Sema: track use in API of declaring and bystanders for cross-import overlay

Cross-import overlays are imported automatically if the declaring
module and the bystanders modules are also imported. In theory,
one could import the declaring module and bystanders without using
them and use only the overlay in API. Let’s make sure we track these
indirect uses to avoid superfluous warning.

rdar://129779460

Author: xymus

lib/AST/Module.cpp

@@ -2716,6 +2716,26 @@ void SourceFile::registerAccessLevelUsingImport(
     ImportsUseAccessLevel[mod] = accessLevel;
   else
     ImportsUseAccessLevel[mod] = std::max(accessLevel, known->second);
+
+  // Also register modules triggering the import of cross-import overlays.
+  auto declaringMod = mod->getDeclaringModuleIfCrossImportOverlay();
+  if (!declaringMod)
+    return;
+
+  SmallVector<Identifier, 1> bystanders;
+  auto bystandersValid =
+    mod->getRequiredBystandersIfCrossImportOverlay(declaringMod, bystanders);
+  if (!bystandersValid)
+    return;
+
+  for (auto &otherImport : *Imports) {
+    auto otherImportMod = otherImport.module.importedModule;
+    auto otherImportModName = otherImportMod->getName();
+    if (otherImportMod == declaringMod ||
+        llvm::find(bystanders, otherImportModName) != bystanders.end()) {
+      registerAccessLevelUsingImport(otherImport, accessLevel);
+    }
+  }
 }
 
 bool HasImportsMatchingFlagRequest::evaluate(Evaluator &evaluator,

test/CrossImport/access-level-imports-errors.swift

@@ -4,11 +4,15 @@
 // RUN: cp -r %S/Inputs/lib-templates/* %t/
 // RUN: split-file --leading-lines %s %t
 
+//--- SomeUnrelatedModule.swift
+// RUN: %target-swift-emit-module-interface(%t/lib/swift/SomeUnrelatedModule.swiftinterface) %t/SomeUnrelatedModule.swift -module-name SomeUnrelatedModule
+
 //--- BothPublic.swift
-// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/BothPublic.swift -enable-cross-import-overlays -I %t/lib/swift -module-name ClientLibrary
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/BothPublic.swift -enable-cross-import-overlays -I %t/lib/swift -module-name ClientLibrary -verify
 
 public import DeclaringLibrary
 public import BystandingLibrary
+public import SomeUnrelatedModule // expected-warning {{public import of 'SomeUnrelatedModule' was not used in public declarations or inlinable code}}
 
 public func fn(_: OverlayLibraryTy) {}
 
@@ -28,7 +32,7 @@ public func fn(_: OverlayLibraryTy) {}
 // RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/FirstHidden.swift -enable-cross-import-overlays -I %t/lib/swift -module-name ClientLibrary -verify
 
 internal import DeclaringLibrary
-public import BystandingLibrary // expected-warning {{public import of 'BystandingLibrary' was not used in public declarations or inlinable code}}
+public import BystandingLibrary
 
 public func fn(_: OverlayLibraryTy) {}
 // expected-error @-1 {{function cannot be declared public because its parameter uses an internal type}}
@@ -38,7 +42,7 @@ public func fn(_: OverlayLibraryTy) {}
 //--- SecondHidden.swift
 // RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/SecondHidden.swift -enable-cross-import-overlays -I %t/lib/swift -module-name ClientLibrary -verify
 
-public import DeclaringLibrary // expected-warning {{public import of 'DeclaringLibrary' was not used in public declarations or inlinable code}}
+public import DeclaringLibrary
 internal import BystandingLibrary
 
 public func fn(_: OverlayLibraryTy) {}
@@ -66,3 +70,11 @@ private import BystandingLibrary
 internal func fn(_: OverlayLibraryTy) {}
 // expected-error @-1 {{function cannot be declared internal because its parameter uses a private type}}
 // expected-note @-2 {{struct 'OverlayLibraryTy' is imported by this file as 'private' from '_OverlayLibrary'}}
+
+
+//--- UnusedOverlay.swift
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/UnusedOverlay.swift -enable-cross-import-overlays -I %t/lib/swift -module-name ClientLibrary -verify
+
+public import DeclaringLibrary // expected-warning {{public import of 'DeclaringLibrary' was not used in public declarations or inlinable code}}
+public import BystandingLibrary // expected-warning {{public import of 'BystandingLibrary' was not used in public declarations or inlinable code}}
+public import SomeUnrelatedModule // expected-warning {{public import of 'SomeUnrelatedModule' was not used in public declarations or inlinable code}}