Remove a number of checks for compilers < 6.1. (#1214)

This PR removes some old/dead code checking for compilers < 6.1. We do
not support building with such compilers anymore.

It also adopts the move-only-type-compatible `ObjectIdentifier.init`
overload added with the 6.2 toolchain.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

CONTRIBUTING.md

@@ -48,11 +48,10 @@ and install a toolchain.
 
 #### Installing a toolchain
 
-1. Download a toolchain. A recent **6.0 development snapshot** toolchain is
-   required to build the testing library. Visit
-   [swift.org](http://swift.org/install) and download the most recent toolchain
-   from the section titled **release/6.0** under **Development Snapshots** on
-   the page for your platform.
+1. Download a toolchain. A recent **development snapshot** toolchain is required
+   to build the testing library. Visit [swift.org](https://swift.org/install),
+   select your platform, and download the most recent toolchain from the section
+   titled **release/6.x** under **Development Snapshots**.
 
    Be aware that development snapshot toolchains aren't intended for day-to-day
    development and may contain defects that affect the programs built with them.

Sources/Testing/Parameterization/TypeInfo.swift

@@ -308,11 +308,7 @@ extension TypeInfo {
     }
     switch _kind {
     case let .type(type):
-#if compiler(>=6.1)
       return _mangledTypeName(type)
-#else
-      return _mangledTypeName(unsafeBitCast(type, to: Any.Type.self))
-#endif
     case let .nameOnly(_, _, mangledName):
       return mangledName
     }
@@ -412,6 +408,7 @@ extension TypeInfo: Hashable {
   }
 }
 
+#if compiler(<6.2)
 // MARK: - ObjectIdentifier support
 
 extension ObjectIdentifier {
@@ -426,6 +423,7 @@ extension ObjectIdentifier {
     self.init(unsafeBitCast(type, to: Any.Type.self))
   }
 }
+#endif
 
 // MARK: - Codable
 

Sources/Testing/Support/Locked+Platform.swift

@@ -41,7 +41,7 @@ extension os_unfair_lock_s: Lockable {
 typealias pthread_mutex_t = _TestingInternals.pthread_mutex_t?
 #endif
 
-#if SWT_TARGET_OS_APPLE || os(Linux) || os(Android) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded)) || os(FreeBSD) || os(OpenBSD)
+#if SWT_TARGET_OS_APPLE || os(Linux) || os(Android) || (os(WASI) && _runtime(_multithreaded)) || os(FreeBSD) || os(OpenBSD)
 extension pthread_mutex_t: Lockable {
   static func initializeLock(at lock: UnsafeMutablePointer<Self>) {
     _ = pthread_mutex_init(lock, nil)
@@ -83,7 +83,7 @@ extension SRWLOCK: Lockable {
 
 #if SWT_TARGET_OS_APPLE && !SWT_NO_OS_UNFAIR_LOCK
 typealias DefaultLock = os_unfair_lock
-#elseif SWT_TARGET_OS_APPLE || os(Linux) || os(Android) || (os(WASI) && compiler(>=6.1) && _runtime(_multithreaded)) || os(FreeBSD) || os(OpenBSD)
+#elseif SWT_TARGET_OS_APPLE || os(Linux) || os(Android) || (os(WASI) && _runtime(_multithreaded)) || os(FreeBSD) || os(OpenBSD)
 typealias DefaultLock = pthread_mutex_t
 #elseif os(Windows)
 typealias DefaultLock = SRWLOCK

Tests/TestingTests/Traits/ConditionTraitTests.swift

@@ -12,29 +12,25 @@
 
 @Suite("Condition Trait Tests", .tags(.traitRelated))
 struct ConditionTraitTests {
-  #if compiler(>=6.1)
   @Test(
     ".enabled trait",
     .enabled { true },
     .bug("https://github.com/swiftlang/swift/issues/76409", "Verify the custom trait with closure causes @Test macro to fail is fixed")
   )
   func enabledTraitClosure() throws {}
-  #endif
 
   @Test(
     ".enabled if trait",
     .enabled(if: true)
   )
   func enabledTraitIf() throws {}
 
-  #if compiler(>=6.1)
   @Test(
     ".disabled trait",
     .disabled { false },
     .bug("https://github.com/swiftlang/swift/issues/76409", "Verify the custom trait with closure causes @Test macro to fail is fixed")
   )
   func disabledTraitClosure() throws {}
-  #endif
 
   @Test(
     ".disabled if trait",