Export CcInfo for staticlib & cdylib allowing rust outputs to be used in c++ rules

Author: GregBowyer

cargo/cargo_build_script.bzl

@@ -1,4 +1,4 @@
-load("@io_bazel_rules_rust//rust:private/rustc.bzl", "BuildInfo", "DepInfo", "get_compilation_mode_opts", "get_linker_and_args")
+load("@io_bazel_rules_rust//rust:private/rustc.bzl", "BuildInfo", "DepInfo", "get_compilation_mode_opts", "get_cc_toolchain", "get_linker_and_args")
 load("@io_bazel_rules_rust//rust:private/utils.bzl", "find_toolchain")
 load("@io_bazel_rules_rust//rust:rust.bzl", "rust_binary")
 load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain")
@@ -41,7 +41,8 @@ def _cargo_build_script_run(ctx, script):
 
     # Pull in env vars which may be required for the cc_toolchain to work (e.g. on OSX, the SDK version).
     # We hope that the linker env is sufficient for the whole cc_toolchain.
-    _, _, linker_env = get_linker_and_args(ctx, None)
+    cc_toolchain, feature_configuration = get_cc_toolchain(ctx)
+    _, _, linker_env = get_linker_and_args(ctx, cc_toolchain, feature_configuration, None)
     env.update(**linker_env)
 
     if cc_toolchain:

examples/ffi/c_calling_rust/BUILD

@@ -1,4 +1,4 @@
-load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
+load("@rules_cc//cc:defs.bzl", "cc_test")
 load("@io_bazel_rules_rust//rust:rust.bzl", "rust_library")
 
 rust_library(
@@ -7,16 +7,8 @@ rust_library(
     crate_type = "staticlib",
 )
 
-# cc_* rules expect cc_* deps, so we need to wrap our rust staticlib.
-cc_library(
-    name = "wrapper",
-    srcs = [":rusty"],
-    # We could link dynamically by setting crate_type to cdylib
-    linkstatic = True,
-)
-
 cc_test(
     name = "main",
     srcs = ["main.c"],
-    deps = [":wrapper"],
+    deps = [":rusty"],
 )

rust/platform/triple_mappings.bzl

@@ -66,6 +66,47 @@ _SYSTEM_TO_DYLIB_EXT = {
     "unknown": ".wasm",
 }
 
+# See https://github.com/rust-lang/rust/blob/master/src/libstd/build.rs
+_SYSTEM_TO_STDLIB_LINKFLAGS = {
+    # TODO(https://github.com/bazelbuild/rules_cc/issues/75):
+    #
+    # Right now bazel cc rules does not specify the exact flag setup needed for calling out system
+    # libs, that is we dont know given a toolchain if it should be, for example,
+    # `-lxxx` or `/Lxxx` or `xxx.lib` etc.
+    #
+    # We include the flag setup as they are _commonly seen_ on various platforms with a cc_rules
+    # style override for people doing things like gnu-mingw on windows.
+    #
+    # If you are reading this ... sorry! set the env var `BAZEL_RUST_STDLIB_LINKFLAGS` to
+    # what you need for your specific setup, for example like so
+    # `BAZEL_RUST_STDLIB_LINKFLAGS="-ladvapi32:-lws2_32:-luserenv"`
+
+    "freebsd": ["-lexecinfo", "-lpthread"],
+    # TODO: This ignores musl. Longer term what does Bazel think about musl?
+    "linux": ["-ldl", "-lpthread"],
+    "darwin": ["-lSystem", "-lresolv"],
+    "uwp": ["ws2_32.lib"],
+    "windows": ["advapi32.lib", "ws2_32.lib", "userenv.lib"],
+    "ios": ["-lSystem", "-lobjc", "-framework Security", "-framework Foundation", "-lresolv"],
+    # NOTE: Rust stdlib `build.rs` treats android as a subset of linux, rust rules treat android
+    # as its own system.
+    "android": ["-ldl", "-llog", "-lgcc"],
+    "emscripten": [],
+    "nacl": [],
+    "bitrig": [],
+    "dragonfly": ["-lpthread"],
+    "netbsd": ["-lpthread", "-lrt"],
+    "openbsd": ["-lpthread"],
+    "solaris": ["-lsocket", "-lposix4", "-lpthread", "-lresolv"],
+    "illumos": ["-lsocket", "-lposix4", "-lpthread", "-lresolv", "-lnsl", "-lumem"],
+    "fuchsia": ["-lzircon", "-lfdio"],
+    # TODO(gregbowyer): If rust stdlib is compiled for cloudabi with the backtrace feature it
+    # includes `-lunwind` but this might not actually be required.
+    # I am not sure which is the common configuration or how we encode it as a link flag.
+    "cloudabi": ["-lunwind", "-lc", "-lcompiler_rt"],
+    "unknown": [],
+}
+
 def cpu_arch_to_constraints(cpu_arch):
     plat_suffix = _CPU_ARCH_TO_BUILTIN_PLAT_SUFFIX[cpu_arch]
 
@@ -110,6 +151,9 @@ def system_to_staticlib_ext(system):
 def system_to_binary_ext(system):
     return _SYSTEM_TO_BINARY_EXT[system]
 
+def system_to_stdlib_linkflags(system):
+    return _SYSTEM_TO_STDLIB_LINKFLAGS[system]
+
 def triple_to_constraint_set(triple):
     component_parts = triple.split("-")
     if len(component_parts) < 3:

rust/private/clippy.bzl

@@ -18,6 +18,7 @@ load(
     "collect_deps",
     "collect_inputs",
     "construct_arguments",
+    "get_cc_toolchain",
     "construct_compile_command",
 )
 load(
@@ -70,10 +71,14 @@ def _clippy_aspect_impl(target, ctx):
         build_info
     )
 
+    cc_toolchain, feature_configuration = get_cc_toolchain(ctx)
+
     args, env, dynamic_env = construct_arguments(
         ctx,
         ctx.rule.file,
         toolchain,
+        cc_toolchain,
+        feature_configuration,
         crate_info,
         dep_info,
         output_hash = repr(hash(root.path)),

rust/private/rustc.bzl

@@ -198,26 +198,35 @@ def collect_deps(label, deps, proc_macro_deps, aliases, toolchain):
         build_info,
     )
 
-def get_linker_and_args(ctx, rpaths):
-    if (len(BAZEL_VERSION) == 0 or
-        versions.is_at_least("0.18.0", BAZEL_VERSION)):
-        user_link_flags = ctx.fragments.cpp.linkopts
-    else:
-        user_link_flags = depset(ctx.fragments.cpp.linkopts)
-
+def get_cc_toolchain(ctx):
     cc_toolchain = find_cpp_toolchain(ctx)
+
     kwargs = {
         "ctx": ctx,
     } if len(BAZEL_VERSION) == 0 or versions.is_at_least(
         "0.25.0",
         BAZEL_VERSION,
     ) else {}
+
     feature_configuration = cc_common.configure_features(
         cc_toolchain = cc_toolchain,
         requested_features = ctx.features,
         unsupported_features = ctx.disabled_features,
         **kwargs
     )
+
+    return cc_toolchain, feature_configuration
+
+def get_cc_user_link_flags(ctx):
+    if (len(BAZEL_VERSION) == 0 or
+        versions.is_at_least("0.18.0", BAZEL_VERSION)):
+        return ctx.fragments.cpp.linkopts
+    else:
+        return depset(ctx.fragments.cpp.linkopts)
+
+def get_linker_and_args(ctx, cc_toolchain, feature_configuration, rpaths):
+    user_link_flags = get_cc_user_link_flags(ctx)
+
     link_variables = cc_common.create_link_variables(
         feature_configuration = feature_configuration,
         cc_toolchain = cc_toolchain,
@@ -290,6 +299,8 @@ def construct_arguments(
         ctx,
         file,
         toolchain,
+        cc_toolchain,
+        feature_configuration,
         crate_info,
         dep_info,
         output_hash,
@@ -340,7 +351,7 @@ def construct_arguments(
     # linker since it won't understand.
     if toolchain.target_arch != "wasm32":
         rpaths = _compute_rpaths(toolchain, output_dir, dep_info)
-        ld, link_args, link_env = get_linker_and_args(ctx, rpaths)
+        ld, link_args, link_env = get_linker_and_args(ctx, cc_toolchain, feature_configuration, rpaths)
         env.update(link_env)
         args.add("--codegen=linker=" + ld)
         args.add_joined("--codegen", link_args, join_with = " ", format_joined = "link-args=%s")
@@ -451,10 +462,14 @@ def rustc_compile_action(
         build_info,
     )
 
+    cc_toolchain, feature_configuration = get_cc_toolchain(ctx)
+
     args, env, dynamic_env = construct_arguments(
         ctx,
         ctx.file,
         toolchain,
+        cc_toolchain,
+        feature_configuration,
         crate_info,
         dep_info,
         output_hash,
@@ -502,7 +517,7 @@ def rustc_compile_action(
     if hasattr(ctx.attr, "out_binary"):
         out_binary = getattr(ctx.attr, "out_binary")
 
-    return [
+    return establish_cc_info(ctx, crate_info, toolchain, cc_toolchain, feature_configuration) + [
         crate_info,
         dep_info,
         DefaultInfo(
@@ -513,6 +528,43 @@ def rustc_compile_action(
         ),
     ]
 
+def establish_cc_info(ctx, crate_info, toolchain, cc_toolchain, feature_configuration):
+    """ If the produced crate is suitable yield a CcInfo to allow for interop with cc rules """
+
+    if crate_info.type not in ("staticlib", "cdylib"):
+        return []
+
+    if crate_info.type == "staticlib":
+        library_to_link = cc_common.create_library_to_link(
+            actions = ctx.actions,
+            feature_configuration = feature_configuration,
+            cc_toolchain = cc_toolchain,
+            static_library = crate_info.output,
+        )
+    elif crate_info.type == "cdylib":
+        library_to_link = cc_common.create_library_to_link(
+            actions = ctx.actions,
+            feature_configuration = feature_configuration,
+            cc_toolchain = cc_toolchain,
+            dynamic_library = crate_info.output,
+        )
+
+    link_input = cc_common.create_linker_input(
+        owner = ctx.label,
+        libraries = depset([library_to_link]),
+        user_link_flags = depset(toolchain.stdlib_linkflags),
+    )
+
+    linking_context = cc_common.create_linking_context(
+        # TODO - What to do for no_std?
+        linker_inputs = depset([link_input]),
+    )
+
+    cc_infos = [dep[CcInfo] for dep in ctx.attr.deps]
+    cc_infos.append(CcInfo(linking_context = linking_context))
+
+    return [cc_common.merge_cc_infos(cc_infos = cc_infos)]
+
 def add_edition_flags(args, crate):
     if crate.edition != "2015":
         args.add("--edition={}".format(crate.edition))

rust/repositories.bzl

@@ -1,5 +1,5 @@
 load(":known_shas.bzl", "FILE_KEY_TO_SHA")
-load("//rust/platform:triple_mappings.bzl", "system_to_binary_ext", "system_to_dylib_ext", "system_to_staticlib_ext", "triple_to_constraint_set", "triple_to_system")
+load("//rust/platform:triple_mappings.bzl", "system_to_binary_ext", "system_to_dylib_ext", "system_to_staticlib_ext", "system_to_stdlib_linkflags", "triple_to_constraint_set", "triple_to_system")
 load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
@@ -181,17 +181,21 @@ filegroup(
         target_triple = target_triple,
     )
 
-def BUILD_for_rust_toolchain(workspace_name, name, exec_triple, target_triple, default_edition = "2015"):
+def BUILD_for_rust_toolchain(workspace_name, name, exec_triple, target_triple,
+                             stdlib_linkflags=None, default_edition = "2015"):
     """Emits a toolchain declaration to match an existing compiler and stdlib.
 
     Args:
       workspace_name: The name of the workspace that this toolchain resides in
       name: The name of the toolchain declaration
       exec_triple: The rust-style target that this compiler runs on
       target_triple: The rust-style target triple of the tool
+      stdlib_linkflags: Overriden flags needed for linking to rust stdlib, akin to BAZEL_LINKLIBS
     """
 
     system = triple_to_system(target_triple)
+    if stdlib_linkflags == None:
+        stdlib_linkflags = ", ".join(['"%s"' % x for x in system_to_stdlib_linkflags(system)])
 
     return """
 rust_toolchain(
@@ -204,6 +208,7 @@ rust_toolchain(
     rustc_lib = "@{workspace_name}//:rustc_lib",
     staticlib_ext = "{staticlib_ext}",
     dylib_ext = "{dylib_ext}",
+    stdlib_linkflags = [{stdlib_linkflags}],
     os = "{system}",
     default_edition = "{default_edition}",
     exec_triple = "{exec_triple}",
@@ -215,6 +220,7 @@ rust_toolchain(
         workspace_name = workspace_name,
         staticlib_ext = system_to_staticlib_ext(system),
         dylib_ext = system_to_dylib_ext(system),
+        stdlib_linkflags = stdlib_linkflags,
         system = system,
         default_edition = default_edition,
         exec_triple = exec_triple,
@@ -376,13 +382,19 @@ def _load_rust_stdlib(ctx, target_triple):
 
     toolchain_prefix = ctx.attr.toolchain_name_prefix or DEFAULT_TOOLCHAIN_NAME_PREFIX
     stdlib_BUILD = BUILD_for_stdlib(target_triple)
+
+    stdlib_linkflags = None
+    if 'BAZEL_RUST_STDLIB_LINKFLAGS' in ctx.os.environ:
+        stdlib_linkflags = ctx.os.environ['BAZEL_RUST_STDLIB_LINKFLAGS'].split(':')
+
     toolchain_BUILD = BUILD_for_rust_toolchain(
         name = "{toolchain_prefix}_{target_triple}".format(
             toolchain_prefix = toolchain_prefix,
             target_triple = target_triple,
         ),
         exec_triple = ctx.attr.exec_triple,
         target_triple = target_triple,
+        stdlib_linkflags = stdlib_linkflags,
         workspace_name = ctx.attr.name,
         default_edition = ctx.attr.edition,
     )

rust/toolchain.bzl

@@ -21,6 +21,7 @@ def _rust_toolchain_impl(ctx):
         rust_lib = ctx.attr.rust_lib,
         staticlib_ext = ctx.attr.staticlib_ext,
         dylib_ext = ctx.attr.dylib_ext,
+        stdlib_linkflags = ctx.attr.stdlib_linkflags,
         target_triple = ctx.attr.target_triple,
         exec_triple = ctx.attr.exec_triple,
         os = ctx.attr.os,
@@ -58,6 +59,10 @@ rust_toolchain = rule(
         ),
         "staticlib_ext": attr.string(mandatory = True),
         "dylib_ext": attr.string(mandatory = True),
+        "stdlib_linkflags": attr.string_list(
+            doc = """Additional linker libs used when std lib is linked,
+                see https://github.com/rust-lang/rust/blob/master/src/libstd/build.rs""",
+            mandatory = True),
         "os": attr.string(mandatory = True),
         "default_edition": attr.string(
             doc = "The edition to use for rust_* rules that don't specify an edition.",
@@ -100,6 +105,7 @@ rust_toolchain(
   rust_doc = "@rust_cpuX//:rustdoc",
   staticlib_ext = ".a",
   dylib_ext = ".so",
+  stdlib_linkflags = ["-lpthread", "-ldl"],
   os = "linux",
 )