Add support for empty maps or lists

pkg/markers/parse.go

@@ -310,15 +310,17 @@ func guessType(scanner *sc.Scanner, raw string, allowSlice bool) *Argument {
 		// We'll cross that bridge when we get there.
 
 		// look ahead till we can figure out if this is a map or a slice
+		hint = peekNoSpace(subScanner)
 		firstElemType := guessType(subScanner, subRaw, false)
 		if firstElemType.Type == StringType {
 			// might be a map or slice, parse the string and check for colon
 			// (blech, basically arbitrary look-ahead due to raw strings).
 			var keyVal string // just ignore this
 			(&Argument{Type: StringType}).parseString(subScanner, raw, reflect.Indirect(reflect.ValueOf(&keyVal)))
 
-			if subScanner.Scan() == ':' {
+			if token := subScanner.Scan(); token == ':' || hint == '}' {
 				// it's got a string followed by a colon -- it's a map
+				// or an empty map in case of {}
 				return &Argument{
 					Type:     MapType,
 					ItemType: &Argument{Type: AnyType},

pkg/markers/parse_test.go

@@ -190,6 +190,7 @@ var _ = Describe("Parsing", func() {
 		It("should support delimitted slices of delimitted slices", argParseTestCase{arg: sliceOSlice, raw: "{{1,1},{2,3},{5,8}}", output: sliceOSliceOut}.Run)
 
 		It("should support maps", argParseTestCase{arg: Argument{Type: MapType, ItemType: &Argument{Type: StringType}}, raw: "{formal: hello, `informal`: `hi!`}", output: map[string]string{"formal": "hello", "informal": "hi!"}}.Run)
+		It("should work with empty maps (which are equal to empty lists in the output)", argParseTestCase{arg: Argument{Type: MapType, ItemType: &Argument{Type: StringType}}, raw: "{}", output: map[string]string{}}.Run)
 
 		Context("with any value", func() {
 			anyArg := Argument{Type: AnyType}