Refactor building DLL example on Windows with windows_dll_library

[meteorcloudy]

@excitoon Instead of #7629, what do you think of this one?
I would recommend to use cc_shared_library to build dll on Windows. One cc_shared_library can even depend on another.

@hlopko Do you have any plan to implement a cc_shared_library in https://github.com/bazelbuild/rules_cc?

[excitoon]

@meteorcloudy This is a good solution, but I wanted a mechanism which would work with multiple extensions (.dll, .so, .dylib) and correspond to current target OS without 2 extra targets and in right way. Personally, I think this is kinda perfectionism, but this is how we do things.

So basically, as a part of plan I switch to one "wrong" (for 2 of 3 cases) extension, like we already have, but in parallel I would like to experiment with cc_common.link in order to write a rule which would link a binary with proper naming depending on target platform - #7538. Can you already tell if that is impossible that way? Or maybe can you provide any example to start hacking from?

BTW, we will keep waiting for C++ Sandwich and Transitive Linking anyway.

[meteorcloudy]

I am not so familiar with the C++ Starlark API, so I'm not sure you can rename the output file name based on target platform. But if

bazel/tools/cpp/cc_toolchain_config.bzl.tpl

Lines 1092 to 1096 in 6793b93

	artifact_name_pattern(
	category_name = "dynamic_library",
	prefix = "",
	extension = ".dll",
	),

is exposed in the API, we can definitely do that. @oquenchil can you confirm if it is available or not?

[meteorcloudy]

Oh, looks like it is!

bazel/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/cpp/CcModuleApi.java

Lines 720 to 728 in cf8ed73

	@Param(
	name = "artifact_name_patterns",
	positional = false,
	named = true,
	defaultValue = "[]",
	type = SkylarkList.class,
	doc =
	"A list of <a href=\"https://github.com/bazelbuild/bazel/blob/master/tools/cpp/"
	+ "cc_toolchain_config_lib.bzl#L516\">artifact_name_patterns</a>."),

[hlopko]

Re cc_shared_library, the tracking issue is #5200, and we plan to work on it in this quarter, definitely by Bazel 1.0.

Re naming, the api you found is what we use to replace CROSSTOOL, because that is where we specify extension names and prefixes (of output artifacts). With C++ sandwich API (#4570) which is being finished these days (and should be available in 0.26), you'll be able to create artifacts without specifying prefix and extension, and C++ toolchain will set those.

[meteorcloudy]

@hlopko Do you think I can merge this change?

[hlopko]

So why do you want to change this at all? cc_shared_library from examples is just an example, it's not supported, and we don't document or recommend people to use it anywhere. Up until this PR I completely forgot it existed :)

[meteorcloudy]

Just to make the example more simple and clear.
People from EA actually asked about how to build DLL on Windows, I recommended this way since cc_shared_library is not yet available. Of course, I don't want to advertise it too much, but for people who want to use this way, this PR can help them having a better interface, which will make it easier to migrate to the proper cc_shared_library in Starlark in the future.

[meteorcloudy]

OK, renamed the macro to windows_dll_library to not cause any confusion with the future cc_shared_library

[meteorcloudy]

@hlopko Does this PR look good now? :)

[hlopko]

Great! Thank you! :)