dotfiles: take the native arm64 rsync now that one is published

[dotfiles] / setup-windows-no-uac.ps1

<#
  setup-windows-no-uac.ps1
  Non-elevated portion of the Windows provisioning. Invoked by setup-windows.bat
  after its winget installs, or run directly from an ordinary (NOT elevated)
  prompt:

      powershell -NoProfile -ExecutionPolicy Bypass -File .\setup-windows-no-uac.ps1

  Run it non-elevated on purpose. Every step here writes per-user state - the
  HKCU PATH and the global .gitconfig under $env:USERPROFILE - so running it
  elevated would configure the *administrator's* profile instead of yours.

  What this installs / configures:
    - WinMerge on the user PATH (x64 only)
    - vswhere.exe on the user PATH: the Visual Studio installer puts it in
      %ProgramFiles(x86)%\Microsoft Visual Studio\Installer, which nothing adds
      to the PATH, so build scripts (and VsDevCmd.bat itself) complain that
      'vswhere.exe' is not recognized
    - BinSkim (binary hardening analyzer) in %LOCALAPPDATA%\Programs\BinSkim,
      on the user PATH (x64 only - the NuGet package publishes win-x64 alone)
    - Global git identity, and core.sshCommand pointed at a Win32-OpenSSH
      client so git shares the Windows ssh-agent: the fast ssh.exe the elevated
      half unpacks beside rsync.exe if it is there, the in-box one otherwise
    - An architecture audit: the real PE machine type of every tool this box
      provisions, resolved the way a shell would. Informational, never fatal.
      Anything running emulated without a listed reason is called out.

  FILL IN $GitUserName / $GitUserEmail below before the first run.

  Steps are independent: one failing warns and the rest still run. The exit code
  is 1 if any step failed, 0 otherwise.
#>

[CmdletBinding()]
param(
    # Skip individual steps. Note that `powershell -File` cannot pass more than
    # one value to an array parameter (neither comma- nor space-separated), so
    # for several, dot-call the script or use -Command:
    #     .\setup-windows-no-uac.ps1 -Skip BinSkim,GitConfig
    #     powershell -File .\setup-windows-no-uac.ps1 -Skip BinSkim
    [ValidateSet('WinMerge', 'VsWhere', 'BinSkim', 'GitConfig', 'NinjaPath', 'LlvmPath', 'ArchAudit')]
    [string[]] $Skip = @()
)

$ErrorActionPreference = 'Stop'

# Host architecture, from the machine environment in the registry. Both of the
# obvious sources report the EMULATED architecture inside an emulated x64
# PowerShell - which is what `powershell` resolves to when launched from an x64
# shell on an ARM64 box. Measured on this machine:
#     [RuntimeInformation]::OSArchitecture      X64     <- wrong
#     $env:PROCESSOR_ARCHITECTURE               AMD64   <- wrong
#     HKLM\...\Session Manager\Environment      ARM64   <- right
# OSArchitecture is documented as the OS's architecture, and on .NET Core it is;
# under .NET Framework on Prism it is not, so it is kept only as a fallback.
# $IsArm64 decides which steps run at all, so this has to be the real one.
$rawArch  = (Get-ItemProperty 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -ErrorAction SilentlyContinue).PROCESSOR_ARCHITECTURE
if (-not $rawArch) { $rawArch = [Runtime.InteropServices.RuntimeInformation]::OSArchitecture.ToString() }
$IsArm64  = ($rawArch -eq 'ARM64')
$HostArch = if ($IsArm64) { 'Arm64' } elseif ($rawArch -eq 'AMD64') { 'X64' } else { $rawArch }

# Steps that do not run on ARM64, with the reason printed in place of the step.
#
# The ARM64 machine is provisioned as a single-compiler build box - see the
# x64-only set in setup-windows.bat - so the packages these three steps wire up
# are not installed there. Skipping the step rather than letting it find nothing
# matters: Install-BinSkim would happily download and PATH the x64 build, and
# Add-LlvmToUserPath is the step that put an emulated-adjacent toolchain on the
# PATH ahead of MSVC in the first place.
#
# -Skip still works on top of this; it can only subtract.
$Arm64Dropped = [ordered]@{
    WinMerge = 'not installed on ARM64 - the only build an unelevated winget can fetch is the emulated x64 one'
    BinSkim  = 'not installed on ARM64 - the NuGet package publishes win-x64 only'
    LlvmPath = 'not installed on ARM64 - this box carries MSVC alone'
}

# --- Global git identity: FILL THESE IN BEFORE RUNNING ---
# Left empty, Set-GlobalGitConfig skips the identity and says so, rather than
# stamping a placeholder onto your commits. Leaving them empty is a legitimate
# choice - it keeps your identity per-repository. core.sshCommand is set either
# way, so the ssh side works regardless.
$GitUserName  = ''   # e.g. 'Ada Lovelace'
$GitUserEmail = ''   # e.g. 'ada@example.com'

# BinSkim's win-x64 build, from the NuGet flat container.
$BinSkimPackage = 'microsoft.codeanalysis.binskim'
$BinSkimDir     = Join-Path $env:LOCALAPPDATA 'Programs\BinSkim'

# Where the elevated half puts rsync.exe and the ssh.exe it ships with. Only
# read here, to prefer that ssh.exe for git - keep it in step with $RsyncDir in
# setup-windows-with-uac.ps1 if you move the install.
$RsyncDir = 'C:\Tools\rsync'

function Write-Step([string]$Msg) {
    Write-Host "`n==> $Msg" -ForegroundColor Cyan
}

function Add-ToUserPath {
    # HKCU PATH, not the process PATH: this must outlive the script. Idempotent,
    # and re-applied on every run so an entry lost to an unrelated PATH edit is
    # repaired without re-doing the install that put it there.
    #
    # -Prepend puts the directory FIRST and moves it there if it is already
    # present further down, which is the difference between "on the PATH" and
    # "the one that wins". Only for entries where that matters; appending is the
    # polite default and stays the default.
    param(
        [string] $Dir,
        [switch] $Prepend
    )
    $user = [Environment]::GetEnvironmentVariable('Path', 'User')
    if (-not $user) { $user = '' }
    # Compare trailing-backslash-insensitively: C:\x and C:\x\ are the same
    # directory, and adding a second spelling of one is just noise.
    $norm    = { param($s) $s.Trim().TrimEnd('\') }
    $entries = @($user -split ';' | Where-Object { $_.Trim() })
    $already = $entries | Where-Object { (& $norm $_) -eq (& $norm $Dir) }

    if (-not $Prepend) {
        if ($already) { Write-Host "    $Dir already in user PATH."; return }
        $new = if ($user.Trim()) { $user.TrimEnd(';') + ';' + $Dir } else { $Dir }
        [Environment]::SetEnvironmentVariable('Path', $new, 'User')
        Write-Host "    Added $Dir to user PATH (restart your shell to pick it up)."
        return
    }

    if ($already -and (& $norm $entries[0]) -eq (& $norm $Dir)) {
        Write-Host "    $Dir already first in user PATH."
        return
    }
    $rest = $entries | Where-Object { (& $norm $_) -ne (& $norm $Dir) }
    [Environment]::SetEnvironmentVariable('Path', (@($Dir) + $rest) -join ';', 'User')
    if ($already) {
        Write-Host "    Moved $Dir to the front of the user PATH (restart your shell to pick it up)."
    } else {
        Write-Host "    Added $Dir to the front of the user PATH (restart your shell to pick it up)."
    }
}

function Add-WinMergeToUserPath {
    Write-Step 'WinMerge on the user PATH'
    $candidates = @(
        (Join-Path $env:ProgramFiles 'WinMerge'),
        (Join-Path ${env:ProgramFiles(x86)} 'WinMerge'),
        (Join-Path $env:LOCALAPPDATA 'Programs\WinMerge')
    )
    $dir = $candidates |
           Where-Object { Test-Path (Join-Path $_ 'WinMergeU.exe') } |
           Select-Object -First 1
    if (-not $dir) {
        Write-Warning 'WinMerge not found; user PATH unchanged.'
        return
    }
    Add-ToUserPath $dir
}

function Add-VsWhereToUserPath {
    # vswhere.exe is how scripts locate Visual Studio (MSBuild, VsDevCmd.bat,
    # the Windows SDK), and the VS installer drops it in a fixed directory that
    # is never on the PATH. VsDevCmd.bat itself prints "'vswhere.exe' is not
    # recognized" on every run without it. The directory is fixed by contract
    # (32-bit Program Files, no version in the path), so there is nothing to
    # search for: if it is missing, Visual Studio is not installed.
    Write-Step 'vswhere on the user PATH'
    $dir = Join-Path ${env:ProgramFiles(x86)} 'Microsoft Visual Studio\Installer'
    if (-not (Test-Path (Join-Path $dir 'vswhere.exe'))) {
        Write-Warning "vswhere.exe not found in $dir (no Visual Studio installer present); user PATH unchanged."
        return
    }
    Add-ToUserPath $dir
}

function Install-BinSkim {
    # BinSkim checks the exact mitigations the native project enables in
    # CMakeLists.txt (CFG/XFG, CET, ASLR/HighEntropyVA, DEP, /GS, stack cookies,
    # DEPENDENTLOADFLAG, ...). The NuGet package ships a self-contained build, so
    # this needs no .NET SDK/runtime: the .nupkg is a zip - extract the tool
    # folder for this architecture and put it on the PATH. After restarting the
    # shell:
    #     binskim analyze path\to\your.exe
    #
    # ARCHITECTURE. The package currently publishes win-x64 only (its other RIDs
    # are linux-x64, linux-arm64 and osx-x64) - there is no win-arm64 build. So on
    # ARM64 this installs the x64 tool and it runs under emulation. That is a
    # slowdown and nothing more: BinSkim READS PE headers and load configs, so the
    # architecture of the binaries it analyses is independent of its own - an
    # emulated x64 BinSkim checks ARM64 binaries perfectly well. $BinSkimRids is
    # ordered preference, so if a win-arm64 build ever ships, an ARM64 box picks
    # it up with no further change here.
    #
    # VERSION CHECK FIRST. The .nupkg is a large download (well over 100 MB), so
    # ask NuGet what the newest stable version is BEFORE fetching anything, and
    # skip the download entirely when the installed copy already matches.
    # Re-provisioning an up-to-date box should not pay for it.
    #
    # The installed version is recorded in nupkg-version.txt next to the tool.
    # For a copy installed before that marker existed, fall back to BinSkim.exe's
    # own ProductVersion; either way the marker is (re)written once we know the
    # version, so the fallback runs at most once per install. The
    # flat-container URL pins the exact version we checked,
    # unlike the v2 /package/<id> endpoint, which just redirects to whatever is
    # newest at the moment of the request.
    Write-Step 'BinSkim'
    [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12

    $exe    = Join-Path $BinSkimDir 'BinSkim.exe'
    $marker = Join-Path $BinSkimDir 'nupkg-version.txt'

    $have = $null
    if (Test-Path $exe) {
        if (Test-Path $marker) {
            $have = (Get-Content $marker -Raw).Trim()
        } else {
            $pv = (Get-Item $exe).VersionInfo.ProductVersion
            # NuGet versions carry no build metadata; ProductVersion may ("1.2.3+sha").
            if ($pv) { $have = $pv.Split('+')[0].Trim() }
        }
    }

    $latest = $null
    try {
        $index = Invoke-RestMethod -UseBasicParsing `
            -Uri "https://api.nuget.org/v3-flatcontainer/$BinSkimPackage/index.json"
        # Versions come back oldest-first; '-' marks a prerelease.
        $latest = $index.versions | Where-Object { $_ -notmatch '-' } | Select-Object -Last 1
    } catch {
        Write-Warning "BinSkim version check failed: $($_.Exception.Message)"
    }

    if (-not $latest) {
        if (-not $have) {
            Write-Warning 'BinSkim not installed and NuGet unreachable; skipping.'
            return
        }
        Write-Host "    BinSkim $have kept (could not reach NuGet to check for a newer one)."
    } elseif ($have -and ($have -eq $latest -or $have -eq "$latest.0")) {
        Write-Host "    BinSkim $have is already the newest stable release; skipping download."
        # Records what the ProductVersion fallback just worked out, so the next
        # run reads the marker instead of re-deriving it.
        Set-Content -Path $marker -Value $latest -Encoding ascii
    } else {
        if ($have) {
            Write-Host "    BinSkim $have -> $latest; downloading."
        } else {
            Write-Host "    BinSkim $latest; downloading."
        }
        $tmp = Join-Path $env:TEMP ('binskim_' + [guid]::NewGuid().ToString('N'))
        New-Item -ItemType Directory -Force -Path $tmp | Out-Null
        try {
            $zip = Join-Path $tmp 'binskim.zip'
            Invoke-WebRequest -UseBasicParsing -OutFile $zip `
                -Uri "https://api.nuget.org/v3-flatcontainer/$BinSkimPackage/$latest/$BinSkimPackage.$latest.nupkg"
            Expand-Archive -Path $zip -DestinationPath $tmp -Force

            # Native RID first, emulatable one second. Matched against the path
            # so the newest matching tools\<tfm>\<rid>\ folder wins, as before.
            $BinSkimRids = if ($IsArm64) { @('win-arm64', 'win-x64') } else { @('win-x64') }
            $src = $null
            $allExes = Get-ChildItem -Path $tmp -Recurse -Filter 'BinSkim.exe'
            foreach ($rid in $BinSkimRids) {
                $src = $allExes | Where-Object { $_.FullName -match [regex]::Escape($rid) } |
                       Sort-Object FullName | Select-Object -Last 1
                if ($src) {
                    if ($rid -ne $BinSkimRids[0]) {
                        Write-Host "    No $($BinSkimRids[0]) build in the package; using $rid (runs under emulation)." -ForegroundColor Yellow
                    }
                    break
                }
            }
            if (-not $src) { throw "BinSkim.exe ($($BinSkimRids -join ' / ')) not found in package." }

            # Replace wholesale rather than merging over the old tree, so files
            # dropped between releases don't linger.
            if (Test-Path $BinSkimDir) { Remove-Item -Recurse -Force $BinSkimDir }
            New-Item -ItemType Directory -Force -Path $BinSkimDir | Out-Null
            Copy-Item -Path (Join-Path $src.Directory.FullName '*') `
                      -Destination $BinSkimDir -Recurse -Force
            # Written last: the marker must only claim a version that fully landed.
            Set-Content -Path $marker -Value $latest -Encoding ascii
            Write-Host "    BinSkim $latest installed to $BinSkimDir"
        } finally {
            Remove-Item -Recurse -Force $tmp -ErrorAction SilentlyContinue
        }
    }

    Add-ToUserPath $BinSkimDir
}

function Get-GitPath {
    # winget installed Git moments ago, but this process inherited its PATH
    # before that happened, so Get-Command can miss it on a first run. Prefer a
    # git already on PATH, then the usual install roots.
    $onPath = Get-Command git.exe -ErrorAction SilentlyContinue
    if ($onPath) { return $onPath.Source }
    $roots = @(
        (Join-Path $env:ProgramFiles 'Git\cmd\git.exe'),
        (Join-Path ${env:ProgramFiles(x86)} 'Git\cmd\git.exe'),
        (Join-Path $env:LOCALAPPDATA 'Programs\Git\cmd\git.exe')
    )
    return $roots | Where-Object { Test-Path $_ } | Select-Object -First 1
}

function Set-GlobalGitConfig {
    Write-Step 'Global git config'
    $git = Get-GitPath
    if (-not $git) {
        Write-Warning 'git.exe not found; skipping global git config.'
        return
    }
    Write-Host "    using $git"

    if (-not $GitUserName -or -not $GitUserEmail) {
        Write-Host '    Identity not configured; leaving user.name / user.email alone.' -ForegroundColor Yellow
        Write-Host '    Fill in $GitUserName / $GitUserEmail at the top of this script, or set' -ForegroundColor Yellow
        Write-Host '    your identity per-repository.' -ForegroundColor Yellow
    } else {
        & $git config --global user.name  $GitUserName
        & $git config --global user.email $GitUserEmail
        Write-Host "    identity: $GitUserName <$GitUserEmail>"
    }

    # --- Make git use a Win32-OpenSSH client ---
    # Git for Windows ships its own MSYS2 ssh.exe and prefers it, and that client
    # cannot reach the Windows ssh-agent service that the elevated half enables:
    # Win32-OpenSSH publishes the agent on a named pipe the MSYS2 build does not
    # speak. So keys added with `ssh-add` from PowerShell stay invisible to git,
    # and a push falls back to hunting for a key file and prompting for its
    # passphrase. Pointing core.sshCommand at a Win32-OpenSSH ssh.exe gives git
    # the same client, the same agent, and the same %USERPROFILE%\.ssh\config as
    # `ssh` from an ordinary shell.
    #
    # Two of those are on the box, and the one beside rsync.exe is preferred.
    # It is the same client from the same source, with the same ~/.ssh, agent
    # and known_hosts, built with a pump on its stdin: the in-box one reads
    # stdin 3KB at a time, which holds anything git PUSHES to ~17MB/s however
    # fast the link is. It only exists once the elevated half has run, so the
    # in-box client stays the fallback - and on a first provisioning run from
    # setup-windows.bat it is the elevated half that runs first, so the fast one
    # is normally already there.
    #
    # ON ARM64 the preference is the same but the trade is different: that build
    # is published for x64 only, so it is the EMULATED client being preferred over
    # a native ARM64 one. It is still the right pick when it runs - a push is
    # bounded by the socket, not by emulated CPU, so lifting the 3KB stdin cap
    # wins by far more than emulation costs - but it may well not run at all,
    # because it links against a System32 libcrypto.dll that is an ARM64 binary
    # here. That is exactly why candidates are tried by RUNNING them below rather
    # than by Test-Path, and why the elevated half deletes that ssh.exe outright
    # when it will not start. Either way this lands on a working client.
    $sshCandidates = @(
        (Join-Path $RsyncDir 'ssh.exe'),
        (Join-Path $env:WINDIR 'System32\OpenSSH\ssh.exe')
    )
    $winSsh = $null
    foreach ($cand in $sshCandidates) {
        if (-not (Test-Path $cand)) { continue }
        # Run it, rather than just believing the file is there: the build beside
        # rsync.exe links against the libcrypto.dll the OpenSSH Client capability
        # puts in System32, and without that capability it is a binary that does
        # not start. Better to find that out here than on the next `git push`.
        #
        # EAP back to Continue for the call: ssh -V writes its version to
        # STDERR, and with $ErrorActionPreference = 'Stop' a native command's
        # stderr becomes a terminating RemoteException - so the working client
        # would look like the broken one.
        $prevEap = $ErrorActionPreference
        $ErrorActionPreference = 'Continue'
        $version = $null
        # Clear the exit code first, explicitly at global scope. An exe that
        # cannot start at all - the missing-libcrypto case - throws here without
        # ever setting one, and the stale 0 from the last native command that DID
        # run would otherwise read as success. $global: because a bare assignment
        # would make a local copy that the native call then does not update.
        $global:LASTEXITCODE = $null
        try { $version = (& $cand -V 2>&1 | Select-Object -First 1) } catch { }
        finally { $ErrorActionPreference = $prevEap }
        if ($LASTEXITCODE -eq 0) { $winSsh = $cand; break }
        $why = if ($null -eq $LASTEXITCODE) { 'it would not start' } else { "exit $LASTEXITCODE" }
        Write-Warning "$cand did not run ($why)$(if ($version) { ": $version" })"
    }
    if (-not $winSsh) {
        Write-Warning "No working Win32-OpenSSH client found (looked in $($sshCandidates -join ', ')). Add the 'OpenSSH Client' optional feature and re-run; until then git uses its own bundled ssh.exe, which cannot see keys held by the Windows ssh-agent service."
        return
    }
    # Forward slashes on purpose: git parses core.sshCommand with shell quoting
    # rules, in which a backslash is an escape character.
    $value = $winSsh -replace '\\', '/'
    & $git config --global core.sshCommand $value
    Write-Host "    core.sshCommand: $value"
    Write-Host "    $version"
}

function Set-NativeNinjaFirst {
    # Make the native ninja.exe the one that wins, including inside a Visual
    # Studio Developer Command Prompt.
    #
    # WHY THIS IS INSURANCE RATHER THAN THE FIX. VS ships an x64 ninja.exe even on
    # ARM64 and puts it on the PATH from
    # Common7\Tools\vsdevcmd\ext\cmake.bat, which does:
    #     set "PATH=%PATH%;...\CMake\bin;...\CMake\Ninja"
    # That APPENDS - the VS directories land at the very end of the composed
    # PATH, behind every machine and user entry. So a native ninja installed
    # anywhere on the user PATH already beats it, and measurement on an ARM64 box
    # confirms it does. (An earlier revision of this script claimed VsDevCmd
    # prepends and that the VS copy therefore always won; that was wrong.)
    #
    # It is still worth pinning the order explicitly: winget appends its package
    # directory to the user PATH, so the margin depends on nothing more than two
    # append orders staying as they are, in a file Microsoft owns and revises.
    # Putting the directory first costs nothing and removes the dependency.
    #
    # Ninja is worth this attention where a one-off tool would not be: it is
    # re-invoked for every edge in the build graph, so it is the one place an
    # emulated binary is paid over and over rather than once.
    Write-Step 'Native ninja ahead of the Visual Studio copy'

    $candidates = @()
    $candidates += Get-ChildItem (Join-Path $env:LOCALAPPDATA 'Microsoft\WinGet\Packages') `
                       -Filter 'ninja.exe' -Recurse -Depth 2 -ErrorAction SilentlyContinue |
                   ForEach-Object { $_.FullName }
    $candidates += @(
        (Join-Path $env:ProgramFiles 'Ninja\ninja.exe')
        (Join-Path $env:LOCALAPPDATA 'Programs\Ninja\ninja.exe')
    )
    # A ninja already on the PATH counts too - but only if it is not the VS one,
    # which is the binary this step exists to get out in front of.
    $onPath = (Get-Command ninja.exe -ErrorAction SilentlyContinue | Select-Object -First 1).Source
    if ($onPath -and $onPath -notmatch 'CommonExtensions\\Microsoft\\CMake') { $candidates += $onPath }

    $native = $null
    foreach ($c in ($candidates | Where-Object { $_ -and (Test-Path $_) } | Select-Object -Unique)) {
        $m = Get-PEMachine $c
        if ($m -eq $(if ($IsArm64) { 'ARM64' } else { 'x64' })) { $native = $c; break }
    }

    if (-not $native) {
        Write-Warning 'No native ninja.exe found. Install it with: winget install Ninja-build.Ninja'
        Write-Warning 'Until then a build using the Ninja generator gets the x64 ninja Visual Studio bundles.'
        return
    }

    Write-Host "    native ninja: $native ($(Get-PEMachine $native))"
    Add-ToUserPath (Split-Path $native -Parent) -Prepend
}

function Add-LlvmToUserPath {
    # Put the upstream LLVM's bin directory on the user PATH.
    #
    # Two reasons this needs a step rather than trusting the installer:
    #
    # 1. WHERE IT LANDS. LLVM's NSIS installer targets %ProgramFiles%\LLVM, and
    #    when it cannot write there - a standard user, no elevation - it does not
    #    fail. It silently falls back to a per-user directory, observed as
    #    %USERPROFILE%\Documents\LLVM, and winget still reports "Successfully
    #    installed". So the package is registered, the compiler is genuinely
    #    there and native, and nothing can find it.
    # 2. PATH. The installer's "add to PATH" option is not taken in a silent
    #    install, so clang-cl is not a command afterwards either way.
    #
    # Appended, not prepended: this is a second compiler kept deliberately
    # alongside MSVC, and it should not quietly win a `clang-cl` that some script
    # meant for Visual Studio's copy. Note VS does NOT put its own
    # VC\Tools\Llvm on the PATH (its clang-cl is reached through CMake's
    # -T ClangCL), so there is no collision to lose here.
    Write-Step 'Upstream LLVM on the user PATH'
    $candidates = @(
        (Join-Path $env:ProgramFiles 'LLVM\bin')
        (Join-Path ${env:ProgramFiles(x86)} 'LLVM\bin')
        (Join-Path $env:LOCALAPPDATA 'Programs\LLVM\bin')
        (Join-Path ([Environment]::GetFolderPath('MyDocuments')) 'LLVM\bin')
        (Join-Path $env:USERPROFILE 'Documents\LLVM\bin')
    )
    $dir = $candidates | Where-Object { Test-Path (Join-Path $_ 'clang-cl.exe') } | Select-Object -First 1
    if (-not $dir) {
        Write-Host '    Not installed (winget install LLVM.LLVM); Visual Studio''s own clang-cl is unaffected.' -ForegroundColor DarkGray
        return
    }
    $exe  = Join-Path $dir 'clang-cl.exe'
    $mach = Get-PEMachine $exe
    Write-Host "    $exe ($mach)"
    if ($IsArm64 -and $mach -ne 'ARM64') {
        Write-Warning "This LLVM is $mach, not ARM64. winget install LLVM.LLVM should resolve to the -woa64 build on this host."
    }
    if ($dir -notmatch [regex]::Escape($env:ProgramFiles)) {
        Write-Host '    Note: not under Program Files - the installer fell back to a per-user' -ForegroundColor Yellow
        Write-Host '    location because it could not write there. Re-run elevated for a machine-wide install.' -ForegroundColor Yellow
    }
    Add-ToUserPath $dir
}

function Get-PEMachine {
    # Architecture of a PE, read straight from the COFF header: the 2 bytes at
    # the e_lfanew offset + 4. Cheap, and it answers the only question that
    # matters here - would this exe run natively, or through emulation?
    #
    # Deliberately NOT Get-Command's .FileVersionInfo or the package metadata:
    # a multi-architecture package (Sysinternals) ships every build in one zip
    # under different names, and an installer's own metadata says nothing about
    # which binary got laid down. The file itself cannot be wrong.
    param([string]$Path)
    if (-not (Test-Path $Path)) { return $null }
    try {
        $fs = [IO.File]::OpenRead($Path)
        $br = New-Object IO.BinaryReader($fs)
        try {
            $fs.Seek(0x3c, 'Begin') | Out-Null
            $pe = $br.ReadInt32()
            if ($pe -le 0 -or $pe -gt ($fs.Length - 6)) { return 'not-PE' }
            $fs.Seek($pe + 4, 'Begin') | Out-Null
            switch ($br.ReadUInt16()) {
                0x8664  { 'x64' }
                0xAA64  { 'ARM64' }
                0x014c  { 'x86' }
                0x01c4  { 'ARM32' }
                default { 'unknown' }
            }
        } finally { $br.Close(); $fs.Close() }
    } catch { $null }
}

function Invoke-ArchAudit {
    # Report the actual architecture of the tools this box provisions, resolved
    # the way a shell would (PATH first, then the usual install roots), so what
    # is printed is what you would really run.
    #
    # This exists because "winget installed it" does not mean "you got the native
    # build", and the gap is not always where you would guess - Visual Studio's
    # own bundled ninja.exe is x64 even on an ARM64 host. A per-run audit turns
    # that from something you trip over into something the log tells you.
    #
    # Purely informational: it never fails the run. On x64 everything is expected
    # to be x64 and the output is dull; the value is on ARM64, where each line is
    # either native or a known, listed exception.
    Write-Step "Architecture audit (host: $HostArch)"

    # Resolve against the PATH a NEW shell would get, not this process's.
    #
    # The steps above write the HKCU PATH, which a running process never sees -
    # so auditing $env:PATH would report the state from before this script ran and
    # warn about a problem it had just fixed. Compose machine + user from the
    # registry (the order Windows itself uses), then append anything extra this
    # process happens to carry: that tail is where a Developer Command Prompt's VS
    # directories live, and keeping it last mirrors how VsDevCmd appends them.
    $composed = @()
    foreach ($scope in 'Machine', 'User') {
        $v = [Environment]::GetEnvironmentVariable('Path', $scope)
        if ($v) { $composed += ($v -split ';' | Where-Object { $_.Trim() }) }
    }
    $composed += ($env:PATH -split ';' | Where-Object { $_.Trim() })
    $seen = New-Object 'System.Collections.Generic.HashSet[string]' ([StringComparer]::OrdinalIgnoreCase)
    $searchPath = @($composed | Where-Object { $seen.Add($_.Trim().TrimEnd('\')) })

    function Resolve-OnPath([string]$Exe) {
        foreach ($d in $searchPath) {
            $p = Join-Path $d $Exe
            if (Test-Path $p -PathType Leaf) { return $p }
        }
        return $null
    }

    # Tools with no native ARM64 build available anywhere, with the reason. These
    # print as expected rather than as problems - see the README's ARM64 section.
    #
    # Shorter than it was: BinSkim, OpenCppCoverage and NASM used to be listed
    # here as accepted emulation, and are now simply not installed on ARM64. That
    # is the whole shape of the change - the exceptions that were tolerable one at
    # a time added up to a VM full of x64 binaries.
    #
    # rsync came off this list when the release started publishing an arm64
    # asset. An x64 rsync.exe on an ARM64 box is now a leftover from a run before
    # that, not an accepted exception, so it warns and gets a remedy below.
    $KnownEmulated = @{
        'iperf3.exe'           = 'no ARM64 build published; network-bound anyway'
        'py.exe'               = 'python.org ships the launcher shim as x86; it execs the native python.exe'
        'vswhere.exe'          = 'Microsoft ships x86 only; runs once per script'
    }

    # Fixable cases: a native build DOES exist, something just resolved ahead of
    # it. Printed with the finding so the log carries the remedy, not just the
    # complaint.
    #
    # ninja is the one that actually bites: Visual Studio bundles an x64 ninja.exe
    # even on ARM64, and it is re-invoked for every edge in the build graph, so
    # an emulated one is paid over and over rather than once. The NinjaPath step
    # puts the native copy first; this is the check that it worked.
    #
    # Only two left, and both are for tools ARM64 still installs. The clang-cl and
    # WinMerge remedies were removed with their rows: advising an install that the
    # x64-only set has just declined to do would be the audit arguing with the
    # provisioning.
    $Remedies = @{
        'ninja.exe' = 'Visual Studio bundles an x64 ninja. Install the native one (winget install Ninja-build.Ninja) and re-run - the NinjaPath step puts its directory at the front of the user PATH.'
        'cmake.exe' = 'Install the native build with: winget install Kitware.CMake (its MSI is machine-scope, so it needs an administrator).'
        'rsync.exe' = 'Left over from before the release published an arm64 asset. Re-run setup-windows-with-uac.ps1 as an administrator to replace it, and the ARM64 ssh.exe beside it, with the native build.'
    }

    $vs = $null
    $vsWhereExe = Join-Path ${env:ProgramFiles(x86)} 'Microsoft Visual Studio\Installer\vswhere.exe'
    if (Test-Path $vsWhereExe) {
        $vs = & $vsWhereExe -products '*' -property installationPath -format value | Select-Object -First 1
    }

    # name -> extra candidate paths searched when the name is not on the PATH.
    $targets = [ordered]@{
        'git.exe'             = @("$env:LOCALAPPDATA\Programs\Git\cmd\git.exe", (Join-Path $env:ProgramFiles 'Git\cmd\git.exe'))
        'python.exe'          = @()
        # Both homes of the launcher: C:\Windows for an all-users install, the
        # per-user Launcher directory otherwise. Often neither - it is a separate
        # component from the interpreter, and "- not installed" here next to a
        # native python.exe is the normal result of an unelevated Python install.
        'py.exe'              = @("$env:WINDIR\py.exe", "$env:LOCALAPPDATA\Programs\Python\Launcher\py.exe")
        'pwsh.exe'            = @()
        'cmake.exe'           = @((Join-Path $env:ProgramFiles 'CMake\bin\cmake.exe'))
        'ninja.exe'           = @()
        # Upstream LLVM. The Documents path is not a typo - see Add-LlvmToUserPath
        # for why an unelevated install lands there.
        'clang-cl.exe'        = @(
            (Join-Path $env:ProgramFiles 'LLVM\bin\clang-cl.exe')
            (Join-Path $env:LOCALAPPDATA 'Programs\LLVM\bin\clang-cl.exe')
            (Join-Path ([Environment]::GetFolderPath('MyDocuments')) 'LLVM\bin\clang-cl.exe')
        )
        'dotnet.exe'          = @((Join-Path $env:ProgramFiles 'dotnet\dotnet.exe'))
        'WinMergeU.exe'       = @((Join-Path $env:ProgramFiles 'WinMerge\WinMergeU.exe'), (Join-Path ${env:ProgramFiles(x86)} 'WinMerge\WinMergeU.exe'))
        'BinSkim.exe'         = @((Join-Path $BinSkimDir 'BinSkim.exe'))
        'rsync.exe'           = @((Join-Path $RsyncDir 'rsync.exe'))
        'ssh.exe'             = @((Join-Path $env:WINDIR 'System32\OpenSSH\ssh.exe'))
        'nasm.exe'            = @()
        'iperf3.exe'          = @()
        'OpenCppCoverage.exe' = @((Join-Path $env:ProgramFiles 'OpenCppCoverage\OpenCppCoverage.exe'), (Join-Path ${env:ProgramFiles(x86)} 'OpenCppCoverage\OpenCppCoverage.exe'))
        'vswhere.exe'         = @($vsWhereExe)
        'xperf.exe'           = @((Join-Path ${env:ProgramFiles(x86)} 'Windows Kits\10\Windows Performance Toolkit\xperf.exe'))
    }
    if ($vs) {
        $targets['MSBuild.exe'] = @((Join-Path $vs 'MSBuild\Current\Bin\arm64\MSBuild.exe'), (Join-Path $vs 'MSBuild\Current\Bin\MSBuild.exe'))
        # The MSVC and VS-Clang compilers, under whichever MSVC version is present.
        $msvc = Get-ChildItem (Join-Path $vs 'VC\Tools\MSVC') -Directory -ErrorAction SilentlyContinue |
                Sort-Object Name | Select-Object -Last 1
        if ($msvc) {
            $hostDir = if ($IsArm64) { 'Hostarm64\arm64' } else { 'Hostx64\x64' }
            $targets['cl.exe (MSVC)'] = @((Join-Path $msvc.FullName "bin\$hostDir\cl.exe"))
        }
        $llvmHost = if ($IsArm64) { 'ARM64\bin' } else { 'x64\bin' }
        $targets['clang-cl.exe (VS)'] = @((Join-Path $vs "VC\Tools\Llvm\$llvmHost\clang-cl.exe"))
    }

    # Tools this box does not provision on ARM64. Dropped from the audit rather
    # than left to print "- not installed", because that line reads as a gap in
    # the provisioning when it is the provisioning working as intended - and a
    # dull audit is one you keep reading.
    #
    # The rows survive on x64, where all of these are installed and expected.
    # Anything still on disk from before the split shows up in the winget list,
    # not here.
    if ($IsArm64) {
        foreach ($gone in 'WinMergeU.exe', 'BinSkim.exe', 'nasm.exe',
                          'OpenCppCoverage.exe', 'clang-cl.exe', 'clang-cl.exe (VS)') {
            $targets.Remove($gone)
        }
    }

    $native = if ($IsArm64) { 'ARM64' } else { 'x64' }
    $unexpected = @()
    foreach ($name in $targets.Keys) {
        # A LABELLED entry - "clang-cl.exe (VS)" - names one specific copy, so it
        # is resolved ONLY from its explicit candidates. Falling back to the PATH
        # there would silently answer with a different installation of the same
        # tool: with upstream LLVM on the PATH, the "(VS)" row reported the
        # upstream compiler and so claimed Visual Studio's was present when it was
        # not. Unlabelled entries still resolve PATH-first, because for those the
        # question is which binary a build would actually invoke.
        $exe      = ($name -split ' ')[0]
        $isPinned = $name -ne $exe
        if ($isPinned) {
            $path = $targets[$name] | Where-Object { $_ -and (Test-Path $_) } | Select-Object -First 1
        } else {
            $path = Resolve-OnPath $exe
            if (-not $path) { $path = $targets[$name] | Where-Object { $_ -and (Test-Path $_) } | Select-Object -First 1 }
        }
        if (-not $path) { Write-Host ("    {0,-22} {1}" -f $name, '- not installed') -ForegroundColor DarkGray; continue }

        $mach = Get-PEMachine $path
        if (-not $mach) { continue }
        if ($mach -eq $native) {
            Write-Host ("    {0,-22} {1,-6} native" -f $name, $mach) -ForegroundColor Green
        } elseif ($KnownEmulated.ContainsKey($exe)) {
            Write-Host ("    {0,-22} {1,-6} expected: {2}" -f $name, $mach, $KnownEmulated[$exe]) -ForegroundColor DarkGray
        } else {
            Write-Host ("    {0,-22} {1,-6} NOT NATIVE - $path" -f $name, $mach) -ForegroundColor Yellow
            if ($Remedies.ContainsKey($exe)) {
                Write-Host ("    {0,-22} {1,-6} -> {2}" -f '', '', $Remedies[$exe]) -ForegroundColor Yellow
            }
            $unexpected += "$name ($mach)"
        }
    }

    if ($unexpected) {
        Write-Warning "Running under emulation with no listed reason: $($unexpected -join ', ')."
        Write-Warning 'If a native build exists, prefer it (see the -> lines above); otherwise add it to $KnownEmulated with the reason.'
    } else {
        Write-Host '    Everything resolved to a native build, or to a listed exception.' -ForegroundColor Green
    }
}

# ---------------------------------------------------------------------------
# Main
# ---------------------------------------------------------------------------
Write-Host "Host architecture: $HostArch" -ForegroundColor Cyan

if (([Security.Principal.WindowsPrincipal][Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole(
        [Security.Principal.WindowsBuiltInRole]::Administrator)) {
    Write-Warning 'Running elevated. The user PATH and .gitconfig changes below will apply to the administrator profile, not yours.'
}

$steps = [ordered]@{
    WinMerge  = { Add-WinMergeToUserPath }
    VsWhere   = { Add-VsWhereToUserPath }
    BinSkim   = { Install-BinSkim }
    GitConfig = { Set-GlobalGitConfig }
    NinjaPath = { Set-NativeNinjaFirst }
    LlvmPath  = { Add-LlvmToUserPath }
    # Last on purpose: it reports on what the steps above (and the winget installs
    # in setup-windows.bat) actually put on the box.
    ArchAudit = { Invoke-ArchAudit }
}

$failed = @()
foreach ($name in $steps.Keys) {
    if ($Skip -contains $name) {
        Write-Host "`n==> $name (skipped)" -ForegroundColor DarkGray
        continue
    }
    if ($IsArm64 -and $Arm64Dropped.Contains($name)) {
        Write-Host "`n==> $name (skipped: $($Arm64Dropped[$name]))" -ForegroundColor DarkGray
        continue
    }
    try {
        & $steps[$name]
    } catch {
        # One broken step must not cost the others. Collect and report at the end.
        Write-Warning "$name failed: $($_.Exception.Message)"
        $failed += $name
    }
}

if ($failed) {
    Write-Host "`n[setup-windows-no-uac] FAILED: $($failed -join ', ')" -ForegroundColor Red
    exit 1
}
Write-Host "`n[setup-windows-no-uac] All steps completed." -ForegroundColor Green
exit 0