From: Robert Griesemer <gri@golang.org>
Date: Tue, 5 Oct 2021 18:45:22 +0000 (-0700)
Subject: go/types: implement generic slice expressions
X-Git-Tag: go1.18beta1~1045
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=7ae83c8f38bc79e999a8657da443d815036c7d72;p=gostls13.git

go/types: implement generic slice expressions

This is a clean port of CL 354070 from types2 to go/types.

Change-Id: I44de1b8e6c0177e2a33e7f36a82465dc520c35aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/354092
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
---

diff --git a/src/go/types/index.go b/src/go/types/index.go
index ca04072f7a..613f6292e4 100644
--- a/src/go/types/index.go
+++ b/src/go/types/index.go
@@ -207,7 +207,7 @@ func (check *Checker) sliceExpr(x *operand, e *ast.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.Slice3 {
@@ -246,11 +246,6 @@ func (check *Checker) sliceExpr(x *operand, e *ast.SliceExpr) {
 	case *Slice:
 		valid = true
 		// x.typ doesn't change
-
-	case *TypeParam:
-		check.errorf(x, _Todo, "generic slice expressions not yet implemented")
-		x.mode = invalid
-		return
 	}
 
 	if !valid {
diff --git a/src/go/types/testdata/check/typeparams.go2 b/src/go/types/testdata/check/typeparams.go2
index bfacb3e1e7..10f84314fd 100644
--- a/src/go/types/testdata/check/typeparams.go2
+++ b/src/go/types/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