feat(protobuf): add opt-in enum value prefixes

[Cameron Taggart (cataggar)]

Summary

Fixes #12102.

Add the opt-in enum-value-prefix: enum-name option to @typespec/protobuf. Every enum value is prefixed with its enum name in UPPER_SNAKE_CASE, so TypeSpec can use short member names without package-scope collisions.

options:
  "@typespec/protobuf":
    enum-value-prefix: enum-name

enum OrderState {
  Unspecified: 0,
  Pending: 1,
  Shipped: 2,
}

enum OrderState {
  ORDER_STATE_UNSPECIFIED = 0;
  ORDER_STATE_PENDING = 1;
  ORDER_STATE_SHIPPED = 2;
}

• Default output remains unchanged (enum-value-prefix: none).
• Preserve already-prefixed names and avoid adding a second prefix after case conversion.
• Preserve numeric values, member order, enum type names, aliases, and documentation. Members and numbers remain explicit; no Unspecified member is synthesized.
• Validate collisions directly from each emitted file, including unnamed packages, and identify the original conflicting enum member or declaration kind/name in diagnostics.
• Reuse the existing catalog's change-case dependency and update the lockfile's protobuf importer only.
• Update the guide, generated option references, and feature changelog. Document generated-API and Protobuf JSON naming implications.

This follows AIP-126 and the Protobuf style guide, which recommends:

Prefix Every Value With the Enum Name (Converted to UPPER_SNAKE_CASE)

Explicit @encodedName support and automatic numbering/member synthesis are outside this change.

Validation

• Confirmed the new tests fail before implementation.
• pnpm build — full workspace build passed.
• pnpm --filter @typespec/protobuf test — 63 tests passed, including 22 prefix-option cases and all existing scenarios.
• pnpm exec oxlint packages/protobuf --type-aware --deny-warnings — passed.
• pnpm format:check — passed.
• Scoped CSpell — passed.
• pnpm chronus verify --since microsoft/main — passed.
• Compiled a standalone TypeSpec example containing two enums with Unspecified members, then compiled the emitted .proto with protoc 36.2.

Local lint limitation after a full build: pnpm lint and pnpm lint:fix fail in the unchanged compiler configuration: packages/compiler/tsconfig.json attempts to emit dist/src/server/tmlanguage.d.ts over an input declaration imported by its generation script. The protobuf package's type-aware lint passes; no unrelated compiler changes are included.

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commit: ffce982

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Copilot review overview

Review effort: Lite
Findings: 3 · 1

Open (4)

• The collision index is keyed only by @package namespaces, and entries are only recorded when… · New
• The collision index is keyed only by @package namespaces, and entries are only recorded when… · New
• The collision index is keyed only by @package namespaces, and entries are only recorded when… · New
• This diagnostic message doesn’t provide enough context to quickly resolve collisions in larger… · New

What changed in this PR

Adds an opt-in Protobuf emitter option to prefix enum value names with their enum name (UPPER_SNAKE_CASE) to avoid package-scope collisions, and documents/tests the new behavior.

Changes:

• Add enum-value-prefix: enum-name emitter option + schema/diagnostic support.
• Implement enum value prefixing + collision detection in the transform pipeline.
• Add docs (guide/reference/README) and a dedicated test suite for the option.

File	Description
website/​src/​content/​docs/​docs/​emitters/​protobuf/​reference/​emitter.md	Documents the new enum-value-prefix option in the reference page.
website/​src/​content/​docs/​docs/​emitters/​protobuf/​guide.md	Adds a guide section explaining enum emission and the new prefixing option.
packages/​protobuf/​test/​enum-prefix.test.ts	Adds tests covering prefixing, normalization, and collision diagnostics.
packages/​protobuf/​src/​transform/​index.ts	Implements enum value prefixing and collision checking across a Protobuf package.
packages/​protobuf/​src/​lib.ts	Extends emitter options + JSON schema and introduces a new collision diagnostic.
packages/​protobuf/​package.json	Adds change-case dependency for name normalization/prefixing.
packages/​protobuf/​README.md	Documents the new emitter option for package consumers.
.chronus/​changes/​protobuf-enum-value-prefix-2026-10-02.md	Adds a feature changelog entry describing the new option.

Files not reviewed (1)

• pnpm-lock.yaml: Generated file

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[github-actions]

All changed packages have been documented.

• ✅ @typespec/protobuf

Show changes

@typespec/protobuf - feature ✏️

Add an opt-in enum-value-prefix: enum-name emitter option to prefix enum values with the enum name in UPPER_SNAKE_CASE, without repeating the prefix in TypeSpec members.,> ,> yaml,> options:,> "@typespec/protobuf":,> enum-value-prefix: enum-name,> ,> ,> For example, the Shipped: 2 member of OrderState emits ORDER_STATE_SHIPPED = 2. Already-prefixed names are preserved, and collisions in the emitted package scope are reported as errors identifying the original conflicting symbol.,> ,> Existing output remains unchanged by default. Enum members and numeric values remain explicit; this option does not add an Unspecified member or infer numbers.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation matches the linked feature requirements and includes appropriate tests, documentation, dependency updates, and changelog coverage.

Review effort: Balanced
Findings: None

Resolved since last review (4)

• The collision index is keyed only by @package namespaces, and entries are only recorded when…
• The collision index is keyed only by @package namespaces, and entries are only recorded when…
• The collision index is keyed only by @package namespaces, and entries are only recorded when…
• This diagnostic message doesn’t provide enough context to quickly resolve collisions in larger…

Files not reviewed (1)

• pnpm-lock.yaml: Generated file