[stdlib] Generalize the signature of type(of:)

`func type(of:)` is wholly magical, but it does have a signature in the stdlib (mostly for documentation purposes), and it currently requires its input to be copyable and escapable.

`type(of:)` is actually usable on all entities, so it seems desirable to update its signature to reflect this.

Additionally, this seems like a good time to mark its exported symbol obsolete. I don’t expect anyone would ever link to it (unless there is/was a bug), so in theory we could also silently remove it — but explicitly marking it as legacy ABI seems the least risky option.

Author: lorentey

stdlib/public/core/Builtin.swift

@@ -940,9 +940,11 @@ func _trueAfterDiagnostics() -> Builtin.Int1 {
 ///
 /// - Parameter value: The value for which to find the dynamic type.
 /// - Returns: The dynamic type, which is a metatype instance.
-@_transparent
+@_alwaysEmitIntoClient
 @_semantics("typechecker.type(of:)")
-public func type<T, Metatype>(of value: T) -> Metatype {
+public func type<T: ~Copyable & ~Escapable, Metatype>(
+  of value: borrowing T
+) -> Metatype {
   // This implementation is never used, since calls to `Swift.type(of:)` are
   // resolved as a special case by the type checker.
   unsafe Builtin.staticReport(_trueAfterDiagnostics(), true._value,
@@ -951,6 +953,17 @@ public func type<T, Metatype>(of value: T) -> Metatype {
   Builtin.unreachable()
 }
 
+@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
+@_silgen_name("$ss4type2ofq_x_tr0_lF")
+@usableFromInline
+func __abi_type<T, Metatype>(of value: T) -> Metatype {
+  // This is a legacy entry point for the original definition of `type(of:)`
+  // that the stdlib originally exported for no good reason. The current
+  // definition no longer exports a symbol, and nothing is expected to link to
+  // it, but we keep it around anyway.
+  Builtin.unreachable()
+}
+
 /// Allows a nonescaping closure to temporarily be used as if it were allowed
 /// to escape.
 ///

test/api-digester/Outputs/stability-stdlib-source-base.swift.expected

@@ -370,3 +370,6 @@ Protocol Error has added inherited protocol SendableMetatype
 Accessor Optional.unsafelyUnwrapped.Get() has generic signature change from <Wrapped> to <Wrapped where Wrapped : ~Escapable>
 Accessor UnsafeBufferPointer.indices.Get() has generic signature change from <Element> to <Element where Element : ~Copyable>
 Accessor UnsafeMutableBufferPointer.indices.Get() has generic signature change from <Element> to <Element where Element : ~Copyable>
+
+Func type(of:) has generic signature change from <T, Metatype> to <T, Metatype where T : ~Copyable, T : ~Escapable>
+Func type(of:) has parameter 0 changing from Default to Shared