Test binaries created with the following commands:

$ cat container.cpp
#include "container.h"
#include <stdlib.h>

struct Container_ivars {
  // real definition here
};

ContainerPtr allocateContainer() {
  Container *c = (Container *)malloc(sizeof(Container));
  c->ivars = (Container_ivars *)malloc(sizeof(Container_ivars));
  return c;
}

extern void doSomething(ContainerPtr);

int main() {
  ContainerPtr c = allocateContainer();
  doSomething(c);
  return 0;
}

$ cat container.h
struct Container_ivars;

struct Container {
  union {
    struct Container_ivars *ivars;
  };
};

typedef Container *ContainerPtr;

$ cat use.cpp
#include "container.h"

void doSomething(ContainerPtr c) {}


$ clang++ -O0 -g container.cpp -c -o container.o
$ clang++ -O0 -g use.cpp -c -o use.o
$ clang++ use.o container.o -o a.out

Note that the link order in the last command matters for this test.

RUN: dsymutil --linker classic -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/union/a.out -o %t.dSYM
RUN: llvm-dwarfdump %t.dSYM | FileCheck %s --check-prefixes=CHECK,CLASSIC
RUN: dsymutil --linker parallel -oso-prepend-path %p/../Inputs %p/../Inputs/private/tmp/union/a.out -o %t.dSYM
RUN: llvm-dwarfdump %t.dSYM | FileCheck %s --check-prefix=CHECK

# The linker must resolve use.cpp's forward declaration of
# Container_ivars to the full definition provided by container.cpp, not
# drop the definition. In either linker the full definition must exist.
# The classic linker additionally preserves the forward declaration DIE
# (DW_AT_declaration=true) from use.cpp; the parallel linker consolidates
# the full definition into an artificial type unit, so the forward-decl
# DIE does not survive there.

# CLASSIC:     DW_AT_name      ("Container_ivars")
# CLASSIC-NEXT:     DW_AT_declaration       (true)

# CHECK: DW_AT_name      ("Container_ivars")
# CHECK-DAG: DW_AT_byte_size (0x01)
# CHECK-DAG: DW_AT_decl_file ("{{.*}}container.cpp")
# CHECK-DAG: DW_AT_decl_line (4)