SQL expressions in dimension definitions are not auto-wrapped in parentheses

From Slack:

Given the following sample schema:

cube:
  - name: items
    sql: SELECT * FROM items
    dimensions:
      - name: id
        sql: id
        type: number
        primaryKey: true
      - name: b
        sql: b
        type: boolean
      - name: c
        sql: c
        type: boolean
      - name: d
        sql: d
        type: boolean
      - name: a
        sql: "{CUBE.b} AND {CUBE.c} AND NOT {cube.d}"
        type: boolean

When I run the following query:

SELECT
	id,
	a
FROM
	items
WHERE
	a IS NULL

I expect output that looks something like the following(records where A is null):

id | a
---|---
 1 | 
 2 |
 3 |
 4 |
 5 |

However what I get is closer to the following:

id |  a
---|-----
 1 | TRUE
 2 | TRUE
 3 | TRUE
 4 | FALSE
 5 | TRUE

Why this arises becomes more clear after looking at the generated SQL:

SELECT
	id,
	b AND c AND NOT d
FROM
	items
WHERE
	b AND c AND NOT d IS NULL

This comes as a in the SQL is replaced with b AND c AND NOT d which creates b AND c AND NOT d IS NULL which is not what I intended. Having come from Looker what I expected/intended as for something like the following.

SELECT
	id,
	(b AND c AND NOT d)
FROM
	items
WHERE
	(b AND c AND NOT d) IS NULL

---

@paveltiunov thinks that "ideally Cube should handle this."