Add support for font-lock-negation-char-face

[danielmartin]

Emacs can show negation characters using a specific face in font-lock.
This commit adds support for it in swift-mode.

[taku0]

It's very attractive. I see some minor cases are missing:

// should be highlighted; OK if !foo {} if !!!!!foo {} if !!!!!(foo) {} if (!foo) {} let x = [!a,!b] let x = [a:!b] // should not be highlighted; Some cases are missing try! foo foo as! Foo foo != bar foo !== bar a.b.c! a.b.c_! a.b.aあ! init! {} let foo: Foo! = bar let x = foo()! // NG let x = foo[0]! // NG // identifiers can be quoted a.b.`c`! // NG // custom operator foo +!+!+!+!+ bbb // NG

How about "\\(?:^\\|\\s-\\|\\s(\\|\\s>\\|[,:;]\\)\\(!+\\)[^=]"? That is:

• any of:
  • beginning of a line
  • whitespaces
  • open brackets
  • comments
  • ,, ;, or :, and
• one or more !s
• any character other than =.

[danielmartin]

@taku0 Thanks for the feedback, I've applied your suggestion. I've also added some font-lock tests to avoid regressions.

[taku0]

Tests for font-locking is a long-awaited feature. It works perfectly on all versions non-interactively and interactively. Thank you.