Mathematical operations need to wrap in parenthesis

[sgrif]

Setup

Versions

• Rust: any
• Diesel: any
• Database: any
• Operating System any

Feature Flags

• diesel:

Problem Description

Parenthesis inserted in Rust to override order of operations are lost in the generated SQL. This can also occur when a value is assigned to a local variable. This will at best result in an incorrect value being generated, and at worst will result in a runtime error because of incorrect types (e.g. interval * (integer - integer) is valid but interval * integer - integer is not)

What is the expected output?

14

What is the actual output?

10

Steps to reproduce

fn test(conn: &Connection) {
    let x = select(2.into_sql::<Integer>() * (3.into_sql::<Integer>() + 4))
        .get_result(conn);
    assert_eq!(Ok(14), x);
}

Checklist

• I have already looked over the issue tracker for similar issues.
• This issue can be reproduced on Rust's stable channel. (Your issue will be
  closed if this is not the case)