```suggestion error("found `%s` when expecting `%s` following `mixin`", token.toChars(), Token.toChars(TOK.leftParentheses)); ```

Would have been better if this refactoring was in another PR

Unrelated

superfluous parens

I'm confused as to why this idiom was used here. It's just a more complicated way of saying... this: ```d override Type syntaxCopy() { Expressions* a = null; if (exps) { a = new Expressions(exps.dim); foreach (i, e; *exps) { (*a)[i] = e ? e.syntaxCopy() : null; } } return new TypeMixin(a); } ```