Sema: ignore inconsistent bare imports from a file generated by Xcode

In Swift 5 mode, the compiler reports when two files import the same
module, where one file has a bare import and the other an access-level
import. This avoids unintentionally promoting the import to public when
preexisting code marked it otherwise.

Exempt a file generated by Xcode from this check as it's not user
modifiable.

In the future, we should identify such generated files properly. Either
with a new attribute or in the way they are passed to the compiler.

rdar://122032472

Author: xymus

lib/Sema/ImportResolution.cpp

@@ -1055,8 +1055,15 @@ CheckInconsistentAccessLevelOnImport::evaluate(
   auto mod = SF->getParentModule();
   auto diagnose = [mod](const ImportDecl *implicitImport,
                         const ImportDecl *otherImport) {
-    auto otherAccessLevel = otherImport->getAccessLevel();
+    // Ignore files generated by Xcode. We should probably identify them via
+    // an attribuite or frontend flag, until them match the file by name.
+    SourceFile *implicitSF =
+      implicitImport->getDeclContext()->getParentSourceFile();
+    StringRef basename = llvm::sys::path::filename(implicitSF->getFilename());
+    if (basename == "GeneratedAssetSymbols.swift")
+      return;
 
+    auto otherAccessLevel = otherImport->getAccessLevel();
     auto &diags = mod->getDiags();
     {
       InFlightDiagnostic error =

test/Sema/access-level-import-inconsistencies.swift

@@ -69,3 +69,16 @@ package import Lib // expected-note {{imported 'package' here}} @:1
 import Lib
 //--- ManyFiles_AmbiguitySwift6_FileB.swift
 internal import Lib
+
+/// Don't report inconsistencies from a file generated by Xcode.
+// RUN: %target-swift-frontend -typecheck -I %t \
+// RUN    -primary-file %t/GeneratedAssetSymbols.swift \
+// RUN:   %t/UserWrittenFile.swift -verify
+// RUN: %target-swift-frontend -typecheck -I %t \
+// RUN    %t/GeneratedAssetSymbols.swift \
+// RUN:   -primary-file %t/UserWrittenFile.swift -verify
+//--- UserWrittenFile.swift
+internal import Lib
+//--- GeneratedAssetSymbols.swift
+import Lib
+