unexpect panic:Embedded type's unexported interface methods have nil function pointers

[luoliwoshang]

Summary

When a type embeds another type from a different package to implement an interface that has unexported methods, the interface method table (itab) contains nil function pointers for those unexported methods. This causes a runtime panic when the interface method is called.

Root Cause

In ssa/abitype.go:426-434, when generating the method table for a type, unexported methods from other packages have their Ifn_ (interface function pointer) set to nil:

if !token.IsExported(mName) {
    name = b.Str(abi.FullName(mPkg, mName)).impl
    skipfn = PathOf(mPkg) != pkgPath  // true when method is from another package
}
// ...
if skipfn {
    tfn = prog.Nil(prog.VoidPtr()).impl
    ifn = tfn  // nil!
}

This means when go/types.(*Scope).Insert calls obj.setParent(s) (an unexported interface method), it attempts to call a nil function pointer.

Minimal Reproduction

package main

import (
      "go/token"
      "go/types"
)

// wrappedFunc embeds *types.Func to implement types.Object
type wrappedFunc struct {
      *types.Func
}

func main() {
      pkg := types.NewPackage("test", "test")
      scope := pkg.Scope()

      // Create a types.Func
      sig := types.NewSignatureType(nil, nil, nil, nil, nil, false)
      fn := types.NewFunc(token.NoPos, pkg, "testFunc", sig)

      // Wrap it
      wrapped := &wrappedFunc{Func: fn}

      // Convert to types.Object interface
      var obj types.Object = wrapped

      // This crashes because setParent (unexported method) has nil function pointer
      scope.Insert(obj)

      println("OK")
}

Steps to Reproduce

llgo run main.go

Expected Behavior

Program prints "OK" and exits normally.

Actual Behavior

panic: runtime error: invalid memory address or nil pointer dereference

[... go/types.(*Scope).Insert+0x18 ...]

Analysis

The types.Object interface has 17 methods (8 exported + 9 unexported). When *wrappedFunc implements this interface through embedding *types.Func:

• Exported methods (Name, String, etc.): Work correctly, have valid function pointers
• Unexported methods (setParent, setType, etc.): Have Ifn_ = 0x0 because they're from go/types package

When scope.Insert(obj) internally calls obj.setParent(s), it reads the nil function pointer from the itab and crashes.

Environment

• llgo version: latest main branch
• Go version: 1.24
• OS: macOS (arm64)