cmd/compile: rename newNamedTypeWithSym, add some commemnts

Renamed newNamedTypeWithSym to newIncompleteNamedType. Added some extra
comments to types.NewNamed and types.SetUnderlying.

Change-Id: Idc5a6379991c26b429d91bae9fe1adef8457a75c
Reviewed-on: https://go-review.googlesource.com/c/go/+/307029
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Ingo Oeser <nightlyone@googlemail.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/types/type.go b/src/cmd/compile/internal/types/type.go
index 31a99781d1..762cdd3258 100644
--- a/src/cmd/compile/internal/types/type.go
+++ b/src/cmd/compile/internal/types/type.go
@@ -1643,7 +1643,10 @@ var (
 	TypeResultMem = newResults([]*Type{TypeMem})
 )
 
-// NewNamed returns a new named type for the given type name. obj should be an ir.Name.
+// NewNamed returns a new named type for the given type name. obj should be an
+// ir.Name. The new type is incomplete, and the underlying type should be set
+// later via SetUnderlying(). References to the type are maintained until the type
+// is filled in, so those references can be updated when the type is complete.
 func NewNamed(obj Object) *Type {
 	t := New(TFORW)
 	t.sym = obj.Sym()
@@ -1659,7 +1662,8 @@ func (t *Type) Obj() Object {
 	return nil
 }
 
-// SetUnderlying sets the underlying type.
+// SetUnderlying sets the underlying type. SetUnderlying automatically updates any
+// types that were waiting for this type to be completed.
 func (t *Type) SetUnderlying(underlying *Type) {
 	if underlying.kind == TFORW {
 		// This type isn't computed yet; when it is, update n.