emser.dll — UNO component OLE embedding server; registers 10 CLSIDs for Writer/Calc/Draw/Impress/Math (6.0 and OASIS formats) so other Windows applications can embed OpenOffice documents via OLE in-place activation.inprocserv.dll — companion in-process COM handler registered under HKLM\...\InprocHandler32 for lightweight OLE embedding without launching the full OO process.Both DLLs require Microsoft ATL headers (VC\ATLMFC\INCLUDE: atlbase.h, atlcom.h, atlctl.h, atldbcli.h). These are only present in Visual Studio Professional or Enterprise editions — not Express or BuildTools.
The targets use target_compatible_with = _ATL_REQUIRED which mirrors the old build system's DISABLE_ATL guard: on machines without ATLMFC the targets are silently skipped by bazel build //....
To build on a qualifying machine, add to user.bazelrc:
build --//build:atl_available=True
When winaccessibility and extensions/activex are migrated they will need the same ATL headers. At that point the right solution is an ext_libraries/modules/atl/ entry wrapping the ReactOS ATL implementation (LGPL, compatible with Apache License 2.0 for header-only compile-time use). ReactOS provides complete, working implementations of CComModule, CComPtr<T>, the object-map macros, and the full COM class-factory registration machinery — not stubs. This work should be done before those layers are attempted.