Fix: No error when assigning to getter-only static class property from another file

[Copilot]

This PR fixes an issue where TypeScript-Go failed to report errors when assigning to getter-only properties imported from another module.

Problem

// export.ts
export class MyClass {
  static get foo() {
    return 42;
  }
}

// import.ts
import { MyClass } from "./export";
MyClass.foo = 0; // Should be error TS2540, but no error was reported

Expected: Error TS2540: "Cannot assign to 'foo' because it is a read-only property"
Actual: No error reported

Root Cause

Two issues in the assignment checking logic in internal/checker/checker.go:

1. Missing readonly check for simple assignments: checkAssignmentOperator only called checkPropertyAccessExpression with writeOnly=true for compound assignments (+=, -=, etc.), but not for simple assignments (=)

2. Early return for named imports: isAssignmentToReadonlyEntity returned early for named imports instead of checking if the target symbol was readonly

Solution

Minimal 7-line fix with two changes:

1. Added readonly check for simple assignments: Now calls checkPropertyAccessExpression(writeOnly=true) for simple assignments to property access expressions, matching the behavior already implemented for compound assignments

2. Fixed alias handling: Modified isAssignmentToReadonlyEntity to only return early for namespace imports, allowing readonly checks to proceed for named imports

Testing

✅ Cross-file assignments to getter-only properties now correctly report TS2540
✅ Same-file behavior unchanged
✅ Properties with setters work correctly (no error)
✅ Both instance and static properties work
✅ All existing checker tests pass

The fix correctly handles various scenarios:

• Static getter-only properties (main issue)
• Instance getter-only properties
• Properties with both getter and setter (should allow assignment)
• Regular properties (should allow assignment)

Fixes #1094.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[RyanCavanaugh]

Almost but not quite