fix(build): #234 use @response file for teensy link on Windows

[zackees]

Summary

Closes #234.

• Teensy boards (notably teensy41 with ~500 .o files) exceeded Windows' ~32 KB CreateProcessW cmdline limit at link time, failing with io error: The filename or extension is too long. (os error 206).
• Linux (~128 KB) and macOS (~256 KB) absorbed the same cmdline, so CI (Ubuntu) was green while Windows developers were blocked.
• ArmLinker (STM32/RP2040/NRF52) and Esp32Linker already use GCC @response files for the link step on Windows. TeensyLinker was the outlier.
• This PR mirrors the existing ArmLinker pattern in crates/fbuild-build/src/teensy/teensy_linker.rs: when cfg!(windows) && args.len() > 50, write the linker args to output_dir/tmp/fbuild_teensy_link_<hash>.rsp via the shared fbuild_core::response_file::write_response_file, then invoke arm-none-eabi-gcc @<rsp>. Linux/macOS keep the direct invocation.

No new utilities, no behavior change for small sketches, no change to the existing Teensy integration test (crates/fbuild-build/tests/teensy_build.rs).

Test plan

• uv run soldr cargo fmt --all
• uv run soldr cargo check --workspace --all-targets
• uv run soldr cargo clippy -p fbuild-build --all-targets -- -D warnings
• uv run soldr cargo test -p fbuild-build --lib (499 passed)
• Manual Windows repro: bash compile teensy41 --examples Blink against a FastLED checkout produces firmware.elf and a .fbuild/build/teensy41/release/tmp/fbuild_teensy_link_*.rsp file. (Best verified post-merge in CI/local Windows; companion FastLED PR for the section-conflict compile error is still needed to actually reach the link step on that branch.)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed Windows build failures when linker argument lists exceed typical command-line limits. The build system now automatically uses a response file mechanism to handle complex linking scenarios, ensuring reliable compilation on Windows platforms regardless of project complexity.

[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: feeadb2c-f757-4308-95c5-ebe0ed063298

📥 Commits

Reviewing files that changed from the base of the PR and between 73c2d2f and 6a452eb.

📒 Files selected for processing (1)

• crates/fbuild-build/src/teensy/teensy_linker.rs

---

📝 Walkthrough

Walkthrough

This PR adds Windows-specific response file handling to the Teensy linker step. When compiling on Windows with over 50 arguments, the linker arguments are written to a response file with normalized path separators, and the linker is invoked using GCC's @file syntax to avoid the 32 KB command-line limit on Windows.

Changes

Windows Linker Response File

Layer / File(s)	Summary
Windows response file for link step crates/fbuild-build/src/teensy/teensy_linker.rs	TeensyLinker::link conditionally creates a response file under output_dir/tmp when running on Windows with more than 50 arguments, normalizes path separators, and invokes the linker with @response_path syntax; otherwise uses the standard argument slice.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐇 A rabbit hops through Windows paths,
With response files in its math,
No more command lines too long and wide—
@symbols guide us through with pride! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: using response files for Teensy linking on Windows, matching the PR's primary objective.
Linked Issues check	✅ Passed	The PR implements the exact solution proposed in #234: writing linker arguments to a response file when on Windows with >50 args and invoking with @, matching all coding requirements.
Out of Scope Changes check	✅ Passed	The changes are scoped to teensy_linker.rs and focus solely on implementing response file support for Windows link failures, with no unrelated modifications.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ 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/issue-234-teensy-link-response-file

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}