Allow dynamic replacement initializers to be non delegating

[aschwaighofer]

rdar://48125765

[aschwaighofer]

@swift-ci Please test

[slavapestov]

Even if the type is resilient?

[aschwaighofer]

Yes I think you should be able to replace resilient constructors via dynamic replacement.

[slavapestov]

Does the dynamic replacement module have visibility past the resilience boundary? It seems like that would require additional code, or building it with the IRGenOptions::EnableResilienceBypass flag set. Did you test this scenario?

[aschwaighofer]

Here is what I have tested:

$ cat ModuleA.swift
struct S {
    let i: Int
    init(i: Int) {
        self.i = i
    }

    init(y: Int) {
      self.init(i: y)
    }
}

$ bin/swiftc -emit-library -Xfrontend -enable-private-imports -Xfrontend -enable-implicit-dynamic ModuleA.swift  -emit-module -enable-resilience

$ cat ModuleB.swift
@_private(sourceFile: "ModuleA.swift") import ModuleA

extension S {
  @_dynamicReplacement(for: init(i:))
  private init(__preview_i: Int) {
    self.i = __preview_i
  }
  @_dynamicReplacement(for: init(y:))
  private init(__preview_y: Int) {
    self.init(i: __preview_y)
  }
}

$ bin/swiftc -emit-library -Xfrontend -enable-private-imports -Xfrontend -enable-implicit-dynamic ModuleB.swift -I. -L. -lModuleA -Xfrontend -enable-resilience -emit-sil

// S.init(__preview_i:)
sil [dynamic_replacement_for "$s7ModuleA1SV1iACSi_tcfC"] @$s7ModuleA1SV0A1BE11__preview_iACSi_tc33_261761554CC3BA78F2BD69544DB6E8C4LlfC : $@convention(method) (Int, @thin S.Type) -> S {
// %0                                             // users: %8, %6, %3
bb0(%0 : $Int, %1 : $@thin S.Type):
  %2 = alloc_stack $S, var, name "self"           // users: %4, %9
  debug_value %0 : $Int, let, name "__preview_i", argno 1 // id: %3
  %4 = begin_access [modify] [static] %2 : $*S    // users: %7, %5
  %5 = struct_element_addr %4 : $*S, #S.i         // user: %6
  store %0 to %5 : $*Int                          // id: %6
  end_access %4 : $*S                             // id: %7
  %8 = struct $S (%0 : $Int)                      // user: %10
  dealloc_stack %2 : $*S                          // id: %9
  return %8 : $S                                  // id: %10
}

[slavapestov]

What if S and S.init are both public?

[aschwaighofer]

Hmm, that just crashes the compiler.

[slavapestov]

I think we could make it work, if the dynamic replacement module is built with EnableResilienceBypass on.

[aschwaighofer]

It crashes in SILGen. There are more dragons. I will deal with that later.

[aschwaighofer]

@swift-ci Please test