cmd/compile/internal/types2: factor out slice elem computation for copy built-in
Implement singleUnder[String] which determines a single underlying type
for a given type: either the underlying type, or the single underlying
type for a type parameter, if it exists. Use singleUnder[String] instead
of optype for copy built-in.
This CL removes a dependency on optype and also makes the copy built-in
slighty more general for generic arguments (the source argument may be
constrained by a slice or string simultaneously).
Change-Id: Ia329e96afc69a09d2ca3b1f82fe712d4f7ba1d9f
Reviewed-on: https://go-review.googlesource.com/c/go/+/357413
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
diff --git a/src/cmd/compile/internal/types2/builtins.go b/src/cmd/compile/internal/types2/builtins.go
index cb4d93c..154395c 100644
--- a/src/cmd/compile/internal/types2/builtins.go
+++ b/src/cmd/compile/internal/types2/builtins.go
@@ -325,33 +325,22 @@
case _Copy:
// copy(x, y []T) int
- var dst Type
- if t := asSlice(x.typ); t != nil {
- dst = t.elem
- }
+ dst, _ := singleUnder(x.typ).(*Slice)
var y operand
arg(&y, 1)
if y.mode == invalid {
return
}
- var src Type
- switch t := optype(y.typ).(type) {
- case *Basic:
- if isString(y.typ) {
- src = universeByte
- }
- case *Slice:
- src = t.elem
- }
+ src, _ := singleUnderString(y.typ).(*Slice)
if dst == nil || src == nil {
check.errorf(x, invalidArg+"copy expects slice arguments; found %s and %s", x, &y)
return
}
- if !Identical(dst, src) {
- check.errorf(x, invalidArg+"arguments to copy %s and %s have different element types %s and %s", x, &y, dst, src)
+ if !Identical(dst.elem, src.elem) {
+ check.errorf(x, invalidArg+"arguments to copy %s and %s have different element types %s and %s", x, &y, dst.elem, src.elem)
return
}
@@ -774,6 +763,46 @@
return true
}
+// If typ is a type parameter, single under returns the single underlying
+// type of all types in the corresponding type constraint if it exists, or
+// nil if it doesn't exist. If typ is not a type parameter, singleUnder
+// just returns the underlying type.
+func singleUnder(typ Type) Type {
+ var su Type
+ if underIs(typ, func(u Type) bool {
+ if su != nil && !Identical(su, u) {
+ return false
+ }
+ // su == nil || Identical(su, u)
+ su = u
+ return true
+ }) {
+ return su
+ }
+ return nil
+}
+
+// singleUnderString is like singleUnder but also considers []byte and
+// string as "identical". In this case, if successful, the result is always
+// []byte.
+func singleUnderString(typ Type) Type {
+ var su Type
+ if underIs(typ, func(u Type) bool {
+ if isString(u) {
+ u = NewSlice(universeByte)
+ }
+ if su != nil && !Identical(su, u) {
+ return false
+ }
+ // su == nil || Identical(su, u)
+ su = u
+ return true
+ }) {
+ return su
+ }
+ return nil
+}
+
// hasVarSize reports if the size of type t is variable due to type parameters.
func hasVarSize(t Type) bool {
switch t := under(t).(type) {
diff --git a/src/cmd/compile/internal/types2/testdata/check/builtins.go2 b/src/cmd/compile/internal/types2/testdata/check/builtins.go2
index 243e888..8376440 100644
--- a/src/cmd/compile/internal/types2/testdata/check/builtins.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/builtins.go2
@@ -78,8 +78,14 @@
func _[T ~[]byte|~string](x T, y []byte) {
copy(x /* ERROR expects slice arguments */ , y)
- // TODO(gri) should this be valid?
- copy(y /* ERROR expects slice arguments */ , x)
+ copy(y, x)
+}
+
+type L0 []int
+type L1 []int
+
+func _[T L0 | L1](x, y T) {
+ copy(x, y)
}
// delete
