ClangImporter: add support for Android API Notes

Introduce the first APINotes injection for the Android platform. This
follows the VCRuntime pattern of permitting the SDK to provide API Notes
that augment the system SDK. This adds a workaround for incorrect
nullability on the `fts_open` function in bionic. The system library
itself is fixed at:
https://android-review.googlesource.com/c/platform/bionic/+/3151616

Author: compnerd

lib/ClangImporter/ClangIncludePaths.cpp

@@ -396,25 +396,49 @@ static void getLibStdCxxFileMapping(
 
 namespace {
 std::string
-GetWindowsAuxiliaryFile(StringRef modulemap, const SearchPathOptions &Options) {
+GetPlatformAuxiliaryFile(StringRef Platform, StringRef File,
+                         const SearchPathOptions &Options) {
   StringRef SDKPath = Options.getSDKPath();
   if (!SDKPath.empty()) {
     llvm::SmallString<261> path{SDKPath};
-    llvm::sys::path::append(path, "usr", "share", modulemap);
+    llvm::sys::path::append(path, "usr", "share", File);
     if (llvm::sys::fs::exists(path))
       return path.str().str();
   }
 
   if (!Options.RuntimeResourcePath.empty()) {
     llvm::SmallString<261> path{Options.RuntimeResourcePath};
-    llvm::sys::path::append(path, "windows", modulemap);
+    llvm::sys::path::append(path, Platform, File);
     if (llvm::sys::fs::exists(path))
       return path.str().str();
   }
 
   return "";
 }
 
+SmallVector<std::pair<std::string, std::string>, 2>
+GetAndroidFileMappings(
+    ASTContext &Context, const std::string &sysroot,
+    const llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> &VFS) {
+  const llvm::Triple &Triple = Context.LangOpts.Target;
+  const SearchPathOptions &SearchPathOpts = Context.SearchPathOpts;
+  SmallVector<std::pair<std::string, std::string>, 2> Mappings;
+  std::string AuxiliaryFile;
+
+  if (!Triple.isAndroid()) return Mappings;
+
+  llvm::SmallString<261> NDKInjection{sysroot};
+  llvm::sys::path::append(NDKInjection, "posix_filesystem.apinotes");
+
+  AuxiliaryFile =
+      GetPlatformAuxiliaryFile("android", "posix_filesystem.apinotes",
+                               SearchPathOpts);
+  if (!AuxiliaryFile.empty())
+    Mappings.emplace_back(std::string(NDKInjection), AuxiliaryFile);
+
+  return Mappings;
+}
+
 SmallVector<std::pair<std::string, std::string>, 2> GetWindowsFileMappings(
     ASTContext &Context,
     const llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> &driverVFS,
@@ -449,7 +473,8 @@ SmallVector<std::pair<std::string, std::string>, 2> GetWindowsFileMappings(
       llvm::sys::path::append(WinSDKInjection, WindowsSDK.IncludeVersion, "um");
     llvm::sys::path::append(WinSDKInjection, "module.modulemap");
 
-    AuxiliaryFile = GetWindowsAuxiliaryFile("winsdk.modulemap", SearchPathOpts);
+    AuxiliaryFile =
+        GetPlatformAuxiliaryFile("windows", "winsdk.modulemap", SearchPathOpts);
     if (!AuxiliaryFile.empty())
       Mappings.emplace_back(std::string(WinSDKInjection), AuxiliaryFile);
   }
@@ -465,7 +490,8 @@ SmallVector<std::pair<std::string, std::string>, 2> GetWindowsFileMappings(
     llvm::sys::path::append(UCRTInjection, "Include", UCRTSDK.Version, "ucrt");
     llvm::sys::path::append(UCRTInjection, "module.modulemap");
 
-    AuxiliaryFile = GetWindowsAuxiliaryFile("ucrt.modulemap", SearchPathOpts);
+    AuxiliaryFile =
+        GetPlatformAuxiliaryFile("windows", "ucrt.modulemap", SearchPathOpts);
     if (!AuxiliaryFile.empty()) {
       // The ucrt module map has the C standard library headers all together.
       // That leads to module cycles with the clang _Builtin_ modules. e.g.
@@ -502,14 +528,16 @@ SmallVector<std::pair<std::string, std::string>, 2> GetWindowsFileMappings(
 
     llvm::sys::path::append(VCToolsInjection, "module.modulemap");
     AuxiliaryFile =
-        GetWindowsAuxiliaryFile("vcruntime.modulemap", SearchPathOpts);
+        GetPlatformAuxiliaryFile("windows", "vcruntime.modulemap",
+                                 SearchPathOpts);
     if (!AuxiliaryFile.empty())
       Mappings.emplace_back(std::string(VCToolsInjection), AuxiliaryFile);
 
     llvm::sys::path::remove_filename(VCToolsInjection);
     llvm::sys::path::append(VCToolsInjection, "vcruntime.apinotes");
     AuxiliaryFile =
-        GetWindowsAuxiliaryFile("vcruntime.apinotes", SearchPathOpts);
+        GetPlatformAuxiliaryFile("windows", "vcruntime.apinotes",
+                                 SearchPathOpts);
     if (!AuxiliaryFile.empty())
       Mappings.emplace_back(std::string(VCToolsInjection), AuxiliaryFile);
   }
@@ -525,6 +553,7 @@ ClangInvocationFileMapping swift::getClangInvocationFileMapping(
     vfs = llvm::vfs::getRealFileSystem();
 
   const llvm::Triple &triple = ctx.LangOpts.Target;
+  llvm::SmallString<256> sysroot;
 
   // For modulemaps that have all the C standard library headers together in
   // a single module, we end up with module cycles with the clang _Builtin_
@@ -560,6 +589,11 @@ ClangInvocationFileMapping swift::getClangInvocationFileMapping(
     StringRef headerFiles[] = {"SwiftAndroidNDK.h", "SwiftBionic.h"};
     libcFileMapping =
         getLibcFileMapping(ctx, "android.modulemap", headerFiles, vfs);
+
+    if (!libcFileMapping.empty()) {
+      sysroot = libcFileMapping[0].first;
+      llvm::sys::path::remove_filename(sysroot);
+    }
   } else if (triple.isOSGlibc() || triple.isOSOpenBSD() ||
              triple.isOSFreeBSD()) {
     // BSD/Linux Mappings
@@ -577,5 +611,8 @@ ClangInvocationFileMapping swift::getClangInvocationFileMapping(
   result.redirectedFiles.append(GetWindowsFileMappings(
       ctx, vfs, result.requiresBuiltinHeadersInSystemModules));
 
+  result.redirectedFiles.append(GetAndroidFileMappings(ctx, sysroot.str().str(),
+                                                       vfs));
+
   return result;
 }

stdlib/public/Platform/CMakeLists.txt

@@ -473,6 +473,11 @@ if("ANDROID" IN_LIST SWIFT_SDKS)
                                  COMPONENT sdk-overlay)
     endif()
   endforeach()
+
+  swift_install_in_component(FILES
+      posix_filesystem.apinotes
+    DESTINATION "share"
+    COMPONENT sdk-overlay)
 endif()
 add_custom_target(android_modulemap DEPENDS ${android_modulemap_target_list})
 set_property(TARGET android_modulemap PROPERTY FOLDER "Miscellaneous")

stdlib/public/Platform/posix_filesystem.apinotes

@@ -0,0 +1,7 @@
+---
+Name: bionic
+Functions:
+- Name: fts_open
+  Parameters:
+  - Position: 0
+    Type: "char * const _Nullable * _Nonnull"