cmd/compile/internal/types2: implement generic slice expressions

For now, the constraint's underlying type set must be a single
type that is sliceable.

Change-Id: I08b6a2e88fe35e8238a95b3f40dc969689021a0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/354070
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/cmd/compile/internal/types2/index.go b/src/cmd/compile/internal/types2/index.go
index 848a70dea8fd600d18b013f463f02c873cc92089..47a5e50f6275bfec3eacf91fbfe82adce0cae117 100644 (file)
--- a/src/cmd/compile/internal/types2/index.go
+++ b/src/cmd/compile/internal/types2/index.go
@@ -207,7 +207,7 @@ func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
 
        valid := false
        length := int64(-1) // valid if >= 0
-       switch typ := under(x.typ).(type) {
+       switch typ := optype(x.typ).(type) {
        case *Basic:
                if isString(typ) {
                        if e.Full {
@@ -246,11 +246,6 @@ func (check *Checker) sliceExpr(x *operand, e *syntax.SliceExpr) {
        case *Slice:
                valid = true
                // x.typ doesn't change
-
-       case *TypeParam:
-               check.error(x, "generic slice expressions not yet implemented")
-               x.mode = invalid
-               return
        }
 
        if !valid {

diff --git a/src/cmd/compile/internal/types2/testdata/check/typeparams.go2 b/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
index 69b6925b9f019eb795535273056b05ea413e587f..29c25b0bb48b523d446aab2f15965f41d110cfb1 100644 (file)
--- a/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
+++ b/src/cmd/compile/internal/types2/testdata/check/typeparams.go2
@@ -115,9 +115,13 @@ func _[T interface{ [10]byte | string }](x T, i int) { _ = x[i]; _ = x[9]; _ = x
 func _[T interface{ [10]int | *[20]int | []int }](x T, i int) { _ = x[i]; _ = x[9]; _ = x[10 /* ERROR out of bounds */ ] }
 
 // slicing
-// TODO(gri) implement this
 
-func _[T interface{ ~string }] (x T, i, j, k int) { _ = x /* ERROR generic slice expressions not yet implemented */ [i:j:k] }
+func _[T interface{ ~[10]E }, E any] (x T, i, j, k int) { var _ []E = x[i:j] }
+func _[T interface{ ~[10]E }, E any] (x T, i, j, k int) { var _ []E = x[i:j:k] }
+func _[T interface{ ~[]byte }] (x T, i, j, k int) { var _ T = x[i:j] }
+func _[T interface{ ~[]byte }] (x T, i, j, k int) { var _ T = x[i:j:k] }
+func _[T interface{ ~string }] (x T, i, j, k int) { var _ T = x[i:j] }
+func _[T interface{ ~string }] (x T, i, j, k int) { var _ T = x /* ERROR 3-index slice of string */ [i:j:k] }
 
 // len/cap built-ins