[finger563]

Description

On ESP-IDF every std::mutex allocates its FreeRTOS semaphore when it is constructed. That is about 116 B of internal RAM (a new std::mutex measured 140 B with heap overhead). Every espp::Logger has one, to guard its tag against set_tag(), and every espp component has a Logger. Almost nothing changes a tag after construction: in this repo only RtspSession and PersistentData did, both from their constructors.

This PR makes the tag's mutability a compile-time option:

• New Kconfig option CONFIG_ESPP_LOGGER_MUTABLE_TAG (menuconfig: ESPP Logger → Mutable tag), default n.
  • Off: the Logger has no mutex, and the log calls lock nothing. Logger::set_tag() and BaseComponent::set_log_tag() become templates that fail to compile with a static_assert naming the option, so existing users see what to turn on to keep building.
  • On: behaves as before.
• Host / Python builds keep the mutable tag by default, since the Python bindings expose set_log_tag(). Defining ESPP_LOGGER_MUTABLE_TAG to 0 or 1 overrides that.
• RtspSession and PersistentData now set their tags in the constructor. RtspSession delegates to a new constructor that takes the session ID, because the tag is set before the members are. generate_session_id() is now static, since it uses no members.
• With the option off, copy and move assignment of a Logger still replace the tag. They are not thread-safe against another thread logging through the same Logger, just like assigning any other object.

Measured

M5Stack Tab5 example on ESP-IDF 6.1, internal RAM free at the same point, with main's Logger vs this branch's:

Point	main	this PR	Difference
before initialize_audio()	287,315	289,743	+2,428
after initialize_audio()	222,999	225,879	+2,880

Possible follow-up

A seqlock-guarded fixed-size tag would allow a mutable tag without a mutex. It would have compile-time options for the tag length, and perhaps std::array vs std::string storage.

Testing

• Default (tag immutable): the logger, persistent_data and rtsp examples build with no warnings (esp32s3, ESP-IDF 6.1).
• set_tag() with the option off: fails with static assertion failed: Logger::set_tag() needs CONFIG_ESPP_LOGGER_MUTABLE_TAG (menuconfig: ESPP Logger -> Mutable tag); or set the tag in the Logger's Config.
• set_tag() with CONFIG_ESPP_LOGGER_MUTABLE_TAG=y: builds.
• Host build: not run locally (the Mac's SDK is missing). CI's desktop, library, wheel and sanitizer jobs cover it, and the host default is the mutable tag, as before.

🤖 Generated with Claude Code

https://claude.ai/code/session_01SFCMzomCZ5wRHJN4sxwkvY

[github-actions]

✅Static analysis result - no issues found! ✅

[Copilot]

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Copilot review overview

No open issues 🎉

What changed in this PR

This PR makes Logger tag mutability a compile-time option (off by default on ESP-IDF) to eliminate per-Logger mutex RAM overhead, and updates components that previously changed tags post-construction to set tags during construction instead.

Changes:

• Add CONFIG_ESPP_LOGGER_MUTABLE_TAG Kconfig option to control whether tags can change after construction.
• Update Logger/BaseComponent to compile-time enable/disable set_tag() / set_log_tag() (with static_assert when disabled), and remove tag mutex usage when disabled.
• Update RtspSession and PersistentData to include additional context in the constructor tag rather than calling set_tag() later.

File	Description
components/​rtsp/​src/​rtsp_session.cpp	Set RTSP session logger tag during base construction via a delegating constructor.
components/​rtsp/​include/​rtsp_session.hpp	Add protected ctor for injected session id; make generate_session_id() static.
components/​persistent_data/​include/​persistent_data.hpp	Bake file name into the logger tag at construction time (no runtime tag mutation).
components/​logger/​include/​logger.hpp	Add compile-time mutable-tag switch and remove tag mutex/locking when disabled.
components/​logger/​Kconfig	Add ESPP_LOGGER_MUTABLE_TAG Kconfig option (default off).
components/​base_component/​include/​base_component.hpp	Gate set_log_tag() behind the mutable-tag option with a clear compile-time failure when disabled.

_{Review effort: Lite}

[Copilot]

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Copilot couldn't run its full agentic review because it didn't start before the timeout. Make sure your repository has a runner available, or add a copilot-code-review.yml file specifying one with the runs-on attribute. See the docs for more details.

Copilot review overview

2 open issues

• ESPP_LOGGER_MUTABLE_TAG is currently defined inside the `#if… · New
• Using nullptr placeholders here makes correct initialization depend on init_motor_channel_1()… · New

_{Review effort: Lite}

[Copilot]

Warning

Copilot couldn't run its full agentic review because it didn't start before the timeout. Make sure your repository has a runner available, or add a copilot-code-review.yml file specifying one with the runs-on attribute. See the docs for more details.

Copilot review overview

2 open issues

• With this change, the default motor channel config contains null driver/sensor pointers. If any… · New
• ESPP_LOGGER_MUTABLE_TAG is enabled based on defined(CONFIG_ESPP_LOGGER_MUTABLE_TAG), which… · New

2 resolved since last review

• ESPP_LOGGER_MUTABLE_TAG is currently defined inside the `#if…
• Using nullptr placeholders here makes correct initialization depend on init_motor_channel_1()…

_{Review effort: Lite}