fix(windows): detect Windows PowerShell in the Night Light script

docs/customization.md

@@ -325,6 +325,12 @@ matching what Windows itself would have done. All writes stay in
 `HKEY_CURRENT_USER` and the script is idempotent — a second run reports zero
 changes.
 
+On a machine where Night Light has never been used the two values do not exist
+yet. Rather than failing the apply, the script seeds them. Sunset and sunrise
+are deliberately left unset in that case: Windows derives them from the machine
+location, and seeding them would only risk storing wrong times. Until Windows
+computes them, the solar window is unknown and Night Light is left off.
+
 Reversal: open Settings > System > Display > Night light and turn it off, or
 delete the two registry values above and sign out.
 

home/.chezmoiscripts/windows/run_onchange_41-set-night-light.ps1

@@ -514,6 +514,56 @@ function Test-NightLightWithinNightWindow {
 
 #endregion
 
+function Test-WindowsHost {
+    <#
+        .SYNOPSIS
+            True when running on Windows, under either PowerShell edition.
+
+        .DESCRIPTION
+            $IsWindows only exists in PowerShell Core. Chezmoi runs .ps1 scripts
+            with `powershell` (Windows PowerShell 5.1, PSEdition "Desktop"),
+            where the variable is undefined, so a guard that negates it directly
+            is always true and skips the script on the very platform it targets.
+            Desktop edition only ships on Windows, so treat it as a match.
+    #>
+    [OutputType([bool])]
+    param()
+
+    if ($PSVersionTable.PSEdition -eq "Desktop") {
+        return $true
+    }
+
+    return [bool](Get-Variable -Name IsWindows -ValueOnly -ErrorAction SilentlyContinue)
+}
+
+function Get-NightLightDefaultSetting {
+    <#
+        .SYNOPSIS
+            Baseline settings for a machine where Night Light was never used.
+
+        .DESCRIPTION
+            Sunset and sunrise are left at their defaults (00:00). Windows
+            recomputes them from the machine location and writes them back, so
+            seeding them here would only risk storing wrong times.
+    #>
+    [OutputType([psobject])]
+    param()
+
+    return [pscustomobject]@{
+        ScheduleEnabled  = $true
+        SetHoursMode     = $false
+        StartHour        = 21
+        StartMinute      = 0
+        EndHour          = 7
+        EndMinute        = 0
+        ColorTemperature = $script:NightLightMaxKelvin
+        SunsetHour       = 0
+        SunsetMinute     = 0
+        SunriseHour      = 0
+        SunriseMinute    = 0
+    }
+}
+
 function Set-NightLightConfiguration {
     <#
         .SYNOPSIS
@@ -561,12 +611,18 @@ function Set-NightLightConfiguration {
     $desiredKelvin = ConvertTo-NightLightColorTemperature -Strength $Strength
 
     $settingsBlob = & $GetRegistryValue -Path $script:NightLightSettingsPath
-    if (-not $settingsBlob) {
-        throw "Night Light settings are not initialised. Open Settings > System > Display > Night light once, then re-run."
+    if ($settingsBlob) {
+        $settings = ConvertFrom-NightLightSettingsPayload -Payload (ConvertFrom-CloudStoreBlob -Blob ([byte[]]$settingsBlob)).Payload
+    }
+    else {
+        # Night Light has never been used on this machine (fresh install, or a
+        # host without the feature). Seed a baseline rather than failing the
+        # whole chezmoi apply.
+        Write-Verbose "Night Light settings not present; creating them from scratch."
+        $settings = Get-NightLightDefaultSetting
     }
 
-    $settings = ConvertFrom-NightLightSettingsPayload -Payload (ConvertFrom-CloudStoreBlob -Blob ([byte[]]$settingsBlob)).Payload
-    $settingsCorrect = $settings.ScheduleEnabled -and -not $settings.SetHoursMode -and $settings.ColorTemperature -eq $desiredKelvin
+    $settingsCorrect = $settingsBlob -and $settings.ScheduleEnabled -and -not $settings.SetHoursMode -and $settings.ColorTemperature -eq $desiredKelvin
 
     if ($settingsCorrect) {
         $results += [pscustomobject]@{ Setting = "Schedule and strength"; Status = "AlreadySet"; Changed = $false }
@@ -605,7 +661,7 @@ function Set-NightLightConfiguration {
 }
 
 if (-not $SkipApply) {
-    if (-not $IsWindows) {
+    if (-not (Test-WindowsHost)) {
         Write-Host "[SKIP] Night Light is a Windows-only setting." -ForegroundColor Yellow
         return
     }

tests/powershell/NightLight.Tests.ps1

@@ -85,6 +85,34 @@ Describe "Night Light script" -Tag "Unit" {
     }
 }
 
+Describe "Windows host detection" -Tag "Unit" {
+    It "reports true on the current Windows host" {
+        Test-WindowsHost | Should -BeTrue
+    }
+
+    It "does not guard on the bare `$IsWindows variable" {
+        # $IsWindows is undefined in Windows PowerShell 5.1, which is the
+        # interpreter chezmoi uses for .ps1 scripts. A bare guard therefore
+        # skips the script on the exact platform it targets.
+        $content = Get-Content -Path $script:ScriptPath -Raw
+        $content | Should -Not -Match '-not\s+\$IsWindows'
+    }
+
+    It "returns true under Windows PowerShell 5.1" -Skip:(-not (Get-Command powershell.exe -ErrorAction SilentlyContinue)) {
+        $output = & powershell.exe -NoLogo -NoProfile -Command @"
+. '$script:ScriptPath' -SkipApply
+if (Test-WindowsHost) { 'True' } else { 'False' }
+"@
+        $LASTEXITCODE | Should -Be 0
+        ($output | Select-Object -Last 1) | Should -Be "True"
+    }
+
+    It "runs without skipping under Windows PowerShell 5.1" -Skip:(-not (Get-Command powershell.exe -ErrorAction SilentlyContinue)) {
+        $output = & powershell.exe -NoLogo -NoProfile -File $script:ScriptPath -WhatIf 2>&1
+        ($output -join "`n") | Should -Not -Match 'Windows-only setting'
+    }
+}
+
 Describe "Bond CompactBinary primitives" -Tag "Unit" {
     It "round-trips varints" -ForEach @(
         @{ Value = [uint64]0 }
@@ -267,6 +295,25 @@ Describe "Strength conversion" -Tag "Unit" {
     }
 }
 
+Describe "Default settings" -Tag "Unit" {
+    It "describes a sunset-to-sunrise schedule with no cached solar times" {
+        $defaults = Get-NightLightDefaultSetting
+        $defaults.ScheduleEnabled | Should -BeTrue
+        $defaults.SetHoursMode | Should -BeFalse
+        $defaults.SunsetHour | Should -Be 0
+        $defaults.SunriseHour | Should -Be 0
+    }
+
+    It "round-trips through the payload codec" {
+        $defaults = Get-NightLightDefaultSetting
+        $payload = ConvertTo-NightLightSettingsPayload -Settings $defaults
+        $decoded = ConvertFrom-NightLightSettingsPayload -Payload $payload
+        $decoded.StartHour | Should -Be $defaults.StartHour
+        $decoded.EndHour | Should -Be $defaults.EndHour
+        $decoded.ScheduleEnabled | Should -BeTrue
+    }
+}
+
 Describe "Night window detection" -Tag "Unit" {
     BeforeAll {
         $script:WindowSettings = [pscustomobject]@{
@@ -368,12 +415,44 @@ Describe "Set-NightLightConfiguration" -Tag "Unit" {
         @($results | Where-Object { $_.Status -eq "WhatIf" }).Count | Should -BeGreaterThan 0
     }
 
-    It "fails with actionable guidance when Night Light was never initialised" {
-        $fake = script:New-FakeNightLightRegistry -SettingsBlob $null
+    It "creates the settings from scratch when Night Light was never initialised" {
+        $fake = script:New-FakeNightLightRegistry -SettingsBlob $null -StateBlob $null
+        $results = Set-NightLightConfiguration -Strength 50 -Now ([DateTime]::Parse("22:00")) `
+            -GetRegistryValue { param([string]$Path) $fake.Store[$Path] } `
+            -SetRegistryValue { param([string]$Path, [byte[]]$Value) $fake.Store[$Path] = $Value; $fake.Writes.Add($Path) }
+
+        @($results | Where-Object { $_.Changed }).Count | Should -BeGreaterThan 0
+        $fake.Store.ContainsKey($script:NightLightSettingsPath) | Should -BeTrue
+
+        $written = ConvertFrom-NightLightSettingsPayload -Payload (ConvertFrom-CloudStoreBlob -Blob $fake.Store[$script:NightLightSettingsPath]).Payload
+        $written.ScheduleEnabled | Should -BeTrue
+        $written.SetHoursMode | Should -BeFalse
+        $written.ColorTemperature | Should -Be 3850
+    }
+
+    It "leaves sunset and sunrise unset when creating from scratch" {
+        # Windows computes these from the machine location; seeding them would
+        # only risk storing wrong times.
+        $fake = script:New-FakeNightLightRegistry -SettingsBlob $null -StateBlob $null
+        Set-NightLightConfiguration -Strength 50 -Now ([DateTime]::Parse("22:00")) `
+            -GetRegistryValue { param([string]$Path) $fake.Store[$Path] } `
+            -SetRegistryValue { param([string]$Path, [byte[]]$Value) $fake.Store[$Path] = $Value; $fake.Writes.Add($Path) } | Out-Null
+
+        $written = ConvertFrom-NightLightSettingsPayload -Payload (ConvertFrom-CloudStoreBlob -Blob $fake.Store[$script:NightLightSettingsPath]).Payload
+        $written.SunsetHour | Should -Be 0
+        $written.SunriseHour | Should -Be 0
+
+        # With no solar window known, Night Light must not be forced on.
+        $state = ConvertFrom-NightLightStatePayload -Payload (ConvertFrom-CloudStoreBlob -Blob $fake.Store[$script:NightLightStatePath]).Payload
+        $state.Enabled | Should -BeFalse
+    }
+
+    It "does not throw on a host where Night Light was never initialised" {
+        $fake = script:New-FakeNightLightRegistry -SettingsBlob $null -StateBlob $null
         {
             Set-NightLightConfiguration -Strength 50 `
                 -GetRegistryValue { param([string]$Path) $fake.Store[$Path] } `
                 -SetRegistryValue { param([string]$Path, [byte[]]$Value) $fake.Store[$Path] = $Value }
-        } | Should -Throw "*not initialised*"
+        } | Should -Not -Throw
     }
 }