From e80f69381fff3b03d342f25422a6ed1eb301fe63 Mon Sep 17 00:00:00 2001
From: John Firebaugh <john.firebaugh@gmail.com>
Date: Wed, 12 Nov 2025 10:11:01 -0800
Subject: [PATCH] fix: `InvalidOperationError` in `addTypeArgument`

Fix `addTypeArgument` for various forms of `PropertyAccessExpression`.

Fixes https://github.com/dsherret/ts-morph/issues/1228.
---
 .../compiler/ast/base/TypeArgumentedNode.ts   |  7 ++++-
 .../ast/base/typeArgumentedNodeTests.ts       | 27 +++++++++++++++++--
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/packages/ts-morph/src/compiler/ast/base/TypeArgumentedNode.ts b/packages/ts-morph/src/compiler/ast/base/TypeArgumentedNode.ts
index 4c60e16f6..60e5a0b2c 100644
--- a/packages/ts-morph/src/compiler/ast/base/TypeArgumentedNode.ts
+++ b/packages/ts-morph/src/compiler/ast/base/TypeArgumentedNode.ts
@@ -86,7 +86,12 @@ export function TypeArgumentedNode<T extends Constructor<TypeArgumentedNodeExten
       index = verifyAndGetIndex(index, typeArguments.length);
 
       if (typeArguments.length === 0) {
-        const identifier = this.getFirstChildByKindOrThrow(SyntaxKind.Identifier);
+        // For property access expressions like `this.foo()`, the identifier is nested
+        // inside the PropertyAccessExpression, not a direct child of the CallExpression
+        const expression = Node.hasExpression(this) ? this.getExpression() : undefined;
+        const identifier = Node.isPropertyAccessExpression(expression)
+          ? expression.getLastChildByKindOrThrow(SyntaxKind.Identifier)
+          : this.getFirstChildByKindOrThrow(SyntaxKind.Identifier);
         insertIntoParentTextRange({
           insertPos: identifier.getEnd(),
           parent: this,
diff --git a/packages/ts-morph/src/tests/compiler/ast/base/typeArgumentedNodeTests.ts b/packages/ts-morph/src/tests/compiler/ast/base/typeArgumentedNodeTests.ts
index 52ea8db14..cba8e1a33 100644
--- a/packages/ts-morph/src/tests/compiler/ast/base/typeArgumentedNodeTests.ts
+++ b/packages/ts-morph/src/tests/compiler/ast/base/typeArgumentedNodeTests.ts
@@ -1,6 +1,6 @@
-import { nameof } from "@ts-morph/common";
+import { nameof, SyntaxKind } from "@ts-morph/common";
 import { expect } from "chai";
-import { ClassDeclaration, TypeArgumentedNode } from "../../../../compiler";
+import { CallExpression, ClassDeclaration, TypeArgumentedNode } from "../../../../compiler";
 import { getInfoFromText } from "../../testHelpers";
 
 describe("TypeArgumentedNode", () => {
@@ -86,6 +86,29 @@ describe("TypeArgumentedNode", () => {
     it("should add a type arg", () => {
       doTest("@dec<1, 2>()\nclass T {}", "3", "@dec<1, 2, 3>()\nclass T {}");
     });
+
+    // Issue #1228: addTypeArgument crashes on property access expressions
+    describe("property access expressions", () => {
+      function doTestPropertyAccess(code: string, text: string, expectedCode: string) {
+        const { sourceFile } = getInfoFromText(code);
+        const callExpr = sourceFile.getDescendantsOfKind(SyntaxKind.CallExpression)[0];
+        const result = callExpr.addTypeArgument(text);
+        expect(result.getText()).to.equal(text);
+        expect(sourceFile.getFullText()).to.equal(expectedCode);
+      }
+
+      it("should add type argument to property access on this", () => {
+        doTestPropertyAccess("this.foo();", "string", "this.foo<string>();");
+      });
+
+      it("should add type argument to property access on constructor", () => {
+        doTestPropertyAccess("new Test().foo();", "string", "new Test().foo<string>();");
+      });
+
+      it("should add type argument to property access on object", () => {
+        doTestPropertyAccess("obj.method();", "string", "obj.method<string>();");
+      });
+    });
   });
 
   describe(nameof<TypeArgumentedNode>("removeTypeArgument"), () => {