Allow var bindings in path expressions (#1347)

The expression in a variable binding is not and must not be seen as
being part of a path expression in which the variable binding appears.

src/compile.c

@@ -893,7 +893,7 @@ block gen_destructure(block var, block matcher, block body) {
   if (body.first && body.first->op == TOP)
     top = inst_block(block_take(&body));
 
-  return BLOCK(top, gen_op_simple(DUP), var, bind_matcher(matcher, body));
+  return BLOCK(top, gen_op_simple(DUP), gen_subexp(var), gen_op_simple(POP), bind_matcher(matcher, body));
 }
 
 // Like gen_var_binding(), but bind `break`'s wildcard unbound variable

tests/jq.test

@@ -1356,3 +1356,9 @@ IN(range(5;20); range(10))
 null
 true
 
+# Regression test for #1347
+(.a as $x | .b) = "b"
+{"a":null,"b":null}
+{"a":null,"b":"b"}
+
+