From 6ee7a647bf25bfc720f8d2bcf74294f8320d919c Mon Sep 17 00:00:00 2001
From: Craig Tiller <ctiller@google.com>
Date: Tue, 6 Sep 2022 12:16:54 -0700
Subject: [PATCH] [experiments] Add support for testing disabling already
 enabled experiments (#30831)

---
 bazel/experiments.bzl                 |  3 +++
 bazel/grpc_build_system.bzl           | 29 ++++++++++++++++++++++++++-
 tools/codegen/core/gen_experiments.py | 17 ++++++++++++++--
 3 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/bazel/experiments.bzl b/bazel/experiments.bzl
index 9f116cefd15..5acd6f60a59 100644
--- a/bazel/experiments.bzl
+++ b/bazel/experiments.bzl
@@ -28,3 +28,6 @@ EXPERIMENTS = {
         "tcp_read_chunks",
     ],
 }
+
+NEGATED_EXPERIMENTS = {
+}
diff --git a/bazel/grpc_build_system.bzl b/bazel/grpc_build_system.bzl
index 4c59d5aa4f1..fc388e9f0c6 100644
--- a/bazel/grpc_build_system.bzl
+++ b/bazel/grpc_build_system.bzl
@@ -29,7 +29,7 @@ Contains macros used throughout the repo.
 
 load("//bazel:cc_grpc_library.bzl", "cc_grpc_library")
 load("//bazel:copts.bzl", "GRPC_DEFAULT_COPTS")
-load("//bazel:experiments.bzl", "EXPERIMENTS")
+load("//bazel:experiments.bzl", "EXPERIMENTS", "NEGATED_EXPERIMENTS")
 load("@upb//bazel:upb_proto_library.bzl", "upb_proto_library", "upb_proto_reflection_library")
 load("@build_bazel_rules_apple//apple:ios.bzl", "ios_unit_test")
 load("@build_bazel_rules_apple//apple/testing/default_runner:ios_test_runner.bzl", "ios_test_runner")
@@ -336,6 +336,14 @@ def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_event_engin
             experiments[experiment] = 1
     experiments = list(experiments.keys())
 
+    negated_experiments = {}
+    for tag in tags:
+        if tag not in NEGATED_EXPERIMENTS:
+            continue
+        for experiment in NEGATED_EXPERIMENTS[tag]:
+            negated_experiments[experiment] = 1
+    negated_experiments = list(negated_experiments.keys())
+
     experiment_config = list(poller_config)
     for experiment in experiments:
         for config in poller_config:
@@ -356,6 +364,25 @@ def expand_tests(name, srcs, deps, tags, args, exclude_pollers, uses_event_engin
                     tags = tags + [tag]
             config["tags"] = tags
             experiment_config.append(config)
+    for experiment in negated_experiments:
+        for config in poller_config:
+            config = dict(config)
+            config["name"] = config["name"] + "@experiment=no_" + experiment
+            config["args"] = config["args"] + ["--experiment=-" + experiment]
+            tags = config["tags"]
+            must_have_tags = [
+                # We don't run experiments on cmake builds
+                "bazel_only",
+                # Nor on windows
+                "no_windows",
+                # Nor on mac
+                "no_mac",
+            ]
+            for tag in must_have_tags:
+                if tag not in tags:
+                    tags = tags + [tag]
+            config["tags"] = tags
+            experiment_config.append(config)
 
     return experiment_config
 
diff --git a/tools/codegen/core/gen_experiments.py b/tools/codegen/core/gen_experiments.py
index 0cbe5d14745..8b131ce758a 100755
--- a/tools/codegen/core/gen_experiments.py
+++ b/tools/codegen/core/gen_experiments.py
@@ -187,9 +187,14 @@ with open('src/core/lib/experiments/experiments.cc', 'w') as C:
     print("}  // namespace grpc_core", file=C)
 
 tags_to_experiments = collections.defaultdict(list)
+tags_to_negated_experiments = collections.defaultdict(list)
 for attr in attrs:
-    for tag in attr['test_tags']:
-        tags_to_experiments[tag].append(attr['name'])
+    if attr['default']:
+        for tag in attr['test_tags']:
+            tags_to_negated_experiments[tag].append(attr['name'])
+    else:
+        for tag in attr['test_tags']:
+            tags_to_experiments[tag].append(attr['name'])
 
 with open('bazel/experiments.bzl', 'w') as B:
     put_copyright(B, "#")
@@ -211,3 +216,11 @@ with open('bazel/experiments.bzl', 'w') as B:
             print("        \"%s\"," % experiment, file=B)
         print("    ],", file=B)
     print("}", file=B)
+    print(file=B)
+    print("NEGATED_EXPERIMENTS = {", file=B)
+    for tag, experiments in sorted(tags_to_negated_experiments.items()):
+        print("    \"%s\": [" % tag, file=B)
+        for experiment in sorted(experiments):
+            print("        \"%s\"," % experiment, file=B)
+        print("    ],", file=B)
+    print("}", file=B)