[experiments] Re-structure experiments codegen to make it more modular and re-usable (#33263)

5 files changed, 491 insertions, 308 deletions

diff --git a/bazel/experiments.bzl b/bazel/experiments.bzl
index 6d9663b777..0c0b83d223 100644
--- a/bazel/experiments.bzl
+++ b/bazel/experiments.bzl
@@ -1,4 +1,4 @@
-# Copyright 2022 gRPC authors.
+# Copyright 2023 gRPC authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Automatically generated by tools/codegen/core/gen_experiments.py
+# Auto generated by tools/codegen/core/gen_experiments.py
 
 """Dictionary of tags to experiments so we know when to test different experiments."""
 
diff --git a/src/core/lib/experiments/experiments.cc b/src/core/lib/experiments/experiments.cc
index b86837118e..dc48e9b928 100644
--- a/src/core/lib/experiments/experiments.cc
+++ b/src/core/lib/experiments/experiments.cc
@@ -1,4 +1,4 @@
-// Copyright 2022 gRPC authors.
+// Copyright 2023 gRPC authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Automatically generated by tools/codegen/core/gen_experiments.py
+// Auto generated by tools/codegen/core/gen_experiments.py
 
 #include <grpc/support/port_platform.h>
 
@@ -25,65 +25,67 @@ const char* const description_tcp_frame_size_tuning =
     "would not indicate completion of a read operation until a specified "
     "number of bytes have been read over the socket. Buffers are also "
     "allocated according to estimated RPC sizes.";
-const char* const additional_constraints_tcp_frame_size_tuning = "";
+const char* const additional_constraints_tcp_frame_size_tuning = "{}";
 const char* const description_tcp_rcv_lowat =
     "Use SO_RCVLOWAT to avoid wakeups on the read path.";
-const char* const additional_constraints_tcp_rcv_lowat = "";
+const char* const additional_constraints_tcp_rcv_lowat = "{}";
 const char* const description_peer_state_based_framing =
     "If set, the max sizes of frames sent to lower layers is controlled based "
     "on the peer's memory pressure which is reflected in its max http2 frame "
     "size.";
-const char* const additional_constraints_peer_state_based_framing = "";
+const char* const additional_constraints_peer_state_based_framing = "{}";
 const char* const description_memory_pressure_controller =
     "New memory pressure controller";
-const char* const additional_constraints_memory_pressure_controller = "";
+const char* const additional_constraints_memory_pressure_controller = "{}";
 const char* const description_unconstrained_max_quota_buffer_size =
     "Discard the cap on the max free pool size for one memory allocator";
 const char* const additional_constraints_unconstrained_max_quota_buffer_size =
-    "";
+    "{}";
 const char* const description_event_engine_client =
     "Use EventEngine clients instead of iomgr's grpc_tcp_client";
-const char* const additional_constraints_event_engine_client = "";
+const char* const additional_constraints_event_engine_client = "{}";
 const char* const description_monitoring_experiment =
     "Placeholder experiment to prove/disprove our monitoring is working";
-const char* const additional_constraints_monitoring_experiment = "";
+const char* const additional_constraints_monitoring_experiment = "{}";
 const char* const description_promise_based_client_call =
     "If set, use the new gRPC promise based call code when it's appropriate "
     "(ie when all filters in a stack are promise based)";
-const char* const additional_constraints_promise_based_client_call = "";
+const char* const additional_constraints_promise_based_client_call = "{}";
 const char* const description_free_large_allocator =
     "If set, return all free bytes from a \042big\042 allocator";
-const char* const additional_constraints_free_large_allocator = "";
+const char* const additional_constraints_free_large_allocator = "{}";
 const char* const description_promise_based_server_call =
     "If set, use the new gRPC promise based call code when it's appropriate "
     "(ie when all filters in a stack are promise based)";
-const char* const additional_constraints_promise_based_server_call = "";
+const char* const additional_constraints_promise_based_server_call = "{}";
 const char* const description_transport_supplies_client_latency =
     "If set, use the transport represented value for client latency in "
     "opencensus";
-const char* const additional_constraints_transport_supplies_client_latency = "";
+const char* const additional_constraints_transport_supplies_client_latency =
+    "{}";
 const char* const description_event_engine_listener =
     "Use EventEngine listeners instead of iomgr's grpc_tcp_server";
-const char* const additional_constraints_event_engine_listener = "";
+const char* const additional_constraints_event_engine_listener = "{}";
 const char* const description_schedule_cancellation_over_write =
     "Allow cancellation op to be scheduled over a write";
-const char* const additional_constraints_schedule_cancellation_over_write = "";
+const char* const additional_constraints_schedule_cancellation_over_write =
+    "{}";
 const char* const description_trace_record_callops =
     "Enables tracing of call batch initiation and completion.";
-const char* const additional_constraints_trace_record_callops = "";
+const char* const additional_constraints_trace_record_callops = "{}";
 const char* const description_event_engine_dns =
     "If set, use EventEngine DNSResolver for client channel resolution";
-const char* const additional_constraints_event_engine_dns = "";
+const char* const additional_constraints_event_engine_dns = "{}";
 const char* const description_work_stealing =
     "If set, use a work stealing thread pool implementation in EventEngine";
-const char* const additional_constraints_work_stealing = "";
+const char* const additional_constraints_work_stealing = "{}";
 const char* const description_client_privacy = "If set, client privacy";
-const char* const additional_constraints_client_privacy = "";
+const char* const additional_constraints_client_privacy = "{}";
 const char* const description_canary_client_privacy =
     "If set, canary client privacy";
-const char* const additional_constraints_canary_client_privacy = "";
+const char* const additional_constraints_canary_client_privacy = "{}";
 const char* const description_server_privacy = "If set, server privacy";
-const char* const additional_constraints_server_privacy = "";
+const char* const additional_constraints_server_privacy = "{}";
 }  // namespace
 
 namespace grpc_core {
diff --git a/src/core/lib/experiments/experiments.h b/src/core/lib/experiments/experiments.h
index e43e20c7fb..ced23dd2b6 100644
--- a/src/core/lib/experiments/experiments.h
+++ b/src/core/lib/experiments/experiments.h
@@ -1,4 +1,4 @@
-// Copyright 2022 gRPC authors.
+// Copyright 2023 gRPC authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// Automatically generated by tools/codegen/core/gen_experiments.py
+// Auto generated by tools/codegen/core/gen_experiments.py
 //
 // This file contains the autogenerated parts of the experiments API.
 //
diff --git a/tools/codegen/core/experiments_compiler.py b/tools/codegen/core/experiments_compiler.py
new file mode 100644
index 0000000000..8d9a7aeaf6
--- /dev/null
+++ b/tools/codegen/core/experiments_compiler.py
@@ -0,0 +1,396 @@
+#!/usr/bin/env python3
+
+# Copyright 2023 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+A module to assist in generating experiment related code and artifacts.
+"""
+
+from __future__ import print_function
+
+import collections
+import ctypes
+import datetime
+import json
+import math
+import os
+import re
+import sys
+
+import yaml
+
+_CODEGEN_PLACEHOLDER_TEXT = """
+This file contains the autogenerated parts of the experiments API.
+
+It generates two symbols for each experiment.
+
+For the experiment named new_car_project, it generates:
+
+- a function IsNewCarProjectEnabled() that returns true if the experiment
+  should be enabled at runtime.
+
+- a macro GRPC_EXPERIMENT_IS_INCLUDED_NEW_CAR_PROJECT that is defined if the
+  experiment *could* be enabled at runtime.
+
+The function is used to determine whether to run the experiment or
+non-experiment code path.
+
+If the experiment brings significant bloat, the macro can be used to avoid
+including the experiment code path in the binary for binaries that are size
+sensitive.
+
+By default that includes our iOS and Android builds.
+
+Finally, a small array is included that contains the metadata for each
+experiment.
+
+A macro, GRPC_EXPERIMENTS_ARE_FINAL, controls whether we fix experiment
+configuration at build time (if it's defined) or allow it to be tuned at
+runtime (if it's disabled).
+
+If you are using the Bazel build system, that macro can be configured with
+--define=grpc_experiments_are_final=true
+"""
+
+
+def ToCStr(s, encoding='ascii'):
+    if isinstance(s, str):
+        s = s.encode(encoding)
+    result = ''
+    for c in s:
+        c = chr(c) if isinstance(c, int) else c
+        if not (32 <= ord(c) < 127) or c in ('\\', '"'):
+            result += '\\%03o' % ord(c)
+        else:
+            result += c
+    return '"' + result + '"'
+
+
+def SnakeToPascal(s):
+    return ''.join(x.capitalize() for x in s.split('_'))
+
+
+def PutBanner(files, banner, prefix):
+    # Print a big comment block into a set of files
+    for f in files:
+        for line in banner:
+            if not line:
+                print(prefix, file=f)
+            else:
+                print('%s %s' % (prefix, line), file=f)
+        print(file=f)
+
+
+def PutCopyright(file, prefix):
+    # copy-paste copyright notice from this file
+    with open(__file__) as my_source:
+        copyright = []
+        for line in my_source:
+            if line[0] != '#':
+                break
+        for line in my_source:
+            if line[0] == '#':
+                copyright.append(line)
+                break
+        for line in my_source:
+            if line[0] != '#':
+                break
+            copyright.append(line)
+        PutBanner([file], [line[2:].rstrip() for line in copyright], prefix)
+
+
+class ExperimentDefinition(object):
+
+    def __init__(self, attributes):
+        self._error = False
+        if 'name' not in attributes:
+            print("ERROR: experiment with no name: %r" % attributes)
+            self._error = True
+        if 'description' not in attributes:
+            print("ERROR: no description for experiment %s" %
+                  attributes['name'])
+            self._error = True
+        if 'owner' not in attributes:
+            print("ERROR: no owner for experiment %s" % attributes['name'])
+            self._error = True
+        if 'expiry' not in attributes:
+            print("ERROR: no expiry for experiment %s" % attributes['name'])
+            self._error = True
+        if attributes['name'] == 'monitoring_experiment':
+            if attributes['expiry'] != 'never-ever':
+                print("ERROR: monitoring_experiment should never expire")
+                self._error = True
+        if self._error:
+            print("Failed to create experiment definition")
+            return
+        self._allow_in_fuzzing_config = True
+        self._name = attributes['name']
+        self._description = attributes['description']
+        self._expiry = attributes['expiry']
+        self._default = None
+        self._additional_constraints = {}
+        self._test_tags = []
+
+        if 'allow_in_fuzzing_config' in attributes:
+            self._allow_in_fuzzing_config = attributes[
+                'allow_in_fuzzing_config']
+
+        if 'test_tags' in attributes:
+            self._test_tags = attributes['test_tags']
+
+    def IsValid(self, check_expiry=False):
+        if self._error:
+            return False
+        if not check_expiry:
+            return True
+        if self._name == 'monitoring_experiment' and self._expiry == 'never-ever':
+            return True
+        today = datetime.date.today()
+        two_quarters_from_now = today + datetime.timedelta(days=180)
+        expiry = datetime.datetime.strptime(self._expiry, '%Y/%m/%d').date()
+        if expiry < today:
+            print("ERROR: experiment %s expired on %s" %
+                  (self._name, self._expiry))
+            self._error = True
+        if expiry > two_quarters_from_now:
+            print("ERROR: experiment %s expires far in the future on %s" %
+                  (self._name, self._expiry))
+            print("expiry should be no more than two quarters from now")
+            self._error = True
+        return not self._error
+
+    def AddRolloutSpecification(self, allowed_defaults, rollout_attributes):
+        if self._error or self._default is not None:
+            return False
+        if rollout_attributes['name'] != self._name:
+            print(
+                "ERROR: Rollout specification does not apply to this experiment: %s"
+                % self._name)
+            return False
+        if 'default' not in rollout_attributes:
+            print("ERROR: no default for experiment %s" %
+                  rollout_attributes['name'])
+            self._error = True
+        if rollout_attributes['default'] not in allowed_defaults:
+            print("ERROR: invalid default for experiment %s: %r" %
+                  (rollout_attributes['name'], rollout_attributes['default']))
+            self._error = True
+        if 'additional_constraints' in rollout_attributes:
+            self._additional_constraints = rollout_attributes[
+                'additional_constraints']
+        self._default = rollout_attributes['default']
+        return True
+
+    @property
+    def name(self):
+        return self._name
+
+    @property
+    def description(self):
+        return self._description
+
+    @property
+    def default(self):
+        return self._default
+
+    @property
+    def test_tags(self):
+        return self._test_tags
+
+    @property
+    def allow_in_fuzzing_config(self):
+        return self._allow_in_fuzzing_config
+
+    @property
+    def additional_constraints(self):
+        return self._additional_constraints
+
+
+class ExperimentsCompiler(object):
+
+    def __init__(self,
+                 defaults,
+                 final_return,
+                 final_define,
+                 bzl_list_for_defaults=None):
+        self._defaults = defaults
+        self._final_return = final_return
+        self._final_define = final_define
+        self._bzl_list_for_defaults = bzl_list_for_defaults
+        self._experiment_definitions = {}
+        self._experiment_rollouts = {}
+
+    def AddExperimentDefinition(self, experiment_definition):
+        if experiment_definition.name in self._experiment_definitions:
+            print("ERROR: Duplicate experiment definition: %s" %
+                  experiment_definition.name)
+            return False
+        self._experiment_definitions[
+            experiment_definition.name] = experiment_definition
+        return True
+
+    def AddRolloutSpecification(self, rollout_attributes):
+        if 'name' not in rollout_attributes:
+            print("ERROR: experiment with no name: %r in rollout_attribute" %
+                  rollout_attributes)
+            return False
+        if rollout_attributes['name'] not in self._experiment_definitions:
+            print("WARNING: rollout for an undefined experiment: %s ignored" %
+                  rollout_attributes['name'])
+        return (self._experiment_definitions[
+            rollout_attributes['name']].AddRolloutSpecification(
+                self._defaults, rollout_attributes))
+
+    def GenerateExperimentsHdr(self, output_file):
+        with open(output_file, 'w') as H:
+            PutCopyright(H, "//")
+            PutBanner(
+                [H],
+                ["Auto generated by tools/codegen/core/gen_experiments.py"] +
+                _CODEGEN_PLACEHOLDER_TEXT.splitlines(), "//")
+
+            print("#ifndef GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
+            print("#define GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
+            print(file=H)
+            print("#include <grpc/support/port_platform.h>", file=H)
+            print(file=H)
+            print("#include <stddef.h>", file=H)
+            print("#include \"src/core/lib/experiments/config.h\"", file=H)
+            print(file=H)
+            print("namespace grpc_core {", file=H)
+            print(file=H)
+            print("#ifdef GRPC_EXPERIMENTS_ARE_FINAL", file=H)
+            for _, exp in self._experiment_definitions.items():
+                define_fmt = self._final_define[exp.default]
+                if define_fmt:
+                    print(define_fmt %
+                          ("GRPC_EXPERIMENT_IS_INCLUDED_%s" % exp.name.upper()),
+                          file=H)
+                print(
+                    "inline bool Is%sEnabled() { %s }" %
+                    (SnakeToPascal(exp.name), self._final_return[exp.default]),
+                    file=H)
+            print("#else", file=H)
+            for i, (_, exp) in enumerate(self._experiment_definitions.items()):
+                print("#define GRPC_EXPERIMENT_IS_INCLUDED_%s" %
+                      exp.name.upper(),
+                      file=H)
+                print(
+                    "inline bool Is%sEnabled() { return IsExperimentEnabled(%d); }"
+                    % (SnakeToPascal(exp.name), i),
+                    file=H)
+            print(file=H)
+            print("constexpr const size_t kNumExperiments = %d;" %
+                  len(self._experiment_definitions.keys()),
+                  file=H)
+            print(
+                "extern const ExperimentMetadata g_experiment_metadata[kNumExperiments];",
+                file=H)
+            print(file=H)
+            print("#endif", file=H)
+            print("}  // namespace grpc_core", file=H)
+            print(file=H)
+            print("#endif  // GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H",
+                  file=H)
+
+    def GenerateExperimentsSrc(self, output_file):
+        with open(output_file, 'w') as C:
+            PutCopyright(C, "//")
+            PutBanner(
+                [C],
+                ["Auto generated by tools/codegen/core/gen_experiments.py"],
+                "//")
+
+            print("#include <grpc/support/port_platform.h>", file=C)
+            print("#include \"src/core/lib/experiments/experiments.h\"", file=C)
+            print(file=C)
+            print("#ifndef GRPC_EXPERIMENTS_ARE_FINAL", file=C)
+            print("namespace {", file=C)
+            have_defaults = set()
+            for _, exp in self._experiment_definitions.items():
+                print("const char* const description_%s = %s;" %
+                      (exp.name, ToCStr(exp.description)),
+                      file=C)
+                print(
+                    "const char* const additional_constraints_%s = %s;" %
+                    (exp.name, ToCStr(json.dumps(exp.additional_constraints))),
+                    file=C)
+                have_defaults.add(exp.default)
+            if 'kDefaultForDebugOnly' in have_defaults:
+                print("#ifdef NDEBUG", file=C)
+                if 'kDefaultForDebugOnly' in have_defaults:
+                    print("const bool kDefaultForDebugOnly = false;", file=C)
+                print("#else", file=C)
+                if 'kDefaultForDebugOnly' in have_defaults:
+                    print("const bool kDefaultForDebugOnly = true;", file=C)
+                print("#endif", file=C)
+            print("}", file=C)
+            print(file=C)
+            print("namespace grpc_core {", file=C)
+            print(file=C)
+            print("const ExperimentMetadata g_experiment_metadata[] = {",
+                  file=C)
+            for _, exp in self._experiment_definitions.items():
+                print(
+                    "  {%s, description_%s, additional_constraints_%s, %s, %s},"
+                    % (ToCStr(exp.name), exp.name, exp.name,
+                       'true' if exp.default else 'false',
+                       'true' if exp.allow_in_fuzzing_config else 'false'),
+                    file=C)
+            print("};", file=C)
+            print(file=C)
+            print("}  // namespace grpc_core", file=C)
+            print("#endif", file=C)
+
+    def GenExperimentsBzl(self, output_file):
+        if self._bzl_list_for_defaults is None:
+            return
+
+        bzl_to_tags_to_experiments = dict(
+            (key, collections.defaultdict(list))
+            for key in self._bzl_list_for_defaults.keys()
+            if key is not None)
+
+        for _, exp in self._experiment_definitions.items():
+            for tag in exp.test_tags:
+                bzl_to_tags_to_experiments[exp.default][tag].append(exp.name)
+
+        with open(output_file, 'w') as B:
+            PutCopyright(B, "#")
+            PutBanner(
+                [B],
+                ["Auto generated by tools/codegen/core/gen_experiments.py"],
+                "#")
+
+            print(
+                "\"\"\"Dictionary of tags to experiments so we know when to test different experiments.\"\"\"",
+                file=B)
+
+            bzl_to_tags_to_experiments = sorted(
+                (self._bzl_list_for_defaults[default], tags_to_experiments)
+                for default, tags_to_experiments in
+                bzl_to_tags_to_experiments.items()
+                if self._bzl_list_for_defaults[default] is not None)
+
+            print(file=B)
+            print("EXPERIMENTS = {", file=B)
+            for key, tags_to_experiments in bzl_to_tags_to_experiments:
+                print("    \"%s\": {" % key, file=B)
+                for tag, experiments in sorted(tags_to_experiments.items()):
+                    print("        \"%s\": [" % tag, file=B)
+                    for experiment in sorted(experiments):
+                        print("            \"%s\"," % experiment, file=B)
+                    print("        ],", file=B)
+                print("    },", file=B)
+            print("}", file=B)
diff --git a/tools/codegen/core/gen_experiments.py b/tools/codegen/core/gen_experiments.py
index 19af812fc9..0dac030e93 100755
--- a/tools/codegen/core/gen_experiments.py
+++ b/tools/codegen/core/gen_experiments.py
@@ -22,28 +22,12 @@ Experiment definitions are in src/core/lib/experiments/experiments.yaml
 
 from __future__ import print_function
 
-import collections
-import ctypes
-import datetime
-import json
-import math
-import os
-import re
+import argparse
 import sys
 
+import experiments_compiler as exp
 import yaml
 
-# TODO(ctiller): if we ever add another argument switch this to argparse
-check_dates = True
-if sys.argv[1:] == ["--check"]:
-    check_dates = False  # for formatting checks we don't verify expiry dates
-
-with open('src/core/lib/experiments/experiments.yaml') as f:
-    attrs = yaml.safe_load(f.read())
-
-with open('src/core/lib/experiments/rollouts.yaml') as f:
-    rollouts = yaml.safe_load(f.read())
-
 DEFAULTS = {
     'broken': 'false',
     False: 'false',
@@ -72,279 +56,80 @@ BZL_LIST_FOR_DEFAULTS = {
     'debug': 'dbg',
 }
 
-error = False
-today = datetime.date.today()
-two_quarters_from_now = today + datetime.timedelta(days=180)
-experiment_annotation = 'gRPC experiments:'
-for rollout_attr in rollouts:
-    if 'name' not in rollout_attr:
-        print("experiment with no name: %r" % attr)
-        error = True
-        continue
-    if 'default' not in rollout_attr:
-        print("no default for experiment %s" % rollout_attr['name'])
-        error = True
-    if rollout_attr['default'] not in DEFAULTS:
-        print("invalid default for experiment %s: %r" %
-              (rollout_attr['name'], rollout_attr['default']))
-        error = True
-for attr in attrs:
-    if 'name' not in attr:
-        print("experiment with no name: %r" % attr)
-        error = True
-        continue  # can't run other diagnostics because we don't know a name
-    if 'description' not in attr:
-        print("no description for experiment %s" % attr['name'])
-        error = True
-    if 'owner' not in attr:
-        print("no owner for experiment %s" % attr['name'])
-        error = True
-    if 'expiry' not in attr:
-        print("no expiry for experiment %s" % attr['name'])
-        error = True
-    if attr['name'] == 'monitoring_experiment':
-        if attr['expiry'] != 'never-ever':
-            print("monitoring_experiment should never expire")
-            error = True
-    else:
-        expiry = datetime.datetime.strptime(attr['expiry'], '%Y/%m/%d').date()
-        if check_dates:
-            if expiry < today:
-                print("experiment %s expired on %s" %
-                      (attr['name'], attr['expiry']))
-                error = True
-            if expiry > two_quarters_from_now:
-                print("experiment %s expires far in the future on %s" %
-                      (attr['name'], attr['expiry']))
-                print("expiry should be no more than two quarters from now")
-                error = True
-            experiment_annotation += attr['name'] + ':0,'
-
-if len(experiment_annotation) > 2000:
-    print("comma-delimited string of experiments is too long")
-    error = True
-
-if error:
-    sys.exit(1)
-
-
-def c_str(s, encoding='ascii'):
-    if isinstance(s, str):
-        s = s.encode(encoding)
-    result = ''
-    for c in s:
-        c = chr(c) if isinstance(c, int) else c
-        if not (32 <= ord(c) < 127) or c in ('\\', '"'):
-            result += '\\%03o' % ord(c)
-        else:
-            result += c
-    return '"' + result + '"'
-
-
-def snake_to_pascal(s):
-    return ''.join(x.capitalize() for x in s.split('_'))
-
-
-# utility: print a big comment block into a set of files
-def put_banner(files, banner, prefix):
-    for f in files:
-        for line in banner:
-            if not line:
-                print(prefix, file=f)
-            else:
-                print('%s %s' % (prefix, line), file=f)
-        print(file=f)
-
-
-def put_copyright(file, prefix):
-    # copy-paste copyright notice from this file
-    with open(sys.argv[0]) as my_source:
-        copyright = []
-        for line in my_source:
-            if line[0] != '#':
-                break
-        for line in my_source:
-            if line[0] == '#':
-                copyright.append(line)
-                break
-        for line in my_source:
-            if line[0] != '#':
-                break
-            copyright.append(line)
-        put_banner([file], [line[2:].rstrip() for line in copyright], prefix)
-
-
-def get_rollout_attr_for_experiment(name):
-    for rollout_attr in rollouts:
-        if rollout_attr['name'] == name:
-            return rollout_attr
-    print('WARNING. experiment: %r has no rollout config. Disabling it.' % name)
-    return {'name': name, 'default': 'false'}
 
+def ParseCommandLineArguments(args):
+    """Wrapper for argparse command line arguments handling.
+
+    Args:
+    args: List of command line arguments.
+
+    Returns:
+    Command line arguments namespace built by argparse.ArgumentParser().
+    """
+    # formatter_class=argparse.ArgumentDefaultsHelpFormatter is not used here
+    # intentionally, We want more formatting than this class can provide.
+    flag_parser = argparse.ArgumentParser()
+    flag_parser.add_argument(
+        '--check',
+        action='store_false',
+        help='If specified, disables checking experiment expiry dates',
+    )
+    flag_parser.add_argument(
+        '--disable_gen_hdrs',
+        action='store_true',
+        help='If specified, disables generation of experiments hdr files',
+    )
+    flag_parser.add_argument(
+        '--disable_gen_srcs',
+        action='store_true',
+        help='If specified, disables generation of experiments source files',
+    )
+    flag_parser.add_argument(
+        '--disable_gen_bzl',
+        action='store_true',
+        help='If specified, disables generation of experiments.bzl file',
+    )
+    return flag_parser.parse_args(args)
+
+
+args = ParseCommandLineArguments(sys.argv[1:])
 
-WTF = """
-This file contains the autogenerated parts of the experiments API.
-
-It generates two symbols for each experiment.
-
-For the experiment named new_car_project, it generates:
-
-- a function IsNewCarProjectEnabled() that returns true if the experiment
-  should be enabled at runtime.
-
-- a macro GRPC_EXPERIMENT_IS_INCLUDED_NEW_CAR_PROJECT that is defined if the
-  experiment *could* be enabled at runtime.
-
-The function is used to determine whether to run the experiment or
-non-experiment code path.
-
-If the experiment brings significant bloat, the macro can be used to avoid
-including the experiment code path in the binary for binaries that are size
-sensitive.
-
-By default that includes our iOS and Android builds.
-
-Finally, a small array is included that contains the metadata for each
-experiment.
-
-A macro, GRPC_EXPERIMENTS_ARE_FINAL, controls whether we fix experiment
-configuration at build time (if it's defined) or allow it to be tuned at
-runtime (if it's disabled).
-
-If you are using the Bazel build system, that macro can be configured with
---define=grpc_experiments_are_final=true
-"""
-
-with open('src/core/lib/experiments/experiments.h', 'w') as H:
-    put_copyright(H, "//")
-
-    put_banner(
-        [H],
-        ["Automatically generated by tools/codegen/core/gen_experiments.py"] +
-        WTF.splitlines(), "//")
-
-    print("#ifndef GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
-    print("#define GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
-    print(file=H)
-    print("#include <grpc/support/port_platform.h>", file=H)
-    print(file=H)
-    print("#include <stddef.h>", file=H)
-    print("#include \"src/core/lib/experiments/config.h\"", file=H)
-    print(file=H)
-    print("namespace grpc_core {", file=H)
-    print(file=H)
-    print("#ifdef GRPC_EXPERIMENTS_ARE_FINAL", file=H)
-    for i, attr in enumerate(attrs):
-        rollout_attr = get_rollout_attr_for_experiment(attr['name'])
-        define_fmt = FINAL_DEFINE[rollout_attr['default']]
-        if define_fmt:
-            print(define_fmt %
-                  ("GRPC_EXPERIMENT_IS_INCLUDED_%s" % attr['name'].upper()),
-                  file=H)
-        print("inline bool Is%sEnabled() { %s }" % (snake_to_pascal(
-            attr['name']), FINAL_RETURN[rollout_attr['default']]),
-              file=H)
-    print("#else", file=H)
-    for i, attr in enumerate(attrs):
-        print("#define GRPC_EXPERIMENT_IS_INCLUDED_%s" % attr['name'].upper(),
-              file=H)
-        print("inline bool Is%sEnabled() { return IsExperimentEnabled(%d); }" %
-              (snake_to_pascal(attr['name']), i),
-              file=H)
-    print(file=H)
-    print("constexpr const size_t kNumExperiments = %d;" % len(attrs), file=H)
-    print(
-        "extern const ExperimentMetadata g_experiment_metadata[kNumExperiments];",
-        file=H)
-    print(file=H)
-    print("#endif", file=H)
-    print("}  // namespace grpc_core", file=H)
-    print(file=H)
-    print("#endif  // GRPC_SRC_CORE_LIB_EXPERIMENTS_EXPERIMENTS_H", file=H)
-
-with open('src/core/lib/experiments/experiments.cc', 'w') as C:
-    put_copyright(C, "//")
-
-    put_banner(
-        [C],
-        ["Automatically generated by tools/codegen/core/gen_experiments.py"],
-        "//")
+with open('src/core/lib/experiments/experiments.yaml') as f:
+    attrs = yaml.safe_load(f.read())
 
-    print("#include <grpc/support/port_platform.h>", file=C)
-    print("#include \"src/core/lib/experiments/experiments.h\"", file=C)
-    print(file=C)
-    print("#ifndef GRPC_EXPERIMENTS_ARE_FINAL", file=C)
-    print("namespace {", file=C)
-    for attr in attrs:
-        print("const char* const description_%s = %s;" %
-              (attr['name'], c_str(attr['description'])),
-              file=C)
-        print("const char* const additional_constraints_%s = \"\";" %
-              attr['name'],
-              file=C)
-    have_defaults = set(
-        DEFAULTS[rollout_attr['default']] for rollout_attr in rollouts)
-    if 'kDefaultForDebugOnly' in have_defaults:
-        print("#ifdef NDEBUG", file=C)
-        if 'kDefaultForDebugOnly' in have_defaults:
-            print("const bool kDefaultForDebugOnly = false;", file=C)
-        print("#else", file=C)
-        if 'kDefaultForDebugOnly' in have_defaults:
-            print("const bool kDefaultForDebugOnly = true;", file=C)
-        print("#endif", file=C)
-    print("}", file=C)
-    print(file=C)
-    print("namespace grpc_core {", file=C)
-    print(file=C)
-    print("const ExperimentMetadata g_experiment_metadata[] = {", file=C)
-    for attr in attrs:
-        rollout_attr = get_rollout_attr_for_experiment(attr['name'])
-        print(
-            "  {%s, description_%s, additional_constraints_%s, %s, %s}," %
-            (c_str(attr['name']), attr['name'], attr['name'],
-             DEFAULTS[rollout_attr['default']],
-             'true' if attr.get('allow_in_fuzzing_config', True) else 'false'),
-            file=C)
-    print("};", file=C)
-    print(file=C)
-    print("}  // namespace grpc_core", file=C)
-    print("#endif", file=C)
+with open('src/core/lib/experiments/rollouts.yaml') as f:
+    rollouts = yaml.safe_load(f.read())
 
-bzl_to_tags_to_experiments = dict((key, collections.defaultdict(list))
-                                  for key in BZL_LIST_FOR_DEFAULTS.keys()
-                                  if key is not None)
+compiler = exp.ExperimentsCompiler(DEFAULTS, FINAL_RETURN, FINAL_DEFINE,
+                                   BZL_LIST_FOR_DEFAULTS)
 
+experiment_annotation = "gRPC Experiments: "
 for attr in attrs:
-    rollout_attr = get_rollout_attr_for_experiment(attr['name'])
-    for tag in attr['test_tags']:
-        bzl_to_tags_to_experiments[rollout_attr['default']][tag].append(
-            attr['name'])
+    exp_definition = exp.ExperimentDefinition(attr)
+    if not exp_definition.IsValid(args.check):
+        sys.exit(1)
+    experiment_annotation += exp_definition.name + ':0,'
+    if not compiler.AddExperimentDefinition(exp_definition):
+        print("Experiment = %s ERROR adding" % exp_definition.name)
+        sys.exit(1)
 
-with open('bazel/experiments.bzl', 'w') as B:
-    put_copyright(B, "#")
+if len(experiment_annotation) > 2000:
+    print("comma-delimited string of experiments is too long")
+    sys.exit(1)
 
-    put_banner(
-        [B],
-        ["Automatically generated by tools/codegen/core/gen_experiments.py"],
-        "#")
+for rollout_attr in rollouts:
+    if not compiler.AddRolloutSpecification(rollout_attr):
+        print("ERROR adding rollout spec")
+        sys.exit(1)
 
-    print(
-        "\"\"\"Dictionary of tags to experiments so we know when to test different experiments.\"\"\"",
-        file=B)
+if not args.disable_gen_hdrs:
+    print("Generating experiments headers")
+    compiler.GenerateExperimentsHdr('src/core/lib/experiments/experiments.h')
 
-    bzl_to_tags_to_experiments = sorted(
-        (BZL_LIST_FOR_DEFAULTS[default], tags_to_experiments)
-        for default, tags_to_experiments in bzl_to_tags_to_experiments.items()
-        if BZL_LIST_FOR_DEFAULTS[default] is not None)
+if not args.disable_gen_srcs:
+    print("Generating experiments srcs")
+    compiler.GenerateExperimentsSrc('src/core/lib/experiments/experiments.cc')
 
-    print(file=B)
-    print("EXPERIMENTS = {", file=B)
-    for key, tags_to_experiments in bzl_to_tags_to_experiments:
-        print("    \"%s\": {" % key, file=B)
-        for tag, experiments in sorted(tags_to_experiments.items()):
-            print("        \"%s\": [" % tag, file=B)
-            for experiment in sorted(experiments):
-                print("            \"%s\"," % experiment, file=B)
-            print("        ],", file=B)
-        print("    },", file=B)
-    print("}", file=B)
+if not args.disable_gen_bzl:
+    print("Generating experiments.bzl")
+    compiler.GenExperimentsBzl('bazel/experiments.bzl')