fix(board-db): add build.extra_flags for nRF52840 boards (Arduino macros)

[zackees]

Summary

• Immediate-unblock subset of fbuild deficiency vs PlatformIO: build.extra_flags stripped from many bundled board JSONs (breaks Arduino board-macro detection) #298: restore build.extra_flags on three nRF52840 board JSONs that FastLED CI currently exercises. Values mirror upstream platformio/platform-nordicnrf52 verbatim.
• Without these, every nRF52 build falls through FastLED's "Unknown nRF52840 variant" fallback block in platforms/arm/nrf52/fastpin_arm_nrf52_variants.h, which marks pin 1 invalid → static_assert "This pin has been marked as an invalid pin" at fl/system/fastpin_base.h:146 on examples/Apa102/Apa102.ino.

board	added
nrf52840_dk	-DARDUINO_NRF52_DK
nrf52840_dk_adafruit	-DARDUINO_NRF52840_PCA10056 -DNRF52840_XXAA
adafruit_feather_nrf52840_sense	-DARDUINO_NRF52840_FEATHER_SENSE -DNRF52840_XXAA

This unblocks FastLED nrf52840_dk, nrf52840_supermini (via real_board_name="nrf52840_dk_adafruit"), and adafruit_feather_nrf52840_sense workflows.

The full sweep — every other bundled board missing extra_flags, including the rest of the nRF52 family — is a separate follow-up tracked at #298 (re-run enrich_boards end-to-end to import extra_flags for everything).

Test plan

• cargo check -p fbuild-config clean.
• cargo test -p fbuild-config --lib board:: — 56/56 (was 53/53 before; +3 regression tests).
• CI on FastLED side: nrf52840_dk, nrf52840_supermini, adafruit_feather_nrf52840_sense workflows should now reach actual compilation past the static_assert.

Refs #298

Generated with Claude Code (https://claude.com/claude-code)

Summary by CodeRabbit

Release Notes

• New Features

  • Enhanced nRF52840 board support with updated compiler definitions for Adafruit Feather, DK, and DK Adafruit variants.

• Tests

  • Added unit tests to verify correct compiler definitions are applied for nRF52840 boards.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: fb037f78-6c75-4a7f-af04-45ff94ed4721

📥 Commits

Reviewing files that changed from the base of the PR and between 4f315ff and f4d0b2b.

📒 Files selected for processing (4)

• crates/fbuild-config/assets/boards/json/adafruit_feather_nrf52840_sense.json
• crates/fbuild-config/assets/boards/json/nrf52840_dk.json
• crates/fbuild-config/assets/boards/json/nrf52840_dk_adafruit.json
• crates/fbuild-config/src/board/tests.rs

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📝 Walkthrough

Walkthrough

Adds compile-time preprocessor flags (extra_flags) to three nRF52840 board configurations and introduces three unit tests that verify BoardConfig::get_defines() includes the expected Arduino-specific macro definitions for each board variant.

Changes

nRF52840 Board Configuration Flags

Layer / File(s)	Summary
Board configuration flags crates/fbuild-config/assets/boards/json/adafruit_feather_nrf52840_sense.json, crates/fbuild-config/assets/boards/json/nrf52840_dk.json, crates/fbuild-config/assets/boards/json/nrf52840_dk_adafruit.json	Adds extra_flags entries under build.core to each of three nRF52840 board JSON files, defining board-specific Arduino preprocessor symbols (ARDUINO_NRF52_DK, ARDUINO_NRF52840_FEATHER_SENSE, ARDUINO_NRF52840_PCA10056) and device family markers (NRF52840_XXAA).
Board configuration tests crates/fbuild-config/src/board/tests.rs	Introduces three regression tests validating that BoardConfig::get_defines() correctly extracts and returns the expected Arduino and nRF52840 preprocessor macros for each board variant.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related issues

• #298: Directly restores the missing build.extra_flags configuration for these nRF52840 board variants and adds comprehensive test coverage for BoardConfig::get_defines() to prevent regression.

Poem

🐰 Three boards now wear their flags with pride,
Arduino macros compile-time-supplied,
The tests stand guard to keep them true,
So nRF52840s know just what to do!
Simple, clean, and oh-so-bright. ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the main change: adding build.extra_flags configuration entries to three nRF52840 board JSON files to define Arduino compiler macros.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/nrf52840-extra-flags

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