diff --git a/include/swift/AST/DeclContext.h b/include/swift/AST/DeclContext.h
index b064f05cfd95d..5076540e8e0a3 100644
--- a/include/swift/AST/DeclContext.h
+++ b/include/swift/AST/DeclContext.h
@@ -202,7 +202,7 @@ struct ConformanceDiagnostic {
   ProtocolDecl *ExistingExplicitProtocol;
 };
 
-/// Used in diagnostic %selects.
+/// Used in diagnostic %selects via FRAGILE_FUNC_KIND.
 struct FragileFunctionKind {
   enum Kind : unsigned {
     Transparent,
@@ -211,6 +211,7 @@ struct FragileFunctionKind {
     DefaultArgument,
     PropertyInitializer,
     BackDeploy,
+    EmbeddedAlwaysEmitIntoClient,
     None
   };
 
diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 9608755f57f0f..0a767cf53a1b0 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -7312,7 +7312,8 @@ ERROR(usable_from_inline_attr_in_protocol,none,
   "an '@_alwaysEmitIntoClient' function|" \
   "a default argument value|" \
   "a property initializer in a '@frozen' type|" \
-  "a '@backDeployed' function'}"
+  "a '@backDeployed' function|" \
+  "an embedded function not marked '@_neverEmitIntoClient'}"
 
 ERROR(local_type_in_inlinable_function,
       none, "type %0 cannot be nested inside " FRAGILE_FUNC_KIND "1",
diff --git a/lib/AST/DeclContext.cpp b/lib/AST/DeclContext.cpp
index 86890830c50d3..56dbbe4cf5678 100644
--- a/lib/AST/DeclContext.cpp
+++ b/lib/AST/DeclContext.cpp
@@ -488,6 +488,11 @@ ResilienceExpansion DeclContext::getResilienceExpansion() const {
   case FragileFunctionKind::PropertyInitializer:
   case FragileFunctionKind::BackDeploy:
     return ResilienceExpansion::Minimal;
+
+  /// Embedded functions are treated as fragile for diagnostics only.
+  /// For code gen they are treated as normal and optimized later.
+  case FragileFunctionKind::EmbeddedAlwaysEmitIntoClient:
+
   case FragileFunctionKind::None:
     return ResilienceExpansion::Maximal;
   }
@@ -551,6 +556,23 @@ swift::FragileFunctionKindRequest::evaluate(Evaluator &evaluator,
       if (AFD->getDeclContext()->isLocalContext())
         continue;
 
+      // Delay checking the implicit conditions after explicit declarations.
+      auto checkEmbeddedAlwaysEmitIntoClient = [&](const ValueDecl *VD) {
+        if (!VD->getASTContext().LangOpts.hasFeature(Feature::Embedded))
+          return FragileFunctionKind::None;
+
+        bool funcIsNEIC = VD->isNeverEmittedIntoClient();
+        bool storageIsNEIC = false;
+        if (auto accessor = dyn_cast<AccessorDecl>(VD))
+          storageIsNEIC = accessor->getStorage()->isNeverEmittedIntoClient();
+
+        // Accessors are implicitly EmbeddedAlwaysEmitIntoClient if neither the
+        // accessor or starage is marked @_neverEmitIntoClient.
+        if (!funcIsNEIC && !storageIsNEIC)
+            return FragileFunctionKind::EmbeddedAlwaysEmitIntoClient;
+        return FragileFunctionKind::None;
+      };
+
       auto funcAccess =
         AFD->getFormalAccessScope(/*useDC=*/nullptr,
                                   /*treatUsableFromInlineAsPublic=*/true);
@@ -558,7 +580,8 @@ swift::FragileFunctionKindRequest::evaluate(Evaluator &evaluator,
       // If the function is not externally visible, we will not be serializing
       // its body.
       if (!funcAccess.isPublic()) {
-        return {FragileFunctionKind::None};
+        // For non-public decls, only check embedded mode correctness.
+        return {checkEmbeddedAlwaysEmitIntoClient(AFD)};
       }
 
       // If the function is public, @_transparent implies @inlinable.
@@ -592,6 +615,10 @@ swift::FragileFunctionKindRequest::evaluate(Evaluator &evaluator,
           return {FragileFunctionKind::BackDeploy};
         }
       }
+
+      auto implicitKind = checkEmbeddedAlwaysEmitIntoClient(AFD);
+      if (implicitKind != FragileFunctionKind::None)
+        return {implicitKind};
     }
   }
 
diff --git a/lib/AST/TypeCheckRequests.cpp b/lib/AST/TypeCheckRequests.cpp
index a4debbb322221..1cb7cd59a79c3 100644
--- a/lib/AST/TypeCheckRequests.cpp
+++ b/lib/AST/TypeCheckRequests.cpp
@@ -687,6 +687,9 @@ void swift::simple_display(llvm::raw_ostream &out,
   case FragileFunctionKind::BackDeploy:
     out << "backDeploy";
     return;
+  case FragileFunctionKind::EmbeddedAlwaysEmitIntoClient:
+    out << "embeddedAlwaysEmitIntoClient";
+    return;
   case FragileFunctionKind::None:
     out << "none";
     return;
diff --git a/lib/Sema/MiscDiagnostics.cpp b/lib/Sema/MiscDiagnostics.cpp
index 780ea16a13dc6..5823e41de508a 100644
--- a/lib/Sema/MiscDiagnostics.cpp
+++ b/lib/Sema/MiscDiagnostics.cpp
@@ -5223,7 +5223,8 @@ static bool diagnoseAvailabilityCondition(PoundAvailableInfo *info,
   // restriction, macros would need to either be expanded when printed in
   // swiftinterfaces or be parsable as macros by module clients.
   auto fragileKind = DC->getFragileFunctionKind();
-  if (fragileKind.kind != FragileFunctionKind::None) {
+  if (fragileKind.kind != FragileFunctionKind::None &&
+      fragileKind.kind != FragileFunctionKind::EmbeddedAlwaysEmitIntoClient) {
     for (auto availSpec : info->getQueries()) {
       if (availSpec->getMacroLoc().isValid()) {
         diags.diagnose(availSpec->getMacroLoc(),
diff --git a/lib/Sema/ResilienceDiagnostics.cpp b/lib/Sema/ResilienceDiagnostics.cpp
index 3a4dbd1112107..4b18f10da903d 100644
--- a/lib/Sema/ResilienceDiagnostics.cpp
+++ b/lib/Sema/ResilienceDiagnostics.cpp
@@ -97,6 +97,14 @@ bool TypeChecker::diagnoseInlinableDeclRefAccess(SourceLoc loc,
     return false;
   }
 
+  // Embedded functions can reference non-public decls as they are visible
+  // to clients. Still report references to decls imported non-publicly
+  // to enforce access-level on imports.
+  ImportAccessLevel problematicImport = D->getImportAccessFrom(DC);
+  if (fragileKind.kind == FragileFunctionKind::EmbeddedAlwaysEmitIntoClient &&
+      !problematicImport)
+    return false;
+
   DowngradeToWarning downgradeToWarning = DowngradeToWarning::No;
 
   // Swift 4.2 did not perform any checks for type aliases.
@@ -127,7 +135,6 @@ bool TypeChecker::diagnoseInlinableDeclRefAccess(SourceLoc loc,
 
   Context.Diags.diagnose(D, diag::resilience_decl_declared_here, D);
 
-  ImportAccessLevel problematicImport = D->getImportAccessFrom(DC);
   if (problematicImport.has_value() &&
       problematicImport->accessLevel < D->getFormalAccess()) {
     Context.Diags.diagnose(problematicImport->importLoc,
diff --git a/lib/Sema/TypeCheckDeclPrimary.cpp b/lib/Sema/TypeCheckDeclPrimary.cpp
index 101d711135eda..9e41ebf8fa5dd 100644
--- a/lib/Sema/TypeCheckDeclPrimary.cpp
+++ b/lib/Sema/TypeCheckDeclPrimary.cpp
@@ -2946,7 +2946,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
     // We don't allow nested types inside inlinable contexts.
     auto kind = DC->getFragileFunctionKind();
-    if (kind.kind != FragileFunctionKind::None) {
+    if (kind.kind != FragileFunctionKind::None &&
+        kind.kind != FragileFunctionKind::EmbeddedAlwaysEmitIntoClient) {
       NTD->diagnose(diag::local_type_in_inlinable_function, NTD->getName(),
                     kind.getSelector());
     }
diff --git a/test/Sema/access-level-import-embedded.swift b/test/Sema/access-level-import-embedded.swift
new file mode 100644
index 0000000000000..b81ac9a7db56f
--- /dev/null
+++ b/test/Sema/access-level-import-embedded.swift
@@ -0,0 +1,182 @@
+/// Test @_implementationOnly internal import exportability diagnostics in embedded mode.
+
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -o %t/indirects.swiftmodule \
+// RUN:   %S/Inputs/implementation-only-imports/indirects.swift \
+// RUN:   -swift-version 5 -target arm64-apple-none-macho \
+// RUN:   -enable-experimental-feature Embedded
+// RUN: %target-swift-frontend -emit-module -o %t/directs.swiftmodule -I %t \
+// RUN:   %S/Inputs/implementation-only-imports/directs.swift \
+// RUN:   -swift-version 5 -target arm64-apple-none-macho \
+// 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:   -enable-experimental-feature Embedded
+
+// REQUIRES: swift_feature_Embedded
+// REQUIRES: embedded_stdlib_cross_compiling
+
+@_implementationOnly internal import directs
+// expected-warning @-1 {{using '@_implementationOnly' without enabling library evolution for 'main' may lead to instability during execution}}
+// expected-note @-2 19 {{struct 'StructFromDirect' imported as 'internal' from 'directs' here}}
+// expected-note @-3 12 {{initializer 'init()' imported as 'internal' from 'directs' here}}
+import indirects
+
+internal func localInternalFunc() {} // expected-note {{global function 'localInternalFunc()' is not '@usableFromInline' or public}}
+
+@inlinable
+public func explicitlyInlinable(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{initializer 'init()' is internal and cannot be referenced from a default argument value}}
+// expected-error @-2 {{struct 'StructFromDirect' is internal and cannot be referenced from a default argument value}}
+// expected-error @-3 {{struct 'StructFromDirect' is internal and cannot be referenced from an '@inlinable' function}}
+// expected-error @-4 {{function cannot be declared public because its parameter uses an internal type}}
+// expected-note @-5 {{struct 'StructFromDirect' is imported by this file as 'internal' from 'directs'}}
+  _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an '@inlinable' function}}
+  // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an '@inlinable' function}}
+
+  if (true) {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an '@inlinable' function}}
+    // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an '@inlinable' function}}
+  }
+
+  func nested() {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an '@inlinable' function}}
+    // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an '@inlinable' function}}
+  }
+  nested()
+
+  localInternalFunc() // expected-error {{global function 'localInternalFunc()' is internal and cannot be referenced from an '@inlinable' function}}
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate() // expected-error {{global function 'implicitlyInlinablePrivate(arg:)' is private and cannot be referenced from an '@inlinable' function}}
+  explicitNonInliable()
+}
+
+public func implicitlyInlinablePublic(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{initializer 'init()' is internal and cannot be referenced from a default argument value}}
+// expected-error @-2 {{struct 'StructFromDirect' is internal and cannot be referenced from a default argument value}}
+// expected-error @-3 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+// expected-error @-4 {{function cannot be declared public because its parameter uses an internal type}}
+// expected-note @-5 {{struct 'StructFromDirect' is imported by this file as 'internal' from 'directs'}}
+  _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+  // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+
+  if (true) {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+    // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+  }
+
+  func nested() {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+    // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+}
+
+private func implicitlyInlinablePrivate(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+// expected-note @-2 {{global function 'implicitlyInlinablePrivate(arg:)' is not '@usableFromInline' or public}}
+  _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+  // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+
+  if (true) {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+    // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+  }
+
+  func nested() {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+    // expected-error@-1 {{struct 'StructFromDirect' is internal and cannot be referenced from an embedded function not marked '@_neverEmitIntoClient'}}
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+}
+
+@_neverEmitIntoClient
+public func explicitNonInliable(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{initializer 'init()' is internal and cannot be referenced from a default argument value}}
+// expected-error @-2 {{struct 'StructFromDirect' is internal and cannot be referenced from a default argument value}}
+// expected-error @-3 {{cannot use struct 'StructFromDirect' here; 'directs' has been imported as implementation-only}}
+// expected-error @-4 {{function cannot be declared public because its parameter uses an internal type}}
+// expected-note @-5 {{struct 'StructFromDirect' is imported by this file as 'internal' from 'directs'}}
+  _ = StructFromDirect()
+
+  if (true) {
+    _ = StructFromDirect()
+  }
+
+  @_neverEmitIntoClient
+  func nested() {
+    _ = StructFromDirect()
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+}
+
+@_neverEmitIntoClient
+internal func explicitNonInliableInternal(arg: StructFromDirect = StructFromDirect()) {
+  _ = StructFromDirect()
+
+  if (true) {
+    _ = StructFromDirect()
+  }
+
+  @_neverEmitIntoClient
+  func nested() {
+    _ = StructFromDirect()
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+}
+
+public func legalAccessToIndirect(arg: StructFromIndirect = StructFromIndirect()) {
+  _ = StructFromIndirect()
+
+  if (true) {
+    _ = StructFromIndirect()
+  }
+
+  func nested() {
+    _ = StructFromIndirect()
+  }
+  nested()
+}
+
+public struct ExposedLayoutPublic {
+  public var publicField: StructFromDirect // expected-error {{property cannot be declared public because its type uses an internal type}}
+  // expected-error @-1 {{cannot use struct 'StructFromDirect' here; 'directs' has been imported as implementation-only}}
+  // expected-note @-2 {{struct 'StructFromDirect' is imported by this file as 'internal' from 'directs'}}
+
+  private var privateField: StructFromDirect
+}
+
+private struct ExposedLayoutPrivate {
+  private var privateField: StructFromDirect
+}
diff --git a/test/Sema/implementation-only-import-embedded.swift b/test/Sema/implementation-only-import-embedded.swift
new file mode 100644
index 0000000000000..831f44f946d2a
--- /dev/null
+++ b/test/Sema/implementation-only-import-embedded.swift
@@ -0,0 +1,210 @@
+/// Test @_implementationOnly import exportability diagnostics in embedded mode.
+
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -o %t/indirects.swiftmodule \
+// RUN:   %S/Inputs/implementation-only-imports/indirects.swift \
+// RUN:   -swift-version 5 -target arm64-apple-none-macho \
+// RUN:   -enable-experimental-feature Embedded
+// RUN: %target-swift-frontend -emit-module -o %t/directs.swiftmodule -I %t\
+// RUN:    %S/Inputs/implementation-only-imports/directs.swift \
+// RUN:   -swift-version 5 -target arm64-apple-none-macho \
+// 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:   -define-availability "availMacro:macOS 26.0, iOS 26.0" \
+// RUN:   -enable-experimental-feature Embedded
+
+// REQUIRES: swift_feature_Embedded
+// REQUIRES: embedded_stdlib_cross_compiling
+
+@_implementationOnly import directs
+// expected-warning @-1 {{using '@_implementationOnly' without enabling library evolution for 'main' may lead to instability during execution}}
+import indirects
+
+internal func localInternalFunc() {} // expected-note {{global function 'localInternalFunc()' is not '@usableFromInline' or public}}
+
+@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}}
+// expected-error @-2 {{struct 'StructFromDirect' cannot be used in a default argument value because 'directs' was imported implementation-only}}
+// expected-error @-3 {{struct 'StructFromDirect' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+  _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+  // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+
+  if (true) {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+    // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+  }
+
+  func nested() {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+    // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an '@inlinable' function because 'directs' was imported implementation-only}}
+  }
+  nested()
+
+  localInternalFunc() // expected-error {{global function 'localInternalFunc()' is internal and cannot be referenced from an '@inlinable' function}}
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate() // expected-error {{global function 'implicitlyInlinablePrivate(arg:)' is private and cannot be referenced from an '@inlinable' function}}
+  explicitNonInliable()
+}
+
+public func implicitlyInlinablePublic(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{initializer 'init()' cannot be used in a default argument value because 'directs' was imported implementation-only}}
+// expected-error @-2 {{struct 'StructFromDirect' cannot be used in a default argument value because 'directs' was imported implementation-only}}
+// expected-error @-3 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+
+  _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+  // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+
+  if (true) {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+    // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+  }
+
+  func nested() {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+    // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+
+  if #available(availMacro, *) { }
+}
+
+private func implicitlyInlinablePrivate(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+// expected-note @-2 {{global function 'implicitlyInlinablePrivate(arg:)' is not '@usableFromInline' or public}}
+
+  _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+  // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+
+  if (true) {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+    // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+  }
+
+  func nested() {
+    _ = StructFromDirect() // expected-error {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+    // expected-error@-1 {{struct 'StructFromDirect' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+}
+
+@_neverEmitIntoClient
+public func explicitNonInliable(arg: StructFromDirect = StructFromDirect()) {
+// expected-error @-1 {{initializer 'init()' cannot be used in a default argument value because 'directs' was imported implementation-only}}
+// expected-error @-2 {{struct 'StructFromDirect' cannot be used in a default argument value because 'directs' was imported implementation-only}}
+// expected-error @-3 {{cannot use struct 'StructFromDirect' here; 'directs' has been imported as implementation-only}}
+
+  _ = StructFromDirect()
+
+  if (true) {
+    _ = StructFromDirect()
+  }
+
+  func nested() {
+    _ = StructFromDirect()
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+}
+
+@_neverEmitIntoClient
+internal func explicitNonInliableInternal(arg: StructFromDirect = StructFromDirect()) {
+  _ = StructFromDirect()
+
+  if (true) {
+    _ = StructFromDirect()
+  }
+
+  func nested() {
+    _ = StructFromDirect()
+  }
+  nested()
+
+  localInternalFunc()
+
+  explicitlyInlinable()
+  implicitlyInlinablePublic()
+  implicitlyInlinablePrivate()
+  explicitNonInliable()
+
+  struct NestedStruct {}
+}
+
+struct Accessors {
+  public var var1: Int {
+    get {
+      globalFunctionFromDirect() // expected-error {{global function 'globalFunctionFromDirect()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+      return 0
+    }
+  }
+
+  @_alwaysEmitIntoClient
+  public var var2: Int {
+    get {
+      globalFunctionFromDirect() // expected-error {{global function 'globalFunctionFromDirect()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'directs' was imported implementation-only}}
+      return 0
+    }
+  }
+
+  @_neverEmitIntoClient
+  public var var3: Int {
+    get {
+      globalFunctionFromDirect()
+      return 0
+    }
+  }
+
+  public var var4: Int {
+    @_neverEmitIntoClient
+    get {
+      globalFunctionFromDirect()
+      return 0
+    }
+  }
+}
+
+public func legalAccessToIndirect(arg: StructFromIndirect = StructFromIndirect()) {
+  _ = StructFromIndirect()
+
+  if (true) {
+    _ = StructFromIndirect()
+  }
+
+  func nested() {
+    _ = StructFromIndirect()
+  }
+  nested()
+}
+
+public struct ExposedLayoutPublic {
+  public var publicField: StructFromDirect // expected-error {{cannot use struct 'StructFromDirect' here; 'directs' has been imported as implementation-only}}
+
+  private var privateField: StructFromDirect // FIXME should error
+}
+
+private struct ExposedLayoutPrivate {
+  private var privateField: StructFromDirect // FIXME should error
+}
diff --git a/test/embedded/implementation-only-import-build.swift b/test/embedded/implementation-only-import-build.swift
new file mode 100644
index 0000000000000..82b0b276deb03
--- /dev/null
+++ b/test/embedded/implementation-only-import-build.swift
@@ -0,0 +1,66 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -o %t/indirects.swiftmodule \
+// RUN:   %S/../Sema/Inputs/implementation-only-imports/indirects.swift \
+// RUN:   -enable-experimental-feature Embedded
+// RUN: %target-swift-frontend -emit-module -o %t/directs.swiftmodule -I %t\
+// RUN:    %S/../Sema/Inputs/implementation-only-imports/directs.swift \
+// RUN:   -enable-experimental-feature Embedded
+
+// RUN: %target-swift-frontend -emit-sil %s -I %t \
+// RUN:   -enable-experimental-feature Embedded
+
+// REQUIRES: swift_feature_Embedded
+// REQUIRES: embedded_stdlib_cross_compiling
+
+@_implementationOnly import directs
+import indirects
+
+internal func localInternalFunc() {}
+
+public func implicitlyInlinablePublic() {
+  localInternalFunc()
+}
+
+private func implicitlyInlinablePrivate() {
+  localInternalFunc()
+}
+
+@_neverEmitIntoClient
+public func explicitNonInliable() {
+  _ = StructFromDirect()
+
+  if (true) {
+    _ = StructFromDirect()
+  }
+
+  @_neverEmitIntoClient
+  func nested() {
+    _ = StructFromDirect()
+  }
+  nested()
+
+  localInternalFunc()
+}
+
+@_alwaysEmitIntoClient
+public func legalAccessToIndirect() {
+  _ = StructFromIndirect()
+
+  if (true) {
+    _ = StructFromIndirect()
+  }
+
+  func nested() {
+    _ = StructFromIndirect()
+  }
+  nested()
+}
+
+extension Array {
+  @_alwaysEmitIntoClient
+  public var myMutableSpan: Int {
+    get {
+      return 0
+    }
+  }
+}
diff --git a/test/embedded/linkage/implementation_only_hiding.swift b/test/embedded/linkage/implementation_only_hiding.swift
index 079c6f02cc7ca..a987f75925594 100644
--- a/test/embedded/linkage/implementation_only_hiding.swift
+++ b/test/embedded/linkage/implementation_only_hiding.swift
@@ -12,7 +12,7 @@
 // RUN: cp %S/Inputs/CHeader.h %t/Dependencies/
 // RUN: cp %S/Inputs/module.modulemap %t/Dependencies/
 
-// RUN: split-file %s %t/Files
+// RUN: split-file %s %t/Files --leading-lines
 
 // Compile the Swift dependencies into that same location.
 // RUN: %target-swift-frontend -parse-as-library -emit-module %t/Dependencies/SwiftDependency.swift -enable-experimental-feature Embedded -o %t/Dependencies/SwiftDependency.swiftmodule
@@ -21,6 +21,9 @@
 // against the dependencies.
 // RUN: %target-swift-frontend -parse-as-library -emit-module %t/Files/Library.swift -enable-experimental-feature Embedded -I %t/Dependencies/ -o %t/Modules/Library.swiftmodule
 
+// Building the library with invalid uses trigger errors.
+// RUN: %target-swift-frontend -parse-as-library -typecheck -verify %t/Files/Library.swift -enable-experimental-feature Embedded -I %t/Dependencies/ -o %t/Modules/Library.swiftmodule -DBAD_IOI_USAGE
+
 // Remove the dependencies so there is no way we can find them later.
 // RUN: rm -rf %t/Dependencies
 
@@ -28,19 +31,12 @@
 // @_neverEmitIntoClient hides the body of test().
 // RUN: %target-swift-frontend -emit-ir -parse-as-library %t/Files/Application.swift -enable-experimental-feature Embedded -I %t/Modules -o %t/Application.ir
 
-// Build the application against the library, but intentionally trigger
-// deserialization of some serialized SIL that refers to an implementation-only
-// dependency. Right now, these fail spectacularly. Over time, we want them to
-// become compile-time errors or start working.
-// RUN: not --crash %target-swift-frontend -emit-ir -parse-as-library %t/Files/Application.swift -enable-experimental-feature Embedded -I %t/Modules -o %t/Application.ir -DBAD_C_USAGE
-// RUN: not --crash %target-swift-frontend -emit-ir -parse-as-library %t/Files/Application.swift -enable-experimental-feature Embedded -I %t/Modules -o %t/Application.ir -DBAD_SWIFT_USAGE
-
 // REQUIRES: swift_in_compiler
 // REQUIRES: swift_feature_Embedded
 
 //--- Library.swift
-@_implementationOnly import CDependency
-@_implementationOnly import SwiftDependency
+@_implementationOnly import CDependency // expected-warning {{using '@_implementationOnly' without enabling library evolution for 'Library' may lead to instability during execution}}
+@_implementationOnly import SwiftDependency // expected-warning {{using '@_implementationOnly' without enabling library evolution for 'Library' may lead to instability during execution}}
 
 @_neverEmitIntoClient
 public func test() {
@@ -48,13 +44,17 @@ public func test() {
   A().doSomething()
 }
 
+#if BAD_IOI_USAGE
 public func badCLibraryUsage() {
-  _ = getPoint(3.14159, 2.71828)
+  _ = getPoint(3.14159, 2.71828) // expected-error {{global function 'getPoint' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'CDependency' was imported implementation-only}}
 }
 
 public func badSwiftLibraryUsage() {
-  A().doSomething()
+  A().doSomething() // expected-error {{struct 'A' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'SwiftDependency' was imported implementation-only}}
+  // expected-error @-1 {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'SwiftDependency' was imported implementation-only}}
+  // expected-error @-2 {{instance method 'doSomething()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'SwiftDependency' was imported implementation-only}}
 }
+#endif
 
 //--- Application.swift
 
@@ -62,12 +62,4 @@ import Library
 
 public func useTest() {
   test()
-
-#if BAD_C_USAGE
-  badCLibraryUsage()
-#endif
-
-#if BAD_SWIFT_USAGE
-  badSwiftLibraryUsage()
-#endif
 }