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Working towards: https://github.com/bazelbuild/bazel/issues/3311
When building dynamic library on Windows, Bazel builds an import library
and a DLL.
Bazel provides a feature called windows_export_all_symbols, if this
feature is enabled(and no_windows_export_all_symbols is not) for a
cc_library, then Bazel parses object files of that cc_library to generate
a DEF file that will be used during linking time to export symbols from
DLL. This feature can be specified at crosstool, package, target and
command line level.
A few differences from Unix platforms:
1. We don't build the shared library on Windows by default, users have to
specifiy --output_groups=dynamic_library for building dynamic libraries.
This output group is also available on other platforms.
2. By default, cc_test is dynamically linked on Unix, but it will be
statically linked on Windows by default. (meaning the default value of
linkstatic in cc_test is 1 on Windows, and 0 on other platforms)
3. For global data symbols, __declspec(dllimport) must still be used in
source files.
Remaining issues:
1. Extensions for import library and DLL are not correct yet.
2. DLLs are not guaranteed to be available during runtime yet.
3. Diamond problem
If a cc_library A is specified as linkstatic=0, then no dynamic library
will be built for it, so if another cc_library B depends on it, A will
be statically linked into B, and if a cc_binary C depends on B, A will
also be statically linked into C and B will be dynamically linked to C.
This is wrong because A is duplicated in both B and C.
It is essentially a diamond problem describled in C++ Transitive Library.
(https://docs.google.com/document/d/1-tv0_79zGyBoDmaP_pYWaBVUwHUteLpAs90_rUl-VY8/edit?usp=sharing)
Hopefully, we can avoid this by using cc_shared_library rule in future.
Change-Id: I23640d4caf8afe65d60b1522af6368536d7a8408
PiperOrigin-RevId: 168829958
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Yun Peng