cmd/compile,go/types: restrict use of unsafe.{Add,Slice} to go1.17 or newer

This CL updates cmd/compile (including types2) and go/types to report
errors about using unsafe.Add and unsafe.Slice when language
compatibility is set to Go 1.16 or older.

Fixes #46525.

Change-Id: I1bfe025a672d9f4b929f443064ad1effd38d0363
Reviewed-on: https://go-review.googlesource.com/c/go/+/324369
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/typecheck/func.go

@@ -981,6 +981,12 @@ func tcRecover(n *ir.CallExpr) ir.Node {
 
 // tcUnsafeAdd typechecks an OUNSAFEADD node.
 func tcUnsafeAdd(n *ir.BinaryExpr) *ir.BinaryExpr {
+	if !types.AllowsGoVersion(curpkg(), 1, 17) {
+		base.ErrorfVers("go1.17", "unsafe.Add")
+		n.SetType(nil)
+		return n
+	}
+
 	n.X = AssignConv(Expr(n.X), types.Types[types.TUNSAFEPTR], "argument to unsafe.Add")
 	n.Y = DefaultLit(Expr(n.Y), types.Types[types.TINT])
 	if n.X.Type() == nil || n.Y.Type() == nil {
@@ -997,6 +1003,12 @@ func tcUnsafeAdd(n *ir.BinaryExpr) *ir.BinaryExpr {
 
 // tcUnsafeSlice typechecks an OUNSAFESLICE node.
 func tcUnsafeSlice(n *ir.BinaryExpr) *ir.BinaryExpr {
+	if !types.AllowsGoVersion(curpkg(), 1, 17) {
+		base.ErrorfVers("go1.17", "unsafe.Slice")
+		n.SetType(nil)
+		return n
+	}
+
 	n.X = Expr(n.X)
 	n.Y = Expr(n.Y)
 	if n.X.Type() == nil || n.Y.Type() == nil {

src/cmd/compile/internal/types2/builtins.go

@@ -579,6 +579,11 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 	case _Add:
 		// unsafe.Add(ptr unsafe.Pointer, len IntegerType) unsafe.Pointer
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.error(call.Fun, "unsafe.Add requires go1.17 or later")
+			return
+		}
+
 		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
 		if x.mode == invalid {
 			return
@@ -675,6 +680,11 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
 
 	case _Slice:
 		// unsafe.Slice(ptr *T, len IntegerType) []T
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.error(call.Fun, "unsafe.Slice requires go1.17 or later")
+			return
+		}
+
 		typ := asPointer(x.typ)
 		if typ == nil {
 			check.errorf(x, invalidArg+"%s is not a pointer", x)

src/go/types/builtins.go

@@ -588,6 +588,11 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 
 	case _Add:
 		// unsafe.Add(ptr unsafe.Pointer, len IntegerType) unsafe.Pointer
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.errorf(call.Fun, _InvalidUnsafeAdd, "unsafe.Add requires go1.17 or later")
+			return
+		}
+
 		check.assignment(x, Typ[UnsafePointer], "argument to unsafe.Add")
 		if x.mode == invalid {
 			return
@@ -684,6 +689,11 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
 
 	case _Slice:
 		// unsafe.Slice(ptr *T, len IntegerType) []T
+		if !check.allowVersion(check.pkg, 1, 17) {
+			check.errorf(call.Fun, _InvalidUnsafeSlice, "unsafe.Slice requires go1.17 or later")
+			return
+		}
+
 		typ := asPointer(x.typ)
 		if typ == nil {
 			check.invalidArg(x, _InvalidUnsafeSlice, "%s is not a pointer", x)

test/fixedbugs/issue46525.go

@@ -0,0 +1,14 @@
+// errorcheck -lang=go1.16
+
+// Copyright 2021 The Go Authors. All rights reserved.  Use of this
+// source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+package p
+
+import "unsafe"
+
+func main() {
+	_ = unsafe.Add(unsafe.Pointer(nil), 0) // ERROR "unsafe.Add requires go1.17 or later"
+	_ = unsafe.Slice(new(byte), 1)         // ERROR "unsafe.Slice requires go1.17 or later"
+}