G0: add a build example to check G0 dependencies

tools/cmake/component_deps.dot.in

@@ -11,7 +11,6 @@ subgraph cluster_g0 {
     esp_common;
     esp_rom;
     ${CONFIG_IDF_TARGET_ARCH};
-    ${CONFIG_IDF_TARGET};
 }
 
 subgraph cluster_g1 {

tools/test_apps/system/g0_components/CMakeLists.txt

@@ -0,0 +1,46 @@
+# For more information about build system see
+# https://docs.espressif.com/projects/esp-idf/en/latest/api-guides/build-system.html
+# The following five lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+
+# Force this project to use only G0 components
+set(all_g0_components esp_rom soc hal esp_common main)  # also <arch>, i.e. xtensa or riscv, will be added below
+set(COMPONENTS ${all_g0_components})
+
+# By default, common components include some G1+ components. Override common components to only have G0 ones
+idf_build_set_property(__COMPONENT_REQUIRES_COMMON "${all_g0_components}")
+# Generate a graph to visually see the dependencies between G0 and G1+ (if any)
+idf_build_set_property(__BUILD_COMPONENT_DEPGRAPH_ENABLED 1)
+
+project(g0_components)
+
+# As a workaround for ESP32-C2, we need to define the MMU page size here, until MMU hal-driver
+# is refactored
+if(CONFIG_IDF_TARGET_ESP32C2)
+    idf_build_set_property(C_COMPILE_OPTIONS "-DCONFIG_MMU_PAGE_SIZE=64" APPEND)
+endif()
+
+# Now that the project has been initialized, let's check which components it is using
+# The following variable lists all the components that shall be used by this project
+set(expected_components
+    ${COMPONENTS}
+    ${CONFIG_IDF_TARGET_ARCH}   # xtensa or riscv
+    )
+
+# Do not include libc into the build, we don't have any libC in G0
+set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -nostdlib")
+
+# Get all the components that were required to initialize this project
+idf_build_get_property(build_components BUILD_COMPONENTS)
+
+# Sort lists to be able to compare them literally
+list(SORT expected_components)
+list(SORT build_components)
+if(NOT "${expected_components}" STREQUAL "${build_components}")
+    message(FATAL_ERROR "Unexpected components list in G0 build\n"
+                        "Expected: ${expected_components}\n"
+                        "Actual: ${build_components}")
+endif()

tools/test_apps/system/g0_components/README.md

@@ -0,0 +1,33 @@
+| Supported Targets | ESP32-C3 | ESP32-C2 | ESP32-H2 |
+| ----------------- | -------- | -------- | -------- |
+
+All Xtensa based targets (ESP32, ESP32-S2, ESP32-S3) are currently not supported by this test, because their components having dependencies on G1+ components.
+
+# "G0"-components-only app
+
+This test application will compile ESP-IDF and this test's main component with G0 components only. The goal is to make sure that no G0 component depends
+on G1 or higher component.
+
+Currently, this test only supports RISC-V based targets as Xtensa ones still have some G0 components depending on G1+ components.
+
+Compiling this test with an Xtensa based target will result in a CMake error, showing all the non-G0 components included in the build file generation.
+
+The purpose of this example is to make sure that any modification to ESP-IDF doesn't violate the G0-G1+ dependency rule.
+
+# Using this test app
+
+Set the target to a RISC-V based, `esp32c3` for example:
+```bash
+idf.py set-target esp32c3
+```
+
+Then, trigger the build:
+```bash
+idf.py build
+```
+
+Build should be successful if there is no dependency problem between G0 and upper layers. 
+
+# Component dependencies graph (`component_deps.dot`)
+
+When this project is configured, `component_deps.dot` file in the build directory is generated. This file contains a Graphviz graph showing the component dependencies. You can visualize this graph (using `dot` tool or online at https://dreampuf.github.io/GraphvizOnline/) to see why an extra component got added. You can also build the project for the base branch, to compare the graph to a known good one.

tools/test_apps/system/g0_components/main/CMakeLists.txt

@@ -0,0 +1,2 @@
+idf_component_register(SRCS "g0_components.c"
+                    INCLUDE_DIRS ".")

tools/test_apps/system/g0_components/main/g0_components.c

@@ -0,0 +1,11 @@
+/*
+ * SPDX-FileCopyrightText: 2015-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <stdio.h>
+
+void app_main(void)
+{
+
+}