Merge pull request #25 from modern-go/fix-go1.18

WIP: update signature of mapiterinit of go 1.18

go.mod

@@ -0,0 +1,3 @@
+module github.com/modern-go/reflect2
+
+go 1.12

go_above_118.go

@@ -0,0 +1,23 @@
+//+build go1.18
+
+package reflect2
+
+import (
+	"unsafe"
+)
+
+// m escapes into the return value, but the caller of mapiterinit
+// doesn't let the return value escape.
+//go:noescape
+//go:linkname mapiterinit reflect.mapiterinit
+func mapiterinit(rtype unsafe.Pointer, m unsafe.Pointer, it *hiter)
+
+func (type2 *UnsafeMapType) UnsafeIterate(obj unsafe.Pointer) MapIterator {
+	var it hiter
+	mapiterinit(type2.rtype, *(*unsafe.Pointer)(obj), &it)
+	return &UnsafeMapIterator{
+		hiter:      &it,
+		pKeyRType:  type2.pKeyRType,
+		pElemRType: type2.pElemRType,
+	}
+}

go_below_118.go

@@ -0,0 +1,21 @@
+//+build !go1.18
+
+package reflect2
+
+import (
+	"unsafe"
+)
+
+// m escapes into the return value, but the caller of mapiterinit
+// doesn't let the return value escape.
+//go:noescape
+//go:linkname mapiterinit reflect.mapiterinit
+func mapiterinit(rtype unsafe.Pointer, m unsafe.Pointer) (val *hiter)
+
+func (type2 *UnsafeMapType) UnsafeIterate(obj unsafe.Pointer) MapIterator {
+	return &UnsafeMapIterator{
+		hiter:      mapiterinit(type2.rtype, *(*unsafe.Pointer)(obj)),
+		pKeyRType:  type2.pKeyRType,
+		pElemRType: type2.pElemRType,
+	}
+}

unsafe_link.go

@@ -19,18 +19,12 @@ func typedslicecopy(elemType unsafe.Pointer, dst, src sliceHeader) int
 
 //go:linkname mapassign reflect.mapassign
 //go:noescape
-func mapassign(rtype unsafe.Pointer, m unsafe.Pointer, key, val unsafe.Pointer)
+func mapassign(rtype unsafe.Pointer, m unsafe.Pointer, key unsafe.Pointer, val unsafe.Pointer)
 
 //go:linkname mapaccess reflect.mapaccess
 //go:noescape
 func mapaccess(rtype unsafe.Pointer, m unsafe.Pointer, key unsafe.Pointer) (val unsafe.Pointer)
 
-// m escapes into the return value, but the caller of mapiterinit
-// doesn't let the return value escape.
-//go:noescape
-//go:linkname mapiterinit reflect.mapiterinit
-func mapiterinit(rtype unsafe.Pointer, m unsafe.Pointer) *hiter
-
 //go:noescape
 //go:linkname mapiternext reflect.mapiternext
 func mapiternext(it *hiter)
@@ -42,9 +36,21 @@ func ifaceE2I(rtype unsafe.Pointer, src interface{}, dst unsafe.Pointer)
 // If you modify hiter, also change cmd/internal/gc/reflect.go to indicate
 // the layout of this structure.
 type hiter struct {
-	key   unsafe.Pointer // Must be in first position.  Write nil to indicate iteration end (see cmd/internal/gc/range.go).
-	value unsafe.Pointer // Must be in second position (see cmd/internal/gc/range.go).
-	// rest fields are ignored
+	key         unsafe.Pointer
+	value       unsafe.Pointer
+	t           unsafe.Pointer
+	h           unsafe.Pointer
+	buckets     unsafe.Pointer
+	bptr        unsafe.Pointer
+	overflow    *[]unsafe.Pointer
+	oldoverflow *[]unsafe.Pointer
+	startBucket uintptr
+	offset      uint8
+	wrapped     bool
+	B           uint8
+	i           uint8
+	bucket      uintptr
+	checkBucket uintptr
 }
 
 // add returns p+x.

unsafe_map.go

@@ -107,14 +107,6 @@ func (type2 *UnsafeMapType) Iterate(obj interface{}) MapIterator {
 	return type2.UnsafeIterate(objEFace.data)
 }
 
-func (type2 *UnsafeMapType) UnsafeIterate(obj unsafe.Pointer) MapIterator {
-	return &UnsafeMapIterator{
-		hiter:      mapiterinit(type2.rtype, *(*unsafe.Pointer)(obj)),
-		pKeyRType:  type2.pKeyRType,
-		pElemRType: type2.pElemRType,
-	}
-}
-
 type UnsafeMapIterator struct {
 	*hiter
 	pKeyRType  unsafe.Pointer