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base / feature_list.cc [blame]
// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/location.h"
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40284755): Remove this and spanify to fix the errors.
#pragma allow_unsafe_buffers
#endif
#include <stddef.h>
#include <algorithm>
#include <string>
#include <string_view>
#include <tuple>
#include "base/base_switches.h"
#include "base/check_is_test.h"
#include "base/containers/contains.h"
#include "base/containers/span.h"
#include "base/debug/crash_logging.h"
#include "base/debug/dump_without_crashing.h"
#include "base/feature_list.h"
#include "base/feature_visitor.h"
#include "base/logging.h"
#include "base/memory/ptr_util.h"
#include "base/memory/raw_ptr.h"
#include "base/metrics/field_trial.h"
#include "base/metrics/field_trial_param_associator.h"
#include "base/metrics/field_trial_params.h"
#include "base/metrics/persistent_memory_allocator.h"
#include "base/no_destructor.h"
#include "base/notreached.h"
#include "base/pickle.h"
#include "base/rand_util.h"
#include "base/strings/string_split.h"
#include "base/strings/string_util.h"
#include "base/strings/stringprintf.h"
#include "build/build_config.h"
#include "build/chromeos_buildflags.h"
namespace base {
namespace {
// Pointer to the FeatureList instance singleton that was set via
// FeatureList::SetInstance(). Does not use base/memory/singleton.h in order to
// have more control over initialization timing. Leaky.
FeatureList* g_feature_list_instance = nullptr;
// Tracks access to Feature state before FeatureList registration.
class EarlyFeatureAccessTracker {
public:
static EarlyFeatureAccessTracker* GetInstance() {
static NoDestructor<EarlyFeatureAccessTracker> instance;
return instance.get();
}
// Invoked when `feature` is accessed before FeatureList registration.
void AccessedFeature(const Feature& feature,
bool with_feature_allow_list = false) {
AutoLock lock(lock_);
if (fail_instantly_) {
Fail(&feature, with_feature_allow_list);
} else if (!feature_) {
feature_ = &feature;
feature_had_feature_allow_list_ = with_feature_allow_list;
}
}
// Asserts that no feature was accessed before FeatureList registration.
void AssertNoAccess() {
AutoLock lock(lock_);
if (feature_) {
Fail(feature_, feature_had_feature_allow_list_);
}
}
// Makes calls to AccessedFeature() fail instantly.
void FailOnFeatureAccessWithoutFeatureList() {
AutoLock lock(lock_);
if (feature_) {
Fail(feature_, feature_had_feature_allow_list_);
}
fail_instantly_ = true;
}
// Resets the state of this tracker.
void Reset() {
AutoLock lock(lock_);
feature_ = nullptr;
fail_instantly_ = false;
}
const Feature* GetFeature() {
AutoLock lock(lock_);
return feature_.get();
}
private:
void Fail(const Feature* feature, bool with_feature_allow_list) {
// TODO(crbug.com/40237050): Enable this check on all platforms.
#if !BUILDFLAG(IS_IOS) && !BUILDFLAG(IS_ANDROID) && !BUILDFLAG(IS_CHROMEOS)
#if !BUILDFLAG(IS_NACL)
// Create a crash key with the name of the feature accessed too early, to
// facilitate crash triage.
SCOPED_CRASH_KEY_STRING256("FeatureList", "feature-accessed-too-early",
feature->name);
SCOPED_CRASH_KEY_BOOL("FeatureList", "early-access-allow-list",
with_feature_allow_list);
#endif // !BUILDFLAG(IS_NACL)
CHECK(!feature) << "Accessed feature " << feature->name
<< (with_feature_allow_list
? " which is not on the allow list passed to "
"SetEarlyAccessInstance()."
: " before FeatureList registration.");
#endif // !BUILDFLAG(IS_IOS) && !BUILDFLAG(IS_ANDROID) &&
// !BUILDFLAG(IS_CHROMEOS)
}
friend class NoDestructor<EarlyFeatureAccessTracker>;
EarlyFeatureAccessTracker() = default;
~EarlyFeatureAccessTracker() = default;
Lock lock_;
// First feature to be accessed before FeatureList registration.
raw_ptr<const Feature> feature_ GUARDED_BY(lock_) = nullptr;
bool feature_had_feature_allow_list_ GUARDED_BY(lock_) = false;
// Whether AccessedFeature() should fail instantly.
bool fail_instantly_ GUARDED_BY(lock_) = false;
};
#if DCHECK_IS_ON()
const char* g_reason_overrides_disallowed = nullptr;
void DCheckOverridesAllowed() {
const bool feature_overrides_allowed = !g_reason_overrides_disallowed;
DCHECK(feature_overrides_allowed) << g_reason_overrides_disallowed;
}
#else
void DCheckOverridesAllowed() {}
#endif
// An allocator entry for a feature in shared memory. The FeatureEntry is
// followed by a base::Pickle object that contains the feature and trial name.
struct FeatureEntry {
// SHA1(FeatureEntry): Increment this if structure changes!
static constexpr uint32_t kPersistentTypeId = 0x06567CA6 + 2;
// Expected size for 32/64-bit check.
static constexpr size_t kExpectedInstanceSize = 16;
// Specifies whether a feature override enables or disables the feature. Same
// values as the OverrideState enum in feature_list.h
uint32_t override_state;
// On e.g. x86, alignof(uint64_t) is 4. Ensure consistent size and alignment
// of `pickle_size` across platforms.
uint32_t padding;
// Size of the pickled structure, NOT the total size of this entry.
uint64_t pickle_size;
// Return a pointer to the pickled data area immediately following the entry.
uint8_t* GetPickledDataPtr() { return reinterpret_cast<uint8_t*>(this + 1); }
const uint8_t* GetPickledDataPtr() const {
return reinterpret_cast<const uint8_t*>(this + 1);
}
// Reads the feature and trial name from the pickle. Calling this is only
// valid on an initialized entry that's in shared memory.
bool GetFeatureAndTrialName(std::string_view* feature_name,
std::string_view* trial_name) const {
Pickle pickle = Pickle::WithUnownedBuffer(
span(GetPickledDataPtr(), checked_cast<size_t>(pickle_size)));
PickleIterator pickle_iter(pickle);
if (!pickle_iter.ReadStringPiece(feature_name)) {
return false;
}
// Return true because we are not guaranteed to have a trial name anyways.
std::ignore = pickle_iter.ReadStringPiece(trial_name);
return true;
}
};
// Splits |text| into two parts by the |separator| where the first part will be
// returned updated in |first| and the second part will be returned as |second|.
// This function returns false if there is more than one |separator| in |first|.
// If there is no |separator| presented in |first|, this function will not
// modify |first| and |second|. It's used for splitting the |enable_features|
// flag into feature name, field trial name and feature parameters.
bool SplitIntoTwo(std::string_view text,
std::string_view separator,
std::string_view* first,
std::string* second) {
std::vector<std::string_view> parts =
SplitStringPiece(text, separator, TRIM_WHITESPACE, SPLIT_WANT_ALL);
if (parts.size() == 2) {
*second = std::string(parts[1]);
} else if (parts.size() > 2) {
DLOG(ERROR) << "Only one '" << separator
<< "' is allowed but got: " << text;
return false;
}
*first = parts[0];
return true;
}
// Checks and parses the |enable_features| flag and sets
// |parsed_enable_features| to be a comma-separated list of features,
// |force_fieldtrials| to be a comma-separated list of field trials that each
// feature want to associate with and |force_fieldtrial_params| to be the field
// trial parameters for each field trial.
// Returns true if |enable_features| is parsable, otherwise false.
bool ParseEnableFeatures(const std::string& enable_features,
std::string* parsed_enable_features,
std::string* force_fieldtrials,
std::string* force_fieldtrial_params) {
std::vector<std::string> enable_features_list;
std::vector<std::string> force_fieldtrials_list;
std::vector<std::string> force_fieldtrial_params_list;
for (const auto& enable_feature :
FeatureList::SplitFeatureListString(enable_features)) {
std::string feature_name;
std::string study;
std::string group;
std::string feature_params;
if (!FeatureList::ParseEnableFeatureString(
enable_feature, &feature_name, &study, &group, &feature_params)) {
return false;
}
// If feature params were set but group and study weren't, associate the
// feature and its feature params to a synthetic field trial as the
// feature params only make sense when it's combined with a field trial.
if (!feature_params.empty()) {
force_fieldtrials_list.push_back(study + "/" + group);
force_fieldtrial_params_list.push_back(study + "." + group + ":" +
feature_params);
}
enable_features_list.push_back(study.empty() ? std::move(feature_name)
: feature_name + "<" + study);
}
*parsed_enable_features = JoinString(enable_features_list, ",");
// Field trial separator is currently a slash. See
// |kPersistentStringSeparator| in base/metrics/field_trial.cc.
*force_fieldtrials = JoinString(force_fieldtrials_list, "/");
*force_fieldtrial_params = JoinString(force_fieldtrial_params_list, ",");
return true;
}
std::pair<FeatureList::OverrideState, uint16_t> UnpackFeatureCache(
uint32_t packed_cache_value) {
return std::make_pair(
static_cast<FeatureList::OverrideState>(packed_cache_value >> 24),
packed_cache_value & 0xFFFF);
}
uint32_t PackFeatureCache(FeatureList::OverrideState override_state,
uint32_t caching_context) {
return (static_cast<uint32_t>(override_state) << 24) |
(caching_context & 0xFFFF);
}
// A monotonically increasing id, passed to `FeatureList`s as they are created
// to invalidate the cache member of `base::Feature` objects that were queried
// with a different `FeatureList` installed.
uint16_t g_current_caching_context = 1;
} // namespace
#if BUILDFLAG(DCHECK_IS_CONFIGURABLE)
BASE_FEATURE(kDCheckIsFatalFeature,
"DcheckIsFatal",
FEATURE_DISABLED_BY_DEFAULT);
#endif // BUILDFLAG(DCHECK_IS_CONFIGURABLE)
FeatureList::FeatureList() : caching_context_(g_current_caching_context++) {}
FeatureList::~FeatureList() = default;
FeatureList::ScopedDisallowOverrides::ScopedDisallowOverrides(
const char* reason)
#if DCHECK_IS_ON()
: previous_reason_(g_reason_overrides_disallowed) {
g_reason_overrides_disallowed = reason;
}
#else
{
}
#endif
FeatureList::ScopedDisallowOverrides::~ScopedDisallowOverrides() {
#if DCHECK_IS_ON()
g_reason_overrides_disallowed = previous_reason_;
#endif
}
void FeatureList::InitFromCommandLine(const std::string& enable_features,
const std::string& disable_features) {
DCHECK(!initialized_);
std::string parsed_enable_features;
std::string force_fieldtrials;
std::string force_fieldtrial_params;
bool parse_enable_features_result =
ParseEnableFeatures(enable_features, &parsed_enable_features,
&force_fieldtrials, &force_fieldtrial_params);
DCHECK(parse_enable_features_result) << StringPrintf(
"The --%s list is unparsable or invalid, please check the format.",
::switches::kEnableFeatures);
// Only create field trials when field_trial_list is available. Some tests
// don't have field trial list available.
if (FieldTrialList::GetInstance()) {
bool associate_params_result = AssociateFieldTrialParamsFromString(
force_fieldtrial_params, &UnescapeValue);
DCHECK(associate_params_result) << StringPrintf(
"The field trial parameters part of the --%s list is invalid. Make "
"sure "
"you %%-encode the following characters in param values: %%:/.,",
::switches::kEnableFeatures);
bool create_trials_result =
FieldTrialList::CreateTrialsFromString(force_fieldtrials);
DCHECK(create_trials_result)
<< StringPrintf("Invalid field trials are specified in --%s.",
::switches::kEnableFeatures);
}
// Process disabled features first, so that disabled ones take precedence over
// enabled ones (since RegisterOverride() uses emplace()).
RegisterOverridesFromCommandLine(disable_features, OVERRIDE_DISABLE_FEATURE);
RegisterOverridesFromCommandLine(parsed_enable_features,
OVERRIDE_ENABLE_FEATURE);
initialized_from_command_line_ = true;
}
void FeatureList::InitFromSharedMemory(PersistentMemoryAllocator* allocator) {
DCHECK(!initialized_);
PersistentMemoryAllocator::Iterator iter(allocator);
const FeatureEntry* entry;
while ((entry = iter.GetNextOfObject<FeatureEntry>()) != nullptr) {
OverrideState override_state =
static_cast<OverrideState>(entry->override_state);
std::string_view feature_name;
std::string_view trial_name;
if (!entry->GetFeatureAndTrialName(&feature_name, &trial_name))
continue;
FieldTrial* trial = FieldTrialList::Find(trial_name);
RegisterOverride(feature_name, override_state, trial);
}
}
bool FeatureList::IsFeatureOverridden(const std::string& feature_name) const {
return GetOverrideEntryByFeatureName(feature_name);
}
bool FeatureList::IsFeatureOverriddenFromCommandLine(
const std::string& feature_name) const {
const OverrideEntry* entry = GetOverrideEntryByFeatureName(feature_name);
return entry && !entry->overridden_by_field_trial;
}
bool FeatureList::IsFeatureOverriddenFromCommandLine(
const std::string& feature_name,
OverrideState state) const {
const OverrideEntry* entry = GetOverrideEntryByFeatureName(feature_name);
return entry && !entry->overridden_by_field_trial &&
entry->overridden_state == state;
}
void FeatureList::AssociateReportingFieldTrial(
const std::string& feature_name,
OverrideState for_overridden_state,
FieldTrial* field_trial) {
DCHECK(
IsFeatureOverriddenFromCommandLine(feature_name, for_overridden_state));
// Only one associated field trial is supported per feature. This is generally
// enforced server-side.
OverrideEntry* entry = &overrides_.find(feature_name)->second;
if (entry->field_trial) {
NOTREACHED() << "Feature " << feature_name
<< " already has trial: " << entry->field_trial->trial_name()
<< ", associating trial: " << field_trial->trial_name();
}
entry->field_trial = field_trial;
}
void FeatureList::RegisterFieldTrialOverride(const std::string& feature_name,
OverrideState override_state,
FieldTrial* field_trial) {
DCHECK(field_trial);
DCHECK(!HasAssociatedFieldTrialByFeatureName(feature_name))
<< "Feature " << feature_name << " is overriden multiple times in these "
<< "trials: "
<< overrides_.find(feature_name)->second.field_trial->trial_name()
<< " and " << field_trial->trial_name() << ". "
<< "Check the trial (study) in (1) the server config, "
<< "(2) fieldtrial_testing_config.json, (3) about_flags.cc, and "
<< "(4) client-side field trials.";
RegisterOverride(feature_name, override_state, field_trial);
}
void FeatureList::RegisterExtraFeatureOverrides(
const std::vector<FeatureOverrideInfo>& extra_overrides,
bool replace_use_default_overrides) {
for (const FeatureOverrideInfo& override_info : extra_overrides) {
RegisterOverride(override_info.first.get().name, override_info.second,
/*field_trial=*/nullptr, replace_use_default_overrides);
}
}
void FeatureList::AddFeaturesToAllocator(PersistentMemoryAllocator* allocator) {
DCHECK(initialized_);
for (const auto& override : overrides_) {
Pickle pickle;
pickle.WriteString(override.first);
if (override.second.field_trial)
pickle.WriteString(override.second.field_trial->trial_name());
size_t total_size = sizeof(FeatureEntry) + pickle.size();
FeatureEntry* entry = allocator->New<FeatureEntry>(total_size);
if (!entry)
return;
entry->override_state = override.second.overridden_state;
entry->pickle_size = pickle.size();
memcpy(entry->GetPickledDataPtr(), pickle.data(), pickle.size());
allocator->MakeIterable(entry);
}
}
void FeatureList::GetFeatureOverrides(std::string* enable_overrides,
std::string* disable_overrides,
bool include_group_name) const {
GetFeatureOverridesImpl(enable_overrides, disable_overrides, false,
include_group_name);
}
void FeatureList::GetCommandLineFeatureOverrides(
std::string* enable_overrides,
std::string* disable_overrides) const {
GetFeatureOverridesImpl(enable_overrides, disable_overrides, true);
}
// static
bool FeatureList::IsEnabled(const Feature& feature) {
if (!g_feature_list_instance ||
!g_feature_list_instance->AllowFeatureAccess(feature)) {
EarlyFeatureAccessTracker::GetInstance()->AccessedFeature(
feature, g_feature_list_instance &&
g_feature_list_instance->IsEarlyAccessInstance());
return feature.default_state == FEATURE_ENABLED_BY_DEFAULT;
}
return g_feature_list_instance->IsFeatureEnabled(feature);
}
// static
bool FeatureList::IsValidFeatureOrFieldTrialName(std::string_view name) {
return IsStringASCII(name) && name.find_first_of(",<*") == std::string::npos;
}
// static
std::optional<bool> FeatureList::GetStateIfOverridden(const Feature& feature) {
if (!g_feature_list_instance ||
!g_feature_list_instance->AllowFeatureAccess(feature)) {
EarlyFeatureAccessTracker::GetInstance()->AccessedFeature(
feature, g_feature_list_instance &&
g_feature_list_instance->IsEarlyAccessInstance());
// If there is no feature list, there can be no overrides.
return std::nullopt;
}
return g_feature_list_instance->IsFeatureEnabledIfOverridden(feature);
}
// static
FieldTrial* FeatureList::GetFieldTrial(const Feature& feature) {
if (!g_feature_list_instance ||
!g_feature_list_instance->AllowFeatureAccess(feature)) {
EarlyFeatureAccessTracker::GetInstance()->AccessedFeature(
feature, g_feature_list_instance &&
g_feature_list_instance->IsEarlyAccessInstance());
return nullptr;
}
return g_feature_list_instance->GetAssociatedFieldTrial(feature);
}
// static
std::vector<std::string_view> FeatureList::SplitFeatureListString(
std::string_view input) {
return SplitStringPiece(input, ",", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
}
// static
bool FeatureList::ParseEnableFeatureString(std::string_view enable_feature,
std::string* feature_name,
std::string* study_name,
std::string* group_name,
std::string* params) {
std::string_view first;
// First, check whether ":" is present. If true, feature parameters were
// set for this feature.
std::string feature_params;
if (!SplitIntoTwo(enable_feature, ":", &first, &feature_params))
return false;
// Then, check whether "." is present. If true, a group was specified for
// this feature.
std::string group;
if (!SplitIntoTwo(first, ".", &first, &group))
return false;
// Finally, check whether "<" is present. If true, a study was specified for
// this feature.
std::string study;
if (!SplitIntoTwo(first, "<", &first, &study))
return false;
std::string enable_feature_name(first);
// If feature params were set but group and study weren't, associate the
// feature and its feature params to a synthetic field trial as the
// feature params only make sense when it's combined with a field trial.
if (!feature_params.empty()) {
study = study.empty() ? "Study" + enable_feature_name : std::move(study);
group = group.empty() ? "Group" + enable_feature_name : std::move(group);
}
feature_name->swap(enable_feature_name);
study_name->swap(study);
group_name->swap(group);
params->swap(feature_params);
return true;
}
// static
bool FeatureList::InitInstance(const std::string& enable_features,
const std::string& disable_features) {
return InitInstance(enable_features, disable_features,
std::vector<FeatureOverrideInfo>());
}
// static
bool FeatureList::InitInstance(
const std::string& enable_features,
const std::string& disable_features,
const std::vector<FeatureOverrideInfo>& extra_overrides) {
// We want to initialize a new instance here to support command-line features
// in testing better. For example, we initialize a dummy instance in
// base/test/test_suite.cc, and override it in content/browser/
// browser_main_loop.cc.
// On the other hand, we want to avoid re-initialization from command line.
// For example, we initialize an instance in chrome/browser/
// chrome_browser_main.cc and do not override it in content/browser/
// browser_main_loop.cc.
// If the singleton was previously initialized from within an accessor, we
// want to prevent callers from reinitializing the singleton and masking the
// accessor call(s) which likely returned incorrect information.
EarlyFeatureAccessTracker::GetInstance()->AssertNoAccess();
bool instance_existed_before = false;
if (g_feature_list_instance) {
if (g_feature_list_instance->initialized_from_command_line_)
return false;
delete g_feature_list_instance;
g_feature_list_instance = nullptr;
instance_existed_before = true;
}
std::unique_ptr<FeatureList> feature_list(new FeatureList);
feature_list->InitFromCommandLine(enable_features, disable_features);
feature_list->RegisterExtraFeatureOverrides(extra_overrides);
FeatureList::SetInstance(std::move(feature_list));
return !instance_existed_before;
}
// static
FeatureList* FeatureList::GetInstance() {
return g_feature_list_instance;
}
// static
void FeatureList::SetInstance(std::unique_ptr<FeatureList> instance) {
DCHECK(!g_feature_list_instance ||
g_feature_list_instance->IsEarlyAccessInstance());
// If there is an existing early-access instance, release it.
if (g_feature_list_instance) {
std::unique_ptr<FeatureList> old_instance =
WrapUnique(g_feature_list_instance);
g_feature_list_instance = nullptr;
}
instance->FinalizeInitialization();
// Note: Intentional leak of global singleton.
g_feature_list_instance = instance.release();
EarlyFeatureAccessTracker::GetInstance()->AssertNoAccess();
// Don't configure random bytes field trials for a possibly early access
// FeatureList instance, as the state of the involved Features might change
// with the final FeatureList for this process.
if (!g_feature_list_instance->IsEarlyAccessInstance()) {
#if !BUILDFLAG(IS_NACL)
// Configured first because it takes precedence over the getrandom() trial.
internal::ConfigureBoringSSLBackedRandBytesFieldTrial();
#endif
}
#if BUILDFLAG(DCHECK_IS_CONFIGURABLE)
// Update the behaviour of LOGGING_DCHECK to match the Feature configuration.
// DCHECK is also forced to be FATAL if we are running a death-test.
// TODO(crbug.com/1057995#c11): --gtest_internal_run_death_test doesn't
// currently run through this codepath, mitigated in
// base::TestSuite::Initialize() for now.
// TODO(asvitkine): If we find other use-cases that need integrating here
// then define a proper API/hook for the purpose.
if (FeatureList::IsEnabled(kDCheckIsFatalFeature) ||
CommandLine::ForCurrentProcess()->HasSwitch(
"gtest_internal_run_death_test")) {
logging::LOGGING_DCHECK = logging::LOGGING_FATAL;
} else {
logging::LOGGING_DCHECK = logging::LOGGING_ERROR;
}
#endif // BUILDFLAG(DCHECK_IS_CONFIGURABLE)
}
// static
void FeatureList::SetEarlyAccessInstance(
std::unique_ptr<FeatureList> instance,
base::flat_set<std::string> allowed_feature_names) {
CHECK(!g_feature_list_instance);
CHECK(!allowed_feature_names.empty());
instance->allowed_feature_names_ = std::move(allowed_feature_names);
SetInstance(std::move(instance));
}
// static
std::unique_ptr<FeatureList> FeatureList::ClearInstanceForTesting() {
FeatureList* old_instance = g_feature_list_instance;
g_feature_list_instance = nullptr;
EarlyFeatureAccessTracker::GetInstance()->Reset();
return WrapUnique(old_instance);
}
// static
void FeatureList::RestoreInstanceForTesting(
std::unique_ptr<FeatureList> instance) {
DCHECK(!g_feature_list_instance);
// Note: Intentional leak of global singleton.
g_feature_list_instance = instance.release();
}
// static
void FeatureList::FailOnFeatureAccessWithoutFeatureList() {
EarlyFeatureAccessTracker::GetInstance()
->FailOnFeatureAccessWithoutFeatureList();
}
// static
const Feature* FeatureList::GetEarlyAccessedFeatureForTesting() {
return EarlyFeatureAccessTracker::GetInstance()->GetFeature();
}
// static
void FeatureList::ResetEarlyFeatureAccessTrackerForTesting() {
EarlyFeatureAccessTracker::GetInstance()->Reset();
}
void FeatureList::AddEarlyAllowedFeatureForTesting(std::string feature_name) {
CHECK(IsEarlyAccessInstance());
allowed_feature_names_.insert(std::move(feature_name));
}
// static
void FeatureList::VisitFeaturesAndParams(FeatureVisitor& visitor,
std::string_view filter_prefix) {
// If there is no feature list, there are no overrides. This should only happen
// in tests.
// TODO(leszeks): Add a CHECK_IS_TEST() to verify the above.
if (!g_feature_list_instance) {
return;
}
FieldTrialParamAssociator* params_associator =
FieldTrialParamAssociator::GetInstance();
using FeatureOverride = std::pair<std::string, OverrideEntry>;
base::span<FeatureOverride> filtered_overrides(
g_feature_list_instance->overrides_);
if (!filter_prefix.empty()) {
// If there is a filter prefix, then change the begin/end range to be the
// range where the values are prefixed with the given prefix (overrides are
// lexically sorted, so this will be a continuous range). This is
// implemented as a binary search of the upper and lower bounds of the
// override iterator, projecting each iterator value to just the
// key, trimmed to the length of the prefix.
DCHECK(std::ranges::is_sorted(
filtered_overrides, std::less<>(),
[](const FeatureOverride& entry) { return entry.first; }));
filtered_overrides = std::ranges::equal_range(
filtered_overrides, filter_prefix, std::less<>(),
[filter_prefix](const FeatureOverride& entry) {
return std::string_view(entry.first).substr(0, filter_prefix.size());
});
}
for (const FeatureOverride& feature_override : filtered_overrides) {
FieldTrial* field_trial = feature_override.second.field_trial;
std::string trial_name;
std::string group_name;
FieldTrialParams params;
if (field_trial) {
trial_name = field_trial->trial_name();
group_name = field_trial->group_name();
params_associator->GetFieldTrialParamsWithoutFallback(
trial_name, group_name, ¶ms);
}
visitor.Visit(feature_override.first,
feature_override.second.overridden_state, params, trial_name,
group_name);
}
}
void FeatureList::FinalizeInitialization() {
DCHECK(!initialized_);
// Store the field trial list pointer for DCHECKing.
field_trial_list_ = FieldTrialList::GetInstance();
initialized_ = true;
}
bool FeatureList::IsFeatureEnabled(const Feature& feature) const {
OverrideState overridden_state = GetOverrideState(feature);
// If marked as OVERRIDE_USE_DEFAULT, simply return the default state below.
if (overridden_state != OVERRIDE_USE_DEFAULT)
return overridden_state == OVERRIDE_ENABLE_FEATURE;
return feature.default_state == FEATURE_ENABLED_BY_DEFAULT;
}
std::optional<bool> FeatureList::IsFeatureEnabledIfOverridden(
const Feature& feature) const {
OverrideState overridden_state = GetOverrideState(feature);
// If marked as OVERRIDE_USE_DEFAULT, fall through to returning empty.
if (overridden_state != OVERRIDE_USE_DEFAULT)
return overridden_state == OVERRIDE_ENABLE_FEATURE;
return std::nullopt;
}
FeatureList::OverrideState FeatureList::GetOverrideState(
const Feature& feature) const {
DCHECK(initialized_);
DCHECK(IsValidFeatureOrFieldTrialName(feature.name)) << feature.name;
DCHECK(CheckFeatureIdentity(feature))
<< feature.name
<< " has multiple definitions. Either it is defined more than once in "
"code or (for component builds) the code is built into multiple "
"components (shared libraries) without a corresponding export "
"statement";
uint32_t current_cache_value =
feature.cached_value.load(std::memory_order_relaxed);
auto unpacked = UnpackFeatureCache(current_cache_value);
if (unpacked.second == caching_context_)
return unpacked.first;
OverrideState state = GetOverrideStateByFeatureName(feature.name);
uint32_t new_cache_value = PackFeatureCache(state, caching_context_);
// Update the cache with the new value.
// In non-test code, this value can be in one of 2 states: either it's unset,
// or another thread has updated it to the same value we're about to write.
// Because of this, a plain `store` yields the correct result in all cases.
// In test code, it's possible for a different thread to have installed a new
// `ScopedFeatureList` and written a value that's different than the one we're
// about to write, although that would be a thread safety violation already
// and such tests should be fixed.
feature.cached_value.store(new_cache_value, std::memory_order_relaxed);
return state;
}
FeatureList::OverrideState FeatureList::GetOverrideStateByFeatureName(
std::string_view feature_name) const {
DCHECK(initialized_);
DCHECK(IsValidFeatureOrFieldTrialName(feature_name)) << feature_name;
if (const OverrideEntry* entry =
GetOverrideEntryByFeatureName(feature_name)) {
// Activate the corresponding field trial, if necessary.
if (entry->field_trial) {
entry->field_trial->Activate();
}
// TODO(asvitkine) Expand this section as more support is added.
return entry->overridden_state;
}
// Otherwise, report that we want to use the default state.
return OVERRIDE_USE_DEFAULT;
}
FieldTrial* FeatureList::GetAssociatedFieldTrial(const Feature& feature) const {
DCHECK(initialized_);
DCHECK(CheckFeatureIdentity(feature)) << feature.name;
return GetAssociatedFieldTrialByFeatureName(feature.name);
}
const base::FeatureList::OverrideEntry*
FeatureList::GetOverrideEntryByFeatureName(std::string_view name) const {
DCHECK(IsValidFeatureOrFieldTrialName(name)) << name;
auto it = overrides_.find(name);
if (it != overrides_.end()) {
const OverrideEntry& entry = it->second;
return &entry;
}
return nullptr;
}
FieldTrial* FeatureList::GetAssociatedFieldTrialByFeatureName(
std::string_view name) const {
DCHECK(initialized_);
if (const OverrideEntry* entry = GetOverrideEntryByFeatureName(name)) {
return entry->field_trial;
}
return nullptr;
}
bool FeatureList::HasAssociatedFieldTrialByFeatureName(
std::string_view name) const {
DCHECK(!initialized_);
const OverrideEntry* entry = GetOverrideEntryByFeatureName(name);
return entry && entry->field_trial;
}
FieldTrial* FeatureList::GetEnabledFieldTrialByFeatureName(
std::string_view name) const {
DCHECK(initialized_);
const base::FeatureList::OverrideEntry* entry =
GetOverrideEntryByFeatureName(name);
if (entry &&
entry->overridden_state == base::FeatureList::OVERRIDE_ENABLE_FEATURE) {
return entry->field_trial;
}
return nullptr;
}
std::unique_ptr<FeatureList::Accessor> FeatureList::ConstructAccessor() {
if (initialized_) {
// This function shouldn't be called after initialization.
NOTREACHED();
}
// Use new and WrapUnique because we want to restrict access to the Accessor's
// constructor.
return base::WrapUnique(new Accessor(this));
}
void FeatureList::RegisterOverridesFromCommandLine(
const std::string& feature_list,
OverrideState overridden_state) {
for (const auto& value : SplitFeatureListString(feature_list)) {
std::string_view feature_name = value;
FieldTrial* trial = nullptr;
// The entry may be of the form FeatureName<FieldTrialName - in which case,
// this splits off the field trial name and associates it with the override.
std::string::size_type pos = feature_name.find('<');
if (pos != std::string::npos) {
feature_name = std::string_view(value.data(), pos);
trial = FieldTrialList::Find(value.substr(pos + 1));
#if !BUILDFLAG(IS_NACL)
// If the below DCHECK fires, it means a non-existent trial name was
// specified via the "Feature<Trial" command-line syntax.
DCHECK(trial) << "trial='" << value.substr(pos + 1) << "' does not exist";
#endif // !BUILDFLAG(IS_NACL)
}
RegisterOverride(feature_name, overridden_state, trial);
}
}
void FeatureList::RegisterOverride(std::string_view feature_name,
OverrideState overridden_state,
FieldTrial* field_trial,
bool replace_use_default_overrides) {
DCHECK(!initialized_);
DCheckOverridesAllowed();
if (field_trial) {
DCHECK(IsValidFeatureOrFieldTrialName(field_trial->trial_name()))
<< field_trial->trial_name();
}
if (StartsWith(feature_name, "*")) {
feature_name = feature_name.substr(1);
overridden_state = OVERRIDE_USE_DEFAULT;
}
// When `replace_use_default_overrides` is true, if an `OVERRIDE_USE_DEFAULT`
// entry exists, it should be replaced.
const std::string feature_name_str(feature_name);
if (replace_use_default_overrides) {
auto found = overrides_.find(feature_name_str);
if (found != overrides_.end() &&
found->second.overridden_state == OVERRIDE_USE_DEFAULT) {
// Also, keep the existing trial if a null trial was passed.
auto* trial = field_trial ? field_trial : &*found->second.field_trial;
found->second = OverrideEntry(overridden_state, trial);
return;
}
}
// Note: The semantics of emplace() is that it does not overwrite the entry if
// one already exists for the key. Thus, only the first override for a given
// feature name takes effect.
overrides_.emplace(feature_name_str,
OverrideEntry(overridden_state, field_trial));
}
void FeatureList::GetFeatureOverridesImpl(std::string* enable_overrides,
std::string* disable_overrides,
bool command_line_only,
bool include_group_name) const {
DCHECK(initialized_);
// Check that the FieldTrialList this is associated with, if any, is the
// active one. If not, it likely indicates that this FeatureList has override
// entries from a freed FieldTrial, which may be caused by an incorrect test
// set up.
if (field_trial_list_)
DCHECK_EQ(field_trial_list_, FieldTrialList::GetInstance());
enable_overrides->clear();
disable_overrides->clear();
// Note: Since |overrides_| is a std::map, iteration will be in alphabetical
// order. This is not guaranteed to users of this function, but is useful for
// tests to assume the order.
for (const auto& entry : overrides_) {
if (command_line_only &&
(entry.second.field_trial != nullptr ||
entry.second.overridden_state == OVERRIDE_USE_DEFAULT)) {
continue;
}
std::string* target_list = nullptr;
switch (entry.second.overridden_state) {
case OVERRIDE_USE_DEFAULT:
case OVERRIDE_ENABLE_FEATURE:
target_list = enable_overrides;
break;
case OVERRIDE_DISABLE_FEATURE:
target_list = disable_overrides;
break;
}
if (!target_list->empty())
target_list->push_back(',');
if (entry.second.overridden_state == OVERRIDE_USE_DEFAULT)
target_list->push_back('*');
target_list->append(entry.first);
if (entry.second.field_trial) {
auto* const field_trial = entry.second.field_trial.get();
target_list->push_back('<');
target_list->append(field_trial->trial_name());
if (include_group_name) {
target_list->push_back('.');
target_list->append(field_trial->GetGroupNameWithoutActivation());
}
}
}
}
bool FeatureList::CheckFeatureIdentity(const Feature& feature) const {
AutoLock auto_lock(feature_identity_tracker_lock_);
auto it = feature_identity_tracker_.find(feature.name);
if (it == feature_identity_tracker_.end()) {
// If it's not tracked yet, register it.
feature_identity_tracker_[feature.name] = &feature;
return true;
}
// Compare address of |feature| to the existing tracked entry.
return it->second == &feature;
}
bool FeatureList::IsEarlyAccessInstance() const {
return !allowed_feature_names_.empty();
}
bool FeatureList::AllowFeatureAccess(const Feature& feature) const {
DCHECK(initialized_);
// If this isn't an instance set with SetEarlyAccessInstance all features are
// allowed to be checked.
if (!IsEarlyAccessInstance()) {
return true;
}
return base::Contains(allowed_feature_names_, feature.name);
}
FeatureList::OverrideEntry::OverrideEntry(OverrideState overridden_state,
FieldTrial* field_trial)
: overridden_state(overridden_state),
field_trial(field_trial),
overridden_by_field_trial(field_trial != nullptr) {}
FeatureList::Accessor::Accessor(FeatureList* feature_list)
: feature_list_(feature_list) {}
FeatureList::OverrideState FeatureList::Accessor::GetOverrideStateByFeatureName(
std::string_view feature_name) {
return feature_list_->GetOverrideStateByFeatureName(feature_name);
}
bool FeatureList::Accessor::GetParamsByFeatureName(
std::string_view feature_name,
std::map<std::string, std::string>* params) {
base::FieldTrial* trial =
feature_list_->GetAssociatedFieldTrialByFeatureName(feature_name);
return FieldTrialParamAssociator::GetInstance()->GetFieldTrialParams(trial,
params);
}
} // namespace base