[Modules] Don't search for modulemaps in the immediate sub-directories of search paths for recent Apple SDKs. (#100005)

Summary:
Such searches can be costly and non-intuitive. We've seen complaints
from developers that they don't expect clang to find modules on their
own and not in search paths that developers provide. Keeping the search
of modulemaps in subdirectories for code completion as it provides
better user experience.

If you are defining module "UsefulCode" in
"include/UnrelatedName/module.modulemap", it is recommended to rename
the directory "UnrelatedName" to "UsefulCode". If you cannot do so, you
can add to "include/module.modulemap" a line like `extern module
UsefulCode "UnrelatedName/module.modulemap"`, so clang can find module
"UsefulCode" without checking each subdirectory in "include/".

rdar://106677321

---------

Co-authored-by: Jan Svoboda <[email protected]>

Test Plan: 

Reviewers: 

Subscribers: 

Tasks: 

Tags: 


Differential Revision: https://phabricator.intern.facebook.com/D60251103

Author: vsapsai

clang/include/clang/Driver/Options.td

@@ -3232,6 +3232,10 @@ def fimplicit_module_maps : Flag <["-"], "fimplicit-module-maps">, Group<f_Group
   Visibility<[ClangOption, CC1Option, CLOption]>,
   HelpText<"Implicitly search the file system for module map files.">,
   MarshallingInfoFlag<HeaderSearchOpts<"ImplicitModuleMaps">>;
+defm modulemap_allow_subdirectory_search : BoolFOption <"modulemap-allow-subdirectory-search",
+  HeaderSearchOpts<"AllowModuleMapSubdirectorySearch">, DefaultTrue,
+  PosFlag<SetTrue, [], [], "Allow to search for module maps in subdirectories of search paths">,
+  NegFlag<SetFalse>, BothFlags<[NoXarchOption], [ClangOption, CC1Option]>>;
 defm modules : BoolFOption<"modules",
   LangOpts<"Modules">, Default<fcxx_modules.KeyPath>,
   PosFlag<SetTrue, [], [ClangOption, CC1Option],

clang/include/clang/Lex/HeaderSearchOptions.h

@@ -270,6 +270,12 @@ class HeaderSearchOptions {
   LLVM_PREFERRED_TYPE(bool)
   unsigned ModulesIncludeVFSUsage : 1;
 
+  /// Whether we should look for a module in module maps only in provided
+  /// header search paths or if we are allowed to look for module maps in
+  /// subdirectories of provided paths too.
+  LLVM_PREFERRED_TYPE(bool)
+  unsigned AllowModuleMapSubdirectorySearch : 1;
+
   HeaderSearchOptions(StringRef _Sysroot = "/")
       : Sysroot(_Sysroot), ModuleFormat("raw"), DisableModuleHash(false),
         ImplicitModuleMaps(false), ModuleMapFileHomeIsCwd(false),
@@ -285,7 +291,8 @@ class HeaderSearchOptions {
         ModulesSkipHeaderSearchPaths(false),
         ModulesSkipPragmaDiagnosticMappings(false),
         ModulesPruneNonAffectingModuleMaps(true), ModulesHashContent(false),
-        ModulesStrictContextHash(false), ModulesIncludeVFSUsage(false) {}
+        ModulesStrictContextHash(false), ModulesIncludeVFSUsage(false),
+        AllowModuleMapSubdirectorySearch(true) {}
 
   /// AddPath - Add the \p Path path to the specified \p Group list.
   void AddPath(StringRef Path, frontend::IncludeDirGroup Group,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3960,6 +3960,9 @@ static bool RenderModulesOptions(Compilation &C, const Driver &D,
                    options::OPT_fno_modules_strict_decluse, false))
     CmdArgs.push_back("-fmodules-strict-decluse");
 
+  Args.addOptOutFlag(CmdArgs, options::OPT_fmodulemap_allow_subdirectory_search,
+                     options::OPT_fno_modulemap_allow_subdirectory_search);
+
   // -fno-implicit-modules turns off implicitly compiling modules on demand.
   bool ImplicitModules = false;
   if (!Args.hasFlag(options::OPT_fimplicit_modules,

clang/lib/Driver/ToolChains/Darwin.cpp

@@ -3036,6 +3036,35 @@ void Darwin::addClangTargetOptions(
   if (!DriverArgs.hasArgNoClaim(options::OPT_fdefine_target_os_macros,
                                 options::OPT_fno_define_target_os_macros))
     CC1Args.push_back("-fdefine-target-os-macros");
+
+  // Disable subdirectory modulemap search on sufficiently recent SDKs.
+  if (SDKInfo &&
+      !DriverArgs.hasFlag(options::OPT_fmodulemap_allow_subdirectory_search,
+                          options::OPT_fno_modulemap_allow_subdirectory_search,
+                          false)) {
+    bool RequiresSubdirectorySearch;
+    VersionTuple SDKVersion = SDKInfo->getVersion();
+    switch (TargetPlatform) {
+    default:
+      RequiresSubdirectorySearch = true;
+      break;
+    case MacOS:
+      RequiresSubdirectorySearch = SDKVersion < VersionTuple(15, 0);
+      break;
+    case IPhoneOS:
+    case TvOS:
+      RequiresSubdirectorySearch = SDKVersion < VersionTuple(18, 0);
+      break;
+    case WatchOS:
+      RequiresSubdirectorySearch = SDKVersion < VersionTuple(11, 0);
+      break;
+    case XROS:
+      RequiresSubdirectorySearch = SDKVersion < VersionTuple(2, 0);
+      break;
+    }
+    if (!RequiresSubdirectorySearch)
+      CC1Args.push_back("-fno-modulemap-allow-subdirectory-search");
+  }
 }
 
 void Darwin::addClangCC1ASTargetOptions(

clang/lib/Lex/HeaderSearch.cpp

@@ -378,20 +378,22 @@ Module *HeaderSearch::lookupModule(StringRef ModuleName, StringRef SearchName,
         break;
     }
 
-    // If we've already performed the exhaustive search for module maps in this
-    // search directory, don't do it again.
-    if (Dir.haveSearchedAllModuleMaps())
-      continue;
+    if (HSOpts->AllowModuleMapSubdirectorySearch) {
+      // If we've already performed the exhaustive search for module maps in
+      // this search directory, don't do it again.
+      if (Dir.haveSearchedAllModuleMaps())
+        continue;
 
-    // Load all module maps in the immediate subdirectories of this search
-    // directory if ModuleName was from @import.
-    if (AllowExtraModuleMapSearch)
-      loadSubdirectoryModuleMaps(Dir);
+      // Load all module maps in the immediate subdirectories of this search
+      // directory if ModuleName was from @import.
+      if (AllowExtraModuleMapSearch)
+        loadSubdirectoryModuleMaps(Dir);
 
-    // Look again for the module.
-    Module = ModMap.findModule(ModuleName);
-    if (Module)
-      break;
+      // Look again for the module.
+      Module = ModMap.findModule(ModuleName);
+      if (Module)
+        break;
+    }
   }
 
   return Module;

clang/test/Driver/modulemap-allow-subdirectory-search.c

@@ -0,0 +1,27 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// Check that with a sufficiently new SDK not searching for module maps in subdirectories.
+
+// New SDK.
+// RUN: %clang -target x86_64-apple-macos10.13 -isysroot %t/MacOSX15.0.sdk -fmodules %t/test.c -### 2>&1 \
+// RUN:   | FileCheck --check-prefix=NO-SUBDIRECTORIES %t/test.c
+// Old SDK.
+// RUN: %clang -target x86_64-apple-macos10.13 -isysroot %t/MacOSX14.0.sdk -fmodules %t/test.c -### 2>&1 \
+// RUN:   | FileCheck --check-prefix=SEARCH-SUBDIRECTORIES %t/test.c
+// Non-Darwin platform.
+// RUN: %clang -target i386-unknown-linux -isysroot %t/MacOSX15.0.sdk -fmodules %t/test.c -### 2>&1 \
+// RUN:   | FileCheck --check-prefix=SEARCH-SUBDIRECTORIES %t/test.c
+// New SDK overriding the default.
+// RUN: %clang -target x86_64-apple-macos10.13 -isysroot %t/MacOSX15.0.sdk -fmodules %t/test.c -fmodulemap-allow-subdirectory-search -### 2>&1 \
+// RUN:   | FileCheck --check-prefix=SEARCH-SUBDIRECTORIES %t/test.c
+
+//--- test.c
+// NO-SUBDIRECTORIES: "-fno-modulemap-allow-subdirectory-search"
+// SEARCH-SUBDIRECTORIES-NOT: "-fno-modulemap-allow-subdirectory-search"
+
+//--- MacOSX15.0.sdk/SDKSettings.json
+{"Version":"15.0", "MaximumDeploymentTarget": "15.0.99"}
+
+//--- MacOSX14.0.sdk/SDKSettings.json
+{"Version":"14.0", "MaximumDeploymentTarget": "14.0.99"}

clang/test/Modules/modulemap-allow-subdirectory-search.m

@@ -0,0 +1,18 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -fsyntax-only -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache -I %t/include %t/test.m
+// RUN: %clang_cc1 -fsyntax-only -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache -I %t/include %t/test.m -fmodulemap-allow-subdirectory-search
+// RUN: not %clang_cc1 -fsyntax-only -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache -I %t/include %t/test.m -fno-modulemap-allow-subdirectory-search
+
+//--- include/UnrelatedName/Header.h
+// empty
+
+//--- include/UnrelatedName/module.modulemap
+module UsefulCode {
+  header "Header.h"
+  export *
+}
+
+//--- test.m
+@import UsefulCode;