[modules] Allow frameworks to have only a private module without a public one.

[vsapsai]

Summary

Support only preferred spelling 'Modules/module.private.modulemap' and
not the deprecated 'module_private.map'.

rdar://problem/57715533

[vsapsai]

Looks like other module-related tracking like LoadedModuleMaps, DirectoryHasModuleMap works without extra changes. And ModuleMapParser relies on a file name to decide if a module map is private or not, so the presence of a public module map doesn't matter for it.

clang/lib/Lex/HeaderSearch.cpp

1463–1470

We don't try to strip/add file extensions, so won't try to load a module map like 'module.private.private.modulemap'.

[bruno]

Sounds great!

clang/lib/Lex/HeaderSearch.cpp

if (needModuleLookup(RequestingModule, SuggestedModule)) {
     // so that this is not possible.
     return suggestModule(*this, File, RequestingModule, SuggestedModule);
   }
   return true;
 }
 
 static const FileEntry *getPrivateModuleMap(const FileEntry *File,
                                             FileManager &FileMgr) {
   StringRef Filename = llvm::sys::path::filename(File->getName());
   SmallString<128>  PrivateFilename(File->getDir()->getName());
   if (Filename == "module.map")
     llvm::sys::path::append(PrivateFilename, "module_private.map");
   else if (Filename == "module.modulemap")
     llvm::sys::path::append(PrivateFilename, "module.private.modulemap");
   else
     return nullptr;
   if (auto File = FileMgr.getFile(PrivateFilename))
     return *File;
   return nullptr;
 }
 
 bool HeaderSearch::loadModuleMapFile(const FileEntry *File, bool IsSystem,
                                      FileID ID, unsigned *Offset,
                                      StringRef OriginalModuleMapFile) {
HeaderSearch::lookupModuleMapFile(const DirectoryEntry *Dir, bool IsFramework) {
   if (auto F = FileMgr.getFile(ModuleMapFileName))
     return *F;
 
   // Continue to allow module.map
   ModuleMapFileName = Dir->getName();
   llvm::sys::path::append(ModuleMapFileName, "module.map");
   if (auto F = FileMgr.getFile(ModuleMapFileName))
     return *F;
+
+  // For frameworks, allow to have a private module map with a preferred
+  // spelling when a public module map is absent.
+  if (IsFramework) {
+    ModuleMapFileName = Dir->getName();
+    llvm::sys::path::append(ModuleMapFileName, "Modules",
+                            "module.private.modulemap");
+    if (auto F = FileMgr.getFile(ModuleMapFileName))
+      return *F;
+  }
   return nullptr;
 }
 
 Module *HeaderSearch::loadFrameworkModule(StringRef Name,
                                           const DirectoryEntry *Dir,
                                           bool IsSystem) {
   if (Module *Module = ModMap.findModule(Name))
     return Module;

clang/test/Modules/Inputs/implicit-private-without-public/DeprecatedModuleMapLocation.framework/PrivateHeaders/A.h

+void a(void);

clang/test/Modules/Inputs/implicit-private-without-public/DeprecatedModuleMapLocation.framework/module_private.map

+framework module DeprecatedModuleMapLocation_Private {
+  header "A.h"
+  export *
+}

clang/test/Modules/Inputs/implicit-private-without-public/Foo.framework/Modules/module.private.modulemap

+framework module Foo_Private {
+  header "Foo_Priv.h"
+  export *
+}

clang/test/Modules/Inputs/implicit-private-without-public/Foo.framework/PrivateHeaders/Foo_Priv.h

+void foo_private(void);

clang/test/Modules/implicit-private-without-public.m

+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t \
+// RUN:   -F%S/Inputs/implicit-private-without-public \
+// RUN:   -fsyntax-only %s -verify
+
+@import Foo_Private;
+
+// Private module map without a public one isn't supported for deprecated module map locations.
+@import DeprecatedModuleMapLocation_Private;
+// expected-error@-1{{module 'DeprecatedModuleMapLocation_Private' not found}}