support etl as an ESP-IDF component

[benedekkupper]

This change is intended to make etl integration into the ESP-IDF ecosystem painless. Without this patch, it took me a while to figure out a way to integrate this library into the build, here is what's needed:

1. In the ESP-IDF project CMakeLists.txt:

include(FetchContent)
FetchContent_Declare(etl SOURCE_DIR ${WORKSPACE_DIR}/etl)
FetchContent_MakeAvailable(etl)

2. In the ESP-IDF component (e.g. main) CMakeLists.txt:

target_link_libraries(${COMPONENT_LIB} # e.g. __idf_main
    PUBLIC etl
)

This change aims to support etl with ESP-IDF's component system. The return from the cmake file processing early is necessary because ESP-IDF runs cmake in script mode, where all paths are flattened, and ${CMAKE_CURRENT_SOURCE_DIR}/cmake/helpers.cmake is resolved incorrectly, failing the build. With this modification, etl can be used with the established component syntax:

list(APPEND EXTRA_COMPONENT_DIRS "${WORKSPACE_DIR}/etl")

idf_component_register(
    REQUIRES
        etl
    INCLUDE_DIRS
    SRCS
        main.cpp
)

[coderabbitai]

Walkthrough

The CMake configuration adds an ESP_PLATFORM-specific branch at the top of CMakeLists.txt. When ESP_PLATFORM is defined, it invokes idf_component_register with INCLUDE_DIRS set to "include" and then terminates further processing (early return), bypassing the remainder of the CMake logic. This creates a short-circuit path for ESP builds that only registers the include directory via ESP-IDF’s component system. No changes are made to exported or public declarations.

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title Check	✅ Passed	The title clearly summarises the main change of integrating ETL into the ESP-IDF component system by supporting it as an ESP-IDF component, and does so in a concise and specific manner that aligns with the pull request intent.
Description Check	✅ Passed	The description clearly explains the motivation for the change, outlines existing integration steps using FetchContent and target_link_libraries, and describes how the patch simplifies ETL usage within the ESP-IDF component system by resolving CMake script mode path issues.
Docstring Coverage	✅ Passed	No functions found in the changes. Docstring coverage check skipped.

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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• CMakeLists.txt (1 hunks)

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• GitHub Check: GCC C++23 Linux - No STL (ubuntu-22.04)
• GitHub Check: GCC C++23 Linux - STL - Force C++03 (ubuntu-22.04)
• GitHub Check: GCC C++23 Linux - No STL - Force C++03 (ubuntu-22.04)
• GitHub Check: Clang C++23 OSX - No STL - Force C++03 (macos-13)
• GitHub Check: GCC C++23 Linux - STL (ubuntu-22.04)
• GitHub Check: Clang C++23 Linux - No STL - Force C++03 (ubuntu-22.04)
• GitHub Check: Clang C++17 Linux - STL (ubuntu-22.04)
• GitHub Check: GCC C++20 Linux - No STL - Force C++03 (ubuntu-22.04)
• GitHub Check: Clang C++14 Linux - STL (ubuntu-22.04)
• GitHub Check: Clang C++23 Linux - No STL (ubuntu-22.04)
• GitHub Check: Clang C++14 Linux - No STL (ubuntu-22.04)
• GitHub Check: Clang C++17 Linux - No STL (ubuntu-22.04)
• GitHub Check: Clang C++23 Linux - STL - Force C++03 (ubuntu-22.04)
• GitHub Check: GCC C++20 Linux - STL (ubuntu-22.04)
• GitHub Check: GCC C++17 Linux - STL (ubuntu-22.04)
• GitHub Check: GCC C++20 Linux - No STL (ubuntu-22.04)
• GitHub Check: GCC C++20 Linux - STL - Force C++03 (ubuntu-22.04)
• GitHub Check: GCC C++11 Linux - STL (ubuntu-22.04)
• GitHub Check: GCC C++11 Linux - No STL (ubuntu-22.04)
• GitHub Check: GCC C++17 Linux - No STL (ubuntu-22.04)

🔇 Additional comments (1)

CMakeLists.txt (1)

6-8: Please confirm return() is supported with CMake 3.10

We still advertise a minimum CMake version of 3.10, yet the new branch relies on return(). That command was introduced in later CMake releases, so on a strict 3.10 toolchain this could hard-fail before ever reaching the helper include. Kindly double-check the minimum version shipped with the ESP-IDF pipeline (and bump cmake_minimum_required here if needed) to avoid a silent regression for downstream users.

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