Sema: Infer '@_usableFromInline' imports by looking at references from inlinable functions (#16326)

Basic fix for <rdar://problem/39338239>, but there are still some more cases we haven't handled yet.

Author: jrose-apple

include/swift/AST/Module.h

@@ -791,7 +791,7 @@ class SourceFile final : public FileUnit {
   /// This is the list of modules that are imported by this module.
   ///
   /// This is filled in by the Name Binding phase.
-  ArrayRef<std::pair<ModuleDecl::ImportedModule, ImportOptions>> Imports;
+  MutableArrayRef<std::pair<ModuleDecl::ImportedModule, ImportOptions>> Imports;
 
   /// A unique identifier representing this file; used to mark private decls
   /// within the file to keep them from conflicting with other files in the
@@ -897,6 +897,8 @@ class SourceFile final : public FileUnit {
 
   bool hasTestableImport(const ModuleDecl *module) const;
 
+  void markUsableFromInlineImport(const ModuleDecl *module);
+
   void clearLookupCache();
 
   void cacheVisibleDecls(SmallVectorImpl<ValueDecl *> &&globals) const;

lib/AST/Module.cpp

@@ -1287,6 +1287,14 @@ bool SourceFile::hasTestableImport(const swift::ModuleDecl *module) const {
   });
 }
 
+void SourceFile::markUsableFromInlineImport(const ModuleDecl *module) {
+  for (auto &Import : Imports) {
+    if (Import.first.second == module) {
+      Import.second |= ImportFlags::UsableFromInline;
+    }
+  }
+}
+
 void SourceFile::clearLookupCache() {
   if (!Cache)
     return;

lib/Sema/TypeCheckAvailability.cpp

@@ -2509,12 +2509,19 @@ bool AvailabilityWalker::diagAvailability(const ValueDecl *D, SourceRange R,
       return true;
   }
 
-  if (FragileKind)
-    if (R.isValid())
+  if (FragileKind) {
+    if (R.isValid()) {
       if (TC.diagnoseInlinableDeclRef(R.Start, D, DC, *FragileKind,
                                       TreatUsableFromInlineAsPublic))
         return true;
 
+      auto *SF = cast<SourceFile>(DC->getModuleScopeContext());
+      auto *M = D->getDeclContext()->getParentModule();
+      if (SF->getParentModule() != M)
+        SF->markUsableFromInlineImport(M);
+    }
+  }
+
   if (TC.diagnoseExplicitUnavailability(D, R, DC, call))
     return true;
 

test/Serialization/Inputs/autolinking_module_inferred.swift

@@ -0,0 +1,7 @@
+@_exported import autolinking_public
+import autolinking_other // inferred as @_usableFromInline
+import autolinking_private
+
+public func bfunc(x: Int = afunc()) {
+  cfunc()
+}

test/Serialization/autolinking-inlinable-inferred.swift

@@ -0,0 +1,32 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend -emit-module %S/Inputs/autolinking_public.swift -emit-module-path %t/autolinking_public.swiftmodule -module-link-name autolinking_public -swift-version 4
+// RUN: %target-swift-frontend -emit-module %S/Inputs/autolinking_other.swift -emit-module-path %t/autolinking_other.swiftmodule -module-link-name autolinking_other -swift-version 4
+// RUN: %target-swift-frontend -emit-module %S/Inputs/autolinking_private.swift -emit-module-path %t/autolinking_private.swiftmodule -module-link-name autolinking_private -I %t -swift-version 4
+// RUN: %target-swift-frontend -emit-module %S/Inputs/autolinking_module_inferred.swift -emit-module-path %t/autolinking_module_inferred.swiftmodule -module-link-name autolinking_module_inferred -I %t -swift-version 4
+// RUN: %target-swift-frontend -emit-ir %s -I %t -swift-version 4 | %FileCheck %s
+
+// This test is identical to autolinking-inlinable, except we also rely on the
+// '@_usableFromInline' attribute getting inferred correctly on the import.
+
+// Linux uses a different autolinking mechanism, based on
+// swift-autolink-extract. This file tests the Darwin mechanism.
+// UNSUPPORTED: OS=linux-gnu
+// UNSUPPORTED: OS=linux-gnueabihf
+// UNSUPPORTED: OS=freebsd
+// UNSUPPORTED: OS=linux-androideabi
+
+import autolinking_module_inferred
+
+bfunc()
+
+// Note: we don't autolink autolinking_private even though autolinking_module imports it also.
+
+// CHECK: !llvm.linker.options = !{[[SWIFTCORE:![0-9]+]], [[SWIFTONONESUPPORT:![0-9]+]], [[MODULE:![0-9]+]], [[PUBLIC:![0-9]+]], [[OTHER:![0-9]+]], [[OBJC:![0-9]+]]}
+
+// CHECK: [[SWIFTCORE]] = !{!"-lswiftCore"}
+// CHECK: [[SWIFTONONESUPPORT]] = !{!"-lswiftSwiftOnoneSupport"}
+// CHECK: [[MODULE]] = !{!"-lautolinking_module_inferred"}
+// CHECK: [[PUBLIC]] = !{!"-lautolinking_public"}
+// CHECK: [[OTHER]] = !{!"-lautolinking_other"}
+// CHECK: [[OBJC]] = !{!"-lobjc"}