feat: TypeChecker - add getAwaitedType (#1643)

Author: JHawk0224

packages/ts-morph/lib/ts-morph.d.ts

@@ -9743,6 +9743,11 @@ export declare class TypeChecker {
    * @param type - Type to get the apparent type of.
    */
   getApparentType(type: Type): Type<ts.Type>;
+  /**
+   * Gets the awaited type of a type (ex. `Promise<string>` -> `string`).
+   * @param type - Type to get the awaited type of.
+   */
+  getAwaitedType(type: Type): Type<ts.Type> | undefined;
   /**
    * Gets the constant value of a declaration.
    * @param node - Node to get the constant value from.
@@ -9889,6 +9894,8 @@ export declare class Type<TType extends ts.Type = ts.Type> {
   getAliasTypeArguments(): Type[];
   /** Gets the apparent type. */
   getApparentType(): Type;
+  /** Gets the awaited type. */
+  getAwaitedType(): Type | undefined;
   /** Gets the array element type or throws if it doesn't exist (ex. for `T[]` it would be `T`). */
   getArrayElementTypeOrThrow(message?: string | (() => string)): Type<ts.Type>;
   /** Gets the array element type or returns undefined if it doesn't exist (ex. for `T[]` it would be `T`). */

packages/ts-morph/src/compiler/tools/TypeChecker.ts

@@ -52,6 +52,15 @@ export class TypeChecker {
     return this.#context.compilerFactory.getType(this.compilerObject.getApparentType(type.compilerType));
   }
 
+  /**
+   * Gets the awaited type of a type (ex. `Promise<string>` -> `string`).
+   * @param type - Type to get the awaited type of.
+   */
+  getAwaitedType(type: Type) {
+    const awaitedType = this.compilerObject.getAwaitedType(type.compilerType);
+    return awaitedType ? this.#context.compilerFactory.getType(awaitedType) : undefined;
+  }
+
   /**
    * Gets the constant value of a declaration.
    * @param node - Node to get the constant value from.

packages/ts-morph/src/compiler/types/Type.ts

@@ -67,6 +67,13 @@ export class Type<TType extends ts.Type = ts.Type> {
     return this._context.typeChecker.getApparentType(this);
   }
 
+  /**
+   * Gets the awaited type.
+   */
+  getAwaitedType(): Type | undefined {
+    return this._context.typeChecker.getAwaitedType(this);
+  }
+
   /**
    * Gets the array element type or throws if it doesn't exist (ex. for `T[]` it would be `T`).
    */

packages/ts-morph/src/tests/compiler/type/typeTests.ts

@@ -69,6 +69,7 @@ let stringWithUndefinedType: string | undefined;
 let stringWithNullType: string | null;
 let stringWithUndefinedAndNullType: string | undefined | null;
 let unknownType: unknown;
+let stringWithPromiseType: Promise<string>;
 `;
     const { sourceFile } = getInfoFromTextWithTypeChecking(text);
     const typesByName: { [name: string]: Type } = {};
@@ -605,6 +606,12 @@ let unknownType: unknown;
       });
     });
 
+    describe(nameof<Type>("getAwaitedType"), () => {
+      it("should get the awaited type", () => {
+        expect(typesByName["stringWithPromiseType"].getAwaitedType()!.getText()).to.equal("string");
+      });
+    });
+
     describe(nameof<Type>("getCallSignatures"), () => {
       it("should return no call signatures when none exist", () => {
         expect(typesByName["stringType"].getCallSignatures().length).to.equal(0);