[SR-308] [XCTAssert] API incompatibility due to usage of StaticString

[briancroom]

Previous ID	SR-308
Radar	None
Original Reporter	@briancroom
Type	Bug
Status	Closed
Resolution	Done

Additional Detail from JIRA

Votes	1
Component/s	XCTest
Labels	Bug
Assignee	@briancroom
Priority	Medium

md5: 04b054794f20358bffdcb2afab563c6d

Issue Description:

Xcode's XCTest has the following signature for XCTAssert:

public func XCTAssert(@autoclosure expression: () -> BooleanType, _ message: String = default, file: String = default, line: UInt = default)

while swift-corelibs-xctest has:

public func XCTAssert(@autoclosure expression: () -> BooleanType, _ message: String = "", file: StaticString = __FILE__, line: UInt = __LINE__)

Note the different types for the `file` parameter. Due to this inconsistency, custom assertion functions which capture file+line from their caller and then delegate to XCTAssert* don't compile on both platforms without resorting to a conditionally-compiled typealias. e.g.:

#if os(Linux)
typealias FileString = StaticString
#else
typealias FileString = String
#endif

func assertAwesomeness(string: String, file: FileString = __FILE__, line: UInt = __LINE__) {
  XCTAssertEqual(string, "Awesome", file: file, line: line)
}

Ideally, the typealias wouldn't be necessary.

[modocache]

Could we change StaticString to String? According to the discussion in #17 (comment) it sounds like its type was set to StaticString due to historical circumstances.

[briancroom]

I spent a little time looking into the possibility of using `String` for the assertion functions. As far as I can tell, the only problem is this `assert` call (made in response to a test failure when `continueAfterFailure` is `false`) which requires a `StaticString` for its `file` parameter.

I can think of a couple of ways to avoid the need to pass in the test failure's file+line into `assert` in that context, especially considering that it is currently unreachable as there is no way to run the tests with `continueAfterFailure` being `false`. On the other hand, I feel that the better, more consistent solution would actually be to use `StaticString` here in both Corelibs-XCTest and Apple's XCTest, although I expect that we can't expect this (breaking!) change to actually happen.

[briancroom]

I have opened PR's for two different approaches to solving this:
#27
swiftlang/swift#888

[briancroom]

This has been fixed by modifying the stdlib XCTest overlay to use StaticString for the file parameter of XCTAssert methods.