[llvm-bugs] [Bug 37878] New: [Modules] Auto loading of modulemap in subdirectories

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https://bugs.llvm.org/show_bug.cgi?id=37878

            Bug ID: 37878
           Summary: [Modules] Auto loading of modulemap in subdirectories
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Modules
          Assignee: unassignedclangbugs at nondot.org
          Reporter: yukatkh at gmail.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

Created attachment 20450
  --> https://bugs.llvm.org/attachment.cgi?id=20450&action=edit
Reproducer

$ tar xvf subdirectory.tar
$ cd module
$ sudo cp input/module.modulemap /usr/include/foobar
$ ~/llvm-build/bin/clang -fmodules -fmodule-name Foo -I input main.cxx

I get:
/usr/include/foobar/module.modulemap:1:8: error: redefinition of module 'a'
module a { header "a.h" }
       ^
input/module.modulemap:1:8: note: previously defined here
module a { header "a.h" }
       ^
/usr/include/foobar/module.modulemap:2:8: error: redefinition of module 'b'
module b { header "b.h" }
       ^
input/module.modulemap:2:8: note: previously defined here
module b { header "b.h" }
       ^
2 errors generated.


In clang/lib/Lex/HeaderSearch.cpp HeaderSearch::lookupModule(StringRef
ModuleName, StringRef SearchName), if it couldn't find ModuleName in search
paths, it comes to this line
 283     // Load all module maps in the immediate subdirectories of this search
 284     // directory.
 285     loadSubdirectoryModuleMaps(SearchDirs[Idx]);
Which results in iterating over all files in the search path subdirectories for
example "/usr/include/foobar" in this case. I think user don't expect Clang to
load modulemaps in subdirectories implicitly.

I could fix this error if I remove 285. Maybe we should add branch here like:
if (LangOpts.ObjC || LangOpts.ObjCpp) ?

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