add buildscript link flags only to parent crate

rust/private/rustc.bzl

@@ -724,15 +724,10 @@ def _create_extra_input_args(ctx, file, build_info, dep_info):
     if build_info:
         out_dir = build_info.out_dir.path
         build_env_file = build_info.rustc_env.path
-
-        # out_dir will be added as input by the transitive_build_infos loop below.
         build_flags_files.append(build_info.flags.path)
-
-    # This should probably only actually be exposed to actions which link.
-    for dep_build_info in dep_info.transitive_build_infos.to_list():
-        input_files.append(dep_build_info.out_dir)
-        build_flags_files.append(dep_build_info.link_flags.path)
-        input_files.append(dep_build_info.link_flags)
+        build_flags_files.append(build_info.link_flags.path)
+        input_files.append(build_info.out_dir)
+        input_files.append(build_info.link_flags)
 
     return input_files, out_dir, build_env_file, build_flags_files
 

test/transitive_lib/BUILD

@@ -0,0 +1,34 @@
+load(
+    "@io_bazel_rules_rust//cargo:cargo_build_script.bzl",
+    "cargo_build_script",
+)
+load("@io_bazel_rules_rust//rust:rust.bzl", "rust_binary", "rust_library")
+
+# sets link alias
+cargo_build_script(
+    name = "buildscript",
+    srcs = ["build.rs"],
+    crate_root = "build.rs",
+    edition = "2018",
+)
+
+# links to a symbol in shell32
+rust_library(
+    name = "dll_user",
+    srcs = ["dll_user.rs"],
+    crate_type = "lib",
+    edition = "2018",
+    deps = [
+        ":buildscript",
+    ],
+)
+
+# does not link to any symbol in shell32
+rust_binary(
+    name = "dll_user_user",
+    srcs = ["dll_user_user.rs"],
+    edition = "2018",
+    deps = [
+        ":dll_user",
+    ],
+)

test/transitive_lib/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+   println!("cargo:rustc-link-lib=alias:shell32");
+}

test/transitive_lib/dll_user.rs

@@ -0,0 +1,5 @@
+#[link(name = "alias")]
+extern "C" {
+    // random symbol from shell32
+    pub fn LocalFree(ptr: *mut std::os::raw::c_void);
+}

test/transitive_lib/dll_user_user.rs

@@ -0,0 +1,5 @@
+fn main() {
+    // this file does not link to any shell32 symbols directly, and
+    // will thus cause a compile error if -lalias:shell32
+    // is present in the link flags
+}