[llvm-bugs] [Bug 52138] New: Class with same name as module causes compilation error due to incorrect resolution to forward declaration in another module

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52138

            Bug ID: 52138
           Summary: Class with same name as module causes compilation
                    error due to incorrect resolution to forward
                    declaration in another module
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Modules
          Assignee: unassignedclangbugs at nondot.org
          Reporter: rhow at fb.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Created attachment 25349
  --> https://bugs.llvm.org/attachment.cgi?id=25349&action=edit
test case

During a migration to using submodules for some of our libraries we have come
across an edge case where a type with the same name as its containing module is
not found in its imported module, but instead incorrectly located in an
unimported submodule that contains a forward declaration to that type.

I have attached a test case that illustrates the issue. Running the `build.sh`
script results in:

```
test.m:7:21: error: definition of 'c' must be imported from module 'b.b2'
before it is required
    return a.cthing.d;
                    ^
./b2.h:2:8: note: definition here is not reachable
@class c;
       ^
1 error generated.
```

Where test.m imports c.h that defines c:

```
#import "a.h"
#import "c.h"

int test(AClass *a);

int test(AClass *a) {
    return a.cthing.d;
}
```

Changing the order of imports, the name of the module or the name of the class
will compile correctly.

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