[bootstrap] Build vcpkg in a clean environment

scripts/VcpkgPowershellUtils-ClearEnvironment.ps1

@@ -0,0 +1,52 @@
+# Capture environment variables for the System and User. Also add some special/built-in variables.
+# These will be used to synthesize a clean environment
+$specialEnvironmentMap = @{ "SystemDrive"=$env:SystemDrive; "SystemRoot"=$env:SystemRoot; "UserProfile"=$env:UserProfile } # These are built-in and not set in the registry
+$machineEnvironmentMap = [Environment]::GetEnvironmentVariables('Machine') # HKEY_CURRENT_USER\Environment
+$userEnvironmentMap = [Environment]::GetEnvironmentVariables('User') # HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
+
+# Identify the keySet of environment variable names
+$nameSet = ($specialEnvironmentMap.Keys + $machineEnvironmentMap.Keys + $userEnvironmentMap.Keys) | Sort-Object | Select-Object -Unique
+
+# Any environment variable in the $nameSet should be restored to its original value
+foreach ($name in $nameSet)
+{
+    if ($specialEnvironmentMap.ContainsKey($name))
+    {
+        [Environment]::SetEnvironmentVariable($name, $specialEnvironmentMap[$name], 'Process')
+        continue;
+    }
+
+    # PATH needs to be concatenated as it has values in both machine and user environment. Any other values should be set.
+    if ($name -match 'path')
+    {
+        $pathValuePartial = @()
+        # Machine values before user values
+        $pathValuePartial += $machineEnvironmentMap[$name] -split ';'
+        $pathValuePartial += $userEnvironmentMap[$name] -split ';'
+        $pathValue = $pathValuePartial -join ';'
+        [Environment]::SetEnvironmentVariable($name, $pathValue, 'Process')
+        continue;
+    }
+
+    if ($userEnvironmentMap.ContainsKey($name))
+    {
+        [Environment]::SetEnvironmentVariable($name, $userEnvironmentMap[$name], 'Process')
+        continue;
+    }
+
+    if ($machineEnvironmentMap.ContainsKey($name))
+    {
+        [Environment]::SetEnvironmentVariable($name, $machineEnvironmentMap[$name], 'Process')
+        continue;
+    }
+
+    throw "Unreachable: Unknown variable $name"
+}
+
+# Any environment variable NOT in the $nameSet should be removed
+$processEnvironmentMap = [Environment]::GetEnvironmentVariables('Process')
+$variablesForRemoval = $processEnvironmentMap.Keys | Where-Object {$nameSet -notcontains $_}
+foreach ($name in $variablesForRemoval)
+{
+    [Environment]::SetEnvironmentVariable($name, $null, 'Process')
+}

scripts/VcpkgPowershellUtils.ps1

@@ -168,10 +168,33 @@ function vcpkgInvokeCommand()
 {
     param ( [Parameter(Mandatory=$true)][string]$executable,
                                         [string]$arguments = "",
-                                        [switch]$wait)
+            [Parameter(Mandatory=$true)][switch]$wait)
 
     Write-Verbose "Executing: ${executable} ${arguments}"
-    $process = Start-Process -FilePath $executable -ArgumentList $arguments -PassThru -NoNewWindow
+    $process = Start-Process -FilePath "`"$executable`"" -ArgumentList $arguments -PassThru -NoNewWindow
+    if ($wait)
+    {
+        Wait-Process -InputObject $process
+        $ec = $process.ExitCode
+        Write-Verbose "Execution terminated with exit code $ec."
+    }
+}
+
+function vcpkgInvokeCommandClean()
+{
+    param ( [Parameter(Mandatory=$true)][string]$executable,
+                                        [string]$arguments = "",
+            [Parameter(Mandatory=$true)][switch]$wait)
+
+    Write-Verbose "Clean-Executing: ${executable} ${arguments}"
+    $scriptsDir = split-path -parent $script:MyInvocation.MyCommand.Definition
+    $cleanEnvScript = "$scriptsDir\VcpkgPowershellUtils-ClearEnvironment.ps1"
+    $command = "& `"$cleanEnvScript`"; & `"$executable`" $arguments"
+    $bytes = [System.Text.Encoding]::Unicode.GetBytes($command)
+    $encodedCommand = [Convert]::ToBase64String($bytes)
+    $arg = "-encodedCommand $encodedCommand"
+
+    $process = Start-Process -FilePath powershell.exe -ArgumentList $arg -PassThru -NoNewWindow
     if ($wait)
     {
         Wait-Process -InputObject $process

scripts/bootstrap.ps1

@@ -5,6 +5,7 @@ param(
 )
 
 $scriptsDir = split-path -parent $script:MyInvocation.MyCommand.Definition
+. "$scriptsDir\VcpkgPowershellUtils.ps1"
 $vcpkgRootDir = & $scriptsDir\findFileRecursivelyUp.ps1 $scriptsDir .vcpkg-root
 Write-Verbose("vcpkg Path " + $vcpkgRootDir)
 
@@ -52,9 +53,11 @@ try
     "/p:PlatformToolset=$platformToolset",
     "/p:TargetPlatformVersion=$windowsSDK",
     "/m",
-    "dirs.proj")
+    "dirs.proj") -join " "
+
+    # vcpkgInvokeCommandClean cmd "/c echo %PATH%" -wait:$true
+    vcpkgInvokeCommandClean $msbuildExe $arguments -wait:$true
 
-    & $msbuildExe $arguments
     if ($LASTEXITCODE -ne 0)
     {
         Write-Error "Building vcpkg.exe failed. Please ensure you have installed Visual Studio with the Desktop C++ workload and the Windows SDK for Desktop C++."