Check for nightly toolchain when enabling split debug info.

rust/private/rustc.bzl

@@ -1778,11 +1778,23 @@ def rustc_compile_action(
         elif ctx.attr.require_explicit_unstable_features == -1:
             require_explicit_unstable_features = toolchain.require_explicit_unstable_features
 
-    use_split_debuginfo = (
+    use_split_debuginfo = False
+    if (
         feature_configuration and
         cc_common.is_enabled(feature_configuration = feature_configuration, feature_name = "per_object_debug_info") and
         ctx.fragments.cpp.fission_active_for_current_compilation_mode()
-    )
+    ):
+        # `-Zsplit-dwarf-out-dir` is only available on nightly.
+        if toolchain.channel == "nightly":
+            use_split_debuginfo = True
+        elif toolchain._skip_fission_for_rust:
+            use_split_debuginfo = False
+        else:
+            fail(
+                "Split debug info (fission) was requested, but `-Zsplit-dwarf-out-dir` requires a nightly Rust toolchain " +
+                "(current toolchain channel is \"{}\"). ".format(toolchain.channel) +
+                "To skip fission for Rust objects and suppress this error, set `--@rules_rust//rust/settings:skip_fission_for_rust`.",
+            )
     if use_split_debuginfo:
         rust_flags = rust_flags + [
             "--codegen=split-debuginfo=unpacked",

rust/private/toolchain.bzl

@@ -647,6 +647,7 @@ def _rust_toolchain_impl(ctx):
         _experimental_use_cc_common_link = _experimental_use_cc_common_link(ctx),
         _experimental_use_global_allocator = experimental_use_global_allocator,
         _experimental_compile_rustdoc_tests = ctx.attr._experimental_compile_rustdoc_tests[BuildSettingInfo].value,
+        _skip_fission_for_rust = ctx.attr._skip_fission_for_rust[BuildSettingInfo].value,
         _experimental_use_coverage_metadata_files = ctx.attr._experimental_use_coverage_metadata_files[BuildSettingInfo].value,
         _toolchain_generated_sysroot = ctx.attr._toolchain_generated_sysroot[BuildSettingInfo].value,
         _incompatible_do_not_include_data_in_compile_data = ctx.attr._incompatible_do_not_include_data_in_compile_data[IncompatibleFlagInfo].enabled,
@@ -925,6 +926,9 @@ rust_toolchain = rule(
         "_rename_first_party_crates": attr.label(
             default = Label("//rust/settings:rename_first_party_crates"),
         ),
+        "_skip_fission_for_rust": attr.label(
+            default = Label("//rust/settings:skip_fission_for_rust"),
+        ),
         "_third_party_dir": attr.label(
             default = Label("//rust/settings:third_party_dir"),
         ),

rust/settings/BUILD.bazel

@@ -36,6 +36,7 @@ load(
     "require_explicit_unstable_features",
     "rustc_output_diagnostics",
     "rustfmt_toml",
+    "skip_fission_for_rust",
     "third_party_dir",
     "toolchain_generated_sysroot",
     "toolchain_linker_preference",
@@ -140,3 +141,5 @@ toolchain_linker_preference()
 unpretty()
 
 zself_profile_events()
+
+skip_fission_for_rust()

rust/settings/settings.bzl

@@ -584,3 +584,11 @@ def zself_profile_events(name = "zself_profile_events"):
         name = name,
         build_setting_default = [],
     )
+
+def skip_fission_for_rust():
+    """A flag to skip split debug info (Fission) for Rust objects when using a non-nightly toolchain.
+    """
+    bool_flag(
+        name = "skip_fission_for_rust",
+        build_setting_default = False,
+    )

test/unit/debug_info/debug_info_analysis_test.bzl

@@ -184,6 +184,37 @@ _FISSION_COMPATIBILITY = ["@platforms//os:linux"] + select({
     "//conditions:default": ["@platforms//:incompatible"],
 })
 
+# `-Zsplit-dwarf-out-dir` requires nightly. When testing split debug info,
+# stable and beta should error out unless `skip_fission_for_rust` is set.
+not_nightly_fission_test = analysistest.make(
+    _no_fission_test_impl,
+    config_settings = {
+        "//command_line_option:features": ["per_object_debug_info"],
+        "//command_line_option:fission": ["yes"],
+        str(Label("//rust/settings:skip_fission_for_rust")): True,
+    },
+)
+
+def _not_nightly_fission_error_test_impl(ctx):
+    env = analysistest.begin(ctx)
+    asserts.expect_failure(env, "skip_fission_for_rust")
+    return analysistest.end(env)
+
+not_nightly_fission_error_test = analysistest.make(
+    _not_nightly_fission_error_test_impl,
+    expect_failure = True,
+    config_settings = {
+        "//command_line_option:features": ["per_object_debug_info"],
+        "//command_line_option:fission": ["yes"],
+    },
+)
+
+_NOT_NIGHTLY_COMPATIBILITY = ["@platforms//os:linux"] + select({
+    "//rust/toolchain/channel:beta": [],
+    "//rust/toolchain/channel:stable": [],
+    "//conditions:default": ["@platforms//:incompatible"],
+})
+
 def debug_info_analysis_test_suite(name):
     """Analysis tests for debug info in cdylib and bin targets.
 
@@ -295,6 +326,16 @@ def debug_info_analysis_test_suite(name):
         name = "lib_no_fission_test",
         target_under_test = ":mylib",
     )
+    not_nightly_fission_test(
+        name = "lib_not_nightly_fission_test",
+        target_under_test = ":mylib",
+        target_compatible_with = _NOT_NIGHTLY_COMPATIBILITY,
+    )
+    not_nightly_fission_error_test(
+        name = "lib_not_nightly_fission_error_test",
+        target_under_test = ":mylib",
+        target_compatible_with = _NOT_NIGHTLY_COMPATIBILITY,
+    )
 
     fission_test(
         name = "bin_fission_test",
@@ -305,6 +346,16 @@ def debug_info_analysis_test_suite(name):
         name = "bin_no_fission_test",
         target_under_test = ":myrustbin",
     )
+    not_nightly_fission_test(
+        name = "bin_not_nightly_fission_test",
+        target_under_test = ":myrustbin",
+        target_compatible_with = _NOT_NIGHTLY_COMPATIBILITY,
+    )
+    not_nightly_fission_error_test(
+        name = "bin_not_nightly_fission_error_test",
+        target_under_test = ":myrustbin",
+        target_compatible_with = _NOT_NIGHTLY_COMPATIBILITY,
+    )
 
     fission_test(
         name = "test_fission_test",
@@ -315,6 +366,16 @@ def debug_info_analysis_test_suite(name):
         name = "test_no_fission_test",
         target_under_test = ":myrusttest",
     )
+    not_nightly_fission_test(
+        name = "test_not_nightly_fission_test",
+        target_under_test = ":myrusttest",
+        target_compatible_with = _NOT_NIGHTLY_COMPATIBILITY,
+    )
+    not_nightly_fission_error_test(
+        name = "test_not_nightly_fission_error_test",
+        target_under_test = ":myrusttest",
+        target_compatible_with = _NOT_NIGHTLY_COMPATIBILITY,
+    )
 
     native.test_suite(
         name = name,
@@ -324,10 +385,16 @@ def debug_info_analysis_test_suite(name):
             ":test_dsym_test",
             ":lib_fission_test",
             ":lib_no_fission_test",
+            ":lib_not_nightly_fission_test",
+            ":lib_not_nightly_fission_error_test",
             ":bin_fission_test",
             ":bin_no_fission_test",
+            ":bin_not_nightly_fission_test",
+            ":bin_not_nightly_fission_error_test",
             ":test_fission_test",
             ":test_no_fission_test",
+            ":test_not_nightly_fission_test",
+            ":test_not_nightly_fission_error_test",
         ] + [
             ":lib_pdb_test_{}".format(compilation_mode)
             for compilation_mode in pdb_file_tests