options.h 11 KB

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  1. // Copyright 2019 The Abseil Authors.
  2. //
  3. // Licensed under the Apache License, Version 2.0 (the "License");
  4. // you may not use this file except in compliance with the License.
  5. // You may obtain a copy of the License at
  6. //
  7. // https://www.apache.org/licenses/LICENSE-2.0
  8. //
  9. // Unless required by applicable law or agreed to in writing, software
  10. // distributed under the License is distributed on an "AS IS" BASIS,
  11. // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12. // See the License for the specific language governing permissions and
  13. // limitations under the License.
  14. //
  15. // -----------------------------------------------------------------------------
  16. // File: options.h
  17. // -----------------------------------------------------------------------------
  18. //
  19. // This file contains Abseil configuration options for setting specific
  20. // implementations instead of letting Abseil determine which implementation to
  21. // use at compile-time. Setting these options may be useful for package or build
  22. // managers who wish to guarantee ABI stability within binary builds (which are
  23. // otherwise difficult to enforce).
  24. //
  25. // *** IMPORTANT NOTICE FOR PACKAGE MANAGERS: It is important that
  26. // maintainers of package managers who wish to package Abseil read and
  27. // understand this file! ***
  28. //
  29. // Abseil contains a number of possible configuration endpoints, based on
  30. // parameters such as the detected platform, language version, or command-line
  31. // flags used to invoke the underlying binary. As is the case with all
  32. // libraries, binaries which contain Abseil code must ensure that separate
  33. // packages use the same compiled copy of Abseil to avoid a diamond dependency
  34. // problem, which can occur if two packages built with different Abseil
  35. // configuration settings are linked together. Diamond dependency problems in
  36. // C++ may manifest as violations to the One Definition Rule (ODR) (resulting in
  37. // linker errors), or undefined behavior (resulting in crashes).
  38. //
  39. // Diamond dependency problems can be avoided if all packages utilize the same
  40. // exact version of Abseil. Building from source code with the same compilation
  41. // parameters is the easiest way to avoid such dependency problems. However, for
  42. // package managers who cannot control such compilation parameters, we are
  43. // providing the file to allow you to inject ABI (Application Binary Interface)
  44. // stability across builds. Settings options in this file will neither change
  45. // API nor ABI, providing a stable copy of Abseil between packages.
  46. //
  47. // Care must be taken to keep options within these configurations isolated
  48. // from any other dynamic settings, such as command-line flags which could alter
  49. // these options. This file is provided specifically to help build and package
  50. // managers provide a stable copy of Abseil within their libraries and binaries;
  51. // other developers should not have need to alter the contents of this file.
  52. //
  53. // -----------------------------------------------------------------------------
  54. // Usage
  55. // -----------------------------------------------------------------------------
  56. //
  57. // For any particular package release, set the appropriate definitions within
  58. // this file to whatever value makes the most sense for your package(s). Note
  59. // that, by default, most of these options, at the moment, affect the
  60. // implementation of types; future options may affect other implementation
  61. // details.
  62. //
  63. // NOTE: the defaults within this file all assume that Abseil can select the
  64. // proper Abseil implementation at compile-time, which will not be sufficient
  65. // to guarantee ABI stability to package managers.
  66. #ifndef ABSL_BASE_OPTIONS_H_
  67. #define ABSL_BASE_OPTIONS_H_
  68. // Include a standard library header to allow configuration based on the
  69. // standard library in use.
  70. #ifdef __cplusplus
  71. #include <ciso646>
  72. #endif
  73. // -----------------------------------------------------------------------------
  74. // Type Compatibility Options
  75. // -----------------------------------------------------------------------------
  76. //
  77. // ABSL_OPTION_USE_STD_ANY
  78. //
  79. // This option controls whether absl::any is implemented as an alias to
  80. // std::any, or as an independent implementation.
  81. //
  82. // A value of 0 means to use Abseil's implementation. This requires only C++11
  83. // support, and is expected to work on every toolchain we support.
  84. //
  85. // A value of 1 means to use an alias to std::any. This requires that all code
  86. // using Abseil is built in C++17 mode or later.
  87. //
  88. // A value of 2 means to detect the C++ version being used to compile Abseil,
  89. // and use an alias only if a working std::any is available. This option is
  90. // useful when you are building your entire program, including all of its
  91. // dependencies, from source. It should not be used otherwise -- for example,
  92. // if you are distributing Abseil in a binary package manager -- since in
  93. // mode 2, absl::any will name a different type, with a different mangled name
  94. // and binary layout, depending on the compiler flags passed by the end user.
  95. // For more info, see https://abseil.io/about/design/dropin-types.
  96. //
  97. // User code should not inspect this macro. To check in the preprocessor if
  98. // absl::any is a typedef of std::any, use the feature macro ABSL_USES_STD_ANY.
  99. #define ABSL_OPTION_USE_STD_ANY 2
  100. // ABSL_OPTION_USE_STD_OPTIONAL
  101. //
  102. // This option controls whether absl::optional is implemented as an alias to
  103. // std::optional, or as an independent implementation.
  104. //
  105. // A value of 0 means to use Abseil's implementation. This requires only C++11
  106. // support, and is expected to work on every toolchain we support.
  107. //
  108. // A value of 1 means to use an alias to std::optional. This requires that all
  109. // code using Abseil is built in C++17 mode or later.
  110. //
  111. // A value of 2 means to detect the C++ version being used to compile Abseil,
  112. // and use an alias only if a working std::optional is available. This option
  113. // is useful when you are building your program from source. It should not be
  114. // used otherwise -- for example, if you are distributing Abseil in a binary
  115. // package manager -- since in mode 2, absl::optional will name a different
  116. // type, with a different mangled name and binary layout, depending on the
  117. // compiler flags passed by the end user. For more info, see
  118. // https://abseil.io/about/design/dropin-types.
  119. // User code should not inspect this macro. To check in the preprocessor if
  120. // absl::optional is a typedef of std::optional, use the feature macro
  121. // ABSL_USES_STD_OPTIONAL.
  122. #define ABSL_OPTION_USE_STD_OPTIONAL 2
  123. // ABSL_OPTION_USE_STD_STRING_VIEW
  124. //
  125. // This option controls whether absl::string_view is implemented as an alias to
  126. // std::string_view, or as an independent implementation.
  127. //
  128. // A value of 0 means to use Abseil's implementation. This requires only C++11
  129. // support, and is expected to work on every toolchain we support.
  130. //
  131. // A value of 1 means to use an alias to std::string_view. This requires that
  132. // all code using Abseil is built in C++17 mode or later.
  133. //
  134. // A value of 2 means to detect the C++ version being used to compile Abseil,
  135. // and use an alias only if a working std::string_view is available. This
  136. // option is useful when you are building your program from source. It should
  137. // not be used otherwise -- for example, if you are distributing Abseil in a
  138. // binary package manager -- since in mode 2, absl::string_view will name a
  139. // different type, with a different mangled name and binary layout, depending on
  140. // the compiler flags passed by the end user. For more info, see
  141. // https://abseil.io/about/design/dropin-types.
  142. //
  143. // User code should not inspect this macro. To check in the preprocessor if
  144. // absl::string_view is a typedef of std::string_view, use the feature macro
  145. // ABSL_USES_STD_STRING_VIEW.
  146. #define ABSL_OPTION_USE_STD_STRING_VIEW 2
  147. // ABSL_OPTION_USE_STD_VARIANT
  148. //
  149. // This option controls whether absl::variant is implemented as an alias to
  150. // std::variant, or as an independent implementation.
  151. //
  152. // A value of 0 means to use Abseil's implementation. This requires only C++11
  153. // support, and is expected to work on every toolchain we support.
  154. //
  155. // A value of 1 means to use an alias to std::variant. This requires that all
  156. // code using Abseil is built in C++17 mode or later.
  157. //
  158. // A value of 2 means to detect the C++ version being used to compile Abseil,
  159. // and use an alias only if a working std::variant is available. This option
  160. // is useful when you are building your program from source. It should not be
  161. // used otherwise -- for example, if you are distributing Abseil in a binary
  162. // package manager -- since in mode 2, absl::variant will name a different
  163. // type, with a different mangled name and binary layout, depending on the
  164. // compiler flags passed by the end user. For more info, see
  165. // https://abseil.io/about/design/dropin-types.
  166. //
  167. // User code should not inspect this macro. To check in the preprocessor if
  168. // absl::variant is a typedef of std::variant, use the feature macro
  169. // ABSL_USES_STD_VARIANT.
  170. #define ABSL_OPTION_USE_STD_VARIANT 2
  171. // ABSL_OPTION_USE_INLINE_NAMESPACE
  172. // ABSL_OPTION_INLINE_NAMESPACE_NAME
  173. //
  174. // These options controls whether all entities in the absl namespace are
  175. // contained within an inner inline namespace. This does not affect the
  176. // user-visible API of Abseil, but it changes the mangled names of all symbols.
  177. //
  178. // This can be useful as a version tag if you are distributing Abseil in
  179. // precompiled form. This will prevent a binary library build of Abseil with
  180. // one inline namespace being used with headers configured with a different
  181. // inline namespace name. Binary packagers are reminded that Abseil does not
  182. // guarantee any ABI stability in Abseil, so any update of Abseil or
  183. // configuration change in such a binary package should be combined with a
  184. // new, unique value for the inline namespace name.
  185. //
  186. // A value of 0 means not to use inline namespaces.
  187. //
  188. // A value of 1 means to use an inline namespace with the given name inside
  189. // namespace absl. If this is set, ABSL_OPTION_INLINE_NAMESPACE_NAME must also
  190. // be changed to a new, unique identifier name. In particular "head" is not
  191. // allowed.
  192. #define ABSL_OPTION_USE_INLINE_NAMESPACE 0
  193. #define ABSL_OPTION_INLINE_NAMESPACE_NAME head
  194. // ABSL_OPTION_HARDENED
  195. //
  196. // This option enables a "hardened" build in release mode (in this context,
  197. // release mode is defined as a build where the `NDEBUG` macro is defined).
  198. //
  199. // A value of 0 means that "hardened" mode is not enabled.
  200. //
  201. // A value of 1 means that "hardened" mode is enabled.
  202. //
  203. // Hardened builds have additional security checks enabled when `NDEBUG` is
  204. // defined. Defining `NDEBUG` is normally used to turn `assert()` macro into a
  205. // no-op, as well as disabling other bespoke program consistency checks. By
  206. // defining ABSL_OPTION_HARDENED to 1, a select set of checks remain enabled in
  207. // release mode. These checks guard against programming errors that may lead to
  208. // security vulnerabilities. In release mode, when one of these programming
  209. // errors is encountered, the program will immediately abort, possibly without
  210. // any attempt at logging.
  211. //
  212. // The checks enabled by this option are not free; they do incur runtime cost.
  213. //
  214. // The checks enabled by this option are always active when `NDEBUG` is not
  215. // defined, even in the case when ABSL_OPTION_HARDENED is defined to 0. The
  216. // checks enabled by this option may abort the program in a different way and
  217. // log additional information when `NDEBUG` is not defined.
  218. #define ABSL_OPTION_HARDENED 1
  219. #endif // ABSL_BASE_OPTIONS_H_