[Experiment] feat(49903): Emit declaration d.ts adds declare on type declarations

src/compiler/transformers/declarations.ts

@@ -1217,14 +1217,18 @@ namespace ts {
 
             const previousNeedsDeclare = needsDeclare;
             switch (input.kind) {
-                case SyntaxKind.TypeAliasDeclaration: // Type aliases get `declare`d if need be (for legacy support), but that's all
-                    return cleanup(factory.updateTypeAliasDeclaration(
+                case SyntaxKind.TypeAliasDeclaration: {
+                    needsDeclare = false;
+                    const clean = cleanup(factory.updateTypeAliasDeclaration(
                         input,
                         ensureModifiers(input),
                         input.name,
                         visitNodes(input.typeParameters, visitDeclarationSubtree, isTypeParameterDeclaration),
                         visitNode(input.type, visitDeclarationSubtree, isTypeNode)
                     ));
+                    needsDeclare = previousNeedsDeclare;
+                    return clean;
+                }
                 case SyntaxKind.InterfaceDeclaration: {
                     return cleanup(factory.updateInterfaceDeclaration(
                         input,

tests/baselines/reference/DeclarationErrorsNoEmitOnError.js

@@ -10,7 +10,7 @@ exports.__esModule = true;
 
 
 //// [DeclarationErrorsNoEmitOnError.d.ts]
-declare type T = {
+type T = {
     x: number;
 };
 export interface I {

tests/baselines/reference/anonClassDeclarationEmitIsAnon.js

@@ -122,7 +122,7 @@ export declare function wrapClass(param: any): {
         foo(): any;
     };
 };
-export declare type Constructor<T = {}> = new (...args: any[]) => T;
+export type Constructor<T = {}> = new (...args: any[]) => T;
 export declare function Timestamped<TBase extends Constructor>(Base: TBase): {
     new (...args: any[]): {
         timestamp: number;

tests/baselines/reference/caseInsensitiveFileSystemWithCapsImportTypeDeclarations.js

@@ -48,15 +48,15 @@ exports.Broken = Broken;
 
 
 //// [types.d.ts]
-export declare type Merge<T, U> = T & U;
+export type Merge<T, U> = T & U;
 //// [type-a.d.ts]
-export declare type TypeA = {
+export type TypeA = {
     a: string;
 };
 //// [type-b.d.ts]
 import { Merge } from './types';
 import { TypeA } from './type-a';
-export declare type TypeB = Merge<TypeA, {
+export type TypeB = Merge<TypeA, {
     b: string;
 }>;
 //// [index.d.ts]

tests/baselines/reference/circularAccessorAnnotations.js

@@ -41,13 +41,13 @@ declare const c3: {
     get foo(): string;
     set foo(value: typeof c3.foo);
 };
-declare type T1 = {
+type T1 = {
     get foo(): T1["foo"];
 };
-declare type T2 = {
+type T2 = {
     set foo(value: T2["foo"]);
 };
-declare type T3 = {
+type T3 = {
     get foo(): string;
     set foo(value: T3["foo"]);
 };

tests/baselines/reference/circularBaseTypes.js

@@ -20,10 +20,10 @@ function f(m) {
 
 
 //// [circularBaseTypes.d.ts]
-declare type M<T> = {
+type M<T> = {
     value: T;
 };
 interface M2 extends M<M3> {
 }
-declare type M3 = M2[keyof M2];
+type M3 = M2[keyof M2];
 declare function f(m: M3): any;

tests/baselines/reference/circularIndexedAccessErrors.js

@@ -56,10 +56,10 @@ function foo() {
 
 
 //// [circularIndexedAccessErrors.d.ts]
-declare type T1 = {
+type T1 = {
     x: T1["x"];
 };
-declare type T2<K extends "x" | "y"> = {
+type T2<K extends "x" | "y"> = {
     x: T2<K>[K];
     y: number;
 };

tests/baselines/reference/coAndContraVariantInferences.js

@@ -50,10 +50,10 @@ call(actionB, printFn);
 
 
 //// [coAndContraVariantInferences.d.ts]
-declare type A = {
+type A = {
     kind: 'a';
 };
-declare type B = {
+type B = {
     kind: 'b';
 };
 declare const a: A;