Support comments in schema (dgraph-io#3133)

* schema/state.go: add comment state to lexer

This adds comment detection to lexer. A comment starts with # and ends with
new line or EOF. When new line is detected, it's emitted so the caller can handle it.
If EOF is found, that should end further parsing.

* schema/parse_test.go: add test for comments in schema types

* gql/parser.go: fixed typo

* schema/state.go: rename func lexComment to lexTextComment

Package gql has another function called lexComment that works slightly
different to this one, so I renamed this one to avoid confusion.

gql/parser.go

@@ -948,7 +948,7 @@ func parseSchemaFields(it *lex.ItemIterator, s *pb.SchemaRequest) error {
 			return item.Errorf("Invalid schema block.")
 		}
 	}
-	return it.Errorf("Expecting }  to end fields list, but none was found")
+	return it.Errorf("Expecting } to end fields list, but none was found")
 }
 
 func getSchema(it *lex.ItemIterator) (*pb.SchemaRequest, error) {

schema/parse_test.go

@@ -526,7 +526,7 @@ func TestParseScalarType(t *testing.T) {
 		type Person {
 			Name: string
 			Nickname: [String]
-			Alive: Bool 
+			Alive: Bool
 		}
 	`)
 	require.NoError(t, err)
@@ -743,6 +743,66 @@ func TestParseTypeErrMissingType(t *testing.T) {
 	require.Contains(t, err.Error(), "Missing field type in type declaration")
 }
 
+func TestParseComments(t *testing.T) {
+	reset()
+	_, err := Parse(`
+		#
+		# This is a test
+		#
+		user: bool .
+		user.name: string @index(exact) . # this should be unique
+		user.email: string @index(exact) . # this should be unique and lower-cased
+		user.password: password .
+		user.code: string . # for password recovery (can be null)
+		node: bool .
+		node.hashid: string @index(exact) . # @username/hashid
+		node.owner: uid @reverse . # (can be null)
+		node.parent: uid . # [uid] (use facet)
+		node.xdata: string . # store custom json data
+		#
+		# End of test
+		#
+	`)
+	require.NoError(t, err)
+}
+
+func TestParseCommentsNoop(t *testing.T) {
+	reset()
+	_, err := Parse(`
+# Spicy jalapeno bacon ipsum dolor amet t-bone kevin spare ribs sausage jowl cow pastrami short.
+# Leberkas alcatra kielbasa chicken pastrami swine bresaola. Spare ribs landjaeger meatloaf.
+# Chicken biltong boudin porchetta jowl swine burgdoggen cow kevin ground round landjaeger ham.
+# Tongue buffalo cow filet mignon boudin sirloin pancetta pork belly beef ribs. Cow landjaeger.
+	`)
+	require.NoError(t, err)
+}
+
+func TestParseCommentsErrMissingType(t *testing.T) {
+	reset()
+	_, err := Parse(`
+		# The definition below should trigger an error
+		# because we commented out its type.
+		node: # bool .
+	`)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "Missing Type")
+}
+
+func TestParseTypeComments(t *testing.T) {
+	reset()
+	_, err := Parse(`
+		# User is a service user
+		type User {
+			# TODO: add more fields
+			Name: string # e.g., srfrog
+									 # expanded comment
+									 # embedded # comments # here
+		}
+		# /User
+	`)
+	require.NoError(t, err)
+}
+
 var ps *badger.DB
 
 func TestMain(m *testing.M) {

schema/state.go

@@ -53,6 +53,8 @@ Loop:
 			l.Emit(itemNewLine)
 		case r == '.':
 			l.Emit(itemDot)
+		case r == '#':
+			return lexTextComment
 		case r == ',':
 			l.Emit(itemComma)
 		case r == '<':
@@ -105,6 +107,25 @@ func lexWord(l *lex.Lexer) lex.StateFn {
 	return lexText
 }
 
+// lexTextComment lexes a comment text inside a schema.
+func lexTextComment(l *lex.Lexer) lex.StateFn {
+	for {
+		r := l.Next()
+		if r == lex.EOF {
+			l.Ignore()
+			l.Emit(lex.ItemEOF)
+			break
+		}
+		if !lex.IsEndOfLine(r) {
+			continue
+		}
+		l.Ignore()
+		l.Emit(itemNewLine)
+		break
+	}
+	return lexText
+}
+
 // isNameBegin returns true if the rune is an alphabet.
 func isNameBegin(r rune) bool {
 	switch {