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Use architecture-appropriate desktop MSBuild and remove Prefer64bit switch #17026

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Use architecture-appropriate desktop MSBuild and remove Prefer64bit switch #17026

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Initial plan
Copilot Jun 18, 2026
4a70bed
Default desktop MSBuild to process-arch (amd64/arm64) binary
Copilot Jun 18, 2026
a45b70c
Remove Prefer64bit switch; always select arch-appropriate MSBuild
Copilot Jun 18, 2026
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30 changes: 25 additions & 5 deletions eng/common/tools.ps1
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Original file line number Diff line number Diff line change
Expand Up @@ -432,11 +432,31 @@ function InitializeVisualStudioMSBuild([object]$vsRequirements = $null) {
$msbuildVersionDir = if ([int]$vsMajorVersion -lt 16) { "$vsMajorVersion.0" } else { "Current" }

$local:BinFolder = Join-Path $vsInstallDir "MSBuild\$msbuildVersionDir\Bin"
$local:Prefer64bit = if (Get-Member -InputObject $vsRequirements -Name 'Prefer64bit') { $vsRequirements.Prefer64bit } else { $false }
if ($local:Prefer64bit -and (Test-Path(Join-Path $local:BinFolder "amd64"))) {
$global:_MSBuildExe = Join-Path $local:BinFolder "amd64\msbuild.exe"
} else {
$global:_MSBuildExe = Join-Path $local:BinFolder "msbuild.exe"

# Use the MSBuild matching the host's process architecture (e.g. amd64 or arm64),
# falling back to the 32-bit MSBuild in the root Bin folder when no matching subfolder exists.

# Determine the architecture of the current process, accounting for a 32-bit process
# running on a 64-bit OS (PROCESSOR_ARCHITEW6432 holds the real machine architecture).
$local:ProcessArchitecture = $env:PROCESSOR_ARCHITECTURE
if (($local:ProcessArchitecture -eq 'x86') -and ($env:PROCESSOR_ARCHITEW6432)) {
$local:ProcessArchitecture = $env:PROCESSOR_ARCHITEW6432
}

# Map the architecture to the corresponding MSBuild subfolder. The 32-bit MSBuild lives in the
# root Bin folder, so x86 maps to an empty subfolder.
$local:MSBuildArchSubFolder = switch ($local:ProcessArchitecture) {
'AMD64' { 'amd64' }
'ARM64' { 'arm64' }
default { '' }
}

$global:_MSBuildExe = Join-Path $local:BinFolder "msbuild.exe"
if ($local:MSBuildArchSubFolder) {
$local:ArchMSBuildExe = Join-Path $local:BinFolder (Join-Path $local:MSBuildArchSubFolder "msbuild.exe")
if (Test-Path $local:ArchMSBuildExe) {
$global:_MSBuildExe = $local:ArchMSBuildExe
}
}

return $global:_MSBuildExe
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