Rename `isAt*` functions in `SwiftParser` to `at*`

[ahoppen]

We have the at(_: TokenSpec) functions to check if we are at a token but some of the more complex at functions like isAtStartOfPostfixExprSuffix start with isAt. To be consistent, we should remove is here.

[ahoppen]

Tracked in Apple’s issue tracker as rdar://113237445

[natikgadzhi]

@ahoppen, I'll grab these next — expect a PR by Friday ;)

[natikgadzhi]

First findings

There are _quite a few functions and properties that follow isAt* notation. Focusing on just the functions, here's the list that I'll rename first:

• Lexer.Cursor.isAtStringInterpolationAnchor — private, so I'll rename it and change any spots where it's invoked. Deprecating the existing function should not be necessary.
• Lexer.Cursor.isAtEscapedNewline — same as above.
• Parser.Lookahead has two fileprivate functions isAtStartOfPostfixExprSuffix and isInBindingPatternPosition — I think it's best to rename both of them so the code in that particular extension is consistent. It would be weird to have atStartOfPostfixExprSuffix and isIn*.
• Parser.isAtPythonStyleInheritanceClause
• In SwiftParser/Statements.swift we have Parser.Lookahead extension with isAtStartOfSwitchCase, isStartOfStatement, isStartOfConditionalSwitchCases.
  • These are not marked as private, so I think we should keep the original version and deprecate it.
  • Should I rename isStartOf* as well for consistency?
• SwiftParser/Types.swift has Parser.Lookahead.isAtFunctionTypeArrow — also not marked as private.

Questions

In some cases, there are isAt* funcs side by side with isSomethingElse, and it's tempting to go over them as well, so the language of the API is consistent, but I also want to keep the scope of this manageable and easy to review.

Does the list above look good for the first PR, @ahoppen? I'm happy to support the migration to the new notation further if we will choose to.