[Sema] @_private imports brings is all SPI of the imported module

lib/AST/Module.cpp

@@ -3419,6 +3419,9 @@ bool SourceFile::isImportedAsSPI(const ValueDecl *targetDecl) const {
   if (shouldImplicitImportAsSPI(targetDecl->getSPIGroups()))
     return true;
 
+  if (hasTestableOrPrivateImport(AccessLevel::Public, targetDecl, PrivateOnly))
+    return true;
+
   lookupImportedSPIGroups(targetModule, importedSPIGroups);
   if (importedSPIGroups.empty())
     return false;

test/SPI/private-import-access-spi.swift

@@ -0,0 +1,68 @@
+/// An `@_private` import opens access to all SPIs of the imported module.
+/// Exports of SPI in API are still reported.
+
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+/// Build the library.
+// RUN: %target-swift-frontend -emit-module %t/Lib_FileA.swift %t/Lib_FileB.swift \
+// RUN:   -module-name Lib -emit-module-path %t/Lib.swiftmodule \
+// RUN:   -enable-library-evolution -swift-version 5 \
+// RUN:   -enable-private-imports
+
+/// Typecheck a @_private client.
+// RUN: %target-swift-frontend -typecheck -verify -I %t %t/PrivateClient.swift
+
+/// Typecheck a regular client building against the same Lib with private imports enabled.
+// RUN: %target-swift-frontend -typecheck -verify -I %t %t/RegularClient.swift
+
+//--- Lib_FileA.swift
+@_spi(S) public func spiFuncA() {}
+@_spi(S) public struct SPITypeA {}
+
+//--- Lib_FileB.swift
+@_spi(S) public func spiFuncB() {}
+@_spi(S) public struct SPITypeB {}
+
+//--- PrivateClient.swift
+@_private(sourceFile: "Lib_FileA.swift") import Lib
+
+func useOnly(a: SPITypeA, b: SPITypeB) {
+  spiFuncA()
+  spiFuncB()
+}
+
+public func export(a: SPITypeA, b: SPITypeB) { // expected-error {{cannot use struct 'SPITypeA' here; it is an SPI imported from 'Lib'}}
+                                           // expected-error @-1 {{cannot use struct 'SPITypeB' here; it is an SPI imported from 'Lib'}}
+  spiFuncA()
+  spiFuncB()
+}
+
+@inlinable
+public func inlinableExport(a: SPITypeA, b: SPITypeB) { // expected-error {{struct 'SPITypeA' cannot be used in an '@inlinable' function because it is an SPI imported from 'Lib'}}
+                                                    // expected-error @-1 {{struct 'SPITypeB' cannot be used in an '@inlinable' function because it is an SPI imported from 'Lib'}}
+  spiFuncA() // expected-error {{global function 'spiFuncA()' cannot be used in an '@inlinable' function because it is an SPI imported from 'Lib'}}
+  spiFuncB() // expected-error {{global function 'spiFuncB()' cannot be used in an '@inlinable' function because it is an SPI imported from 'Lib'}}
+}
+
+//--- RegularClient.swift
+import Lib
+
+func useOnly(a: SPITypeA, b: SPITypeB) { // expected-error {{cannot find type 'SPITypeA' in scope}}
+                                     // expected-error @-1 {{cannot find type 'SPITypeB' in scope}}
+  spiFuncA() // expected-error {{cannot find 'spiFuncA' in scope}}
+  spiFuncB() // expected-error {{cannot find 'spiFuncB' in scope}}
+}
+
+public func export(a: SPITypeA, b: SPITypeB) { // expected-error {{cannot find type 'SPITypeA' in scope}}
+                                           // expected-error @-1 {{cannot find type 'SPITypeB' in scope}}
+  spiFuncA() // expected-error {{cannot find 'spiFuncA' in scope}}
+  spiFuncB() // expected-error {{cannot find 'spiFuncB' in scope}}
+}
+
+@inlinable
+public func inlinableExport(a: SPITypeA, b: SPITypeB) { // expected-error {{cannot find type 'SPITypeA' in scope}}
+                                                    // expected-error @-1 {{cannot find type 'SPITypeB' in scope}}
+  spiFuncA() // expected-error {{cannot find 'spiFuncA' in scope}}
+  spiFuncB() // expected-error {{cannot find 'spiFuncB' in scope}}
+}