go/types, types2: implement type checking of "clear" built-in

Will become available with Go 1.21. Recognizing the `clear` built-in early is not causing any problems: if existing code defines a `clear`, that will be used as before. If code doesn't define `clear` the error message will make it clear that with 1.21 the function will be available. It's still possible to define a local `clear` and get rid of the error; but more likely the name choice should be avoided going forward, so this provides a useful early "heads-up". For #56351. Change-Id: I3d0fb1eb3508fbc78d7514b6238eac89610158c9 Reviewed-on: https://go-review.googlesource.com/c/go/+/448076 Run-TryBot: Robert Griesemer <[email protected]> TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Robert Findley <[email protected]> Reviewed-by: Robert Griesemer <[email protected]> Auto-Submit: Robert Griesemer <[email protected]>
cloudflare · Nov 17, 2022 · 5c834a2 · 5c834a2
1 parent cafb49a
commit 5c834a2
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diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
@@ -232,6 +232,33 @@ func (check *Checker) builtin(x *operand, call *syntax.CallExpr, id builtinId) (
  x.typ = Typ[Int]
  x.val = val
 
+ case _Clear:
+ // clear(m)
+ if !check.allowVersion(check.pkg, 1, 21) {
+ check.versionErrorf(call.Fun, "go1.21", "clear")
+ return
+ }
+
+ if !underIs(x.typ, func(u Type) bool {
+ switch u := u.(type) {
+ case *Map, *Slice:
+ return true
+ case *Pointer:
+ if _, ok := under(u.base).(*Array); ok {
+ return true
+ }
+ }
+ check.errorf(x, InvalidClear, invalidArg+"cannot clear %s: argument must be (or constrained by) map, slice, or array pointer", x)
+ return false
+ }) {
+ return
+ }
+
+ x.mode = novalue
+ if check.recordTypes() {
+ check.recordBuiltinType(call.Fun, makeSig(nil, x.typ))
+ }
+
  case _Close:
  // close(c)
  if !underIs(x.typ, func(u Type) bool {

diff --git a/src/cmd/compile/internal/types2/builtins_test.go b/src/cmd/compile/internal/types2/builtins_test.go
@@ -41,6 +41,11 @@ var builtinCalls = []struct {
  {"len", `type S []byte; var s S; _ = len(s)`, `func(p.S) int`},
  {"len", `var s P; _ = len(s)`, `func(P) int`},
 
+ {"clear", `var m map[float64]int; clear(m)`, `func(map[float64]int)`},
+ {"clear", `var s []byte; clear(s)`, `func([]byte)`},
+ {"clear", `var p *[10]int; clear(p)`, `func(*[10]int)`},
+ {"clear", `var s P; clear(s)`, `func(P)`},
+
  {"close", `var c chan int; close(c)`, `func(chan int)`},
  {"close", `var c chan<- chan string; close(c)`, `func(chan<- chan string)`},
 

diff --git a/src/cmd/compile/internal/types2/universe.go b/src/cmd/compile/internal/types2/universe.go
@@ -145,6 +145,7 @@ const (
  // universe scope
  _Append builtinId = iota
  _Cap
+ _Clear
  _Close
  _Complex
  _Copy
@@ -182,6 +183,7 @@ var predeclaredFuncs = [...]struct {
 }{
  _Append: {"append", 1, true, expression},
  _Cap: {"cap", 1, false, expression},
+ _Clear: {"clear", 1, false, statement},
  _Close: {"close", 1, false, statement},
  _Complex: {"complex", 2, false, expression},
  _Copy: {"copy", 2, false, statement},

diff --git a/src/go/types/builtins.go b/src/go/types/builtins.go
@@ -233,6 +233,33 @@ func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ b
  x.typ = Typ[Int]
  x.val = val
 
+ case _Clear:
+ // clear(m)
+ if !check.allowVersion(check.pkg, 1, 21) {
+ check.error(call.Fun, UnsupportedFeature, "clear requires go1.21 or later")
+ return
+ }
+
+ if !underIs(x.typ, func(u Type) bool {
+ switch u := u.(type) {
+ case *Map, *Slice:
+ return true
+ case *Pointer:
+ if _, ok := under(u.base).(*Array); ok {
+ return true
+ }
+ }
+ check.errorf(x, InvalidClear, invalidArg+"cannot clear %s: argument must be (or constrained by) map, slice, or array pointer", x)
+ return false
+ }) {
+ return
+ }
+
+ x.mode = novalue
+ if check.Types != nil {
+ check.recordBuiltinType(call.Fun, makeSig(nil, x.typ))
+ }
+
  case _Close:
  // close(c)
  if !underIs(x.typ, func(u Type) bool {

diff --git a/src/go/types/builtins_test.go b/src/go/types/builtins_test.go
@@ -42,6 +42,11 @@ var builtinCalls = []struct {
  {"len", `type S []byte; var s S; _ = len(s)`, `func(p.S) int`},
  {"len", `var s P; _ = len(s)`, `func(P) int`},
 
+ {"clear", `var m map[float64]int; clear(m)`, `func(map[float64]int)`},
+ {"clear", `var s []byte; clear(s)`, `func([]byte)`},
+ {"clear", `var p *[10]int; clear(p)`, `func(*[10]int)`},
+ {"clear", `var s P; clear(s)`, `func(P)`},
+
  {"close", `var c chan int; close(c)`, `func(chan int)`},
  {"close", `var c chan<- chan string; close(c)`, `func(chan<- chan string)`},
 

diff --git a/src/go/types/universe.go b/src/go/types/universe.go
@@ -146,6 +146,7 @@ const (
  // universe scope
  _Append builtinId = iota
  _Cap
+ _Clear
  _Close
  _Complex
  _Copy
@@ -183,6 +184,7 @@ var predeclaredFuncs = [...]struct {
 }{
  _Append: {"append", 1, true, expression},
  _Cap: {"cap", 1, false, expression},
+ _Clear: {"clear", 1, false, statement},
  _Close: {"close", 1, false, statement},
  _Complex: {"complex", 2, false, expression},
  _Copy: {"copy", 2, false, statement},

diff --git a/src/internal/types/errors/codes.go b/src/internal/types/errors/codes.go
@@ -1430,4 +1430,13 @@ const (
  // InvalidUnsafeStringData occurs if it is used in a package
  // compiled for a language version before go1.20.
  _ // not used anymore
+
+ // InvalidClear occurs when clear is called with an argument
+ // that is not of map, slice, or pointer-to-array type.
+ //
+ // Example:
+ // func _(x int) {
+ // clear(x)
+ // }
+ InvalidClear
 )
diff --git a/src/internal/types/testdata/check/builtins0.go b/src/internal/types/testdata/check/builtins0.go
@@ -139,6 +139,17 @@ func cap3() {
  )
 }
 
+func clear1() {
+ var a [10]int
+ var m map[float64]string
+ var s []byte
+ clear(a /* ERROR cannot clear a */)
+ clear(&a)
+ clear(m)
+ clear(s)
+ clear([]int{})
+}
+
 func close1() {
  var c chan int
  var r <-chan int

diff --git a/src/internal/types/testdata/check/builtins1.go b/src/internal/types/testdata/check/builtins1.go
@@ -8,6 +8,20 @@ package builtins
 
 import "unsafe"
 
+// clear
+
+func _[T any](x T) {
+ clear(x /* ERROR cannot clear x */)
+}
+
+func _[T ~map[int]string | ~[]byte | ~*[10]int](x T) {
+ clear(x)
+}
+
+func _[T ~map[int]string | ~[]byte | ~*[10]int | string](x T) {
+ clear(x /* ERROR cannot clear x */)
+}
+
 // close
 
 type C0 interface{ int }

diff --git a/src/internal/types/testdata/fixedbugs/issue56351.go b/src/internal/types/testdata/fixedbugs/issue56351.go
@@ -0,0 +1,11 @@
+// -lang=go1.20
+
+// Copyright 2022 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
+
+func _(s []int) {
+ clear /* ERROR clear requires go1\.21 or later */ (s)
+}