Forward CXX env and arguments from cargo_build_script

We need to forward the C++ command line arguments and env to ``bin.rs``
to make sure cargo_build libraries are compiled with the same options
as `cc_*` targets.

Fixes bazelbuild#1003

Author: Ivan Kalchev

AUTHORS

@@ -8,6 +8,7 @@
 
 Google Inc.
 Spotify AB
+VMware Inc.
 Damien Martin-Guillerez <[email protected]>
 David Chen <[email protected]>
 Florian Weikert <[email protected]>

CONTRIBUTORS

@@ -20,3 +20,4 @@ Philipp Wollermann <[email protected]>
 Ulf Adams <[email protected]>
 Justine Alexandra Roberts Tunney <[email protected]>
 John Edmonds <[email protected]>
+Ivan Kalchev <[email protected]>

cargo/cargo_build_script.bzl

@@ -1,5 +1,9 @@
 # buildifier: disable=module-docstring
-load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "C_COMPILE_ACTION_NAME")
+load(
+    "@bazel_tools//tools/build_defs/cc:action_names.bzl",
+    "C_COMPILE_ACTION_NAME",
+    "CPP_COMPILE_ACTION_NAME"
+)
 load("@bazel_tools//tools/cpp:toolchain_utils.bzl", "find_cpp_toolchain")
 load("//rust:defs.bzl", "rust_binary", "rust_common")
 
@@ -29,6 +33,37 @@ def get_cc_compile_env(cc_toolchain, feature_configuration):
         variables = compile_variables,
     )
 
+def get_cxx_compile_opts(cc_toolchain, feature_configuration):
+    """Gather command line arguments and env for the ``CPP_COMPILE_ACTION_NAME``
+    action from the given cc_toolchain.
+
+    Args:
+        cc_toolchain (cc_toolchain): The current rule's `cc_toolchain`.
+        feature_configuration (FeatureConfiguration): Class used to construct command lines from CROSSTOOL features.
+
+    Returns:
+        tuple: Returns the command line arguments as the first element and the
+        env as the second element.
+    """
+    compile_variables = cc_common.create_compile_variables(
+        cc_toolchain = cc_toolchain,
+        feature_configuration = feature_configuration,
+    )
+
+    compile_args_from_toolchain = cc_common.get_memory_inefficient_command_line(
+        feature_configuration = feature_configuration,
+        action_name = CPP_COMPILE_ACTION_NAME,
+        variables = compile_variables,
+    )
+
+    cc_compile_env = cc_common.get_environment_variables(
+        feature_configuration = feature_configuration,
+        action_name = CPP_COMPILE_ACTION_NAME,
+        variables = compile_variables,
+    )
+
+    return (compile_args_from_toolchain, cc_compile_env)
+
 def _build_script_impl(ctx):
     """The implementation for the `_build_script_run` rule.
 
@@ -101,6 +136,17 @@ def _build_script_impl(ctx):
     if include:
         env["INCLUDE"] = include
 
+    compile_args_from_toolchain, _ = get_cxx_compile_opts(cc_toolchain, feature_configuration)
+    # XXX: Skip adding the CXX env since we already added the C env. Should we stick to just CXX?
+    # Remove --sysroot since we pass it in the SYSROOT env var (we need to
+    # use the absolute path for it). See ``cargo_build_script_runner/bin.rs``
+    # for how this is handled.
+    compile_args_from_toolchain = [
+        arg for arg in compile_args_from_toolchain
+        if not arg.startswith("--sysroot")
+    ]
+    env["CXXFLAGS"] = " ".join(compile_args_from_toolchain)
+
     if cc_toolchain:
         toolchain_tools.append(cc_toolchain.all_files)
 

test/cargo_build_script/BUILD.bazel

@@ -7,7 +7,10 @@ load("//rust:defs.bzl", "rust_test")
 cargo_build_script(
     name = "tools_exec_build_rs",
     srcs = ["build.rs"],
-    build_script_env = {"TOOL": "$(execpath :tool)"},
+    build_script_env = {
+        "TOOL": "$(execpath :tool)",
+        "CXXFLAGS": "-DMY_DEFINE"
+    },
     tools = [":tool"],
 )
 

test/cargo_build_script/build.rs

@@ -4,6 +4,10 @@ fn main() {
         "cargo:rustc-env=TOOL_PATH={}",
         std::env::var("TOOL").unwrap()
     );
+    println!(
+        "cargo:rustc-env=CXXFLAGS={}",
+        std::env::var("CXXFLAGS").unwrap()
+    );
 
     // Assert that the CC and CXX env vars existed and were executable.
     // We don't assert what happens when they're executed (in particular, we don't check for a

test/cargo_build_script/tools_exec.rs

@@ -7,3 +7,13 @@ pub fn test_tool_exec() {
         tool_path
     );
 }
+
+#[test]
+pub fn test_cxxflags() {
+    let cxxflags = env!("CXXFLAGS");
+    assert!(
+        cxxflags.contains("-DMY_DEFINE"),
+        "CXXFLAGS did not contain '-DMY_DEFINE', {}",
+        cxxflags
+    );
+}