go/types: allow conversion from slice to array ptr

These match the changes to cmd/compile/internal/types2 in CL 301650.

Updates #395

Change-Id: I1e85b6355c8c8fdba0996c26a2505c65fab908d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/301651
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/types/api_test.go

@@ -1430,6 +1430,9 @@ func TestConvertibleTo(t *testing.T) {
 		{newDefined(new(Struct)), new(Struct), true},
 		{newDefined(Typ[Int]), new(Struct), false},
 		{Typ[UntypedInt], Typ[Int], true},
+		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Int], 10)), true},
+		{NewSlice(Typ[Int]), NewArray(Typ[Int], 10), false},
+		{NewSlice(Typ[Int]), NewPointer(NewArray(Typ[Uint], 10)), false},
 		// Untyped string values are not permitted by the spec, so the below
 		// behavior is undefined.
 		{Typ[UntypedString], Typ[String], true},

src/go/types/conversions.go

@@ -133,6 +133,18 @@ func (x *operand) convertibleTo(check *Checker, T Type) bool {
 		return true
 	}
 
+	// "x is a slice, T is a pointer-to-array type,
+	// and the slice and array types have identical element types."
+	if s := asSlice(V); s != nil {
+		if p := asPointer(T); p != nil {
+			if a := asArray(p.Elem()); a != nil {
+				if check.identical(s.Elem(), a.Elem()) {
+					return true
+				}
+			}
+		}
+	}
+
 	return false
 }
 

src/go/types/stdlib_test.go

@@ -163,10 +163,6 @@ func TestStdTest(t *testing.T) {
 		"embedfunc.go",   // tests //go:embed
 		"embedvers.go",   // tests //go:embed
 		"linkname2.go",   // go/types doesn't check validity of //go:xxx directives
-
-		"convert2.go",     // temporary: go/types doesn't know yet about converting from slices to array pointers
-		"convert4.go",     // temporary: go/types doesn't know yet about converting from slices to array pointers
-		"escape_slice.go", // temporary: go/types doesn't know yet about converting from slices to array pointers
 	)
 }