Backfill TypeReference.typeArguments in the API (#33714)

Author: weswigham

src/services/services.ts

@@ -452,6 +452,15 @@ namespace ts {
         isClass(): this is InterfaceType {
             return !!(getObjectFlags(this) & ObjectFlags.Class);
         }
+        /**
+         * This polyfills `referenceType.typeArguments` for API consumers
+         */
+        get typeArguments() {
+            if (getObjectFlags(this) & ObjectFlags.Reference) {
+                return this.checker.getTypeArguments(this as Type as TypeReference);
+            }
+            return undefined;
+        }
     }
 
     class SignatureObject implements Signature {

src/services/types.ts

@@ -68,6 +68,10 @@ namespace ts {
         isClass(): this is InterfaceType;
     }
 
+    export interface TypeReference {
+        typeArguments?: readonly Type[];
+    }
+
     export interface Signature {
         getDeclaration(): SignatureDeclaration;
         getTypeParameters(): TypeParameter[] | undefined;

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

@@ -4902,6 +4902,9 @@ declare namespace ts {
         isClassOrInterface(): this is InterfaceType;
         isClass(): this is InterfaceType;
     }
+    interface TypeReference {
+        typeArguments?: readonly Type[];
+    }
     interface Signature {
         getDeclaration(): SignatureDeclaration;
         getTypeParameters(): TypeParameter[] | undefined;

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

@@ -4902,6 +4902,9 @@ declare namespace ts {
         isClassOrInterface(): this is InterfaceType;
         isClass(): this is InterfaceType;
     }
+    interface TypeReference {
+        typeArguments?: readonly Type[];
+    }
     interface Signature {
         getDeclaration(): SignatureDeclaration;
         getTypeParameters(): TypeParameter[] | undefined;