Add Clang -ftime-trace support to rules_cc

Declare trace JSON files as compile action outputs and expose them via the trace_files output group, enabled with features = ["trace"] on Clang toolchains.

Author: PikachuHyA

cc/common/cc_helper.bzl

@@ -208,6 +208,13 @@ def _build_output_groups_for_emitting_compile_providers(
     else:
         output_groups_builder["module_files"] = depset(compilation_outputs._module_files)
 
+    # Add trace JSON files to output groups
+    if hasattr(compilation_outputs, "_trace_files") and compilation_outputs._trace_files:
+        output_groups_builder["trace_files"] = depset(compilation_outputs._trace_files)
+    if hasattr(compilation_outputs, "_pic_trace_files") and compilation_outputs._pic_trace_files:
+        pic_trace_group = output_groups_builder.get("trace_files", depset())
+        output_groups_builder["trace_files"] = depset(transitive = [pic_trace_group, depset(compilation_outputs._pic_trace_files)])
+
     if generate_hidden_top_level_group:
         output_groups_builder["_hidden_top_level_INTERNAL_"] = _collect_library_hidden_top_level_artifacts(
             ctx,

cc/private/compile/cc_compilation_outputs.bzl

@@ -33,6 +33,8 @@ CcCompilationOutputsInfo = provider(
         "_pic_dwo_files": "(list[File]) All .pic.dwo files built by the target, corresponding to .pic.o outputs.",
         "_gcno_files": "(list[File]) All .gcno files built by the target, corresponding to .o outputs.",
         "_pic_gcno_files": "(list[File]) All .pic.gcno files built by the target, corresponding to .pic.gcno outputs.",
+        "_trace_files": "(list[File]) All .json files built by the target, corresponding to .o outputs.",
+        "_pic_trace_files": "(list[File]) All .pic.json files built by the target, corresponding to .pic.o outputs.",
         "temps": '(() -> depset[File]) All artifacts that are created if "--save_temps" is true.',
         "_header_tokens": "(list[File]) All token .h.processed files created when preprocessing or parsing headers.",
         "_module_files": "(list[File]) All .pcm files built by the target.",
@@ -52,6 +54,8 @@ def create_compilation_outputs_internal(
         pic_dwo_files = [],
         gcno_files = [],
         pic_gcno_files = [],
+        trace_files = [],
+        pic_trace_files = [],
         temps = [],
         header_tokens = [],
         module_files = [],
@@ -69,6 +73,8 @@ def create_compilation_outputs_internal(
         pic_dwo_files: A list of PIC dwo files.
         gcno_files: A list of gcno files.
         pic_gcno_files: A list of PIC gcno files.
+        trace_files: A list of trace JSON files.
+        pic_trace_files: A list of PIC trace JSON files.
         temps: A depset of temporary files.
         header_tokens: A list of header tokens.
         module_files: A list of module files.
@@ -91,6 +97,8 @@ def create_compilation_outputs_internal(
         _lto_compilation_context = lto_compilation_context,
         _gcno_files = _cc_internal.freeze(gcno_files),
         _pic_gcno_files = _cc_internal.freeze(pic_gcno_files),
+        _trace_files = _cc_internal.freeze(trace_files),
+        _pic_trace_files = _cc_internal.freeze(pic_trace_files),
         _dwo_files = _cc_internal.freeze(dwo_files),
         _pic_dwo_files = _cc_internal.freeze(pic_dwo_files),
         cpp_module_files = _cc_internal.freeze(cpp_module_files),
@@ -194,6 +202,8 @@ def merge_compilation_outputs(*, compilation_outputs):
     pic_dwo_files = []
     gcno_files = []
     pic_gcno_files = []
+    trace_files = []
+    pic_trace_files = []
     lto_compilation_contexts = []
     transitive_temps = []
     header_tokens = []
@@ -206,6 +216,8 @@ def merge_compilation_outputs(*, compilation_outputs):
         pic_dwo_files.extend(co._pic_dwo_files)
         gcno_files.extend(co._gcno_files)
         pic_gcno_files.extend(co._pic_gcno_files)
+        trace_files.extend(co._trace_files)
+        pic_trace_files.extend(co._pic_trace_files)
         transitive_temps.append(co.temps())
         header_tokens.extend(co._header_tokens)
         module_files.extend(co._module_files)
@@ -220,6 +232,8 @@ def merge_compilation_outputs(*, compilation_outputs):
         _pic_dwo_files = pic_dwo_files,
         _gcno_files = gcno_files,
         _pic_gcno_files = pic_gcno_files,
+        _trace_files = trace_files,
+        _pic_trace_files = pic_trace_files,
         temps = wrap_with_check_private_api(depset(transitive = transitive_temps)),
         _header_tokens = header_tokens,
         _module_files = module_files,

cc/private/compile/compile.bzl

@@ -52,6 +52,9 @@ load("//cc/private/compile:lto_compilation_context.bzl", "create_lto_compilation
 
 _VALID_CPP_SOURCE_TYPES = set([CPP_SOURCE_TYPE_SOURCE, CPP_SOURCE_TYPE_HEADER, CPP_SOURCE_TYPE_CLIF_INPUT_PROTO])
 
+def _clang_trace_enabled(feature_configuration):
+    return feature_configuration.is_enabled("clang_trace")
+
 def _cpp_source_init(*, label, source, type):
     if type not in _VALID_CPP_SOURCE_TYPES:
         fail("invalid type of cpp source, got:", type, "expected one of:", _VALID_CPP_SOURCE_TYPES)
@@ -347,6 +350,8 @@ def compile(
         "lto_compilation_context": {},
         "gcno_files": [],
         "pic_gcno_files": [],
+        "trace_files": [],
+        "pic_trace_files": [],
         "dwo_files": [],
         "pic_dwo_files": [],
         "cpp_module_files": [],
@@ -837,6 +842,7 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
             cpp_module_map = cc_compilation_context._module_map,
             add_object = True,
             enable_coverage = is_code_coverage_enabled,
+            enable_trace = _clang_trace_enabled(feature_configuration),
             generate_dwo = should_create_per_object_debug_info(feature_configuration, cpp_configuration),
             bitcode_output = bitcode_output,
             fdo_context = fdo_context,
@@ -985,6 +991,7 @@ def _create_cc_compile_actions_with_cpp20_module_helper(
             cpp_module_map = cc_compilation_context._module_map,
             add_object = True,
             enable_coverage = is_code_coverage_enabled,
+            enable_trace = _clang_trace_enabled(feature_configuration),
             generate_dwo = should_create_per_object_debug_info(feature_configuration, cpp_configuration),
             bitcode_output = bitcode_output,
             fdo_context = fdo_context,
@@ -1268,6 +1275,7 @@ def _create_cc_compile_actions(
                 cpp_module_map = cc_compilation_context._module_map,
                 add_object = True,
                 enable_coverage = is_code_coverage_enabled,
+                enable_trace = _clang_trace_enabled(feature_configuration),
                 generate_dwo = should_create_per_object_debug_info(feature_configuration, cpp_configuration),
                 bitcode_output = bitcode_output,
                 fdo_context = fdo_context,
@@ -1420,6 +1428,7 @@ def _create_pic_nopic_compile_source_actions(
         cpp_module_map,
         add_object,
         enable_coverage,
+        enable_trace,
         generate_dwo,
         bitcode_output,
         fdo_context,
@@ -1454,6 +1463,7 @@ def _create_pic_nopic_compile_source_actions(
             cpp_module_map = cpp_module_map,
             add_object = add_object,
             enable_coverage = enable_coverage,
+            enable_trace = enable_trace,
             generate_dwo = generate_dwo,
             bitcode_output = bitcode_output,
             fdo_context = fdo_context,
@@ -1491,6 +1501,7 @@ def _create_pic_nopic_compile_source_actions(
             cpp_module_map = cpp_module_map,
             add_object = add_object,
             enable_coverage = enable_coverage,
+            enable_trace = enable_trace,
             generate_dwo = generate_dwo,
             bitcode_output = bitcode_output,
             fdo_context = fdo_context,
@@ -1529,6 +1540,7 @@ def _create_compile_source_action(
         cpp_module_map,
         add_object,
         enable_coverage,
+        enable_trace,
         generate_dwo,
         bitcode_output,
         fdo_context,
@@ -1592,6 +1604,11 @@ def _create_compile_source_action(
         configuration = configuration,
         enable_coverage = enable_coverage,
     )
+    trace_file = _maybe_declare_trace_file(
+        ctx = action_construction_context,
+        enable_trace = enable_trace,
+        object_file = object_file,
+    )
 
     dwo_file = None
     if generate_dwo and not bitcode_output:
@@ -1680,14 +1697,20 @@ def _create_compile_source_action(
     if add_object and fdo_context_has_artifacts:
         additional_inputs = additional_compilation_inputs + auxiliary_fdo_inputs.to_list()
 
+    all_additional_outputs = list(additional_outputs)
+    if trace_file:
+        all_additional_outputs.append(trace_file)
+
     # Provide these args conditionally as they require a recent version of Bazel.
     if modmap_file:
         module_args = {
-            "additional_outputs": additional_outputs,
+            "additional_outputs": all_additional_outputs,
             "module_files": module_files,
             "modmap_file": modmap_file,
             "modmap_input_file": modmap_input_file,
         }
+    elif all_additional_outputs:
+        module_args = {"additional_outputs": all_additional_outputs}
     else:
         module_args = {}
 
@@ -1736,6 +1759,11 @@ def _create_compile_source_action(
             outputs["pic_gcno_files"].append(gcno_file)
         else:
             outputs["gcno_files"].append(gcno_file)
+    if trace_file:
+        if use_pic:
+            outputs["pic_trace_files"].append(trace_file)
+        else:
+            outputs["trace_files"].append(trace_file)
     return object_file
 
 def _create_temps_action(
@@ -2136,6 +2164,7 @@ def _create_module_action(
         cpp_module_map = cpp_module_map,
         add_object = False,
         enable_coverage = False,
+        enable_trace = False,
         generate_dwo = False,
         bitcode_output = False,
         additional_compilation_inputs = additional_compilation_inputs,
@@ -2297,12 +2326,25 @@ def _maybe_declare_gcno_file(
         )
     return gcno_file
 
+def _maybe_declare_trace_file(
+        ctx,
+        enable_trace,
+        object_file):
+    if not enable_trace:
+        return None
+    return _cc_internal.declare_other_output_file(
+        ctx = ctx,
+        output_name = paths.replace_extension(paths.basename(object_file.path), ".json"),
+        object_file = object_file,
+    )
+
 def _create_compile_action(
         *,
         action_construction_context = None,
         action_name = None,
         additional_compilation_inputs = None,
         additional_include_scanning_roots = [],
+        additional_outputs = [],
         cc_compilation_context = None,
         cc_toolchain = None,
         compile_build_variables = None,
@@ -2329,6 +2371,7 @@ def _create_compile_action(
         action_name = action_name,
         additional_compilation_inputs = additional_compilation_inputs,
         additional_include_scanning_roots = additional_include_scanning_roots,
+        additional_outputs = additional_outputs,
         cc_compilation_context = cc_compilation_context,
         cc_toolchain = cc_toolchain,
         compile_build_variables = compile_build_variables,

cc/private/compile/compile_build_variables.bzl

@@ -343,7 +343,6 @@ def get_specific_compile_build_variables(
         # TODO: Blaze currently uses `gcov_gcno_file` to detect if code coverage
         # is enabled. It should use a different signal.
         result[_VARS.GCOV_GCNO_FILE] = ""
-
     if dwo_file:
         result[_VARS.PER_OBJECT_DEBUG_INFO_FILE] = dwo_file
     if using_fission:

cc/private/toolchain/unix_cc_toolchain_config.bzl

@@ -1869,6 +1869,35 @@ def _impl(ctx):
 
     skip_virtual_includes_feature = feature(name = "skip_virtual_includes")
 
+    # Clang -ftime-trace support
+    trace_feature = feature(
+        name = "trace",
+        provides = ["trace"],
+    )
+
+    clang_trace_feature = feature(
+        name = "clang_trace",
+        flag_sets = [
+            flag_set(
+                actions = [
+                    ACTION_NAMES.preprocess_assemble,
+                    ACTION_NAMES.c_compile,
+                    ACTION_NAMES.cpp_compile,
+                    ACTION_NAMES.cpp_module_compile,
+                    ACTION_NAMES.objc_compile,
+                    ACTION_NAMES.objcpp_compile,
+                ],
+                flag_groups = [
+                    flag_group(
+                        flags = ["-ftime-trace"],
+                    ),
+                ],
+            ),
+        ],
+        requires = [feature_set(features = ["trace"])],
+        enabled = True,
+    )
+
     # TODO(#8303): Mac crosstool should also declare every feature.
     if is_linux:
         # Linux artifact name patterns are the default.
@@ -2016,6 +2045,11 @@ def _impl(ctx):
     extra_rules_based_features = depset(ctx.attr.extra_enabled_features + ctx.attr.extra_known_features)
     features.extend([convert_feature(extra_feature[FeatureInfo], enabled = extra_feature in ctx.attr.extra_enabled_features) for extra_feature in extra_rules_based_features.to_list()])
 
+    features.extend([
+        trace_feature,
+    ])
+    if ctx.attr.compiler == "clang":
+        features.append(clang_trace_feature)
     return cc_common.create_cc_toolchain_config_info(
         ctx = ctx,
         features = features,

tests/integration/BUILD

@@ -43,3 +43,14 @@ rules_cc_integration_test(
     target_compatible_with = VERSION_GATE,
     test_script = "cc_static_library_failure_tests.sh",
 )
+
+rules_cc_integration_test(
+    name = "ftime_trace_tests",
+    timeout = "long",
+    target_compatible_with = select({
+        "@platforms//os:macos": ["@platforms//:incompatible"],
+        "@platforms//os:windows": ["@platforms//:incompatible"],
+        "//conditions:default": [],
+    }),
+    test_script = "ftime_trace_tests.sh",
+)

tests/integration/ftime_trace_tests.sh

@@ -0,0 +1,76 @@
+set -euo pipefail
+
+source "$(rlocation rules_cc/tests/test_utils.sh)"
+source "$(rlocation rules_cc/tests/unittest.bash)"
+
+function set_up() {
+  if is_windows; then
+    echo "Skipping on Windows."
+    return 1
+  fi
+
+  local -r clang="$(which clang || true)"
+  local -r clangxx="$(which clang++ || true)"
+  if [[ ! -x "$clang" || ! -x "$clangxx" ]]; then
+    echo "clang/clang++ not installed. Skipping test."
+    return 1
+  fi
+
+  add_to_bazelrc "common --repo_env=CC=$clang"
+  add_to_bazelrc "common --repo_env=CXX=$clangxx"
+}
+
+function test_ftime_trace_outputs() {
+  # Bazel versions before 9 use the built-in native C++ rules, not rules_cc.
+  # This integration test exercises the rules_cc -ftime-trace implementation only.
+  local bazel_version=""
+  bazel_version="$(bazel version 2>/dev/null | awk '/^(Build label|Release label):/ { print $3; exit }')"
+  local bazel_major="${bazel_version%%.*}"
+  if [[ -z "$bazel_major" || "$bazel_major" -lt 9 ]]; then
+    echo "Bazel ${bazel_version:-unknown} is older than 9.0; native C++ rules are used instead of rules_cc. Skipping test."
+    return 0
+  fi
+
+  cat > BUILD << EOF
+load("@rules_cc//cc:cc_library.bzl", "cc_library")
+
+cc_library(
+    name = "lib_with_trace",
+    srcs = ["foo.cc"],
+    features = ["trace"],
+)
+EOF
+
+  cat > foo.cc << EOF
+int foo() {
+  return 42;
+}
+EOF
+
+  bazel build //:lib_with_trace --output_groups=trace_files >& "$TEST_log" || fail "Build failed"
+
+  trace_json="$(find bazel-bin/_objs/lib_with_trace -name '*.json' | head -1)"
+  if [[ -z "$trace_json" ]]; then
+    fail "Expected a Clang -ftime-trace JSON file under bazel-bin/_objs/lib_with_trace"
+  fi
+
+  if [[ ! -s "$trace_json" ]]; then
+    fail "Trace file is empty: $trace_json"
+  fi
+
+  python3 - "$trace_json" << 'PY'
+import json
+import sys
+
+path = sys.argv[1]
+with open(path, encoding="utf-8") as input_file:
+    data = json.load(input_file)
+
+if "traceEvents" not in data:
+    raise SystemExit(f"missing traceEvents key in {path}")
+if not isinstance(data["traceEvents"], list) or not data["traceEvents"]:
+    raise SystemExit(f"traceEvents is empty in {path}")
+PY
+}
+
+run_suite "Integration tests for Clang -ftime-trace with rules_cc"