JSON pretty: empty containers

For the JSON writer in pretty mode ensure that empty objects and array
are printed on the same line.

zio/jsonio/writer.go

@@ -95,47 +95,57 @@ func (w *Writer) writeRecord(tab int, typ *zed.TypeRecord, bytes zcode.Bytes) {
 	tab += w.tab
 	w.punc('{')
 	it := bytes.Iter()
-	for i, f := range typ.Fields {
-		if i != 0 {
+	var k int
+	for ; !it.Done(); k++ {
+		if k != 0 {
 			w.punc(',')
 		}
+		f := typ.Fields[k]
 		w.writeEntry(tab, f.Name, w.arena.New(f.Type, it.Next()))
 	}
-	w.newline()
-	w.indent(tab - w.tab)
+	if k > 0 {
+		w.newline()
+		w.indent(tab - w.tab)
+	}
 	w.punc('}')
 }
 
 func (w *Writer) writeArray(tab int, typ zed.Type, bytes zcode.Bytes) {
 	tab += w.tab
 	w.punc('[')
 	it := bytes.Iter()
-	for i := 0; !it.Done(); i++ {
-		if i != 0 {
+	var k int
+	for ; !it.Done(); k++ {
+		if k != 0 {
 			w.punc(',')
 		}
 		w.newline()
 		w.indent(tab)
 		w.writeAny(tab, w.arena.New(typ, it.Next()))
 	}
-	w.newline()
-	w.indent(tab - w.tab)
+	if k > 0 {
+		w.newline()
+		w.indent(tab - w.tab)
+	}
 	w.punc(']')
 }
 
 func (w *Writer) writeMap(tab int, typ *zed.TypeMap, bytes zcode.Bytes) {
 	tab += w.tab
 	w.punc('{')
 	it := bytes.Iter()
-	for i := 0; !it.Done(); i++ {
-		if i != 0 {
+	var k int
+	for ; !it.Done(); k++ {
+		if k != 0 {
 			w.punc(',')
 		}
 		key := mapKey(typ.KeyType, it.Next())
 		w.writeEntry(tab, key, w.arena.New(typ.ValType, it.Next()))
 	}
-	w.newline()
-	w.indent(tab - w.tab)
+	if k > 0 {
+		w.newline()
+		w.indent(tab - w.tab)
+	}
 	w.punc('}')
 }
 

zio/jsonio/ztests/pretty.yaml

@@ -8,6 +8,9 @@ input: |
     f4: "a string",
     f5: [1,2,3],
     f6: {foo: "bar"},
+    f7: {},
+    f8: |{}|,
+    f9: [],
   }
 
 output-flags: -f json -pretty 4
@@ -25,5 +28,8 @@ output: |
       ],
       "f6": {
           "foo": "bar"
-      }
+      },
+      "f7": {},
+      "f8": {},
+      "f9": []
   }