Add map[string]struct{} support

Empty structs used as map values would generate invalid code.

Fixes #298

_generated/def.go

@@ -46,27 +46,31 @@ type TestType struct {
 		ValueA string `msg:"value_a"`
 		ValueB []byte `msg:"value_b"`
 	} `msg:"object"`
-	Child      *TestType   `msg:"child"`
-	Time       time.Time   `msg:"time"`
-	Any        interface{} `msg:"any"`
-	Appended   msgp.Raw    `msg:"appended"`
-	Num        msgp.Number `msg:"num"`
-	Byte       byte
-	Rune       rune
-	RunePtr    *rune
-	RunePtrPtr **rune
-	RuneSlice  []rune
-	Slice1     []string
-	Slice2     []string
-	SlicePtr   *[]string
+	Child           *TestType   `msg:"child"`
+	Time            time.Time   `msg:"time"`
+	Any             interface{} `msg:"any"`
+	Appended        msgp.Raw    `msg:"appended"`
+	Num             msgp.Number `msg:"num"`
+	Byte            byte
+	Rune            rune
+	RunePtr         *rune
+	RunePtrPtr      **rune
+	RuneSlice       []rune
+	Slice1          []string
+	Slice2          []string
+	SlicePtr        *[]string
+	MapStringEmpty  map[string]struct{}
+	MapStringEmpty2 map[string]EmptyStruct
 }
 
 //msgp:tuple Object
 type Object struct {
-	ObjectNo string   `msg:"objno"`
-	Slice1   []string `msg:"slice1"`
-	Slice2   []string `msg:"slice2"`
-	MapMap   map[string]map[string]string
+	ObjectNo        string   `msg:"objno"`
+	Slice1          []string `msg:"slice1"`
+	Slice2          []string `msg:"slice2"`
+	MapMap          map[string]map[string]string
+	MapStringEmpty  map[string]struct{}
+	MapStringEmpty2 map[string]EmptyStruct
 }
 
 //msgp:tuple TestBench
@@ -266,8 +270,11 @@ type NonMsgStructTags struct {
 		B          string   `json:"b"`
 		C          []string `json:"c"`
 		VeryNested []struct {
-			A []string `json:"a"`
-			B []string `msg:"bbbb" xml:"-"`
+			A []string            `json:"a"`
+			B []string            `msg:"bbbb" xml:"-"`
+			C map[string]struct{} `msg:"cccc"`
 		}
 	}
 }
+
+type EmptyStruct struct{}

_generated/gen_test.go

@@ -68,6 +68,15 @@ func (a *TestType) Equal(b *TestType) bool {
 	if !bytes.Equal(aa, ab) {
 		return false
 	}
+	if len(a.MapStringEmpty) == 0 && len(b.MapStringEmpty) == 0 {
+		a.MapStringEmpty = nil
+		b.MapStringEmpty = nil
+	}
+	if len(a.MapStringEmpty2) == 0 && len(b.MapStringEmpty2) == 0 {
+		a.MapStringEmpty2 = nil
+		b.MapStringEmpty2 = nil
+	}
+
 	a.Time, b.Time = time.Time{}, time.Time{}
 	aa, ab = nil, nil
 	ok := reflect.DeepEqual(a, b)
@@ -97,9 +106,11 @@ func Test1EncodeDecode(t *testing.T) {
 			ValueA: "here's the first inner value",
 			ValueB: []byte("here's the second inner value"),
 		},
-		Child:    nil,
-		Time:     time.Now(),
-		Appended: msgp.Raw([]byte{}), // 'nil'
+		Child:           nil,
+		Time:            time.Now(),
+		Appended:        msgp.Raw([]byte{}), // 'nil'
+		MapStringEmpty:  map[string]struct{}{"Key": {}, "Key2": {}},
+		MapStringEmpty2: map[string]EmptyStruct{"Key3": {}, "Key4": {}},
 	}
 
 	var buf bytes.Buffer
@@ -117,8 +128,8 @@ func Test1EncodeDecode(t *testing.T) {
 	}
 
 	if !tt.Equal(tnew) {
-		t.Logf("in: %v", tt)
-		t.Logf("out: %v", tnew)
+		t.Logf("in:  %#v", tt)
+		t.Logf("out: %#v", tnew)
 		t.Fatal("objects not equal")
 	}
 

gen/decode.go

@@ -197,6 +197,7 @@ func (d *decodeGen) gMap(m *Map) {
 
 	// for element in map, read string/value
 	// pair and assign
+	d.needsField()
 	d.p.printf("\nfor %s > 0 {\n%s--", sz, sz)
 	d.p.declare(m.Keyidx, "string")
 	d.p.declare(m.Validx, m.Value.TypeName())

gen/encode.go

@@ -175,6 +175,7 @@ func (e *encodeGen) structmap(s *Struct) {
 		e.p.printf("\n// map header, size %d", nfields)
 		e.Fuse(data)
 		if len(s.Fields) == 0 {
+			e.p.printf("\n_ = %s", s.vname)
 			e.fuseHook()
 		}
 

gen/marshal.go

@@ -170,6 +170,7 @@ func (m *marshalGen) mapstruct(s *Struct) {
 		m.p.printf("\n// map header, size %d", len(s.Fields))
 		m.Fuse(data)
 		if len(s.Fields) == 0 {
+			m.p.printf("\n_ = %s", s.vname)
 			m.fuseHook()
 		}
 

gen/unmarshal.go

@@ -208,6 +208,10 @@ func (u *unmarshalGen) gMap(m *Map) {
 	// allocate or clear map
 	u.p.resizeMap(sz, m)
 
+	// We likely need a field.
+	// Add now to not be inside for scope.
+	u.needsField()
+
 	// loop and get key,value
 	u.p.printf("\nfor %s > 0 {", sz)
 	u.p.printf("\nvar %s string; var %s %s; %s--", m.Keyidx, m.Validx, m.Value.TypeName(), sz)