From 335cea47f44739f18198b78a2726f9cf4df2c753 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 17 Nov 2023 11:39:52 -0800
Subject: [PATCH 1/2] Export isTypeAssignableTo on TypeChecker

---
 src/compiler/types.ts                         | 2 +-
 tests/baselines/reference/api/typescript.d.ts | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 34a2835822302..eed89d2326d3e 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5158,7 +5158,7 @@ export interface TypeChecker {
     /** @internal */ getPromiseLikeType(): Type;
     /** @internal */ getAsyncIterableType(): Type | undefined;
 
-    /** @internal */ isTypeAssignableTo(source: Type, target: Type): boolean;
+    isTypeAssignableTo(source: Type, target: Type): boolean;
     /** @internal */ createAnonymousType(symbol: Symbol | undefined, members: SymbolTable, callSignatures: Signature[], constructSignatures: Signature[], indexInfos: IndexInfo[]): Type;
     /** @internal */ createSignature(
         declaration: SignatureDeclaration | undefined,
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 7135bb7863324..1e21d2b07f651 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -6829,6 +6829,7 @@ declare namespace ts {
          * is `never`. Instead, use `type.flags & TypeFlags.Never`.
          */
         getNeverType(): Type;
+        isTypeAssignableTo(source: Type, target: Type): boolean;
         /**
          * True if this type is the `Array` or `ReadonlyArray` type from lib.d.ts.
          * This function will _not_ return true if passed a type which

From 1ef7d153a02477da9146fd9ce85e51d8e5907e3b Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 17 Nov 2023 13:51:11 -0800
Subject: [PATCH 2/2] Add some sort of docstring

---
 src/compiler/types.ts                         | 13 +++++++++++++
 tests/baselines/reference/api/typescript.d.ts | 13 +++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index eed89d2326d3e..01084e4ed6e53 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5158,6 +5158,19 @@ export interface TypeChecker {
     /** @internal */ getPromiseLikeType(): Type;
     /** @internal */ getAsyncIterableType(): Type | undefined;
 
+    /**
+     * Returns true if the "source" type is assignable to the "target" type.
+     *
+     * ```ts
+     * declare const abcLiteral: ts.Type; // Type of "abc"
+     * declare const stringType: ts.Type; // Type of string
+     *
+     * isTypeAssignableTo(abcLiteral, abcLiteral); // true; "abc" is assignable to "abc"
+     * isTypeAssignableTo(abcLiteral, stringType); // true; "abc" is assignable to string
+     * isTypeAssignableTo(stringType, abcLiteral); // false; string is not assignable to "abc"
+     * isTypeAssignableTo(stringType, stringType); // true; string is assignable to string
+     * ```
+     */
     isTypeAssignableTo(source: Type, target: Type): boolean;
     /** @internal */ createAnonymousType(symbol: Symbol | undefined, members: SymbolTable, callSignatures: Signature[], constructSignatures: Signature[], indexInfos: IndexInfo[]): Type;
     /** @internal */ createSignature(
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 1e21d2b07f651..dc285d91c2eaf 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -6829,6 +6829,19 @@ declare namespace ts {
          * is `never`. Instead, use `type.flags & TypeFlags.Never`.
          */
         getNeverType(): Type;
+        /**
+         * Returns true if the "source" type is assignable to the "target" type.
+         *
+         * ```ts
+         * declare const abcLiteral: ts.Type; // Type of "abc"
+         * declare const stringType: ts.Type; // Type of string
+         *
+         * isTypeAssignableTo(abcLiteral, abcLiteral); // true; "abc" is assignable to "abc"
+         * isTypeAssignableTo(abcLiteral, stringType); // true; "abc" is assignable to string
+         * isTypeAssignableTo(stringType, abcLiteral); // false; string is not assignable to "abc"
+         * isTypeAssignableTo(stringType, stringType); // true; string is assignable to string
+         * ```
+         */
         isTypeAssignableTo(source: Type, target: Type): boolean;
         /**
          * True if this type is the `Array` or `ReadonlyArray` type from lib.d.ts.