[dev.typeparams] cmd/compile/internal/syntax: fix printing of channel types

Change-Id: I80a3ca77d0642711913c9584e70059e4ed668860
Reviewed-on: https://go-review.googlesource.com/c/go/+/262444
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

2 files changed, 30 insertions, 6 deletions

diff --git a/src/cmd/compile/internal/syntax/printer.go b/src/cmd/compile/internal/syntax/printer.go
index 8ff3bfa794..c8bf59675a 100644
--- a/src/cmd/compile/internal/syntax/printer.go
+++ b/src/cmd/compile/internal/syntax/printer.go
@@ -484,7 +484,15 @@ func (p *printer) printRawNode(n Node) {
 		if n.Dir == SendOnly {
 			p.print(_Arrow)
 		}
-		p.print(blank, n.Elem)
+		p.print(blank)
+		if e, _ := n.Elem.(*ChanType); n.Dir == 0 && e != nil && e.Dir == RecvOnly {
+			// don't print chan (<-chan T) as chan <-chan T
+			p.print(_Lparen)
+			p.print(n.Elem)
+			p.print(_Rparen)
+		} else {
+			p.print(n.Elem)
+		}
 
 	// statements
 	case *DeclStmt:
diff --git a/src/cmd/compile/internal/syntax/printer_test.go b/src/cmd/compile/internal/syntax/printer_test.go
index c3b9aca229..cae2c40f6c 100644
--- a/src/cmd/compile/internal/syntax/printer_test.go
+++ b/src/cmd/compile/internal/syntax/printer_test.go
@@ -30,12 +30,28 @@ func TestPrint(t *testing.T) {
 	}
 }
 
+var stringTests = []string{
+	"package p",
+	"package p; type _ int; type T1 = struct{}; type ( _ *struct{}; T2 = float32 )",
+
+	// channels
+	"package p; type _ chan chan int",
+	"package p; type _ chan (<-chan int)",
+	"package p; type _ chan chan<- int",
+
+	"package p; type _ <-chan chan int",
+	"package p; type _ <-chan <-chan int",
+	"package p; type _ <-chan chan<- int",
+
+	"package p; type _ chan<- chan int",
+	"package p; type _ chan<- <-chan int",
+	"package p; type _ chan<- chan<- int",
+
+	// TODO(gri) expand
+}
+
 func TestPrintString(t *testing.T) {
-	for _, want := range []string{
-		"package p",
-		"package p; type _ = int; type T1 = struct{}; type ( _ = *struct{}; T2 = float32 )",
-		// TODO(gri) expand
-	} {
+	for _, want := range stringTests {
 		ast, err := Parse(nil, strings.NewReader(want), nil, nil, 0)
 		if err != nil {
 			t.Error(err)