Expand bazel build to include configuration options and broader support. (#1731)

* Add host Bazel build

Updates target_compatible_with across the repo to ensure that wildcard
builds for both host and rp2040 succeed.

* Get unit tests building

* Add Python script to identify build system differences

Uses the build system tags to make it easier to identify differences
between the CMake and Bazel builds.

* Temporarily disable pico divider test

* Support PICO_BARE_METAL in Bazel

* Support PICO_NO_GC_SECTIONS in Bazel

* Support boot2 configuration in Bazel

Adds support for PICO_DEFAULT_BOOT_STAGE2 and
PICO_DEFAULT_BOOT_STAGE2_FILE in the Bazel build.

* Allowlist some CMake-only options

* Support CXX configuration options in Bazel

* Move multiple_choice_flag.bzl

* Support all pico boards

* Support linking multiple stdio implementations

Changes the Bazel build so stdio implementations are no longer mutually
exclusive.

* Add PICO_BOOT_STAGE2_LINK_IMAGE

* Support PICO_CMSIS_PATH in Bazel

* Support PICO_USE_DEFAULT_MAX_PAGE_SIZE in Bazel

* Silence PICO_CMSIS_VENDOR and PICO_CMSIS_DEVICE differences

* Support PICO_STDIO_USB_CONNECT_WAIT_TIMEOUT_MS in Bazel

* Properly support version defines

* Support embedding binary info in Bazel

* Embed build type in binary

* Support different linker scripts in Bazel build

* Finish out missing PICO_BUILD_DEFINE in Bazel build

* Support PICO_NO_TARGET_NAME

* Reorganize initial configuration options in Bazel

Cleans up and reorganizes some of the initial configuration options
added to the Bazel build so everything is consistent.

* Add builds for pioasm and elf2uf2

* Use Python rules from rules_python

* Actually link in output formats in pioasm tool

* Make tools have public visibility

* Add UF2 Bazel aspect

* Add TODOs for pioasm/uf2 helpers

* Fix compile flag typo

* Update Bazel SDK configuration strings to match recent CMake changes

* Fix pico_divider test

* Clean up straggling TODOs

* Clarify pico_stdio_test compatibility

* Initial Bazel Pico W support

* Add new files from develop

* Clean up compatibility expressions in Bazel build

* Clean up rp2 constraint handling in Bazel

* More Bazel docs cleanup

* Format Bazel build files

* Consolidate transitions in the Pico SDK

* Make every _allowlist_function_transition explicit

* More docs cleanup

* Add a few missing defines

* Improve PICO_CONFIG_HEADER correctness in Bazel

* Minor docs clarifications

Author: armandomontanez

MODULE.bazel

@@ -8,7 +8,7 @@ bazel_dep(name = "bazel_skylib", version = "1.6.1")
 # module will not ensure that the root Bazel module has that same version of
 # rules_cc. For that reason, this primarily acts as a FYI. You'll still need
 # to explicitly list this dependency in your own project's MODULE.bazel file.
-bazel_dep(name = "rules_cc", version = "0.0.10")
+bazel_dep(name = "rules_cc", version = "0.0.9")
 
 # rules_cc v0.0.10 is not yet cut, so manually pull in the desired version.
 # This does not apply to dependent projects, so it needs to be copied to your
@@ -63,6 +63,33 @@ http_archive(
     sha256 = "ac57109bba00d26ffa33312d5f334990ec9a9a4d82bf890ed8b825b4610d1da2",
 )
 
+# TODO: Provide btstack as a proper Bazel module.
+http_archive(
+    name = "btstack",
+    url = "https://github.com/bluekitchen/btstack/archive/72ef1732c954d938091467961e41f4aa9b976b34.zip",
+    strip_prefix = "btstack-72ef1732c954d938091467961e41f4aa9b976b34",
+    build_file = "//src/rp2_common/pico_btstack:btstack.BUILD",
+    sha256 = "f45d72b5d404dd2f8e311287de6f2ba3561fc8ae956737eeb611b277aadc2391",
+)
+
+# TODO: Provide btstack as a proper Bazel module.
+http_archive(
+    name = "cyw43-driver",
+    url = "https://github.com/georgerobotics/cyw43-driver/archive/8ef38a6d32c54f850bff8f189bdca19ded33792a.zip",
+    strip_prefix = "cyw43-driver-8ef38a6d32c54f850bff8f189bdca19ded33792a",
+    build_file = "//src/rp2_common/pico_cyw43_driver:cyw43-driver.BUILD",
+    sha256 = "0b44a19ea58537ee954357606cde5ed20c3a42be77adfebb07b7c0e4740f6228",
+)
+
+# TODO: Provide lwip as a proper Bazel module.
+http_archive(
+    name = "lwip",
+    url = "https://github.com/lwip-tcpip/lwip/archive/239918ccc173cb2c2a62f41a40fd893f57faf1d6.zip",
+    strip_prefix = "lwip-239918ccc173cb2c2a62f41a40fd893f57faf1d6",
+    build_file = "//src/rp2_common/pico_lwip:lwip.BUILD",
+    sha256 = "7ee9e02f2719c0422377e1fcce5a21716ca2e2e855cca56695f9ef7cb020e5dd",
+)
+
 register_toolchains(
     "//bazel/toolchain:arm_gcc_linux-x86_64",
     "//bazel/toolchain:arm_gcc_win-x86_64",

bazel/BUILD.bazel

@@ -1,3 +1,5 @@
+load("@rules_python//python:defs.bzl", "py_binary")
+
 package(default_visibility = ["//visibility:public"])
 
 py_binary(
@@ -18,17 +20,38 @@ py_binary(
 # configuring these `label_flag`s:
 #
 #     # Specify the library that provides "pico_config_extra_headers.h"
-#     --@pico-sdk//bazel/config:pico_config_extra_headers=//my_proj:my_custom_headers
+#     --@pico-sdk//bazel/config:PICO_CONFIG_EXTRA_HEADER=//my_proj:my_custom_headers
 #
 #     # Specify the library that provides "pico_config_platform_headers.h"
-#     --@pico-sdk//bazel/config:pico_config_platform_headers=//my_proj:my_custom_platform_headers
+#     --@pico-sdk//bazel/config:PICO_CONFIG_PLATFORM_HEADER=//my_proj:my_custom_platform_headers
 cc_library(
     name = "generate_config_header",
     hdrs = ["include/pico/config_autogen.h"],
     includes = ["include"],
     visibility = ["//:__subpackages__"],
     deps = [
-        "//bazel/config:pico_config_extra_headers",
-        "//bazel/config:pico_config_platform_headers",
+        "//bazel/config:PICO_CONFIG_EXTRA_HEADER",
+        "//bazel/config:PICO_CONFIG_PLATFORM_HEADER",
     ],
 )
+
+genrule(
+    name = "empty_extra_headers_file",
+    outs = ["generated_extra_include/pico_config_extra_headers.h"],
+    cmd = "echo > $@",
+    cmd_bat = "copy NUL $@",
+    visibility = ["//visibility:private"],
+)
+
+cc_library(
+    name = "no_extra_headers",
+    hdrs = ["generated_extra_include/pico_config_extra_headers.h"],
+    includes = ["generated_extra_include"],
+    visibility = ["//visibility:private"],
+)
+
+# An empty stub, useful for label_flag flags that need to point to a library,
+# but for some purposes the library needs to be a no-op.
+cc_library(
+    name = "empty_cc_lib",
+)

bazel/README.md

@@ -1,10 +1,4 @@
 # Bazel build
-The Bazel build for the Pico SDK is currently community-maintained, and should
-be considered an experimental work-in-progress. There are missing features,
-and you may encounter significant breakages with future versions.
-
-You are welcome and encouraged to file issues for any problems you encounter
-along the way.
 
 ## Using the Pico SDK in a Bazel project.
 
@@ -23,7 +17,7 @@ Second, in the same file you'll need to add an explicit dependency on
 # module will not ensure that the root Bazel module has that same version of
 # rules_cc. For that reason, this primarily acts as a FYI. You'll still need
 # to explicitly list this dependency in your own project's MODULE.bazel file.
-bazel_dep(name = "rules_cc", version = "0.0.10")
+bazel_dep(name = "rules_cc", version = "0.0.9")
 
 # rules_cc v0.0.10 is not yet cut, so manually pull in the desired version.
 # This does not apply to dependent projects, so it needs to be copied to your
@@ -65,45 +59,33 @@ Raspberry Pi Pico:
 $ bazelisk build --platforms=@pico-sdk//bazel/platform:rp2040 //...
 ```
 
-## SDK configuration [experimental]
-These configuration options are a work in progress and may see significant
-breaking changes in future versions.
+## SDK configuration
+An exhaustive list of build system configuration options is available in
+`//bazel/config:BUILD.bazel`.
 
 ### Selecting a different board
-Currently there are three configurable flags for targeting a different board:
-1. `pico_config_extra_headers`: This should always point to a `cc_library `that
-   provides a `"pico_config_extra_headers.h"` header. You can configure this
-   by including a flag like the following in your build invocation:
-   ```
-   --@pico-sdk//bazel/config:pico_config_extra_headers=//path/to:custom_extra_headers
-   ```
-2. `pico_config_platform_headers`: This should always point to a `cc_library`
-   that provides a `"pico_config_platform_headers.h"` header.
-   ```
-   --@pico-sdk//bazel/config:pico_config_platform_headers=//path/to:custom_platform_headers
-   ```
-3. `pico_config_header`: This should point to a `cc_library` that sets all
-   necessary SDK defines. Most notably, `PICO_BOARD`, `PICO_CONFIG_HEADER`,
-   `PICO_ON_DEVICE`, `PICO_NO_HARDWARE`, and `PICO_BUILD`. See
-   `//src/boards:BUILD.bazel` for working examples. Any `defines` set on this
-   library will propagate to the rest of the Pico SDK. To set this configuration
-   option, pass a flag like the following in your Bazel build invocation:
-   ```
-   --@pico-sdk//bazel/config:pico_config_platform_headers=//path/to:pico_board_config
-   ```
-
-### Selecting a stdio mode
-To select a different stdio mode, add it to your `platform` definition. For
-example:
-```python
-platform(
-    name = "rp2040",
-    constraint_values = [
-        "@pico-sdk//bazel/constraint:rp2040",
-        "@pico-sdk//bazel/constraint:stdio_usb", # Configures stdio_mode.
-        "@platforms//cpu:armv6-m",
-    ],
-)
+A different board can be selected specifying `--@pico-sdk//bazel/config:PICO_BOARD`:
+```console
+$ bazelisk build --platforms=//bazel/platform:rp2040 --@pico-sdk//bazel/config:PICO_BOARD=pico_w //...
+```
+
+If you have a bespoke board definition, you can configure the Pico SDK to use it
+by pointing `--@pico-sdk//bazel/config:PICO_CONFIG_HEADER` to a `cc_library`
+that defines `PICO_BOARD` and either a `PICO_CONFIG_HEADER` define or a
+`pico/config_autogen.h` header. Make sure any required `includes`, `hdrs`, and
+`deps` are also provided.
+
+## Generating UF2 firmware images
+Creation of UF2 images can be done as explicit build steps on a per-binary
+rule basis, or through an aspect. Running a wildcard build with the
+`pico_uf2_aspect` enabled is the easiest way to create a UF2 for every ELF
+firmware image.
+
+```console
+$ bazel build --platforms=@pico-sdk//bazel/platform:rp2040 \
+    --aspects @pico-sdk//tools:uf2_aspect.bzl%pico_uf2_aspect \
+    --output_groups=+pico_uf2_files \
+    //...
 ```
 
 ## Building the Pico SDK itself
@@ -121,17 +103,14 @@ To build all of the Pico SDK, run the following command:
 $ bazelisk build --platforms=//bazel/platform:rp2040 //...
 ```
 
-**Note:** Since the Bazel build does not yet have any `cc_binary` rules with a
-`main()` function, there won't be any binaries to flash on your board. For now,
-this only builds the SDK as a collection of libraries.
-
 ## Known issues and limitations
-The Bazel build is currently experimental and incomplete. At this time, only the
-stock Pi Pico board is supported, and the only configuration options are
-changing the STDIO mode between UART and USB serial.
-
-Keep in mind the following limitations:
-* Pico-W is not yet supported.
-* Selecting an alternative board is not yet supported.
-* Nearly all preexisting CMake configuration options are not yet supported.
-* Targeting the host build of the Pico SDK is not yet supported.
+The Bazel build for the Pico SDK is relatively new, but most features and
+configuration options available in the CMake build are also available in Bazel.
+You are welcome and encouraged to file issues for any problems and limitations
+you encounter along the way.
+
+Currently, the following features are not supported:
+
+* "None" variants of pico_double, pico_float, and pico_printf are not yet
+  supported.
+* The pioasm parser cannot be built from source via Bazel.