Invoke Mercury compiler using PowerShell. Discovers MSVC compiler as well.

Invoke-MercuryCompiler.ps1

    
function Invoke-MercuryCompiler {
    param (
      [String] $mercuryHome
    )

    $env_Orig = Get-Environment

    try {

        if (-not (Test-PathAllowNull $mercuryHome)) {
            $mercuryHome = $env:MERCURY_HOME
        }

        if (-not (Test-PathAllowNull $mercuryHome)) {
            $mercuryOnPath = Get-Command "mercury_compile.exe" -ErrorAction SilentlyContinue
            if (Test-PathAllowNull $mercuryOnPath) {
                $mercuryHome = Split-Path (Split-Path $mercuryOnPath)
            }
        }

        if (-not (Test-PathAllowNull $mercuryHome)) {
            throw [System.ArgumentException]::New("Mercury home '${mercuryHome}' `
                does not point to a valid Mercury installation", 'mercuryHome')
        }

        Invoke-CmdScript $(join-path (Get-LatestVSInstallationPath) "Common7\Tools\VsDevCmd.bat")

        $env:Path = "$mercuryHome/bin;$env:Path"

        $env:MERCURY_STDLIB_DIR = "$mercuryHome/lib/mercury"
        & "$mercuryHome/bin/mercury_compile.exe" --install-command copy $args -ErrorAction SilentlyContinue
        Write-Error $LASTEXITCODE
    }
    finally {
        Restore-Environment $env_Orig
    }
}

function Test-PathAllowNull {
    param (
        [string] $path
    )

    ($null -ne $path) -and ($path -ne '') -and (Test-Path $path)
}

function Get-ProgramFilesX86 {
    switch ($null -ne ${env:ProgramFiles(x86)}) {
        $true  { ${env:ProgramFiles(x86)} }
        $false { ${env:ProgramFiles} }
    }
}

function Get-LatestVSInstallationPath {
    &"$(Get-ProgramFilesX86)\Microsoft Visual Studio\Installer\vswhere.exe" `
        -format value -utf8 -products * `
        -requires Microsoft.VisualStudio.Component.VC.Tools.x86.x64 `
        -property installationPath -latest
}

# courtesy of https://www.itprotoday.com/powershell/take-charge-environment-variables-powershell

# Invokes a Cmd.exe shell script and updates the environment.
function Invoke-CmdScript {
    param(
        [String] $scriptName
    )
    $cmdLine = """$scriptName"" $args & set"
    & "$env:ComSpec" /s /c $cmdLine |
        select-string '^([^=]*)=(.*)$' |
        foreach-object {
            $varName = $_.Matches[0].Groups[1].Value
            $varValue = $_.Matches[0].Groups[2].Value
            Set-Item Env:$varName $varValue
        }
}

# Returns the current environment.
function Get-Environment {
    get-childitem Env:
}

# Restores the environment to a previous state.
function Restore-Environment {
    param(
        [parameter(Mandatory=$TRUE)]
        [System.Collections.DictionaryEntry[]] $oldEnv
    )
    # Removes any added variables.
    compare-object $oldEnv $(Get-Environment) -property Key -passthru |
        where-object { $_.SideIndicator -eq "=>" } |
        ForEach-Object { remove-item Env:$($_.Name) }
    # Reverts any changed variables to original values.
    compare-object $oldEnv $(Get-Environment) -property Value -passthru |
        where-object { $_.SideIndicator -eq "<=" } |
        ForEach-Object { set-item Env:$($_.Name) $_.Value }
}