Fix all parsing warnings & errors in rule examples

[jpsim]

Many rule examples are very succinct, focusing just on the syntax that is meant to be linted/corrected. For example: if foo == nil. However, this doesn't parse successfully:

$ echo "if foo == nil" > file.swift
$ swiftc -parse file.swift
file.swift:1:14: error: expected '{' after 'if' condition
if foo == nil
             ^

In an upcoming PR, I'll want to introduce a change to avoid correcting files if they have parser errors or warnings, since SwiftLint isn't designed to handle all possibilities of invalid Swift code. Generally, it's still useful for SwiftLint to lint Swift files that don't parse 100% cleanly as a feedback mechanism, but we shouldn't attempt to correct files with violations that don't parse cleanly, because that can mangle or delete code in unintended ways.

Because there are currently over 500 rule examples with parser diagnostics, I don't have time to fix all of them, but we probably should do that eventually.

This is a good starter task if someone's interested in contributing to SwiftLint.

[lo1tuma]

Generally, it's still useful for SwiftLint to lint Swift files that don't parse 100% cleanly

What is the reasoning behind this? And does this mean that just SwiftLint should be able to handle invalid code or does this apply for the examples as well. Maybe we could introduce a mechanism to parse all examples and check if there are any parse errors (maybe directly in the Example init method). That way we could make sure all examples are valid while still allowing invalid code to go through SwiftLint.

I think there is not much value in fixing all those parse errors now, without a way to enforcing examples to be valid. If we don’t enforce it, then we would end up in the same situation again after a while, because examples are added or get modified and might become invalid again.