[dev.typeparams] cmd/compile/internal/types2: minor cleanup of writeTParamList

Change-Id: Iaa58b17ad65e93548bb3da8231e0cb6da0c48105
Reviewed-on: https://go-review.googlesource.com/c/go/+/339903
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

2 files changed, 14 insertions, 10 deletions

diff --git a/src/cmd/compile/internal/types2/infer.go b/src/cmd/compile/internal/types2/infer.go
index a3772aa713..ff4bb3ea17 100644
--- a/src/cmd/compile/internal/types2/infer.go
+++ b/src/cmd/compile/internal/types2/infer.go
@@ -83,7 +83,7 @@ func (check *Checker) infer(pos syntax.Pos, tparams []*TypeName, targs []Type, p
 
 	// Substitute type arguments for their respective type parameters in params,
 	// if any. Note that nil targs entries are ignored by check.subst.
-	// TODO(gri) Can we avoid this (we're setting known type argumemts below,
+	// TODO(gri) Can we avoid this (we're setting known type arguments below,
 	//           but that doesn't impact the isParameterized check for now).
 	if params.Len() > 0 {
 		smap := makeSubstMap(tparams, targs)
diff --git a/src/cmd/compile/internal/types2/typestring.go b/src/cmd/compile/internal/types2/typestring.go
index b3675424a5..ead17ba2f3 100644
--- a/src/cmd/compile/internal/types2/typestring.go
+++ b/src/cmd/compile/internal/types2/typestring.go
@@ -246,23 +246,27 @@ func writeTParamList(buf *bytes.Buffer, list []*TypeName, qf Qualifier, visited
 	buf.WriteString("[")
 	var prev Type
 	for i, p := range list {
-		// TODO(gri) support 'any' sugar here.
-		var b Type = &emptyInterface
-		if t, _ := p.typ.(*TypeParam); t != nil && t.bound != nil {
-			b = t.bound
+		// Determine the type parameter and its constraint.
+		// list is expected to hold type parameter names,
+		// but don't crash if that's not the case.
+		tpar, _ := p.typ.(*TypeParam)
+		var bound Type
+		if tpar != nil {
+			bound = tpar.bound // should not be nil but we want to see it if it is
 		}
+
 		if i > 0 {
-			if b != prev {
-				// type bound changed - write previous one before advancing
+			if bound != prev {
+				// bound changed - write previous one before advancing
 				buf.WriteByte(' ')
 				writeType(buf, prev, qf, visited)
 			}
 			buf.WriteString(", ")
 		}
-		prev = b
+		prev = bound
 
-		if t, _ := p.typ.(*TypeParam); t != nil {
-			writeType(buf, t, qf, visited)
+		if tpar != nil {
+			writeType(buf, tpar, qf, visited)
 		} else {
 			buf.WriteString(p.name)
 		}