Sema: Allow embedded code to reference SPI

Embedded mode use only binary swiftmodules for distribution, SPI will
always be visible. We can allow implicitly always-emit-into-client
function bodies from the embedded mode to references SPIs.

rdar://163519075

Author: xymus

lib/Sema/ResilienceDiagnostics.cpp

@@ -296,6 +296,7 @@ static bool diagnoseValueDeclRefExportability(SourceLoc loc, const ValueDecl *D,
         }
       });
 
+  auto fragileKind = where.getFragileFunctionKind();
   switch (originKind) {
   case DisallowedOriginKind::None:
     // The decl does not come from a source that needs to be checked for
@@ -327,11 +328,15 @@ static bool diagnoseValueDeclRefExportability(SourceLoc loc, const ValueDecl *D,
     if (reason && reason == ExportabilityReason::AvailableAttribute &&
         ctx.LangOpts.LibraryLevel == LibraryLevel::API)
       return false;
-    break;
+    LLVM_FALLTHROUGH;
 
-  case DisallowedOriginKind::ImplementationOnly:
   case DisallowedOriginKind::SPIImported:
   case DisallowedOriginKind::SPILocal:
+    if (fragileKind.kind == FragileFunctionKind::EmbeddedAlwaysEmitIntoClient)
+      return false;
+    break;
+
+  case DisallowedOriginKind::ImplementationOnly:
   case DisallowedOriginKind::FragileCxxAPI:
     break;
   }
@@ -343,7 +348,6 @@ static bool diagnoseValueDeclRefExportability(SourceLoc loc, const ValueDecl *D,
       return false;
   }
 
-  auto fragileKind = where.getFragileFunctionKind();
   if (fragileKind.kind == FragileFunctionKind::None) {
     DiagnosticBehavior limit = downgradeToWarning == DowngradeToWarning::Yes
                              ? DiagnosticBehavior::Warning

test/Sema/Inputs/implementation-only-imports/indirects.swift

@@ -6,3 +6,5 @@ public typealias GenericAliasFromIndirect<T> = (StructFromIndirect, T)
 
 public func globalFunctionFromIndirect() {}
 public var globalVariableFromIndirect = 0
+
+@_spi(S) public func spiFunctionFromDirect() {}

test/Sema/implementation-only-import-embedded.swift

@@ -11,7 +11,7 @@
 // RUN:   -enable-experimental-feature Embedded
 
 // RUN: %target-swift-frontend -typecheck -verify -verify-ignore-unrelated %s -I %t \
-// RUN:   -swift-version 5 -target arm64-apple-none-macho \
+// RUN:   -swift-version 6 -target arm64-apple-none-macho \
 // RUN:   -define-availability "availMacro:macOS 26.0, iOS 26.0" \
 // RUN:   -enable-experimental-feature Embedded
 
@@ -20,10 +20,12 @@
 
 @_implementationOnly import directs
 // expected-warning @-1 {{using '@_implementationOnly' without enabling library evolution for 'main' may lead to instability during execution}}
-import indirects
+@_spi(S) @_spiOnly import indirects
 
 internal func localInternalFunc() {} // expected-note {{global function 'localInternalFunc()' is not '@usableFromInline' or public}}
 
+@_spi(S) public func localSPI() {}
+
 @inlinable
 public func explicitlyInlinable(arg: StructFromDirect = StructFromDirect()) {
 // expected-error @-1 {{initializer 'init()' cannot be used in a default argument value because 'directs' was imported implementation-only}}
@@ -77,6 +79,9 @@ public func implicitlyInlinablePublic(arg: StructFromDirect = StructFromDirect()
   explicitNonInliable()
 
   if #available(availMacro, *) { }
+
+  localSPI()
+  spiFunctionFromDirect()
 }
 
 private func implicitlyInlinablePrivate(arg: StructFromDirect = StructFromDirect()) {
@@ -186,6 +191,7 @@ struct Accessors {
   }
 }
 
+@_spi(S)
 public func legalAccessToIndirect(arg: StructFromIndirect = StructFromIndirect()) {
   _ = StructFromIndirect()