fix(rp2040): do not infer Bluetooth-only Arduino-Pico libraries when Bluetooth is off

[zackees]

Problem

A plain Raspberry Pi Pico 2 (rp2350, board = rpipico2, no Bluetooth) FastLED build has failed since fbuild 2.5.28. The framework-library selector picks Arduino-Pico's BTstackLib, and compiling it fails:

libraries/BTstackLib/src/BTstackLib.cpp
cores/rp2040/_needsbt.h:4:24: error: static assertion failed: This library needs Bluetooth enabled.

Bisect

Clean builds (--clean) of the same generated project (.build/fbuild/rp2350 from FastLED bash compile rp2350 --examples Blink, earlephilhower core 5.7.0):

fbuild	result
2.5.26	pass
2.5.27	pass
2.5.28	fail
2.5.29	fail

The only build change in 2.5.27..2.5.28 is ae0cf3a (#1473): "compile only reached lib/ libraries ... only selected local libraries seed framework-library selection".

Root cause

1. Seeds changed. Before fix(build): fail oversize images, compile only reached lib/ libraries, warn on ignored version pins #1473, collect_local_library_seeds walked lib/<name>/ through should_scan_entry, which prunes any directory named build. FastLED ships flat in lib/FastLED/ and keeps all of its translation units in fl/build/*.cpp, which are unity TUs. So fbuild 2.5.27 seeded only one FastLED file (platforms/esp/32/drivers/gpio_isr_rx/fast_isr.S). Since fix(build): fail oversize images, compile only reached lib/ libraries, warn on ignored version pins #1473, seeds come from InstalledLibrary::get_source_files(), which is what the build actually compiles. That adds all 29 fl/build/*+.cpp unity TUs. The new seeding is correct ("what compiles is what seeds"). The old behaviour got this right only by accident.
2. Guard is undecidable. fl/build/platforms+.cpp → platforms/_build.cpp.hpp → platforms/arm/rp/_build.cpp.hpp → platforms/arm/rp/ble_rp.cpp.hpp. That file has #include <BTstackLib.h> under #if FL_BLE_AVAILABLE && defined(FL_IS_RP2350). FastLED headers #define both macros, so by design (docs/architecture/library-selection.md, "undecidable" row, Framework-library scan misses <SPI.h> for SAMD: neither the active conditional include nor the #if 0 LDF hint is seen #1371) the scanner scans every arm. BTstackLib gets selected.
3. The selected library cannot compile. BTstackLib.h does #include <_needsbt.h>, which static_asserts ENABLE_CLASSIC. Only the board's Bluetooth ipbtstack menu entries set that macro (-DENABLE_CLASSIC=1 -DENABLE_BLE=1 ...).

arduino-cli (it preprocesses) and PlatformIO chain (it does not scan every TU of a dependency library) would not select BTstackLib here.

Confirmed directly. Removing only the #include <BTstackLib.h> line from the project's ble_rp.cpp.hpp (with the selection cache cleared) makes the unfixed build pass.

Fix

Arduino-Pico marks every Bluetooth-only library with #include <_needsbt.h>. Picking one of those by inference when ENABLE_CLASSIC is unset can never produce a working build. The new rp2040/bluetooth_libs.rs removes these libraries from the RP2040 framework-library candidates unless one of the following holds:

• ENABLE_CLASSIC is truthy, from the board menu defines or from the user's build_flags, or
• lib_deps names the library. An explicit declaration still wins, and the framework's own error then explains the missing menu.

Generic selection semantics are unchanged. fbuild_library_select::declared_dep_name becomes pub so the lib_deps matching is reused rather than duplicated. A short note was added to docs/architecture/library-selection.md.

Tests

• New unit tests in crates/fbuild-build-arm/src/rp2040/bluetooth_libs.rs. RED against a pass-through stub: drops_bluetooth_library_when_bluetooth_is_disabled and drops_bluetooth_library_when_enable_classic_is_zero failed. GREEN after the fix: all 5 pass. They cover the menu enabling Bluetooth, a lib_deps declaration, and a commented-out include.
• soldr cargo test -p fbuild-build-arm -p fbuild-library-select: all pass (233 + 32 + ...).
• soldr cargo clippy -p fbuild-build-arm -p fbuild-library-select --all-targets -- -D warnings: clean.

End-to-end (locally built FBUILD_DEV_MODE=1 target/debug/fbuild build <proj> -e <env> --clean)

project	before (origin/main 144635a)	after
rp2350 (rpipico2, no BT)	fail: BTstackLib.cpp → _needsbt.h static assertion	pass: build succeeded in 36.2s (flash: 618464 bytes, ram: 60168 bytes). Daemon log shows skipping framework library ... BTstackLib (plus SerialBT, HID_Bluetooth, BluetoothHIDMaster, ...)
rp2350w (rpipico2w, board_build.ipbtstack = ipv4btcble, lib_deps = BTstackLib, HTTPUpdate)	(passes on 2.5.29)	pass: build succeeded in 42.8s, BTstackLib still selected

Related, not fixed here

The library-select cache key hashes seed (TU) contents and each library's canonical header, but not the project headers the walk reaches. Editing only ble_rp.cpp.hpp therefore produced a cache hit with the same key and the stale selection. That made a "remove the include and rebuild" experiment look like the include was not the cause. --clean does not clear ~/.fbuild/<mode>/cache/library-selection. This deserves its own issue.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between 144635a and a792277.

📒 Files selected for processing (5)

• crates/fbuild-build-arm/src/rp2040/bluetooth_libs.rs
• crates/fbuild-build-arm/src/rp2040/mod.rs
• crates/fbuild-build-arm/src/rp2040/orchestrator.rs
• crates/fbuild-library-select/src/lib.rs
• docs/architecture/library-selection.md

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