feat(compiler): add setAutoDecorator API and generate auto-decorator setters in tspd

[timotheeguerin]

Summary

Infrastructure for programmatically applying auto decorators, extracted from the GraphQL emitter work.

• @typespec/compiler: Add a public setAutoDecorator(program, decoratorFqn, target, value?) API that programmatically applies an auto decorator to a target, storing its argument values the same way the synthesized auto dec implementation does when the decorator is written in source. This lets emitters and mutators mark synthetic types without reaching into the program state map directly.

  import { setAutoDecorator } from "@typespec/compiler";
  
  setAutoDecorator(program, "MyLib.myFlag", target);

• @typespec/tspd: gen-extern-signature now generates a typed set* setter (e.g. setMyFlag, setMyLabel) for each auto decorator, alongside the existing is*/get* readers. Single-arg setters accept the bare value (parity with the get* reader); multi-arg setters accept the { paramName: value } record.

• @typespec/compiler (testing): createTester now mounts each discovered library's tspconfig.yaml into the virtual file system, so experimental features a library opts into (e.g. auto-decorators) are honored when compiling against the tester.

Testing

• Added a unit test for setAutoDecorator (decorators.test.ts).
• Updated tspd gen-extern-signature golden tests to cover the generated setters (no-arg, single-arg, rest-arg, multi-arg).
• Added a createTester test verifying a library's tspconfig.yaml features are honored (fails without the mount fix).

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commit: 6c0f023

[github-actions]

All changed packages have been documented.

• ✅ @typespec/compiler
• ✅ @typespec/tspd

Show changes

@typespec/compiler - feature ✏️

Add setAutoDecorator API to programmatically apply an auto decorator to a target, mirroring what the synthesized auto dec implementation does when the decorator is written in source. This lets emitters and mutators mark synthetic types without reaching into the program state map directly.,> ,> ts,> import { setAutoDecorator } from "@typespec/compiler";,> ,> setAutoDecorator(program, "MyLib.myFlag", target);,>

@typespec/compiler - feature ✏️

createTester now mounts each discovered library's tspconfig.yaml into the virtual file system, so experimental features a library opts into (e.g. auto-decorators) are honored when compiling against the tester.

@typespec/tspd - feature ✏️

tspd gen-extern-signature now also generates a typed setter (e.g. setMyFlag, setMyLabel) for each auto decorator, alongside the existing is*/get* readers.

[azure-sdk-automation]

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