err on missing rhs to unary operator within subexpr

Author: zephyrtronium

parse.go

@@ -409,6 +409,9 @@ func parselhs(scan *lexer, p *parsectx, until operator) (*node, error) {
 		if err != nil {
 			return nil, err
 		}
+		if rhs == nil {
+			return nil, &EmptyExpressionError{Col: tok.pos, End: scan.must().text}
+		}
 		n = &node{kind: prec.op, left: rhs}
 	case tokenOpen:
 		match := rightbracket(tok.text)

parse_test.go

@@ -434,6 +434,7 @@ func TestParseErrors(t *testing.T) {
 
 		// Cases identified with fuzzing.
 		{"op-paren", "(b*)", new(EmptyExpressionError), []string{`\)`}, nil},
+		{"haskell", "(+)", new(EmptyExpressionError), []string{`\)`}, nil},
 	}
 	preset := ParsingPreset(DisableDefaultFuncs(), ParseFuncs(testfns))
 	for _, c := range cases {

testdata/fuzz/FuzzEval/4cc6c0996d3499cfcd061a6e00019cac24a06f63ee6c45ceb2a775052d2c50fa

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("(+)")