swiftlint open brace rule

Question

I'm using Swiftlint to enforce some practices in our codebase. I want to add a custom rule that makes sure a { always appears after a newline. I thought I knew regexes, but can't seem to figure it out. I just check if a line contains any characters other than whitespace before the {. It is allowed to have stuff after the {.

What I have now:

invalid_open_brace:
    name: "Open brace should start on its own line"
    regex: "(\S+.*\{)"
    message: "Open brace should start on its own line"
    severity: warning

Here are some example strings that should and should not match:

// NO MATCH
else if let var1 = var1 as? String, !var1.isEmpty 
{

//NO MATCH
class Person
{
    // MATCH
    int() 
    {
    }

    // NO MATCH
    function() 
    {

    }
 }

// MATCH
function() {

}

Answer 1

Your (\S+.*\{) regex matches any char that is not whitespace (one or more reptitions - \S+), then any char other than linebreak (including non-whitespaces - here is the root cause of your issue), and {.

You may use

\S[ \t]+\{

See the regex demo.

Details:

• \S - any non-whitespace char
• [ \t]+ - one or more (+) horizontal whitesapces (can be replaced with [\t\p{Zs}]+ where \p{Zs} matches all horizontal Unicode whitespace without a tab).
• \{ - a literal { symbol.