feat(night-shift): default Night Shift to always on - #2091
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Night Shift state lives in the per-user CoreBrightness session and is not exposed through any plist system.defaults can write, so express it as a home-manager launchd user agent that calls nightlight on login. Clear the schedule before turning it on, since sunset-to-sunrise would otherwise flip Night Shift back off at sunrise. RunAtLoad without a StartInterval keeps this a default rather than an enforcement: a manual toggle sticks until the next login.
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Code Review
This pull request introduces a new night-shift service for macOS (Darwin) systems, which configures a launchd agent to set a default screen temperature and enable Night Shift on login. It includes a shell script to apply the settings and a shell spec test suite to verify its behavior. Feedback on the pull request highlights two important issues in the Nix configuration: static log paths in /tmp that can cause permission conflicts on multi-user systems, and top-level evaluation of Darwin-only packages on non-Darwin platforms. A refactoring is suggested to wrap the module in a Darwin-conditional block and remove the static log paths.
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| { pkgs }: | ||
| let | ||
| # 0 = least warm, 100 = warmest. | ||
| temperature = 100; | ||
|
|
||
| applyNightShiftScript = pkgs.replaceVars ./apply-night-shift.sh { | ||
| nightlightBin = "${pkgs.nightlight}/bin/nightlight"; | ||
| inherit temperature; | ||
| }; | ||
| in | ||
| { | ||
| # Night Shift state lives in the per-user CoreBrightness session and is not | ||
| # exposed through any plist `system.defaults` can write, so the only way to | ||
| # express "on by default" is to talk to that session on login. | ||
| # | ||
| # RunAtLoad without a StartInterval deliberately makes this a default rather | ||
| # than an enforcement: a manual toggle sticks until the next login. | ||
| launchd.agents.night-shift = pkgs.lib.mkIf pkgs.stdenv.isDarwin { | ||
| enable = true; | ||
| config = { | ||
| ProgramArguments = [ | ||
| "${pkgs.bash}/bin/bash" | ||
| "${applyNightShiftScript}" | ||
| ]; | ||
| RunAtLoad = true; | ||
| StandardOutPath = "/tmp/night-shift.log"; | ||
| StandardErrorPath = "/tmp/night-shift.error.log"; | ||
| }; | ||
| }; | ||
| } |
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This refactoring addresses two important issues:
- Multi-user Permission Conflicts: Writing logs to static paths in
/tmp(like/tmp/night-shift.log) causes permission conflicts on multi-user macOS systems. When the first user logs in, the log file is created under their ownership. When a subsequent user logs in, their launchd agent will fail to start because they lack write permissions to the existing log file. Since this is a simple run-once script, we can safely removeStandardOutPathandStandardErrorPathentirely. - Platform Evaluation Isolation: Defining
applyNightShiftScript(which referencespkgs.nightlight) in the top-levelletblock forces its evaluation even on non-Darwin systems (like Linux). Sincenightlightis a Darwin-only package, this can cause evaluation or platform-support errors on Linux. Wrapping the entire module inpkgs.lib.optionalAttrs pkgs.stdenv.isDarwinensures that Darwin-specific derivations are only evaluated on Darwin.
{ pkgs }:
pkgs.lib.optionalAttrs pkgs.stdenv.isDarwin (
let
# 0 = least warm, 100 = warmest.
temperature = 100;
applyNightShiftScript = pkgs.replaceVars ./apply-night-shift.sh {
nightlightBin = "${pkgs.nightlight}/bin/nightlight";
inherit temperature;
};
in
{
# Night Shift state lives in the per-user CoreBrightness session and is not
# exposed through any plist `system.defaults` can write, so the only way to
# express "on by default" is to talk to that session on login.
#
# RunAtLoad without a StartInterval deliberately makes this a default rather
# than an enforcement: a manual toggle sticks until the next login.
launchd.agents.night-shift = {
enable = true;
config = {
ProgramArguments = [
"${pkgs.bash}/bin/bash"
"${applyNightShiftScript}"
];
RunAtLoad = true;
};
};
}
)
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Performed full review of 9feacad...f165c67
Analysis
No significant architectural issues identified. The PR implements a well-structured macOS service module with appropriate boundary selection (home-manager vs system-level), proper platform gating, deterministic dependency injection, and a pragmatic imperative bridge pattern consistent with existing precedent. The design appropriately respects user preferences while providing sensible defaults, and includes test coverage for implementation verification.
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| # A sunset-to-sunrise schedule turns Night Shift back off at sunrise, so the | ||
| # schedule has to be cleared before `on` can mean "stays on". | ||
| "$nightlight_bin" schedule stop | ||
| "$nightlight_bin" temp "$temperature" |
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Login resets temperature too, not just on/off: The PR description frames this agent as a default that a manual toggle can override until next login, and that's true for on/off — but this line unconditionally re-applies temp 100 at every login, so a manual nightlight temp 60 (or any other value) gets silently stomped on the next login. If that's intentional (i.e. the 'default' is really on @ temp=100, not just on), consider calling it out in the module comment; if not, gating the temp call on the current preference (or dropping it and relying on macOS to remember the last temp) would keep temperature adjustments sticky the same way on/off is.
Mesa DescriptionTL;DRDefaults macOS Night Shift to "always on" (warmest temperature, no schedule) via a per-user What changed?
Description generated by Mesa. Update settings |
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1 issue found across 4 files
Prompt for AI agents (unresolved issues)
Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.
<file name="home-manager/services/night-shift/default.nix">
<violation number="1" location="home-manager/services/night-shift/default.nix:26">
P2: Using fixed paths in `/tmp` for `StandardOutPath` and `StandardErrorPath` will cause permission conflicts on multi-user macOS systems. The first user's login creates these files with their ownership; subsequent users' launchd agents will fail to write to them. Since this is a simple run-once script, consider removing these log paths entirely (launchd will route output to the system log), or use a per-user path like `~/Library/Logs/night-shift.log`.</violation>
</file>
Reply with feedback, questions, or to request a fix.
Re-trigger cubic
| "${applyNightShiftScript}" | ||
| ]; | ||
| RunAtLoad = true; | ||
| StandardOutPath = "/tmp/night-shift.log"; |
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P2: Using fixed paths in /tmp for StandardOutPath and StandardErrorPath will cause permission conflicts on multi-user macOS systems. The first user's login creates these files with their ownership; subsequent users' launchd agents will fail to write to them. Since this is a simple run-once script, consider removing these log paths entirely (launchd will route output to the system log), or use a per-user path like ~/Library/Logs/night-shift.log.
Prompt for AI agents
Check if this issue is valid — if so, understand the root cause and fix it. At home-manager/services/night-shift/default.nix, line 26:
<comment>Using fixed paths in `/tmp` for `StandardOutPath` and `StandardErrorPath` will cause permission conflicts on multi-user macOS systems. The first user's login creates these files with their ownership; subsequent users' launchd agents will fail to write to them. Since this is a simple run-once script, consider removing these log paths entirely (launchd will route output to the system log), or use a per-user path like `~/Library/Logs/night-shift.log`.</comment>
<file context>
@@ -0,0 +1,30 @@
+ "${applyNightShiftScript}"
+ ];
+ RunAtLoad = true;
+ StandardOutPath = "/tmp/night-shift.log";
+ StandardErrorPath = "/tmp/night-shift.error.log";
+ };
</file context>
treefmt expands multi-element lists one entry per line. Unformatted since the gh-stack extension was added in 797139f.
Closes the shell-test failure introduced in #2091, which added apply-night-shift.sh and its spec without registering the script in coverage_spec.sh.
1 participant
What
Makes Night Shift the default color mode on macOS: always on, rather than the previous sunset-to-sunrise schedule.
Adds a home-manager service at
home-manager/services/night-shift/, wired intohome-manager/services/default.nix, with a shellspec covering the apply script.Why this shape
Night Shift state lives in the per-user CoreBrightness session and is not exposed through any plist
system.defaultscan write, so there is no declarative nix-darwin option for it. The only way to express "on by default" is to talk to that session, which is why this shells out tonightlight(in nixpkgs, darwin-only) from a launchd agent. Same reasoning as the keyboard module shelling out tohidutil.It lives in home-manager rather than nix-darwin because the state is per-user, not system-wide.
Notes for reviewers
Two deliberate choices worth a look:
schedule stopbeforeon. A sunset-to-sunrise schedule turns Night Shift back off at sunrise, so the schedule has to be cleared beforeoncan mean "stays on".RunAtLoadwith noStartInterval. This makes the setting a default rather than an enforcement — a manual toggle off sticks until the next login. A periodic re-assert would fight the user every few minutes.Temperature is pinned at 100 (warmest), matching what the machine was already set to, so the mode is fully declarative rather than half-pinned.
Commits
feat(night-shift): default Night Shift to always on— the change itself.style(gh): format extensions list— drive-by treefmt fix onhome-manager/programs/gh/default.nix, unformatted on main since the gh-stack commit (797139f). Whitespace only, unrelated to Night Shift; separated out so it stays easy to skip.Verification
spec/night_shift_spec.shpasses (4 examples, 0 failures); picked up by normal shellspec discovery.nix build .#checks.aarch64-darwin.eval-darwin-defaultpasses.nix build .#checks.aarch64-darwin.treefmtpasses (failed on main before commit 2).on until sunrise->on, schedulesunset to sunrise->off, temp100.nightlightpackage does not break Linux evaluation — the Linux home config errors at the identical pre-existingdocker.serviceplatform mismatch (same drv hash) with and without this change.