Expose TypeChecker. getAwaitedType to public (#59268)

Co-authored-by: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Co-authored-by: Ron Buckton <ron.buckton@microsoft.com>

src/compiler/types.ts

@@ -5051,7 +5051,26 @@ export interface TypeChecker {
     getWidenedLiteralType(type: Type): Type;
     /** @internal */
     getPromisedTypeOfPromise(promise: Type, errorNode?: Node): Type | undefined;
-    /** @internal */
+    /**
+     * Gets the "awaited type" of a type.
+     *
+     * If an expression has a Promise-like type, the "awaited type" of the expression is
+     * derived from the type of the first argument of the fulfillment callback for that
+     * Promise's `then` method. If the "awaited type" is itself a Promise-like, it is
+     * recursively unwrapped in the same manner until a non-promise type is found.
+     *
+     * If an expression does not have a Promise-like type, its "awaited type" is the type
+     * of the expression.
+     *
+     * If the resulting "awaited type" is a generic object type, then it is wrapped in
+     * an `Awaited<T>`.
+     *
+     * In the event the "awaited type" circularly references itself, or is a non-Promise
+     * object-type with a callable `then()` method, an "awaited type" cannot be determined
+     * and the value `undefined` will be returned.
+     *
+     * This is used to reflect the runtime behavior of the `await` keyword.
+     */
     getAwaitedType(type: Type): Type | undefined;
     /** @internal */
     isEmptyAnonymousObjectType(type: Type): boolean;

tests/baselines/reference/api/typescript.d.ts

@@ -6121,6 +6121,27 @@ declare namespace ts {
         getBaseTypes(type: InterfaceType): BaseType[];
         getBaseTypeOfLiteralType(type: Type): Type;
         getWidenedType(type: Type): Type;
+        /**
+         * Gets the "awaited type" of a type.
+         *
+         * If an expression has a Promise-like type, the "awaited type" of the expression is
+         * derived from the type of the first argument of the fulfillment callback for that
+         * Promise's `then` method. If the "awaited type" is itself a Promise-like, it is
+         * recursively unwrapped in the same manner until a non-promise type is found.
+         *
+         * If an expression does not have a Promise-like type, its "awaited type" is the type
+         * of the expression.
+         *
+         * If the resulting "awaited type" is a generic object type, then it is wrapped in
+         * an `Awaited<T>`.
+         *
+         * In the event the "awaited type" circularly references itself, or is a non-Promise
+         * object-type with a callable `then()` method, an "awaited type" cannot be determined
+         * and the value `undefined` will be returned.
+         *
+         * This is used to reflect the runtime behavior of the `await` keyword.
+         */
+        getAwaitedType(type: Type): Type | undefined;
         getReturnTypeOfSignature(signature: Signature): Type;
         getNullableType(type: Type, flags: TypeFlags): Type;
         getNonNullableType(type: Type): Type;