The new [iter] package provides the basic definitions for working with
user-defined iterators.

The [slices] package adds several functions that work with iterators:
- [All](/pkg/slices#All) returns an iterator over slice indexes and values.
- [Values](/pkg/slices#Values) returns an iterator over slice elements.
- [Backward](/pkg/slices#Backward) returns an iterator that loops over
  a slice backward.

package types2

import (
	"cmd/compile/internal/syntax"
	"fmt"
)

// This file should not be copied to go/types.  See go.dev/issue/67477

// RenameResult takes an array of (result) fields and an index, and if the indexed field
// does not have a name and if the result in the signature also does not have a name,
// then the signature and field are renamed to
//
//	fmt.Sprintf("#rv%d", i+1)`
//

	auxInt8                   // auxInt is an 8-bit integer
	auxInt16                  // auxInt is a 16-bit integer
	auxInt32                  // auxInt is a 32-bit integer
	auxInt64                  // auxInt is a 64-bit integer
	auxInt128                 // auxInt represents a 128-bit integer.  Always 0.
	auxUInt8                  // auxInt is an 8-bit unsigned integer

// The general forms and their encodings are:
//
//	sym±offset(symkind)(reg)(index*scale)
//		Memory reference at address &sym(symkind) + offset + reg + index*scale.
//		Any of sym(symkind), ±offset, (reg), (index*scale), and *scale can be omitted.
//		If (reg) and *scale are both omitted, the resulting expression (index) is parsed as (reg).
//		To force a parsing as index*scale, write (index*1).
//		Encoding:
//			type = TYPE_MEM

		return nil
	})
	if err != nil {
		return nil, err
	}
	return encodeModuleBytes(packages), nil
}

// indexPackage indexes the package at the given directory and returns its
// encoded representation. It returns ErrNotIndexed if the package can't
// be indexed.
func indexPackage(modroot, pkgdir string) []byte {
	fsys.Trace("indexPackage", pkgdir)
	p := importRaw(modroot, relPath(pkgdir, modroot))

// locationIDMap is like a map[uint64]*Location, but provides efficiency for
// ids that are densely numbered, which is often the case.
type locationIDMap struct {
	dense  []*Location          // indexed by id for id < len(dense)
	sparse map[uint64]*Location // indexed by id for id >= len(dense)
}

func makeLocationIDMap(n int) locationIDMap {
	return locationIDMap{
		dense:  make([]*Location, n),
		sparse: map[uint64]*Location{},
	}
}

func walkAssignMapRead(init *ir.Nodes, n *ir.AssignListStmt) ir.Node {
	init.Append(ir.TakeInit(n)...)

	r := n.Rhs[0].(*ir.IndexExpr)
	walkExprListSafe(n.Lhs, init)
	r.X = walkExpr(r.X, init)
	r.Index = walkExpr(r.Index, init)
	t := r.X.Type()

	fast := mapfast(t)
	key := mapKeyArg(fast, r, r.Index, false)

	// from:
	//   a,b = m[i]
	// to:
	//   var,b = mapaccess2*(t, m, i)
	//   a = *var
	a := n.Lhs[0]

		case *KeyValueExpr:
			m = n.Value
		case *FuncLit:
			m = n.Body
		case *ParenExpr:
			m = n.X
		case *SelectorExpr:
			m = n.Sel
		case *IndexExpr:
			m = n.Index
		case *SliceExpr:
			for i := len(n.Index) - 1; i >= 0; i-- {
				if x := n.Index[i]; x != nil {
					m = x
					continue
				}
			}
			m = n.X
		case *AssertExpr:
			m = n.Type
		case *TypeSwitchGuard:
			m = n.X

			// These appear to be fine, but they fail the
			// integer constraint below, so okay them here.
			// Sample non-integer conversion: map[string]string -> *uint8
			return v
		}

		if etypesign(from.Kind()) == 0 {
			s.Fatalf("CONVNOP unrecognized non-integer %v -> %v\n", from, to)
			return nil
		}

		// integer, same width, same sign
		return v

	case ir.OCONV:

		}

		if argErr.Index != test.wantAt {
			t.Errorf("Instantiate(%v, %v): error at index %d, want index %d", T, test.targs, argErr.Index, test.wantAt)
		}
	}
}

func TestArgumentErrorUnwrapping(t *testing.T) {
	var err error = &ArgumentError{
		Index: 1,
		Err:   Error{Msg: "test"},
	}
	var e Error
	if !errors.As(err, &e) {