cmd/cloner: simplify code

Change from a single-case type switch to a type assertion
with an early return.

That exposes that the name arg to gen is unneeded.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

cmd/cloner/cloner.go

@@ -85,7 +85,7 @@ func main() {
 						continue
 					}
 					pkg := typeNameObj.Pkg()
-					gen(buf, imports, typeName, typ, pkg)
+					gen(buf, imports, typ, pkg)
 					found = true
 				}
 			}
@@ -150,7 +150,7 @@ package %s
 
 `
 
-func gen(buf *bytes.Buffer, imports map[string]struct{}, name string, typ *types.Named, thisPkg *types.Package) {
+func gen(buf *bytes.Buffer, imports map[string]struct{}, typ *types.Named, thisPkg *types.Package) {
 	pkgQual := func(pkg *types.Package) string {
 		if thisPkg == pkg {
 			return ""
@@ -162,8 +162,11 @@ func gen(buf *bytes.Buffer, imports map[string]struct{}, name string, typ *types
 		return types.TypeString(t, pkgQual)
 	}
 
-	switch t := typ.Underlying().(type) {
-	case *types.Struct:
+	t, ok := typ.Underlying().(*types.Struct)
+	if !ok {
+		return
+	}
+
 	name := typ.Obj().Name()
 	fmt.Fprintf(buf, "// Clone makes a deep copy of %s.\n", name)
 	fmt.Fprintf(buf, "// The result aliases no memory with the original.\n")
@@ -245,7 +248,6 @@ func gen(buf *bytes.Buffer, imports map[string]struct{}, name string, typ *types
 
 	buf.Write(codegen.AssertStructUnchanged(t, name, "Clone", thisPkg, imports))
 }
-}
 
 func hasBasicUnderlying(typ types.Type) bool {
 	switch typ.Underlying().(type) {