Fix false positive in pointless-reassignment (#1286)

That would happen despite the left hand side not being a var

Fixes #1285

Signed-off-by: Anders Eknert <anders@styra.com>

bundle/regal/rules/style/pointless-reassignment/pointless_reassignment.rego

@@ -26,7 +26,10 @@ report contains violation if {
 
 	not expr["with"]
 
-	ast.assignment_terms(expr)[1].type == "var"
+	[lhs, rhs] := ast.assignment_terms(expr)
+
+	lhs.type == "var"
+	rhs.type == "var"
 
 	violation := result.fail(rego.metadata.chain(), result.infix_expr_location(expr.terms))
 }

bundle/regal/rules/style/pointless-reassignment/pointless_reassignment_test.rego

@@ -7,7 +7,7 @@ import data.regal.config
 
 import data.regal.rules.style["pointless-reassignment"] as rule
 
-test_pointless_reassignment_in_rule_head if {
+test_fail_pointless_reassignment_in_rule_head if {
 	module := ast.with_rego_v1(`
 	foo := "foo"
 
@@ -37,7 +37,7 @@ test_pointless_reassignment_in_rule_head if {
 	}}
 }
 
-test_pointless_reassignment_in_rule_body if {
+test_fail_pointless_reassignment_in_rule_body if {
 	module := ast.with_rego_v1(`
 	rule if {
 		foo := "foo"
@@ -69,7 +69,7 @@ test_pointless_reassignment_in_rule_body if {
 	}}
 }
 
-test_pointless_reassignment_in_rule_body_using_with if {
+test_success_pointless_reassignment_in_rule_body_using_with if {
 	module := ast.with_rego_v1(`
 	foo := input
 
@@ -83,3 +83,16 @@ test_pointless_reassignment_in_rule_body_using_with if {
 	r := rule.report with input as module
 	r == set()
 }
+
+test_success_not_pointless_reassignment_to_array if {
+	module := ast.with_rego_v1(`
+	parts := split(input.arr, ".")
+
+	rule := [b, a] if {
+		[a, b] := parts
+	}
+	`)
+
+	r := rule.report with input as module
+	r == set()
+}