Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 1 | .. _docs-module-structure: |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 2 | |
Keir Mierle | 086ef1c | 2020-03-19 02:03:51 -0700 | [diff] [blame] | 3 | ---------------- |
| 4 | Module Structure |
| 5 | ---------------- |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 6 | The Pigweed module structure is designed to keep as much code as possible for a |
| 7 | particular slice of functionality in one place. That means including the code |
| 8 | from multiple languages, as well as all the related documentation and tests. |
| 9 | |
| 10 | Additionally, the structure is designed to limit the number of places a file |
| 11 | could go, so that when reading callsites it is obvious where a header is from. |
| 12 | That is where the duplicated ``<module>`` occurrences in file paths comes from. |
| 13 | |
| 14 | Example module structure |
| 15 | ------------------------ |
| 16 | .. code-block:: python |
| 17 | |
| 18 | pw_foo/... |
| 19 | |
| 20 | docs.rst # If there is just 1 docs file, call it docs.rst |
| 21 | README.md # All modules must have a short README for gittiles |
| 22 | |
| 23 | BUILD.gn # GN build required |
| 24 | BUILD # Bazel build required |
| 25 | |
| 26 | # C++ public headers; the repeated module name is required |
| 27 | public/pw_foo/foo.h |
| 28 | public/pw_foo/baz.h |
| 29 | |
Wyatt Hepler | e0575f7 | 2020-10-16 10:47:03 -0700 | [diff] [blame^] | 30 | # Exposed private headers go under internal/ |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 31 | public/pw_foo/internal/bar.h |
| 32 | public/pw_foo/internal/qux.h |
| 33 | |
| 34 | # Public override headers must go in 'public_overrides' |
| 35 | public_overrides/gtest/gtest.h |
| 36 | public_overrides/string.h |
| 37 | |
| 38 | # Private headers go into <module>_*/... |
| 39 | pw_foo_internal/zap.h |
| 40 | pw_foo_private/zip.h |
| 41 | pw_foo_secret/alxx.h |
| 42 | |
| 43 | # C++ implementations go in the root |
| 44 | foo_impl.cc |
| 45 | foo.cc |
| 46 | baz.cc |
| 47 | bar.cc |
| 48 | zap.cc |
| 49 | zip.cc |
| 50 | alxx.cc |
| 51 | |
| 52 | # C++ tests also go in the root |
| 53 | foo_test.cc |
| 54 | bar_test.cc |
| 55 | zip_test.cc |
| 56 | |
| 57 | # Python files go into 'py/<module>/...' |
| 58 | py/setup.py # All Python must be a Python module with setup.py |
| 59 | py/foo_test.py # Tests go in py/ but outside of the Python module |
| 60 | py/bar_test.py |
| 61 | py/pw_foo/__init__.py |
| 62 | py/pw_foo/__main__.py |
| 63 | py/pw_foo/bar.py |
| 64 | |
| 65 | # Go files go into 'go/...' |
| 66 | go/... |
| 67 | |
| 68 | # Examples go in examples/, mixing different languages |
| 69 | examples/demo.py |
| 70 | examples/demo.cc |
| 71 | examples/demo.go |
| 72 | examples/BUILD.gn |
| 73 | examples/BUILD |
| 74 | |
| 75 | # Size reports go under size_report/ |
| 76 | size_report/BUILD.gn |
| 77 | size_report/base.cc |
| 78 | size_report/use_case_a.cc |
| 79 | size_report/use_case_b.cc |
| 80 | |
| 81 | # Protobuf definition files go into <module>_protos/... |
| 82 | pw_foo_protos/foo.proto |
| 83 | pw_foo_protos/internal/zap.proto |
| 84 | |
| 85 | # Other directories are fine, but should be private. |
| 86 | data/... |
| 87 | graphics/... |
| 88 | collection_of_tests/... |
| 89 | code_relating_to_subfeature/... |
| 90 | |
| 91 | Module name |
Ewout van Bekkum | e072fab | 2020-07-17 16:34:00 -0700 | [diff] [blame] | 92 | ----------- |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 93 | Pigweed upstream modules are always named with a prefix ``pw_`` to enforce |
| 94 | namespacing. Projects using Pigweed that wish to make their own modules can use |
| 95 | whatever name they like, but we suggest picking a short prefix to namespace |
| 96 | your product (e.g. for an Internet of Toast project, perhaps the prefix could |
| 97 | be ``it_``). |
| 98 | |
Keir Mierle | 16f86f4 | 2020-08-09 01:01:20 -0700 | [diff] [blame] | 99 | C++ module structure |
| 100 | -------------------- |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 101 | |
| 102 | C++ public headers |
Ewout van Bekkum | e072fab | 2020-07-17 16:34:00 -0700 | [diff] [blame] | 103 | ~~~~~~~~~~~~~~~~~~ |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 104 | Located ``{pw_module_dir}/public/<module>``. These are headers that must be |
| 105 | exposed due to C++ limitations (i.e. are included from the public interface, |
| 106 | but are not intended for public use). |
| 107 | |
| 108 | **Public headers** should take the form: |
| 109 | |
| 110 | ``{pw_module_dir}/public/<module>/*.h`` |
| 111 | |
| 112 | **Exposed private headers** should take the form: |
| 113 | |
| 114 | ``{pw_module_dir}/public/<module>/internal/*.h`` |
| 115 | |
| 116 | Examples: |
| 117 | |
| 118 | .. code-block:: |
| 119 | |
| 120 | pw_foo/... |
| 121 | public/pw_foo/foo.h |
| 122 | public/pw_foo/a_header.h |
| 123 | public/pw_foo/baz.h |
| 124 | |
| 125 | For headers that must be exposed due to C++ limitations (i.e. are included from |
| 126 | the public interface, but are not intended for use), place the headers in a |
| 127 | ``internal`` subfolder under the public headers directory; as |
| 128 | ``{pw_module_dir}/public/<module>/internal/*.h``. For example: |
| 129 | |
| 130 | .. code-block:: |
| 131 | |
| 132 | pw_foo/... |
| 133 | public/pw_foo/internal/secret.h |
| 134 | public/pw_foo/internal/business.h |
| 135 | |
| 136 | .. note:: |
| 137 | |
| 138 | These headers must not override headers from other modules. For |
| 139 | that, there is the ``public_overrides/`` directory. |
| 140 | |
Keir Mierle | 16f86f4 | 2020-08-09 01:01:20 -0700 | [diff] [blame] | 141 | C++ public override headers |
| 142 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 143 | Located ``{pw_module_dir}/public_overrides/<module>``. In general, the Pigweed |
| 144 | philosophy is to avoid having "things hiding under rocks", and having header |
| 145 | files with the same name that can override each other is considered a rock |
| 146 | where surprising things can hide. Additionally, a design goal of the Pigweed |
| 147 | module structure is to make it so there is ideally exactly one obvious place |
| 148 | to find a header based on an ``#include``. |
| 149 | |
| 150 | However, in some cases header overrides are necessary to enable flexibly |
| 151 | combining modules. To make this as explicit as possible, headers which override |
| 152 | other headers must go in |
| 153 | |
| 154 | ``{pw_module_dir}/public_overrides/...``` |
| 155 | |
| 156 | For example, the ``pw_unit_test`` module provides a header override for |
| 157 | ``gtest/gtest.h``. The structure of the module is (omitting some files): |
| 158 | |
| 159 | .. code-block:: |
| 160 | |
| 161 | pw_unit_test/... |
| 162 | |
| 163 | public_overrides/gtest |
| 164 | public_overrides/gtest/gtest.h |
| 165 | |
| 166 | public/pw_unit_test |
| 167 | public/pw_unit_test/framework.h |
| 168 | public/pw_unit_test/simple_printing_event_handler.h |
| 169 | public/pw_unit_test/event_handler.h |
| 170 | |
| 171 | Note that the overrides are in a separate directory ``public_overrides``. |
| 172 | |
| 173 | C++ implementation files |
Ewout van Bekkum | e072fab | 2020-07-17 16:34:00 -0700 | [diff] [blame] | 174 | ~~~~~~~~~~~~~~~~~~~~~~~~ |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 175 | Located ``{pw_module_dir}/``. C++ implementation files go at the top level of |
| 176 | the module. Implementation files must always use "" style includes. |
| 177 | |
| 178 | Example: |
| 179 | |
| 180 | .. code-block:: |
| 181 | |
| 182 | pw_unit_test/... |
| 183 | main.cc |
| 184 | framework.cc |
| 185 | test.gni |
| 186 | BUILD.gn |
| 187 | README.md |
| 188 | |
Wyatt Hepler | e0575f7 | 2020-10-16 10:47:03 -0700 | [diff] [blame^] | 189 | Compile-time configuration |
| 190 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| 191 | Pigweed modules are intended to be used in a wide variety of environments. |
| 192 | In support of this, some modules expose compile-time configuration options. |
| 193 | Pigweed has an established pattern for declaring and overriding module |
| 194 | configuration. |
| 195 | |
| 196 | .. tip:: |
| 197 | |
| 198 | Compile-time configuration provides flexibility, but also imposes |
| 199 | restrictions. A module can only have one configuration in a given build. |
| 200 | Compile-time configuration also makes testing more difficult. Where |
| 201 | appropriate, consider alternatives such as C++ templates or runtime |
| 202 | configuration. |
| 203 | |
| 204 | Declaring configuration |
| 205 | ^^^^^^^^^^^^^^^^^^^^^^^ |
| 206 | Configuration values are declared in a header file with macros. If the macro |
| 207 | value is not already defined, a default definition is provided. Otherwise, |
| 208 | nothing is done. Configuration headers may include ``static_assert`` statements |
| 209 | to validate configuration values. |
| 210 | |
| 211 | .. code-block:: c++ |
| 212 | |
| 213 | // Example configuration header |
| 214 | |
| 215 | #ifndef PW_FOO_INPUT_BUFFER_SIZE_BYTES |
| 216 | #define PW_FOO_INPUT_BUFFER_SIZE_BYTES 128 |
| 217 | #endif // PW_FOO_INPUT_BUFFER_SIZE_BYTES |
| 218 | |
| 219 | static_assert(PW_FOO_INPUT_BUFFER_SIZE_BYTES >= 64); |
| 220 | |
| 221 | The configuration header may go in one of three places in the module, depending |
| 222 | on whether the header should be exposed by the module or not. |
| 223 | |
| 224 | .. code-block:: |
| 225 | |
| 226 | pw_foo/... |
| 227 | |
| 228 | # Publicly accessible configuration header |
| 229 | public/pw_foo/config.h |
| 230 | |
| 231 | # Internal configuration header that is included by other module headers |
| 232 | public/pw_foo/internal/config.h |
| 233 | |
| 234 | # Internal configuration header |
| 235 | pw_foo_private/config.h |
| 236 | |
| 237 | The configuration header is provided by a build system library. This library |
| 238 | acts as a :ref:`facade<docs-module-structure-facades>`. The facade uses a |
| 239 | variable such as ``pw_foo_CONFIG``. In upstream Pigweed, all config facades |
| 240 | default to the ``pw_build_DEFAULT_MODULE_CONFIG`` backend. In the GN build |
| 241 | system, the config facade is declared as follows: |
| 242 | |
| 243 | .. code-block:: |
| 244 | |
| 245 | declare_args() { |
| 246 | # The build target that overrides the default configuration options for this |
| 247 | # module. This should point to a source set that provides defines through a |
| 248 | # public config (which may -include a file or add defines directly). |
| 249 | pw_foo_CONFIG = pw_build_DEFAULT_MODULE_CONFIG |
| 250 | } |
| 251 | |
| 252 | # Publicly accessible configuration header (most common) |
| 253 | pw_source_set("config") { |
| 254 | public = [ "public/pw_foo/config.h" ] |
| 255 | public_configs = [ ":public_include_path" ] |
| 256 | public_deps = [ pw_foo_CONFIG ] |
| 257 | } |
| 258 | |
| 259 | # Internal configuration header that is included by other module headers |
| 260 | pw_source_set("config") { |
| 261 | sources = [ "public/pw_foo/internal/config.h" ] |
| 262 | public_configs = [ ":public_include_path" ] |
| 263 | public_deps = [ pw_foo_CONFIG ] |
| 264 | visibility = [":*"] # Only allow this module to depend on ":config" |
| 265 | friend = [":*"] # Allow this module to access the config.h header. |
| 266 | } |
| 267 | |
| 268 | # Internal configuration header |
| 269 | pw_source_set("config") { |
| 270 | public = [ "pw_foo_private/config.h" ] |
| 271 | public_deps = [ pw_foo_CONFIG ] |
| 272 | visibility = [":*"] # Only allow this module to depend on ":config" |
| 273 | } |
| 274 | |
| 275 | Overriding configuration |
| 276 | ^^^^^^^^^^^^^^^^^^^^^^^^ |
| 277 | As noted above, all module configuration facades default to the same backend |
| 278 | (``pw_build_DEFAULT_MODULE_CONFIG``). This allows projects to override |
| 279 | configuration values for multiple modules from a single configuration backend, |
| 280 | if desired. The configuration values may also be overridden individually by |
| 281 | setting backends for the individual module configurations (e.g. in GN, |
| 282 | ``pw_foo_CONFIG = "//configuration:my_foo_config"``). |
| 283 | |
| 284 | Configurations are overridden by setting compilation options in the config |
| 285 | backend. These options could be set through macro definitions, such as |
| 286 | ``-DPW_FOO_INPUT_BUFFER_SIZE_BYTES=256``, or in a header file included with the |
| 287 | ``-include`` option. |
| 288 | |
| 289 | This example shows how two ways to configure a module in the GN build system. |
| 290 | |
| 291 | .. code-block:: |
| 292 | |
| 293 | # In the toolchain, set either pw_build_DEFAULT_MODULE_CONFIG or pw_foo_CONFIG |
| 294 | pw_build_DEFAULT_MODULE_CONFIG = get_path_info(":define_overrides", "abspath") |
| 295 | |
| 296 | # This configuration sets PW_FOO_INPUT_BUFFER_SIZE_BYTES using the -D macro. |
| 297 | pw_source_set("define_overrides") { |
| 298 | public_configs = [ ":define_options" ] |
| 299 | } |
| 300 | |
| 301 | config("define_options") { |
| 302 | defines = [ "-DPW_FOO_INPUT_BUFFER_SIZE_BYTES=256" ] |
| 303 | } |
| 304 | |
| 305 | # This configuration sets PW_FOO_INPUT_BUFFER_SIZE_BYTES with a header file. |
| 306 | pw_source_set("include_overrides") { |
| 307 | public_configs = [ ":header_options" ] |
| 308 | |
| 309 | # Header file with #define PW_FOO_INPUT_BUFFER_SIZE_BYTES 256 |
| 310 | sources = [ "my_config_overrides.h" ] |
| 311 | } |
| 312 | |
| 313 | config("header_options") { |
| 314 | cflags = [ |
| 315 | "-include", |
| 316 | "my_config_overrides.h", |
| 317 | ] |
| 318 | } |
| 319 | |
| 320 | .. _docs-module-structure-facades: |
| 321 | |
| 322 | Facades |
| 323 | ------- |
| 324 | In Pigweed, facades represent a dependency that can be swapped at compile time. |
| 325 | Facades are similar in concept to a virtual interface, but the implementation is |
| 326 | set by the build system. Runtime polymorphism with facades is not |
| 327 | possible, and each facade may only have one implementation (backend) per |
| 328 | toolchain compilation. |
| 329 | |
| 330 | In the simplest sense, a facade is just a dependency represented by a variable. |
| 331 | For example, the ``pw_log`` facade is represented by the ``pw_log_BACKEND`` |
| 332 | build variable. Facades typically are bundled with a build system library that |
| 333 | depends on the backend. |
| 334 | |
| 335 | Modules should only use facades when necessary. Since they are fixed at compile |
| 336 | time, runtime dependency injection is not possible. Where appropriate, modules |
| 337 | should use other mechanisms, such as virtual interfaces or callbacks, in place |
| 338 | of facades. |
| 339 | |
| 340 | Facades are essential in some circumstances: |
| 341 | |
| 342 | * Low-level, platform-specific features (:ref:`module-pw_cpu_exception`). |
| 343 | * Features that require a macro or non-virtual function interface |
| 344 | (:ref:`module-pw_tokenizer`), |
| 345 | * Highly leveraged code where a virtual interface or callback is too costly or |
| 346 | cumbersome (:ref:`module-pw_log`, :ref:`module-pw_assert`). |
| 347 | |
| 348 | The GN build system provides the |
| 349 | :ref:`pw_facade template<module-pw_build-facade>` as a convenient way to declare |
| 350 | facades. |
| 351 | |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 352 | Documentation |
Keir Mierle | 16f86f4 | 2020-08-09 01:01:20 -0700 | [diff] [blame] | 353 | ------------- |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 354 | Documentation should go in the root module folder, typically in the |
| 355 | ``docs.rst`` file. There must be a docgen entry for the documentation in the |
| 356 | ``BUILD.gn`` file with the target name ``docs``; so the full target for the |
| 357 | docs would be ``<module>:docs``. |
| 358 | |
| 359 | .. code-block:: |
| 360 | |
| 361 | pw_example_module/... |
| 362 | |
| 363 | docs.rst |
| 364 | |
| 365 | For modules with more involved documentation, create a separate directory |
| 366 | called ``docs/`` under the module root, and put the ``.rst`` files and other |
| 367 | related files (like images and diagrams) there. |
| 368 | |
| 369 | .. code-block:: |
| 370 | |
| 371 | pw_example_module/... |
| 372 | |
| 373 | docs/docs.rst |
| 374 | docs/bar.rst |
| 375 | docs/foo.rst |
| 376 | docs/image/screenshot.png |
| 377 | docs/image/diagram.svg |
| 378 | |
Keir Mierle | 16f86f4 | 2020-08-09 01:01:20 -0700 | [diff] [blame] | 379 | Creating a new Pigweed module |
| 380 | ----------------------------- |
| 381 | To create a new Pigweed module, follow the below steps. |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 382 | |
Keir Mierle | 16f86f4 | 2020-08-09 01:01:20 -0700 | [diff] [blame] | 383 | .. tip:: |
| 384 | |
| 385 | Connect with the Pigweed community (by `mailing the Pigweed list |
| 386 | <https://groups.google.com/forum/#!forum/pigweed>`_ or `raising your idea |
| 387 | in the Pigweed chat <https://discord.gg/M9NSeTA>`_) to discuss your module |
| 388 | idea before getting too far into the implementation. This can prevent |
| 389 | accidentally duplicating work, or avoiding writing code that won't get |
| 390 | accepted. |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 391 | |
| 392 | 1. Create module folder following `Module name`_ guidelines |
| 393 | 2. Add `C++ public headers`_ files in |
| 394 | ``{pw_module_dir}/public/{pw_module_name}/`` |
| 395 | 3. Add `C++ implementation files`_ files in ``{pw_module_dir}/`` |
| 396 | 4. Add module documentation |
| 397 | |
| 398 | - Add ``{pw_module_dir}/README.md`` that has a module summary |
| 399 | - Add ``{pw_module_dir}/docs.rst`` that contains the main module |
| 400 | documentation |
| 401 | |
| 402 | 5. Add build support inside of new module |
| 403 | |
| 404 | - Add GN with ``{pw_module_dir}/BUILD.gn`` |
| 405 | - Add Bazel with ``{pw_module_dir}/BUILD`` |
| 406 | - Add CMake with ``{pw_module_dir}/CMakeLists.txt`` |
| 407 | |
| 408 | 6. Add folder alias for new module variable in ``/modules.gni`` |
| 409 | |
| 410 | - dir_pw_new = "$dir_pigweed/pw_new" |
| 411 | |
| 412 | 7. Add new module to main GN build |
| 413 | |
| 414 | - in ``/BUILD.gn`` to ``group("pw_modules")`` using folder alias variable |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 415 | |
| 416 | 8. Add test target for new module in ``/BUILD.gn`` to |
| 417 | ``pw_test_group("pw_module_tests")`` |
| 418 | 9. Add new module to CMake build |
| 419 | |
| 420 | - In ``/CMakeLists.txt`` add ``add_subdirectory(pw_new)`` |
| 421 | |
| 422 | 10. Add the new module to docs module |
| 423 | |
| 424 | - Add in ``docs/BUILD.gn`` to ``pw_doc_gen("docs")`` |
| 425 | |
Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 426 | 11. Run :ref:`module-pw_module-module-check` |
Alexei Frolov | b3f7fda | 2020-03-18 14:59:20 -0700 | [diff] [blame] | 427 | |
| 428 | - ``$ pw module-check {pw_module_dir}`` |
| 429 | |
Wyatt Hepler | f9fb90f | 2020-09-30 18:59:33 -0700 | [diff] [blame] | 430 | 12. Contribute your module to upstream Pigweed (optional but encouraged!) |