1//
2// Copyright 2019 The Abseil Authors.
3//
4// Licensed under the Apache License, Version 2.0 (the "License");
5// you may not use this file except in compliance with the License.
6// You may obtain a copy of the License at
7//
8// https://www.apache.org/licenses/LICENSE-2.0
9//
10// Unless required by applicable law or agreed to in writing, software
11// distributed under the License is distributed on an "AS IS" BASIS,
12// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13// See the License for the specific language governing permissions and
14// limitations under the License.
15
16#ifndef ABSL_FLAGS_INTERNAL_REGISTRY_H_
17#define ABSL_FLAGS_INTERNAL_REGISTRY_H_
18
19#include <functional>
20#include <map>
21#include <string>
22
23#include "absl/base/macros.h"
24#include "absl/flags/internal/commandlineflag.h"
25
26// --------------------------------------------------------------------
27// Global flags registry API.
28
29namespace absl {
30namespace flags_internal {
31
32// CommandLineFlagInfo holds all information for a flag.
33struct CommandLineFlagInfo {
34 std::string name; // the name of the flag
35 std::string type; // DO NOT use. Use flag->IsOfType<T>() instead.
36 std::string description; // the "help text" associated with the flag
37 std::string current_value; // the current value, as a std::string
38 std::string default_value; // the default value, as a std::string
39 std::string filename; // 'cleaned' version of filename holding the flag
40 bool has_validator_fn; // true if RegisterFlagValidator called on this flag
41
42 bool is_default; // true if the flag has the default value and
43 // has not been set explicitly from the cmdline
44 // or via SetCommandLineOption.
45
46 // nullptr for ABSL_FLAG. A pointer to the flag's current value
47 // otherwise. E.g., for DEFINE_int32(foo, ...), flag_ptr will be
48 // &FLAGS_foo.
49 const void* flag_ptr;
50};
51
52//-----------------------------------------------------------------------------
53
54void FillCommandLineFlagInfo(CommandLineFlag* flag,
55 CommandLineFlagInfo* result);
56
57//-----------------------------------------------------------------------------
58
59CommandLineFlag* FindCommandLineFlag(absl::string_view name);
60CommandLineFlag* FindCommandLineV1Flag(const void* flag_ptr);
61CommandLineFlag* FindRetiredFlag(absl::string_view name);
62
63// Executes specified visitor for each non-retired flag in the registry.
64// Requires the caller hold the registry lock.
65void ForEachFlagUnlocked(std::function<void(CommandLineFlag*)> visitor);
66// Executes specified visitor for each non-retired flag in the registry. While
67// callback are executed, the registry is locked and can't be changed.
68void ForEachFlag(std::function<void(CommandLineFlag*)> visitor);
69
70//-----------------------------------------------------------------------------
71
72// Store the list of all flags in *OUTPUT, sorted by file.
73void GetAllFlags(std::vector<CommandLineFlagInfo>* OUTPUT);
74
75//-----------------------------------------------------------------------------
76
77bool RegisterCommandLineFlag(CommandLineFlag*, const void* ptr = nullptr);
78
79//-----------------------------------------------------------------------------
80// Retired registrations:
81//
82// Retired flag registrations are treated specially. A 'retired' flag is
83// provided only for compatibility with automated invocations that still
84// name it. A 'retired' flag:
85// - is not bound to a C++ FLAGS_ reference.
86// - has a type and a value, but that value is intentionally inaccessible.
87// - does not appear in --help messages.
88// - is fully supported by _all_ flag parsing routines.
89// - consumes args normally, and complains about type mismatches in its
90// argument.
91// - emits a complaint but does not die (e.g. LOG(ERROR)) if it is
92// accessed by name through the flags API for parsing or otherwise.
93//
94// The registrations for a flag happen in an unspecified order as the
95// initializers for the namespace-scope objects of a program are run.
96// Any number of weak registrations for a flag can weakly define the flag.
97// One non-weak registration will upgrade the flag from weak to non-weak.
98// Further weak registrations of a non-weak flag are ignored.
99//
100// This mechanism is designed to support moving dead flags into a
101// 'graveyard' library. An example migration:
102//
103// 0: Remove references to this FLAGS_flagname in the C++ codebase.
104// 1: Register as 'retired' in old_lib.
105// 2: Make old_lib depend on graveyard.
106// 3: Add a redundant 'retired' registration to graveyard.
107// 4: Remove the old_lib 'retired' registration.
108// 5: Eventually delete the graveyard registration entirely.
109//
110// Returns bool to enable use in namespace-scope initializers.
111// For example:
112//
113// static const bool dummy = base::RetiredFlag<int32_t>("myflag");
114//
115// Or to declare several at once:
116//
117// static bool dummies[] = {
118// base::RetiredFlag<std::string>("some_string_flag"),
119// base::RetiredFlag<double>("some_double_flag"),
120// base::RetiredFlag<int32_t>("some_int32_flag")
121// };
122
123// Retire flag with name "name" and type indicated by ops.
124bool Retire(FlagOpFn ops, FlagMarshallingOpFn marshalling_ops,
125 const char* name);
126
127// Registered a retired flag with name 'flag_name' and type 'T'.
128template <typename T>
129inline bool RetiredFlag(const char* flag_name) {
130 return flags_internal::Retire(flags_internal::FlagOps<T>,
131 flags_internal::FlagMarshallingOps<T>,
132 flag_name);
133}
134
135// If the flag is retired, returns true and indicates in |*type_is_bool|
136// whether the type of the retired flag is a bool.
137// Only to be called by code that needs to explicitly ignore retired flags.
138bool IsRetiredFlag(absl::string_view name, bool* type_is_bool);
139
140//-----------------------------------------------------------------------------
141// Saves the states (value, default value, whether the user has set
142// the flag, registered validators, etc) of all flags, and restores
143// them when the FlagSaver is destroyed.
144//
145// This class is thread-safe. However, its destructor writes to
146// exactly the set of flags that have changed value during its
147// lifetime, so concurrent _direct_ access to those flags
148// (i.e. FLAGS_foo instead of {Get,Set}CommandLineOption()) is unsafe.
149
150class FlagSaver {
151 public:
152 FlagSaver();
153 ~FlagSaver();
154
155 FlagSaver(const FlagSaver&) = delete;
156 void operator=(const FlagSaver&) = delete;
157
158 // Prevents saver from restoring the saved state of flags.
159 void Ignore();
160
161 private:
162 class FlagSaverImpl* impl_; // we use pimpl here to keep API steady
163};
164
165} // namespace flags_internal
166} // namespace absl
167
168#endif // ABSL_FLAGS_INTERNAL_REGISTRY_H_
169