Reviewing files that changed from the base of the PR and between e62c108 and 8d6f680.

📒 Files selected for processing (3)

• .changeset/escape-discriminated-union-key.md
• packages/schema-compat/src/json-to-zod.test.ts
• packages/schema-compat/src/json-to-zod.ts

---

Walkthrough

In json-to-zod.ts, the discriminator argument in z.discriminatedUnion(...) generation is changed from a template string to JSON.stringify(discriminator). A test is added verifying correct escaping and runtime evaluation when the discriminator property name contains a double quote. A changeset entry documents the patch.

Changes

Discriminator key escaping in z.discriminatedUnion codegen

Layer / File(s)	Summary
Fix and test for quoted discriminator key packages/schema-compat/src/json-to-zod.ts, packages/schema-compat/src/json-to-zod.test.ts, .changeset/escape-discriminated-union-key.md	Discriminator argument construction switches from template string to JSON.stringify(discriminator); new test confirms escaping and runtime validity; changeset documents the patch.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the schema-compat fix for escaping discriminator keys in generated discriminated unions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[dane-ai-mastra]

PR triage

This PR needs to fix an existing issue. Please link an issue in the PR description, for example with Fixes #1234 or Closes #1234.

Applied label: needs-issue

PRs without a linked issue will automatically close after 1 day(s) with the label.

---

Changed test gate

Changed Test Gate is pending. The Changed Test Gate / changed-tests check will update the test label when it completes.