[ModuleInterface] Filter using access control and @usableFromInline (#18521)

These are the parts of a (resilient) module that affect the public
interface and ABI; everything else is uninteresting. Or at least ought
to be.

lib/AST/ASTPrinter.cpp

@@ -71,7 +71,24 @@ PrintOptions PrintOptions::printTextualInterfaceFile() {
   result.PrintIfConfig = false;
   result.FullyQualifiedTypes = true;
   result.SkipImports = true;
-  result.AccessFilter = AccessLevel::Public;
+
+  class UsableFromInlineOnly : public ShouldPrintChecker {
+    bool shouldPrint(const Decl *D, PrintOptions &options) override {
+      if (auto *VD = dyn_cast<ValueDecl>(D)) {
+        AccessScope accessScope =
+            VD->getFormalAccessScope(/*useDC*/nullptr,
+                                     /*treatUsableFromInlineAsPublic*/true);
+        if (!accessScope.isPublic())
+          return false;
+      }
+      return ShouldPrintChecker::shouldPrint(D, options);
+    }
+  };
+  result.CurrentPrintabilityChecker = std::make_shared<UsableFromInlineOnly>();
+
+  // FIXME: We don't really need 'public' on everything; we could just change
+  // the default to 'public' and mark the 'internal' things.
+  result.PrintAccess = true;
 
   // FIXME: We'll need the actual default parameter expression.
   result.PrintDefaultParameterPlaceholder = false;

test/ModuleInterface/access-filter.swift

@@ -0,0 +1,99 @@
+// RUN: %target-swift-frontend -emit-interface-path %t.swiftinterface -emit-module -o /dev/null %s
+// RUN: %FileCheck %s < %t.swiftinterface
+// RUN: %FileCheck -check-prefix NEGATIVE %s < %t.swiftinterface
+
+// NEGATIVE-NOT: BAD
+
+// CHECK: public func publicFn(){{$}}
+public func publicFn() {}
+internal func internalFn_BAD() {}
+private func privateFn_BAD() {}
+
+// CHECK: @usableFromInline
+// CHECK-NEXT: internal func ufiFn(){{$}}
+@usableFromInline internal func ufiFn() {}
+
+
+// CHECK: public struct PublicStruct {{[{]$}}
+public struct PublicStruct {
+  // CHECK: public func publicMethod(){{$}}
+  public func publicMethod() {}
+  internal func internalMethod_BAD() {}
+
+  // CHECK: @usableFromInline
+  // CHECK-NEXT: internal func ufiMethod(){{$}}
+  @usableFromInline internal func ufiMethod() {}
+} // CHECK: {{^[}]$}}
+
+internal struct InternalStruct_BAD {
+  public func publicMethod_BAD() {}
+  internal func internalMethod_BAD() {}
+  @usableFromInline internal func ufiMethod_BAD() {}
+}
+
+// CHECK: @usableFromInline
+// CHECK-NEXT: internal struct UFIStruct {{[{]$}}
+@usableFromInline
+internal struct UFIStruct {
+  // FIXME: Arguably this should be downgraded to "@usableFromInline internal".
+  // CHECK: public func publicMethod(){{$}}
+  public func publicMethod() {}
+  internal func internalMethod_BAD() {}
+
+  // CHECK: @usableFromInline
+  // CHECK-NEXT: internal func ufiMethod(){{$}}
+  @usableFromInline internal func ufiMethod() {}
+} // CHECK: {{^[}]$}}
+
+// CHECK: public protocol PublicProto {{[{]$}}
+public protocol PublicProto {
+} // CHECK: {{^[}]$}}
+
+// CHECK: extension PublicProto {{[{]$}}
+extension PublicProto {
+  // CHECK: public func publicMethod(){{$}}
+  public func publicMethod() {}
+  internal func internalMethod_BAD() {}
+
+  // CHECK: @usableFromInline
+  // CHECK-NEXT: internal func ufiMethod(){{$}}
+  @usableFromInline internal func ufiMethod() {}
+} // CHECK: {{^[}]$}}
+
+// FIXME: We shouldn't print access on extensions in textual interface files.
+// CHECK: {{^}}public extension PublicProto {{[{]$}}
+public extension PublicProto {
+  // CHECK: public func publicExtPublicMethod(){{$}}
+  func publicExtPublicMethod() {}
+  internal func publicExtInternalMethod_BAD() {}
+
+  // CHECK: @usableFromInline
+  // CHECK-NEXT: internal func publicExtUFIMethod(){{$}}
+  @usableFromInline internal func publicExtUFIMethod() {}
+}
+
+internal protocol InternalProto_BAD {
+}
+
+extension InternalProto_BAD {
+  public func publicMethod_BAD() {}
+  internal func internalMethod_BAD() {}
+  @usableFromInline internal func ufiMethod_BAD() {}
+}
+
+// CHECK: @usableFromInline
+// CHECK-NEXT: internal protocol UFIProto {{[{]$}}
+@usableFromInline
+internal protocol UFIProto {
+} // CHECK: {{^[}]$}}
+
+// CHECK: extension UFIProto {{[{]$}}
+extension UFIProto {
+  // CHECK: public func publicMethod(){{$}}
+  public func publicMethod() {}
+  internal func internalMethod_BAD() {}
+
+  // CHECK: @usableFromInline
+  // CHECK-NEXT: internal func ufiMethod(){{$}}
+  @usableFromInline internal func ufiMethod() {}
+} // CHECK: {{^[}]$}}

test/ModuleInterface/print-from-partial-modules.swift

@@ -3,7 +3,7 @@
 // RUN: %target-swift-frontend -emit-module -o %t/other~partial.swiftmodule %s -primary-file %S/Inputs/other.swift -module-name main
 // RUN: %target-swift-frontend -merge-modules -emit-module -o /dev/null -emit-interface-path - %t/main~partial.swiftmodule -module-name main %t/other~partial.swiftmodule | %FileCheck %s
 
-// CHECK: {{^}}func verySimpleFunction(){{$}}
+// CHECK: {{^}}public func verySimpleFunction(){{$}}
 public func verySimpleFunction() {}
 
-// CHECK: {{^}}func otherFileFunction(){{$}}
+// CHECK: {{^}}public func otherFileFunction(){{$}}