feat(compiler): add experimental $onInfo hook and program.getTypeInfo API

[timotheeguerin]

Fixes #1993

Summary

Adds a new experimental $onInfo library hook and program.getTypeInfo(type) API that lets libraries contribute extra, domain-specific information about types. This information is surfaced in IDE hover tooltips and can be queried programmatically by tooling (e.g. AI agents).

Unlike $onValidate, this hook:

• is never run during compilation — it is invoked lazily and on demand.
• must not mutate the type graph — it only reads the program to answer questions about a type.

The feature is gated behind a new type-info-hook compiler feature flag.

API

A library exports an $onInfo provider (using the defineInfoHook typing helper). The hook receives an InfoContext ({ program, target }) and returns a single TypeInfo ({ content: string }) or undefined:

import { defineInfoHook } from "@typespec/compiler";

export const $onInfo = defineInfoHook(({ program, target }) => {
  if (target.kind !== "Operation") return undefined;
  return { content: "extra info about this operation" };
});

Tooling / the language server queries it. Contributions from every library are merged into a single TypeInfo (or undefined when nothing is contributed or the feature is disabled):

const info = program.getTypeInfo(type);
// { content: "`HTTP Route`: `GET /pets/{id}`\n\n`Responses`: `204`" }

Enable it in tspconfig.yaml:

features:
  - type-info-hook

@typespec/http reference provider

@typespec/http now ships an $onInfo provider that surfaces the resolved HTTP route (verb + URI template) and response status codes of an operation.

Changes

• compiler: $onInfo hook, defineInfoHook helper, InfoContext/TypeInfo/OnInfoHook types, program.getTypeInfo, binder auto-discovery, type-info-hook feature flag, LSP hover wiring.
• http: $onInfo provider (verb + URI template + response status codes).
• docs: new "Providing IDE & tooling info" extending-typespec page.

Testing

• New packages/compiler/test/info-hook.test.ts (merge, no-contributor, feature-disabled, provider-crash).
• Updated get-hover.test.ts to cover hover enrichment.
• New packages/http/test/info.test.ts.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/compiler@11489

npm i https://pkg.pr.new/@typespec/http@11489

commit: ddd2cac

[github-actions]

All changed packages have been documented.

• ✅ @typespec/compiler
• ✅ @typespec/http

Show changes

@typespec/compiler - feature ✏️

Add a new experimental $onInfo library hook and program.getTypeInfo(type) API allowing libraries to contribute extra, domain-specific information about types. Unlike $onValidate, this hook never runs during compilation and must not mutate the type graph — it is invoked lazily and on demand (e.g. by the language server for hover documentation, or by tooling querying the type). The feature is gated behind the type-info-hook compiler feature flag.,> ,> ts,> // A library exports a provider (use `defineInfoHook` for typing):,> export const $onInfo = defineInfoHook(({ program, target }) => {,> if (target.kind !== "Operation") return undefined;,> return { content: "extra info about this operation" };,> });,> ,> // Tooling / language server queries it (merges every library's contribution):,> const info = program.getTypeInfo(type);,>

@typespec/http - feature ✏️

Add an $onInfo provider that surfaces the resolved HTTP route (verb and URI template) and response status codes of an operation. This is shown when hovering an operation in the IDE and can be queried programmatically via program.getTypeInfo(operation). Requires the experimental type-info-hook compiler feature flag.

[azure-sdk-automation]

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