Sema: Limit error on LE importing non-LE modules to SDK modules

Limit reporting as an error imports of a non-library-evolution module
from a library-evolution enabled module to sources that are part of the
SDK. The error also requires having enabled `InternalImportsByDefault`.
This should help prevent SDK breaking regressions while loosening the
restriction elsewhere.

Framework owners can enable `-library-level api` or `spi` to get this
check as an error, along with more sanity checks.

Other cases remain as a warning. We should look to silence it in some
cases or offer a flag to do so.

rdar://160414667

Author: xymus

lib/Sema/ImportResolution.cpp

@@ -908,21 +908,24 @@ void UnboundImport::validateResilience(NullablePtr<ModuleDecl> topLevelModule,
                                      targetName, importerName);
 
   if (ctx.LangOpts.hasFeature(Feature::InternalImportsByDefault)) {
-    // This will catch Swift 6 language mode as well where
-    // it will be reported as an error.
     inFlight.fixItRemove(import.accessLevelRange);
   } else {
     SourceRange attrRange = import.accessLevelRange;
     if (attrRange.isValid())
       inFlight.fixItReplace(attrRange, "internal");
     else
       inFlight.fixItInsert(import.importLoc, "internal ");
-
-    // Downgrade to warning only in pre-Swift 6 mode and
-    // when not using the experimental flag.
-    if (!ctx.LangOpts.hasFeature(Feature::AccessLevelOnImport))
-      inFlight.limitBehavior(DiagnosticBehavior::Warning);
   }
+
+  // Report as an error when InternalImportsByDefault is enabled or
+  // the experimental AccessLevelOnImport (but not Swift 6), only in libraries
+  // that are meant to be distributed.
+  auto featureEnabled =
+    ctx.LangOpts.hasFeature(Feature::AccessLevelOnImport) ||
+    ctx.LangOpts.hasFeature(Feature::InternalImportsByDefault);
+  if (!featureEnabled ||
+      SF.getParentModule()->getLibraryLevel() < LibraryLevel::SPI)
+    inFlight.limitBehavior(DiagnosticBehavior::Warning);
 }
 
 void UnboundImport::diagnoseInvalidAttr(DeclAttrKind attrKind,

test/ModuleInterface/imports-swift7.swift

@@ -5,8 +5,31 @@
 // RUN: %target-swift-frontend -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -emit-module -o %t/nonResilient.swiftmodule %t/empty.swift
 // RUN: %target-swift-frontend -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -emit-module -o %t/resilient.swiftmodule %t/empty.swift -enable-library-evolution
 
-/// Check errors.
-// RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/clientWithError.swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -I %t -verify -enable-upcoming-feature InternalImportsByDefault
+/// Warning vs error on public import of a non-LE module from LE.
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) \
+// RUN:     %t/clientWithError.swift -I %t -verify \
+// RUN:     -disable-implicit-concurrency-module-import \
+// RUN:     -disable-implicit-string-processing-module-import \
+// RUN:     -enable-upcoming-feature InternalImportsByDefault \
+// RUN:     -verify-additional-prefix library-level-private-
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) \
+// RUN:     %t/clientWithError.swift -I %t -verify \
+// RUN:     -disable-implicit-concurrency-module-import \
+// RUN:     -disable-implicit-string-processing-module-import \
+// RUN:     -enable-upcoming-feature InternalImportsByDefault \
+// RUN:     -verify-additional-prefix library-level-private- -library-level ipi
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) \
+// RUN:     %t/clientWithError.swift -I %t -verify \
+// RUN:     -disable-implicit-concurrency-module-import \
+// RUN:     -disable-implicit-string-processing-module-import \
+// RUN:     -enable-upcoming-feature InternalImportsByDefault \
+// RUN:     -verify-additional-prefix library-level-public- -library-level spi
+// RUN: %target-swift-emit-module-interface(%t.swiftinterface) \
+// RUN:     %t/clientWithError.swift -I %t -verify \
+// RUN:     -disable-implicit-concurrency-module-import \
+// RUN:     -disable-implicit-string-processing-module-import \
+// RUN:     -enable-upcoming-feature InternalImportsByDefault \
+// RUN:     -verify-additional-prefix library-level-public- -library-level api
 
 /// Check Swift 7 imports printed in swiftinterface from 2 source files.
 // RUN: %target-swift-emit-module-interface(%t.swiftinterface) %t/main.swift %t/main-other.swift -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -I %S/Inputs/imports-clang-modules/ -I %t -verify -enable-upcoming-feature InternalImportsByDefault
@@ -38,8 +61,11 @@ public import D // expected-warning {{public import of 'D' was not used in publi
 public import NotSoSecret // expected-warning {{'NotSoSecret' inconsistently imported as implementation-only}}
 // expected-warning @-1 {{public import of 'NotSoSecret' was not used in public declarations or inlinable code}}
 @_implementationOnly import NotSoSecret2 // expected-note {{imported as implementation-only here}}
+
 //--- clientWithError.swift
-@_exported public import nonResilient // expected-error {{module 'nonResilient' was not compiled with library evolution support; using it means binary compatibility for 'clientWithError' can't be guaranteed}}
+@_exported public import nonResilient
+// expected-library-level-public-error @-1 {{module 'nonResilient' was not compiled with library evolution support; using it means binary compatibility for 'clientWithError' can't be guaranteed}}
+// expected-library-level-private-warning @-2 {{module 'nonResilient' was not compiled with library evolution support; using it means binary compatibility for 'clientWithError' can't be guaranteed}}
 
 // CHECK-7-NOT: import
 // CHECK-7: {{^}}public import A{{$}}

test/Sema/access-level-and-non-resilient-import.swift

@@ -13,24 +13,25 @@
 // RUN: %target-swift-frontend -emit-module %t/PrivateLib.swift -o %t
 
 /// A resilient client will error on public imports.
-/// Keep AccessLevelOnImport to get the error from Swift 6 in Swift 5.
+/// Use AccessLevelOnImport or InternalImportsByDefault to get the error
+/// from Swift 7 in Swift 5.
 // RUN: %target-swift-frontend -typecheck %t/Client_Swift5.swift -I %t \
 // RUN:   -enable-library-evolution -swift-version 5 \
 // RUN:   -enable-experimental-feature AccessLevelOnImport -verify \
-// RUN:   -package-name pkg
-// RUN: %target-swift-frontend -typecheck %t/Client_Swift6.swift -I %t \
+// RUN:   -package-name pkg -library-level api
+// RUN: %target-swift-frontend -typecheck %t/Client_Swift7.swift -I %t \
 // RUN:   -enable-library-evolution \
 // RUN:   -enable-upcoming-feature InternalImportsByDefault \
-// RUN:   -verify -package-name pkg
+// RUN:   -verify -package-name pkg -library-level api
 
 /// A non-resilient client doesn't complain.
 // RUN: %target-swift-frontend -typecheck %t/Client_Swift5.swift -I %t \
 // RUN:   -swift-version 5 \
 // RUN:   -enable-experimental-feature AccessLevelOnImport \
-// RUN:   -package-name pkg
-// RUN: %target-swift-frontend -typecheck %t/Client_Swift6.swift -I %t \
+// RUN:   -package-name pkg -library-level api
+// RUN: %target-swift-frontend -typecheck %t/Client_Swift7.swift -I %t \
 // RUN:   -enable-upcoming-feature InternalImportsByDefault \
-// RUN:   -package-name pkg
+// RUN:   -package-name pkg -library-level api
 
 // REQUIRES: swift_feature_AccessLevelOnImport
 // REQUIRES: swift_feature_InternalImportsByDefault
@@ -53,10 +54,10 @@ internal import InternalLib
 fileprivate import FileprivateLib
 private import PrivateLib
 
-//--- Client_Swift6.swift
+//--- Client_Swift7.swift
 
 import DefaultLib
-public import PublicLib // expected-error {{module 'PublicLib' was not compiled with library evolution support; using it means binary compatibility for 'Client_Swift6' can't be guaranteed}} {{1-8=}}
+public import PublicLib // expected-error {{module 'PublicLib' was not compiled with library evolution support; using it means binary compatibility for 'Client_Swift7' can't be guaranteed}} {{1-8=}}
 // expected-warning @-1 {{public import of 'PublicLib' was not used in public declarations or inlinable code}}
 package import PackageLib
 // expected-warning @-1 {{package import of 'PackageLib' was not used in package declarations}}