Added check for extern flags as well

rust/private/rustc.bzl

@@ -866,7 +866,7 @@ def _crate_to_link_flag(crate_info):
     Returns:
         list: Link flags for the current crate info
     """
-    return ["--extern", "{}={}".format(crate_info.name, crate_info.dep.output.path)]
+    return ["--extern={}={}".format(crate_info.name, crate_info.dep.output.path)]
 
 def _get_crate_dirname(crate):
     """A helper macro used by `add_crate_link_flags` for getting the directory name of the current crate's output path

test/unit/common.bzl

@@ -29,6 +29,18 @@ def assert_argv_contains_prefix_suffix(env, action, prefix, suffix):
         ),
     )
 
+def assert_argv_contains_prefix(env, action, prefix):
+    for found_flag in action.argv:
+        if found_flag.startswith(prefix):
+            return
+    unittest.fail(
+        env,
+        "Expected an arg with prefix '{prefix}' in {args}".format(
+            prefix = prefix,
+            args = action.argv,
+        ),
+    )
+
 def assert_action_mnemonic(env, action, mnemonic):
     if not action.mnemonic == mnemonic:
         unittest.fail(

test/unit/exports/exports_test.bzl

@@ -1,9 +1,9 @@
 """Unittest to verify re-exported symbols propagate to downstream crates"""
 
 load("@bazel_skylib//lib:unittest.bzl", "analysistest", "asserts")
-load("//test/unit:common.bzl", "assert_argv_contains_prefix_suffix")
+load("//test/unit:common.bzl", "assert_argv_contains_prefix", "assert_argv_contains_prefix_suffix")
 
-def _exports_test_impl(ctx, deps):
+def _exports_test_impl(ctx, dependencies, externs):
     env = analysistest.begin(ctx)
     target = analysistest.target_under_test(env)
 
@@ -13,25 +13,40 @@ def _exports_test_impl(ctx, deps):
     # Transitive symbols that get re-exported are expected to be located by a `-Ldependency` flag.
     # The assert below ensures that each dependnecy flag is passed to the Rustc action. For details see
     # https://doc.rust-lang.org/rustc/command-line-arguments.html#-l-add-a-directory-to-the-library-search-path
-    for dep in deps:
+    for dep in dependencies:
         assert_argv_contains_prefix_suffix(
             env = env,
             action = action,
             prefix = "-Ldependency",
             suffix = dep,
         )
 
+    for dep in externs:
+        assert_argv_contains_prefix(
+            env = env,
+            action = action,
+            prefix = "--extern={}=".format(dep),
+        )
+
     return analysistest.end(env)
 
 def _lib_exports_test_impl(ctx):
     # This test is only expected to be used with
     # `//test/unit/exports/lib_c`
-    return _exports_test_impl(ctx, ["lib_a", "lib_b"])
+    return _exports_test_impl(
+        ctx = ctx,
+        dependencies = ["lib_a", "lib_b"],
+        externs = ["lib_b"],
+    )
 
 def _test_exports_test_impl(ctx):
     # This test is only expected to be used with
     # `//test/unit/exports/lib_c:lib_c_test`
-    return _exports_test_impl(ctx, ["lib_a", "lib_b"])
+    return _exports_test_impl(
+        ctx = ctx,
+        dependencies = ["lib_a", "lib_b"],
+        externs = ["lib_b"],
+    )
 
 lib_exports_test = analysistest.make(_lib_exports_test_impl)
 test_exports_test = analysistest.make(_test_exports_test_impl)