[llvm-bugs] [Bug 33924] New: Unexpected error "definition with same mangled name as another definition"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=33924

            Bug ID: 33924
           Summary: Unexpected error "definition with same mangled name as
                    another definition"
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Modules
          Assignee: unassignedclangbugs at nondot.org
          Reporter: pank.dm at gmail.com
                CC: dgregor at apple.com, llvm-bugs at lists.llvm.org

Created attachment 18843
  --> https://bugs.llvm.org/attachment.cgi?id=18843&action=edit
Files that reproduce the error

It triggers on the following piece of code when we try to instantiate templated
function `format` in 2 separate modules:

// -- format.h
class Formatter {
public:
  template <class T>
  void doFormat(T& out) {}
};

template <class T>
void format(T t) {
  Formatter f;
  auto lambda = [] {};
  f.doFormat(lambda);
}

(see full set of files in attachment)
Error message:

In module 'foo1' imported from main.cpp:1:
In module 'format' imported from ./foo1.h:3:
./format.h:6:8: error: definition with same mangled name as another
definition
           void doFormat(T& out) {}
       ^
./format.h:6:8: note: previous definition is here

Seems like this is related to passing lambda from templated function. If I try
to call `doFormat` on regular class or move body of `format` into module `foo`
itself, then the error goes away.

Worth noting there is also assertion triggering when using clang built from
source in debug mode:

llvm/lib/IR/Value.cpp:402: void llvm::Value::doRAUW(llvm::Value*, bool):
Assertion `New->getType() == getType(
) && "replaceAllUses of value with new value of different type!"' failed.

Repro command line:
clang++ --std=c++14 -I .  -fmodules -fcxx-modules
-fmodules-cache-path=./modules_out/_module_cache -c main.cpp -o main.o


A non-modular compilation that uses the same set of files finishes fine.
Let me know if you need any extra information.

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