chore: drop oldNixpkgs from shell.nix

[M1nd3r]

Importing oldNixpkgs is no longer needed, as SDL2 was replaced by SDL3, and they are not used anywhere else.

SDL2 libraries moved to fullDeps nix-shell to be used with upgrade tests.

Follows: #6858

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 8afa238a-33a9-4f2e-bf02-1e15b3af2e5e

📥 Commits

Reviewing files that changed from the base of the PR and between 5faec34 and e5aae86.

📒 Files selected for processing (3)

• docs/tests/upgrade-tests.md
• shell.nix
• tests/download_emulators.sh

✅ Files skipped from review due to trivial changes (1)

• docs/tests/upgrade-tests.md

🚧 Files skipped from review as they are similar to previous changes (2)

• tests/download_emulators.sh
• shell.nix

---

Walkthrough

Updates shell.nix to import a pinned nixpkgs with rustOverlay via overlays, enable unfree packages, and set segger-jlink.acceptLicense from TREZOR_FIRMWARE_ACCEPT_JLINK_LICENSE; removes oldNixpkgs and migrates SDL2 references to sdl2-compat/SDL2_image in fullDeps. Changes docs/tests/upgrade-tests.md to recommend running nix-shell --arg fullDeps true and adds SDL troubleshooting for older emulators. Updates tests/download_emulators.sh to call nix-shell --arg fullDeps true when available.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• trezor/trezor-firmware#6927: Related changes to the fullDeps nix-shell/environment and when fullDeps is passed or enabled.

Suggested reviewers

• mmilata
• matejcik

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: removing the oldNixpkgs import from shell.nix, which is the core objective of this PR.
Description check	✅ Passed	The description provides clear context for the change and references the related PR, but lacks the recommended template sections like development status and project assignments for core developers.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 m1nd3r/drop-oldNixpkgs

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[github-actions]

en main(all)

model	device_test	click_test	persistence_test
T2T1	test(all) main(all)	test(all) main(all)	test(all) main(all)
T3B1	test(all) main(all)	test(all) main(all)	test(all) main(all)
T3T1	test(all) main(all)	test(all) main(all)	test(all) main(all)
T3W1	test(all) main(all)	test(all) main(all)	test(all) main(all)

Latest CI run: 25911049278

[mmilata]

Sorry, missed the comment in the original PR. We can postpone this until later.

[mmilata]

Oh, did not realize it's needed for old emulators. This is going to use SDL2 and SDL2_image from user's current nixpkgs channel, not what's in shell.nix, which is not good for reproducibility.

I propose to do one of the following:

1. Put SDL2 SDL2_image (or sdl2-compat SDL2_image, same thing) under the fullDeps section in shell.nix. Add a note that --arg fullDeps true is needed and the SDL_VIDEODRIVER=x11 workaround in doc/tests/upgrade-tests.md.
2. Put oldNixpkgs.SDL2 oldNixpkgs.SDL2_image in there and only the first note in upgrade-tests.md

[M1nd3r]

I've implemented the variant 1 8631e69