Fix separator-printing when skipping zero-fields

Also, incorporate more tests

example_test.go

@@ -10,18 +10,17 @@ func Example() {
 		a, b int
 	}
 	var x = []myType{{1, 2}, {3, 4}, {5, 6}}
-	fmt.Printf("%# v", pretty.Formatter(x))
+	fmt.Printf("%# v\n", pretty.Formatter(x))
+
+	var zeroedFields = []myType{{33, 0}, {a: 0, b: 34}}
+	// Note the '+' in the format
+	fmt.Printf("%# +v", pretty.Formatter(zeroedFields))
 	// output:
 	// []pretty_test.myType{
 	//     {a:1, b:2},
 	//     {a:3, b:4},
 	//     {a:5, b:6},
 	// }
-
-	var zeroedFields = []myType{{33, 0}, {a: 0, b: 34}}
-	// Note the '+' in the format
-	fmt.Printf("%# +v", pretty.Formatter(zeroedFields))
-	// output:
 	// []pretty_test.myType{
 	//     {a:33},
 	//     {b:34},

formatter.go

@@ -178,24 +178,35 @@ func (p *printer) printValue(v reflect.Value, showType, quote bool) {
 				writeByte(p, '\n')
 				pp = p.indent()
 			}
+			type field struct {
+				name  string
+				t     reflect.Type
+				value reflect.Value
+			}
+			fields := make([]field, 0, v.NumField())
+			// Collect fields, filtering out zero fields if needed
 			for i := 0; i < v.NumField(); i++ {
-				fValue := getField(v, i)
-				if p.skipZeroFields && !nonzero(fValue) {
+				value := getField(v, i)
+				if p.skipZeroFields && !nonzero(value) {
 					continue
 				}
+				f := t.Field(i)
+				fields = append(fields, field{f.Name, f.Type, value})
+			}
+			for i, field := range fields {
 				showTypeInStruct := true
-				if f := t.Field(i); f.Name != "" {
-					io.WriteString(pp, f.Name)
+				if field.name != "" {
+					io.WriteString(pp, field.name)
 					writeByte(pp, ':')
 					if expand {
 						writeByte(pp, '\t')
 					}
-					showTypeInStruct = labelType(f.Type)
+					showTypeInStruct = labelType(field.t)
 				}
-				pp.printValue(fValue, showTypeInStruct, true)
+				pp.printValue(field.value, showTypeInStruct, true)
 				if expand {
 					io.WriteString(pp, ",\n")
-				} else if i < v.NumField()-1 {
+				} else if i < len(fields)-1 {
 					io.WriteString(pp, ", ")
 				}
 			}

formatter_test.go

@@ -218,6 +218,22 @@ var gosyntaxSkipZeroFields = []test{
     otherLongFieldName: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
 }`,
 	},
+	{
+		LongStructTypeName{
+			longFieldName:      long,
+			otherLongFieldName: "",
+		},
+		`pretty.LongStructTypeName{
+    longFieldName: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
+}`,
+	},
+	{
+		LongStructTypeName{
+			longFieldName:      "",
+			otherLongFieldName: "",
+		},
+		`pretty.LongStructTypeName{}`,
+	},
 	{
 		&LongStructTypeName{
 			longFieldName:      &LongStructTypeName{},
@@ -249,12 +265,16 @@ var gosyntaxSkipZeroFields = []test{
 			LongStructTypeName{nil, nil},
 			[]byte{1, 2, 3},
 			T{3, 4},
+			T{0, 4},
+			T{3, 0},
 			LongStructTypeName{long, nil},
 		},
 		`[]interface {}{
     pretty.LongStructTypeName{},
     []uint8{0x1, 0x2, 0x3},
     pretty.T{x:3, y:4},
+    pretty.T{y:4},
+    pretty.T{x:3},
     pretty.LongStructTypeName{
         longFieldName: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789",
     },