Add optional array access like foo?.[42] (#550)

expr_test.go

@@ -1184,6 +1184,18 @@ func TestExpr(t *testing.T) {
 			`"hello"[1:3]`,
 			"el",
 		},
+		{
+			`[1, 2, 3]?.[0]`,
+			1,
+		},
+		{
+			`[[1, 2], 3, 4]?.[0]?.[1]`,
+			2,
+		},
+		{
+			`[nil, 3, 4]?.[0]?.[1]`,
+			nil,
+		},
 	}
 
 	for _, tt := range tests {
@@ -1281,6 +1293,16 @@ func TestExpr_optional_chaining_nested_chains(t *testing.T) {
 	assert.Equal(t, "baz", got)
 }
 
+func TestExpr_optional_chaining_array(t *testing.T) {
+	env := map[string]any{}
+	program, err := expr.Compile("foo?.[1]?.[2]?.[3]", expr.Env(env), expr.AllowUndefinedVariables())
+	require.NoError(t, err)
+
+	got, err := expr.Run(program, env)
+	require.NoError(t, err)
+	assert.Equal(t, nil, got)
+}
+
 func TestExpr_eval_with_env(t *testing.T) {
 	_, err := expr.Eval("true", expr.Env(map[string]any{}))
 	assert.Error(t, err)

parser/parser.go

@@ -575,10 +575,16 @@ end:
 func (p *parser) parsePostfixExpression(node Node) Node {
 	postfixToken := p.current
 	for (postfixToken.Is(Operator) || postfixToken.Is(Bracket)) && p.err == nil {
+		optional := postfixToken.Value == "?."
+	parseToken:
 		if postfixToken.Value == "." || postfixToken.Value == "?." {
 			p.next()
 
 			propertyToken := p.current
+			if optional && propertyToken.Is(Bracket, "[") {
+				postfixToken = propertyToken
+				goto parseToken
+			}
 			p.next()
 
 			if propertyToken.Kind != Identifier &&
@@ -662,8 +668,12 @@ func (p *parser) parsePostfixExpression(node Node) Node {
 					node = &MemberNode{
 						Node:     node,
 						Property: from,
+						Optional: optional,
 					}
 					node.SetLocation(postfixToken.Location)
+					if optional {
+						node = &ChainNode{Node: node}
+					}
 					p.expect(Bracket, "]")
 				}
 			}

parser/parser_test.go

@@ -747,6 +747,19 @@ func TestParse_optional_chaining(t *testing.T) {
 				},
 			},
 		},
+		{
+			"foo.bar?.[0]",
+			&ChainNode{
+				Node: &MemberNode{
+					Node: &MemberNode{
+						Node:     &IdentifierNode{Value: "foo"},
+						Property: &StringNode{Value: "bar"},
+					},
+					Property: &IntegerNode{Value: 0},
+					Optional: true,
+				},
+			},
+		},
 	}
 	for _, test := range parseTests {
 		actual, err := parser.Parse(test.input)