Add support for linking optional libraries in PlatformIO

CMakeLists.txt

@@ -314,4 +314,7 @@ if(NOT MBED_IS_NATIVE_BUILD)
     # Make sure that things linking mbed-core-flags can also get the target-specific include dirs and flags.
     mbed_extract_flags(${MBED_TARGET_CMAKE_NAME}-flags ${MBED_TARGET_CMAKE_NAME})
     target_link_libraries(mbed-core-flags INTERFACE ${MBED_TARGET_CMAKE_NAME}-flags)
+
+    # If the user specified default link libraries in their mbed_app.json, link those to mbed-os
+    target_link_libraries(${MBED_OS_CORE_LIB_NAME} INTERFACE ${MBED_DEFAULT_LINK_LIBRARIES})
 endif()

tools/python/mbed_platformio/build_mbed_ce.py

@@ -56,6 +56,7 @@
     extract_flags,
     extract_includes,
     extract_link_args,
+    extract_link_libraries,
     find_included_files,
 )
 from mbed_platformio.pio_variants import PIO_VARIANT_TO_MBED_TARGET
@@ -281,6 +282,7 @@ def get_app_defines(app_config: dict) -> list[tuple[str, str]]:
 project_defines = get_app_defines(app_target_json)
 project_flags = extract_flags(app_target_json)
 app_includes = extract_includes(app_target_json)
+app_link_libraries = extract_link_libraries(app_target_json)
 
 ## Linker flags --------------------------------------------------------------------------------------------------------
 
@@ -290,6 +292,14 @@ def get_app_defines(app_config: dict) -> list[tuple[str, str]]:
 link_args = ["-Wl,--whole-archive", '"' + str(mbed_ce_lib_path) + '"', "-Wl,--no-whole-archive"]
 _ = env.Depends("$BUILD_DIR/$PROGNAME$PROGSUFFIX", str(mbed_ce_lib_path))
 
+# Now link optional libraries. Note that according to normal link order rules, we'd link the optional libraries
+# first since they reference libmbed-os.a. However, mbed-os can also reference the optional libraries
+# (e.g. usb for USB serial support), and all of libmbed-os.a is already being considered for linking thanks
+# to --whole-archive. So we actually want to link these second.
+for lib in app_link_libraries:
+    link_args.append(str(lib))
+    _ = env.Depends("$BUILD_DIR/$PROGNAME$PROGSUFFIX", str(lib))
+
 # Get other linker flags from Mbed. We want these to appear after the application objects and Mbed libraries
 # because they contain the C/C++ library link flags.
 link_args.extend(extract_link_args(app_target_json))

tools/python/mbed_platformio/cmake_to_scons_converter.py

@@ -221,3 +221,16 @@ def extract_link_args(target_json: dict) -> list[str]:
             result.extend(args)
 
     return result
+
+
+def extract_link_libraries(target_json: dict) -> list[pathlib.Path]:
+    """
+    Extract the link libraries from a CMake target and return a list of libraries to link, in order.
+
+    Note that this is currently set up to handle only static libraries.
+    """
+    return [
+        pathlib.Path("$BUILD_DIR") / (fragment["fragment"])
+        for fragment in target_json.get("link", {}).get("commandFragments", [])
+        if fragment["role"] == "libraries"
+    ]

tools/python/mbed_platformio/pio_variants.py

@@ -25,4 +25,5 @@
     "nucleo_h743zi": "NUCLEO_H743ZI2",
     "genericSTM32F103RB": "NUCLEO_F103RB",
     "disco_h747xi": "DISCO_H747I",
+    "rpipico": "RASPBERRY_PI_PICO",
 }

tools/python/mbed_tools/build/_internal/config/schemas.py

@@ -619,6 +619,17 @@ class MbedAppJSON(BaseJSONConfig):
     results may not be what you expect.
     """
 
+    link_libraries: list[str] = Field(default_factory=list)
+    """
+    Default link libraries to link along with the base ``mbed-os`` (or ``mbed-baremetal``) library to your application.
+
+    This should be a set to a list of strings containing CMake library names built in to Mbed to link, such as
+    "mbed-netsocket" or "mbed-storage".
+
+    This is simply a shortcut for linking libraries in CMake, if you don't want to or can't
+    (e.g. because you are using PlatformIO so you don't have direct access to CMake scripts).
+    """
+
     @model_validator(mode="after")
     def verify_target_memory_bank_config_used_where_appropriate(self) -> Self:
         for overrides in self.target_overrides.values():

tools/python/mbed_tools/build/_internal/templates/mbed_config.tmpl

@@ -10,6 +10,7 @@ set(MBED_C_LIB "{{c_lib}}")
 set(MBED_PRINTF_LIB "{{printf_lib}}")
 set(MBED_OUTPUT_EXT "{{OUTPUT_EXT}}")
 set(MBED_GREENTEA_TEST_RESET_TIMEOUT "{{forced_reset_timeout}}")
+set(MBED_DEFAULT_LINK_LIBRARIES {% for lib in link_libraries %} {{lib}} {%- endfor %})
 
 # JSON files used to generate this config.  If any of these change, the Python config generation
 # scripts must be rerun.