Remove all circular references in TypeSpec Compiler (#3308)

They cause vitest to not be happy randomly. This is only a problem with
non type import so adding `type` helps finding which ones are a real
problem

Use madge with this command to find them
```
npx madge --circular --extensions ts ./src/
```

with this config
```
{
  "detectiveOptions": {
    "ts": {
      "skipTypeImports": true,
      "skipAsyncImports": true
    }
  }
}
```

.chronus/changes/fix-compiler-circular-refs-2024-4-9-14-57-38.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: internal
+packages:
+  - "@typespec/compiler"
+  - "@typespec/http"
+  - "@typespec/playground"
+---

packages/compiler/src/config/types.ts

@@ -1,5 +1,5 @@
-import { Diagnostic, RuleRef } from "../core/index.js";
-import { YamlScript } from "../yaml/types.js";
+import type { Diagnostic, RuleRef } from "../core/index.js";
+import type { YamlScript } from "../yaml/types.js";
 
 /**
  * Represent the normalized user configuration.

packages/compiler/src/core/binder.ts

@@ -1,8 +1,8 @@
 import { mutate } from "../utils/misc.js";
 import { compilerAssert } from "./diagnostics.js";
-import { getLocationContext } from "./helpers/index.js";
+import { getLocationContext } from "./helpers/location-context.js";
 import { visitChildren } from "./parser.js";
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 import {
   AliasStatementNode,
   ConstStatementNode,

packages/compiler/src/core/checker.ts

@@ -12,14 +12,14 @@ import {
   reportDeprecated,
 } from "./diagnostics.js";
 import { validateInheritanceDiscriminatedUnions } from "./helpers/discriminator-utils.js";
+import { getLocationContext } from "./helpers/location-context.js";
+import { explainStringTemplateNotSerializable } from "./helpers/string-template-utils.js";
 import {
-  TypeNameOptions,
   getEntityName,
-  getLocationContext,
   getNamespaceFullName,
   getTypeName,
-} from "./helpers/index.js";
-import { explainStringTemplateNotSerializable } from "./helpers/string-template-utils.js";
+  type TypeNameOptions,
+} from "./helpers/type-name-utils.js";
 import {
   getMaxItems,
   getMaxLength,

packages/compiler/src/core/decorator-utils.ts

@@ -1,8 +1,7 @@
-import { getPropertyType } from "../lib/decorators.js";
 import { compilerAssert, ignoreDiagnostics } from "./diagnostics.js";
 import { getTypeName } from "./helpers/type-name-utils.js";
 import { createDiagnostic, reportDiagnostic } from "./messages.js";
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 import {
   DecoratorContext,
   DecoratorFunction,
@@ -516,3 +515,14 @@ export function validateDecoratorNotOnType(
     }
   }
 }
+
+/**
+ * Return the type of the property or the model itself.
+ */
+export function getPropertyType(target: Scalar | ModelProperty): Type {
+  if (target.kind === "ModelProperty") {
+    return target.type;
+  } else {
+    return target;
+  }
+}

packages/compiler/src/core/deprecation.ts

@@ -1,4 +1,4 @@
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 import { BaseNode, Node, SyntaxKind, Type } from "./types.js";
 
 function createStateSymbol(name: string) {

packages/compiler/src/core/diagnostics.ts

@@ -1,4 +1,4 @@
-import { formatLog } from "./logger/index.js";
+import { formatLog } from "./logger/console-sink.js";
 import type { Program } from "./program.js";
 import { createSourceFile } from "./source-file.js";
 import {

packages/compiler/src/core/emitter-utils.ts

@@ -1,5 +1,5 @@
 import { getDirectoryPath } from "./path-utils.js";
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 
 export type NewLine = "lf" | "crlf";
 export interface EmitFileOptions {

packages/compiler/src/core/helpers/discriminator-utils.ts

@@ -1,8 +1,8 @@
-import { Discriminator, getDiscriminatedTypes } from "../../lib/decorators.js";
 import { DuplicateTracker } from "../../utils/duplicate-tracker.js";
 import { isDefined } from "../../utils/misc.js";
+import { Discriminator, getDiscriminatedTypes } from "../intrinsic-type-state.js";
 import { createDiagnostic } from "../messages.js";
-import { Program } from "../program.js";
+import type { Program } from "../program.js";
 import { isTemplateDeclarationOrInstance } from "../type-utils.js";
 import { Diagnostic, Model, Type, Union } from "../types.js";
 

packages/compiler/src/core/helpers/location-context.ts

@@ -1,6 +1,6 @@
 import { getSourceLocation } from "../diagnostics.js";
-import { Program } from "../program.js";
-import { DiagnosticTarget, LocationContext } from "../types.js";
+import type { Program } from "../program.js";
+import type { DiagnosticTarget, LocationContext } from "../types.js";
 
 export function getLocationContext(program: Program, type: DiagnosticTarget): LocationContext {
   const sourceLocation = getSourceLocation(type);

packages/compiler/src/core/helpers/projected-names-utils.ts

@@ -1,5 +1,6 @@
-import { Program, ProjectedProgram, projectProgram } from "../program.js";
-import { Projector, Type } from "../types.js";
+import type { Program, ProjectedProgram } from "../program.js";
+import { projectProgram } from "../program.js";
+import type { Projector, Type } from "../types.js";
 
 export interface ProjectedNameView {
   program: ProjectedProgram;

packages/compiler/src/core/index.ts

@@ -7,6 +7,8 @@ export * from "./emitter-utils.js";
 export * from "./formatter.js";
 export * from "./helpers/index.js";
 export {
+  getDiscriminatedTypes,
+  getDiscriminator,
   getDocData,
   getMaxItems,
   getMaxItemsAsNumeric,
@@ -45,6 +47,7 @@ export { getPositionBeforeTrivia } from "./parser-utils.js";
 export * from "./parser.js";
 export * from "./path-utils.js";
 export * from "./program.js";
+export { isProjectedProgram } from "./projected-program.js";
 export * from "./scanner.js";
 export * from "./semantic-walker.js";
 export { createSourceFile, getSourceFileKindFromExt } from "./source-file.js";

packages/compiler/src/core/intrinsic-type-state.ts

@@ -1,7 +1,7 @@
 // Contains all intrinsic data setter or getter
 // Anything that the TypeSpec check might should be here.
 
-import type { Type } from "./index.js";
+import type { Model, Type, Union } from "./index.js";
 import type { Numeric } from "./numeric.js";
 import type { Program } from "./program.js";
 
@@ -22,6 +22,8 @@ const stateKeys = {
   docs: createStateSymbol("docs"),
   returnDocs: createStateSymbol("returnsDocs"),
   errorsDocs: createStateSymbol("errorDocs"),
+
+  discriminator: createStateSymbol("discriminator"),
 };
 
 // #region @minValue
@@ -208,3 +210,23 @@ export function getDocData(program: Program, target: Type): DocData | undefined
   return getDocDataInternal(program, target, "self");
 }
 // #endregion doc
+
+// #region discriminator
+
+export interface Discriminator {
+  readonly propertyName: string;
+}
+
+export function setDiscriminator(program: Program, entity: Type, discriminator: Discriminator) {
+  program.stateMap(stateKeys.discriminator).set(entity, discriminator);
+}
+
+export function getDiscriminator(program: Program, entity: Type): Discriminator | undefined {
+  return program.stateMap(stateKeys.discriminator).get(entity);
+}
+
+export function getDiscriminatedTypes(program: Program): [Model | Union, Discriminator][] {
+  return [...program.stateMap(stateKeys.discriminator).entries()] as any;
+}
+
+// #endregion

packages/compiler/src/core/js-marshaller.ts

@@ -1,4 +1,4 @@
-import { Checker } from "./checker.js";
+import type { Checker } from "./checker.js";
 import { compilerAssert } from "./diagnostics.js";
 import { numericRanges } from "./numeric-ranges.js";
 import { Numeric } from "./numeric.js";

packages/compiler/src/core/library.ts

@@ -1,6 +1,6 @@
 import { createDiagnosticCreator } from "./diagnostic-creator.js";
 import { compilerAssert } from "./diagnostics.js";
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 import { createJSONSchemaValidator } from "./schema-validator.js";
 import {
   DiagnosticMessages,

packages/compiler/src/core/linter.ts

@@ -1,7 +1,7 @@
 import { DiagnosticCollector, compilerAssert, createDiagnosticCollector } from "./diagnostics.js";
-import { getLocationContext } from "./helpers/index.js";
+import { getLocationContext } from "./helpers/location-context.js";
 import { createDiagnostic } from "./messages.js";
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 import { EventEmitter, mapEventEmitterToNodeListener, navigateProgram } from "./semantic-walker.js";
 import {
   Diagnostic,

packages/compiler/src/core/program.ts

@@ -37,6 +37,7 @@ import { isImportStatement, parse, parseStandaloneTypeReference } from "./parser
 import { getDirectoryPath, joinPaths, resolvePath } from "./path-utils.js";
 import { createProjector } from "./projector.js";
 import { createSourceFile } from "./source-file.js";
+import { StateMap, StateSet, createStateAccessors } from "./state-accessors.js";
 import {
   CompilerHost,
   Diagnostic,
@@ -73,10 +74,12 @@ export interface ProjectedProgram extends Program {
   projector: Projector;
 }
 
-export function isProjectedProgram(
-  program: Program | ProjectedProgram
-): program is ProjectedProgram {
-  return "projector" in program;
+export function projectProgram(
+  program: Program,
+  projections: ProjectionApplication[],
+  startNode?: Type
+): ProjectedProgram {
+  return createProjector(program, projections, startNode);
 }
 
 export interface Program {
@@ -132,146 +135,11 @@ interface Validator {
   callback: (program: Program) => void | Promise<void>;
 }
 
-class StateMap extends Map<undefined | Projector, Map<Type, unknown>> {}
-class StateSet extends Map<undefined | Projector, Set<Type>> {}
-
-class StateMapView<V> implements Map<Type, V> {
-  public constructor(
-    private state: StateMap,
-    private projector?: Projector
-  ) {}
-
-  has(t: Type) {
-    return this.dispatch(t)?.has(t) ?? false;
-  }
-
-  set(t: Type, v: any) {
-    this.dispatch(t).set(t, v);
-    return this;
-  }
-
-  get(t: Type) {
-    return this.dispatch(t).get(t);
-  }
-
-  delete(t: Type) {
-    return this.dispatch(t).delete(t);
-  }
-
-  forEach(cb: (value: V, key: Type, map: Map<Type, V>) => void, thisArg?: any) {
-    this.dispatch().forEach(cb, thisArg);
-    return this;
-  }
-
-  get size() {
-    return this.dispatch().size;
-  }
-
-  clear() {
-    return this.dispatch().clear();
-  }
-
-  entries() {
-    return this.dispatch().entries();
-  }
-
-  values() {
-    return this.dispatch().values();
-  }
-
-  keys() {
-    return this.dispatch().keys();
-  }
-
-  [Symbol.iterator]() {
-    return this.entries();
-  }
-
-  [Symbol.toStringTag] = "StateMap";
-
-  dispatch(keyType?: Type): Map<Type, V> {
-    const key = keyType ? keyType.projector : this.projector;
-    if (!this.state.has(key)) {
-      this.state.set(key, new Map());
-    }
-
-    return this.state.get(key)! as any;
-  }
-}
-
-class StateSetView implements Set<Type> {
-  public constructor(
-    private state: StateSet,
-    private projector?: Projector
-  ) {}
-
-  has(t: Type) {
-    return this.dispatch(t)?.has(t) ?? false;
-  }
-
-  add(t: Type) {
-    this.dispatch(t).add(t);
-    return this;
-  }
-
-  delete(t: Type) {
-    return this.dispatch(t).delete(t);
-  }
-
-  forEach(cb: (value: Type, value2: Type, set: Set<Type>) => void, thisArg?: any) {
-    this.dispatch().forEach(cb, thisArg);
-    return this;
-  }
-
-  get size() {
-    return this.dispatch().size;
-  }
-
-  clear() {
-    return this.dispatch().clear();
-  }
-
-  values() {
-    return this.dispatch().values();
-  }
-
-  keys() {
-    return this.dispatch().keys();
-  }
-
-  entries() {
-    return this.dispatch().entries();
-  }
-
-  [Symbol.iterator]() {
-    return this.values();
-  }
-
-  [Symbol.toStringTag] = "StateSet";
-
-  dispatch(keyType?: Type): Set<Type> {
-    const key = keyType ? keyType.projector : this.projector;
-    if (!this.state.has(key)) {
-      this.state.set(key, new Set());
-    }
-
-    return this.state.get(key)!;
-  }
-}
-
 interface TypeSpecLibraryReference {
   path: string;
   manifest: NodePackage;
 }
 
-export function projectProgram(
-  program: Program,
-  projections: ProjectionApplication[],
-  startNode?: Type
-): ProjectedProgram {
-  return createProjector(program, projections, startNode);
-}
-
 export async function compile(
   host: CompilerHost,
   mainFile: string,
@@ -1228,36 +1096,6 @@ export async function compile(
   }
 }
 
-export function createStateAccessors(
-  stateMaps: Map<symbol, StateMap>,
-  stateSets: Map<symbol, StateSet>,
-  projector?: Projector
-) {
-  function stateMap<T>(key: symbol): StateMapView<T> {
-    let m = stateMaps.get(key);
-
-    if (!m) {
-      m = new StateMap();
-      stateMaps.set(key, m);
-    }
-
-    return new StateMapView(m, projector);
-  }
-
-  function stateSet(key: symbol): StateSetView {
-    let s = stateSets.get(key);
-
-    if (!s) {
-      s = new StateSet();
-      stateSets.set(key, s);
-    }
-
-    return new StateSetView(s, projector);
-  }
-
-  return { stateMap, stateSet };
-}
-
 /**
  * Resolve compiler options from input options.
  */

packages/compiler/src/core/projected-program.ts

@@ -0,0 +1,7 @@
+import type { Program, ProjectedProgram } from "./index.js";
+
+export function isProjectedProgram(
+  program: Program | ProjectedProgram
+): program is ProjectedProgram {
+  return "projector" in program;
+}

packages/compiler/src/core/projection-members.ts

@@ -1,7 +1,7 @@
 import { camelCase, kebabCase, pascalCase, snakeCase } from "change-case";
-import { Checker } from "./checker.js";
+import type { Checker } from "./checker.js";
 import { ProjectionError, assertType } from "./diagnostics.js";
-import { ObjectType, Type, UnionVariant } from "./types.js";
+import type { ObjectType, Type, UnionVariant } from "./types.js";
 
 export function createProjectionMembers(checker: Checker): {
   [TKind in Type["kind"]]?: Record<string, (base: Type & { kind: TKind }) => Type>;

packages/compiler/src/core/projector.ts

@@ -1,9 +1,11 @@
 import { createRekeyableMap, mutate } from "../utils/misc.js";
 import { finishTypeForProgram } from "./checker.js";
 import { compilerAssert } from "./diagnostics.js";
-import { Program, ProjectedProgram, createStateAccessors, isProjectedProgram } from "./program.js";
+import type { Program, ProjectedProgram } from "./program.js";
+import { isProjectedProgram } from "./projected-program.js";
+import { createStateAccessors } from "./state-accessors.js";
 import { getParentTemplateNode, isNeverType, isTemplateInstance, isValue } from "./type-utils.js";
-import {
+import type {
   DecoratorApplication,
   DecoratorArgument,
   Enum,

packages/compiler/src/core/semantic-walker.ts

@@ -1,4 +1,4 @@
-import { Program } from "./program.js";
+import type { Program } from "./program.js";
 import { isTemplateDeclaration } from "./type-utils.js";
 import {
   Decorator,

packages/compiler/src/core/state-accessors.ts

@@ -0,0 +1,158 @@
+import type { Projector, Type } from "./types.js";
+
+export class StateMap extends Map<undefined | Projector, Map<Type, unknown>> {}
+export class StateSet extends Map<undefined | Projector, Set<Type>> {}
+
+class StateMapView<V> implements Map<Type, V> {
+  public constructor(
+    private state: StateMap,
+    private projector?: Projector
+  ) {}
+
+  has(t: Type) {
+    return this.dispatch(t)?.has(t) ?? false;
+  }
+
+  set(t: Type, v: any) {
+    this.dispatch(t).set(t, v);
+    return this;
+  }
+
+  get(t: Type) {
+    return this.dispatch(t).get(t);
+  }
+
+  delete(t: Type) {
+    return this.dispatch(t).delete(t);
+  }
+
+  forEach(cb: (value: V, key: Type, map: Map<Type, V>) => void, thisArg?: any) {
+    this.dispatch().forEach(cb, thisArg);
+    return this;
+  }
+
+  get size() {
+    return this.dispatch().size;
+  }
+
+  clear() {
+    return this.dispatch().clear();
+  }
+
+  entries() {
+    return this.dispatch().entries();
+  }
+
+  values() {
+    return this.dispatch().values();
+  }
+
+  keys() {
+    return this.dispatch().keys();
+  }
+
+  [Symbol.iterator]() {
+    return this.entries();
+  }
+
+  [Symbol.toStringTag] = "StateMap";
+
+  dispatch(keyType?: Type): Map<Type, V> {
+    const key = keyType ? keyType.projector : this.projector;
+    if (!this.state.has(key)) {
+      this.state.set(key, new Map());
+    }
+
+    return this.state.get(key)! as any;
+  }
+}
+
+class StateSetView implements Set<Type> {
+  public constructor(
+    private state: StateSet,
+    private projector?: Projector
+  ) {}
+
+  has(t: Type) {
+    return this.dispatch(t)?.has(t) ?? false;
+  }
+
+  add(t: Type) {
+    this.dispatch(t).add(t);
+    return this;
+  }
+
+  delete(t: Type) {
+    return this.dispatch(t).delete(t);
+  }
+
+  forEach(cb: (value: Type, value2: Type, set: Set<Type>) => void, thisArg?: any) {
+    this.dispatch().forEach(cb, thisArg);
+    return this;
+  }
+
+  get size() {
+    return this.dispatch().size;
+  }
+
+  clear() {
+    return this.dispatch().clear();
+  }
+
+  values() {
+    return this.dispatch().values();
+  }
+
+  keys() {
+    return this.dispatch().keys();
+  }
+
+  entries() {
+    return this.dispatch().entries();
+  }
+
+  [Symbol.iterator]() {
+    return this.values();
+  }
+
+  [Symbol.toStringTag] = "StateSet";
+
+  dispatch(keyType?: Type): Set<Type> {
+    const key = keyType ? keyType.projector : this.projector;
+    if (!this.state.has(key)) {
+      this.state.set(key, new Set());
+    }
+
+    return this.state.get(key)!;
+  }
+}
+
+export function createStateAccessors(
+  stateMaps: Map<symbol, StateMap>,
+  stateSets: Map<symbol, StateSet>,
+  projector?: Projector
+) {
+  function stateMap<T>(key: symbol): StateMapView<T> {
+    let m = stateMaps.get(key);
+
+    if (!m) {
+      m = new StateMap();
+      stateMaps.set(key, m);
+    }
+
+    return new StateMapView(m, projector);
+  }
+
+  function stateSet(key: symbol): StateSetView {
+    let s = stateSets.get(key);
+
+    if (!s) {
+      s = new StateSet();
+      stateSets.set(key, s);
+    }
+
+    return new StateSetView(s, projector);
+  }
+
+  return { stateMap, stateSet };
+}

packages/compiler/src/emitter-framework/asset-emitter.ts

@@ -1,14 +1,8 @@
-import {
-  compilerAssert,
-  EmitContext,
-  getTypeName,
-  isTemplateDeclaration,
-  joinPaths,
-  Model,
-  Namespace,
-  Program,
-  Type,
-} from "../core/index.js";
+import { compilerAssert } from "../core/diagnostics.js";
+import { getTypeName } from "../core/helpers/type-name-utils.js";
+import type { EmitContext, Model, Namespace, Program, Type } from "../core/index.js";
+import { joinPaths } from "../core/path-utils.js";
+import { isTemplateDeclaration } from "../core/type-utils.js";
 import { CustomKeyMap } from "./custom-key-map.js";
 import { Placeholder } from "./placeholder.js";
 import { resolveDeclarationReferenceScope } from "./ref-scope.js";
@@ -20,9 +14,9 @@ import {
   ContextState,
   Declaration,
   EmitEntity,
+  EmitTypeReferenceOptions,
   EmitterResult,
   EmitterState,
-  EmitTypeReferenceOptions,
   LexicalTypeStackEntry,
   NamespaceScope,
   NoEmit,

packages/compiler/src/emitter-framework/ref-scope.ts

@@ -1,4 +1,4 @@
-import { Declaration, Scope } from "./types.js";
+import type { Declaration, Scope } from "./types.js";
 
 export function scopeChain<T>(scope: Scope<T> | null) {
   const chain = [];

packages/compiler/src/emitter-framework/reference-cycle.ts

@@ -1,5 +1,6 @@
-import { Type, getTypeName } from "../core/index.js";
-import { EmitEntity } from "./types.js";
+import { getTypeName } from "../core/helpers/type-name-utils.js";
+import type { Type } from "../core/index.js";
+import type { EmitEntity } from "./types.js";
 
 export interface ReferenceCycleEntry {
   type: Type;

packages/compiler/src/emitter-framework/type-emitter.ts

@@ -1,18 +1,18 @@
-import {
+import { compilerAssert } from "../core/diagnostics.js";
+import { emitFile } from "../core/emitter-utils.js";
+import type { Program } from "../core/program.js";
+import { isTemplateDeclaration } from "../core/type-utils.js";
+import type {
   BooleanLiteral,
-  compilerAssert,
-  emitFile,
   Enum,
   EnumMember,
   Interface,
   IntrinsicType,
-  isTemplateDeclaration,
   Model,
   ModelProperty,
   Namespace,
   NumericLiteral,
   Operation,
-  Program,
   Scalar,
   StringLiteral,
   StringTemplate,
@@ -20,8 +20,8 @@ import {
   Type,
   Union,
   UnionVariant,
-} from "../core/index.js";
-import { code, StringBuilder } from "./builders/string-builder.js";
+} from "../core/types.js";
+import { StringBuilder, code } from "./builders/string-builder.js";
 import { Placeholder } from "./placeholder.js";
 import { resolveDeclarationReferenceScope } from "./ref-scope.js";
 import { ReferenceCycle } from "./reference-cycle.js";

packages/compiler/src/emitter-framework/types.ts

@@ -1,4 +1,4 @@
-import {
+import type {
   Enum,
   Interface,
   IntrinsicType,
@@ -12,7 +12,7 @@ import {
   Union,
 } from "../core/index.js";
 import { Placeholder } from "./placeholder.js";
-import { TypeEmitter } from "./type-emitter.js";
+import type { TypeEmitter } from "./type-emitter.js";
 
 type AssetEmitterOptions<TOptions extends object> = {
   noEmit: boolean;

packages/compiler/src/init/file-templating.ts

@@ -1,7 +1,7 @@
 import { camelCase, kebabCase, pascalCase } from "change-case";
 import Mustache from "mustache";
-import { InitTemplate } from "./init-template.js";
-import { ScaffoldingConfig } from "./scaffold.js";
+import type { InitTemplate } from "./init-template.js";
+import type { ScaffoldingConfig } from "./scaffold.js";
 
 export type FileTemplatingContext = Omit<InitTemplate, "libraries"> &
   ScaffoldingConfig & {

packages/compiler/src/lib/decorators.ts

@@ -37,6 +37,7 @@ import type {
   WithoutOmittedPropertiesDecorator,
 } from "../../generated-defs/TypeSpec.js";
 import {
+  getPropertyType,
   isIntrinsicType,
   validateDecoratorNotOnType,
   validateDecoratorTarget,
@@ -53,6 +54,7 @@ import {
   validateDecoratorUniqueOnNode,
 } from "../core/index.js";
 import {
+  Discriminator,
   DocData,
   getDocDataInternal,
   getMaxItemsAsNumeric,
@@ -63,6 +65,7 @@ import {
   getMinLengthAsNumeric,
   getMinValueAsNumeric,
   getMinValueExclusiveAsNumeric,
+  setDiscriminator,
   setDocData,
   setMaxItems,
   setMaxLength,
@@ -310,17 +313,6 @@ function validateTargetingAString(
   return valid;
 }
 
-/**
- * Return the type of the property or the model itself.
- */
-export function getPropertyType(target: Scalar | ModelProperty): Type {
-  if (target.kind === "ModelProperty") {
-    return target.type;
-  } else {
-    return target;
-  }
-}
-
 // -- @error decorator ----------------------
 
 const errorKey = createStateSymbol("error");
@@ -1343,12 +1335,6 @@ function validateRange(
   return true;
 }
 
-export interface Discriminator {
-  propertyName: string;
-}
-
-const discriminatorKey = createStateSymbol("discriminator");
-
 export const $discriminator: DiscriminatorDecorator = (
   context: DecoratorContext,
   entity: Model | Union,
@@ -1364,17 +1350,9 @@ export const $discriminator: DiscriminatorDecorator = (
       return;
     }
   }
-  context.program.stateMap(discriminatorKey).set(entity, discriminator);
+  setDiscriminator(context.program, entity, discriminator);
 };
 
-export function getDiscriminator(program: Program, entity: Type): Discriminator | undefined {
-  return program.stateMap(discriminatorKey).get(entity);
-}
-
-export function getDiscriminatedTypes(program: Program): [Model | Union, Discriminator][] {
-  return [...program.stateMap(discriminatorKey).entries()] as any;
-}
-
 const parameterVisibilityKey = createStateSymbol("parameterVisibility");
 
 export const $parameterVisibility: ParameterVisibilityDecorator = (

packages/compiler/src/lib/encoded-names.ts

@@ -1,7 +1,7 @@
 import { reportDiagnostic } from "../core/messages.js";
 import { parseMimeType } from "../core/mime-type.js";
-import { Program } from "../core/program.js";
-import { DecoratorContext, Enum, Model, Type, Union } from "../core/types.js";
+import type { Program } from "../core/program.js";
+import type { DecoratorContext, Enum, Model, Type, Union } from "../core/types.js";
 import { DuplicateTracker } from "../utils/index.js";
 
 function createStateSymbol(name: string) {

packages/compiler/src/lib/service.ts

@@ -2,7 +2,7 @@ import { ServiceDecorator } from "../../generated-defs/TypeSpec.js";
 import { validateDecoratorUniqueOnNode } from "../core/decorator-utils.js";
 import { Type, getTypeName, reportDeprecated } from "../core/index.js";
 import { reportDiagnostic } from "../core/messages.js";
-import { Program } from "../core/program.js";
+import type { Program } from "../core/program.js";
 import { DecoratorContext, Namespace } from "../core/types.js";
 
 export interface ServiceDetails {

packages/compiler/src/server/serverlib.ts

@@ -54,7 +54,7 @@ import { ResolveModuleHost, resolveModule } from "../core/index.js";
 import { getPositionBeforeTrivia } from "../core/parser-utils.js";
 import { getNodeAtPosition, visitChildren } from "../core/parser.js";
 import { ensureTrailingDirectorySeparator, getDirectoryPath } from "../core/path-utils.js";
-import { Program } from "../core/program.js";
+import type { Program } from "../core/program.js";
 import { skipTrivia, skipWhiteSpace } from "../core/scanner.js";
 import { createSourceFile, getSourceFileKindFromExt } from "../core/source-file.js";
 import {

packages/compiler/src/server/type-signature.ts

@@ -1,6 +1,6 @@
 import { compilerAssert } from "../core/diagnostics.js";
 import { getEntityName, getTypeName, isStdNamespace } from "../core/helpers/type-name-utils.js";
-import { Program } from "../core/program.js";
+import type { Program } from "../core/program.js";
 import { getFullyQualifiedSymbolName } from "../core/type-utils.js";
 import {
   AliasStatementNode,

packages/compiler/src/server/types.ts

@@ -37,7 +37,7 @@ import {
   WorkspaceFoldersChangeEvent,
 } from "vscode-languageserver";
 import { TextDocument, TextEdit } from "vscode-languageserver-textdocument";
-import { CompilerHost, Program, SourceFile, TypeSpecScriptNode } from "../index.js";
+import type { CompilerHost, Program, SourceFile, TypeSpecScriptNode } from "../core/index.js";
 
 export interface ServerHost {
   readonly compilerHost: CompilerHost;

packages/compiler/src/testing/expect.ts

@@ -1,7 +1,7 @@
 import { fail, match, strictEqual } from "assert";
 import { Diagnostic, NoTarget, Type, formatDiagnostic, getSourceLocation } from "../core/index.js";
 import { isArray } from "../utils/misc.js";
-import { resolveVirtualPath } from "./test-host.js";
+import { resolveVirtualPath } from "./test-utils.js";
 
 /**
  * Assert there is no diagnostics.

packages/compiler/src/testing/rule-tester.ts

@@ -10,8 +10,7 @@ import {
 } from "../core/index.js";
 import { createLinterRuleContext } from "../core/linter.js";
 import { DiagnosticMatch, expectDiagnosticEmpty, expectDiagnostics } from "./expect.js";
-import { resolveVirtualPath } from "./test-host.js";
-import { trimBlankLines } from "./test-utils.js";
+import { resolveVirtualPath, trimBlankLines } from "./test-utils.js";
 import { BasicTestRunner } from "./types.js";
 
 export interface LinterRuleTester {

packages/compiler/src/testing/test-host.ts

@@ -1,5 +1,5 @@
 import assert from "assert";
-import { RmOptions } from "fs";
+import type { RmOptions } from "fs";
 import { readFile } from "fs/promises";
 import { globby } from "globby";
 import { fileURLToPath, pathToFileURL } from "url";
@@ -9,11 +9,11 @@ import { NodeHost } from "../core/node-host.js";
 import { CompilerOptions } from "../core/options.js";
 import { getAnyExtensionFromPath, resolvePath } from "../core/path-utils.js";
 import { Program, compile as compileProgram } from "../core/program.js";
-import { CompilerHost, Diagnostic, StringLiteral, Type } from "../core/types.js";
+import type { CompilerHost, Diagnostic, StringLiteral, Type } from "../core/types.js";
 import { createSourceFile, getSourceFileKindFromExt } from "../index.js";
 import { createStringMap } from "../utils/misc.js";
 import { expectDiagnosticEmpty } from "./expect.js";
-import { createTestWrapper, findTestPackageRoot } from "./test-utils.js";
+import { createTestWrapper, findTestPackageRoot, resolveVirtualPath } from "./test-utils.js";
 import {
   BasicTestRunner,
   TestFileSystem,
@@ -29,14 +29,6 @@ export interface TestHostOptions {
   compilerHostOverrides?: Partial<CompilerHost>;
 }
 
-export function resolveVirtualPath(path: string, ...paths: string[]) {
-  // NB: We should always resolve an absolute path, and there is no absolute
-  // path that works across OSes. This ensures that we can still rely on API
-  // like pathToFileURL in tests.
-  const rootDir = process.platform === "win32" ? "Z:/test" : "/test";
-  return resolvePath(rootDir, path, ...paths);
-}
-
 function createTestCompilerHost(
   virtualFs: Map<string, string>,
   jsImports: Map<string, Record<string, any>>,

packages/compiler/src/testing/test-server-host.ts

@@ -6,12 +6,8 @@ import { parse, visitChildren } from "../core/parser.js";
 import { IdentifierNode, SyntaxKind } from "../core/types.js";
 import { Server, ServerHost, createServer } from "../server/index.js";
 import { createStringMap } from "../utils/misc.js";
-import {
-  StandardTestLibrary,
-  TestHostOptions,
-  createTestFileSystem,
-  resolveVirtualPath,
-} from "./test-host.js";
+import { StandardTestLibrary, TestHostOptions, createTestFileSystem } from "./test-host.js";
+import { resolveVirtualPath } from "./test-utils.js";
 import { TestFileSystem } from "./types.js";
 
 export interface TestServerHost extends ServerHost, TestFileSystem {

packages/compiler/src/testing/test-utils.ts

@@ -9,6 +9,14 @@ import {
   TypeSpecTestLibraryInit,
 } from "./types.js";
 
+export function resolveVirtualPath(path: string, ...paths: string[]) {
+  // NB: We should always resolve an absolute path, and there is no absolute
+  // path that works across OSes. This ensures that we can still rely on API
+  // like pathToFileURL in tests.
+  const rootDir = process.platform === "win32" ? "Z:/test" : "/test";
+  return resolvePath(rootDir, path, ...paths);
+}
+
 /** Find the package root from the provided file */
 export function findTestPackageRoot(fileUrl: string): Promise<string> {
   return findProjectRoot(NodeHost.stat, fileURLToPath(fileUrl)) as Promise<string>;

packages/compiler/test/binder.test.ts

@@ -4,7 +4,7 @@ import { Binder, createBinder } from "../src/core/binder.js";
 import { createLogger } from "../src/core/logger/logger.js";
 import { createTracer } from "../src/core/logger/tracer.js";
 import { parse } from "../src/core/parser.js";
-import { Program } from "../src/core/program.js";
+import type { Program } from "../src/core/program.js";
 import { createSourceFile } from "../src/core/source-file.js";
 import {
   AliasStatementNode,

packages/compiler/test/checker/clone-type.test.ts

@@ -1,6 +1,6 @@
 import { deepStrictEqual, ok, strictEqual } from "assert";
 import { beforeEach, describe, it } from "vitest";
-import { Program } from "../../src/core/program.js";
+import type { Program } from "../../src/core/program.js";
 import { DecoratorContext, Type } from "../../src/core/types.js";
 import { TestHost, createTestHost } from "../../src/testing/index.js";
 import { createRekeyableMap } from "../../src/utils/misc.js";

packages/compiler/test/checker/namespaces.test.ts

@@ -1,7 +1,7 @@
 import { ok, strictEqual } from "assert";
 import { beforeEach, describe, it } from "vitest";
 import { getTypeName } from "../../src/core/index.js";
-import { Program } from "../../src/core/program.js";
+import type { Program } from "../../src/core/program.js";
 import { Model, Namespace, Type } from "../../src/core/types.js";
 import {
   TestHost,

packages/compiler/test/projection/projection-logic.test.ts

@@ -1,8 +1,8 @@
 import { deepStrictEqual, fail, ok, strictEqual } from "assert";
 import { beforeEach, describe, it } from "vitest";
-import { Program, projectProgram } from "../../src/core/program.js";
+import type { Program } from "../../src/core/program.js";
 import { createProjector } from "../../src/core/projector.js";
-import {
+import type {
   DecoratorArgumentValue,
   DecoratorContext,
   Enum,
@@ -17,6 +17,7 @@ import {
   Type,
   Union,
 } from "../../src/core/types.js";
+import { projectProgram } from "../../src/index.js";
 import { getDoc } from "../../src/lib/decorators.js";
 import { TestHost, createTestHost } from "../../src/testing/index.js";
 

packages/http/src/validate.ts

@@ -1,4 +1,4 @@
-import { Program } from "@typespec/compiler";
+import type { Program } from "@typespec/compiler";
 import { reportDiagnostic } from "./lib.js";
 import { getAllHttpServices } from "./operations.js";
 import { isSharedRoute } from "./route.js";

packages/playground/src/react/output-view/output-view.tsx

@@ -1,5 +1,5 @@
 import { tokens } from "@fluentui/react-components";
-import { Program } from "@typespec/compiler";
+import type { Program } from "@typespec/compiler";
 import { ColorPalette, ColorProvider, TypeSpecProgramViewer } from "@typespec/html-program-viewer";
 import { FunctionComponent, useCallback, useEffect, useMemo, useState } from "react";
 import { FileOutput } from "../file-output/file-output.js";

packages/playground/src/react/types.ts

@@ -1,4 +1,4 @@
-import { Program } from "@typespec/compiler";
+import type { Program } from "@typespec/compiler";
 import { ReactElement } from "react";
 
 export type CompilationCrashed = {