Hande Swift Testing-specific prefixes

[gmedori]

Depends on swiftlang/swift-testing#1531

This PR accompanies swiftlang/swift-testing#1531 as the implementation for ST-0025, which enables users to pass an argument prefixed with tag: to swift test --filter in order to filter tests by tag in Swift Testing.

Motivation:

This particular PR accounts for what happens to XCTests when we pass in such a filter. XCTest doesn't have a concept of tags. Another way of saying this is that every XCTest has an empty set of tags, which means that supplying --filter tag:foo should not run any XCTests, since none of them have the appropriate tag. Similarly, supplying --skip tag:foo should not skip any XCTests.

We generalize this idea by saying that if any prefix is encountered (with one exception), we shouldn't match any XCTests. The exception is the id: prefix which behaves the same as passing no prefix at all. We only introduced the id: prefix in swiftlang/swift-testing#1531 in order to allow for disambiguation purposes, which don't apply when dealing with XCTests.

Examples

Here's a table of select examples to help illustrate what happens when you pass in various combinations of filter & skip specifiers:

Argument	Swift Testing	XCTest
--filter id:myTestName	runs matching tests	runs tests whose ID matches myTestName
--filter tag:integration	runs tests tagged integration	runs nothing (XCTest tests have no tags)
--filter id:… --filter tag:…	runs tests matching the id and tag	runs nothing (the tag can't be satisfied)
--skip id:myTestName	skips matching tests	skips tests whose ID matches
--skip tag:integration	skips tests tagged integration	skips nothing (all XCTest tests run)

Modifications:

• Renamed testCaseSpecifier → xctestFilterSpecifier, skippedTests → xctestSkippedSpecifier to indicate their XCTest-specific nature (for Swift Testing, the arguments are passed directly and parsed over there).
• Added a function that normalizes the specifier for XCTest by stripping id: prefixes and deriving the correct behavior for other prefixes.
• Accounted for the slightly different semantics of the --filter and --skip specifiers.

Result:

Existing uses won't change, but you will now be able to pass prefixes to --filter and --skip and have well-defined behavior as described above.

[owenv]

LGTM, although we should probably not merge until the swift-testing parts land

[owenv]

@swift-ci test

[plemarquand]

looks good, thanks!

[bkhouri]

praise: This is a wonderful rename and give clarity that it applies only to XCTest