Improve logic for handling a system where dotnet has never been installed

Author: JamesWTruher

build.psm1

@@ -202,6 +202,9 @@ function Start-ScriptAnalyzerBuild
         try {
             Push-Location $projectRoot/Rules
             Write-Progress "Building ScriptAnalyzer for PSVersion '$PSVersion' using framework '$framework' and configuration '$Configuration'"
+            if ( -not $script:DotnetExe ) {
+                $script:dotnetExe = Get-DotnetExe
+            }
             $buildOutput = & $script:dotnetExe build --framework $framework --configuration "$config"
             if ( $LASTEXITCODE -ne 0 ) { throw "$buildOutput" }
         }
@@ -308,6 +311,11 @@ function Install-Dotnet
         If ( $PSCmdlet.ShouldProcess("$installScriptName for $version")) {
             & "${installScriptPath}" -c release -version $version
         }
+        # this may be the first time that dotnet has been installed,
+        # set up the executable variable
+        if ( -not $script:DotnetExe ) {
+            $script:DotnetExe = Get-DotnetExe
+        }
     }
     catch {
         throw $_
@@ -336,7 +344,10 @@ function ConvertTo-PortableVersion {
     foreach ( $v in $strVersion ) {
         $ver, $pre = $v.split("-",2)
         try {
-            [int]$major, [int]$minor, [int]$patch = $ver.Split(".")
+            [int]$major, [int]$minor, [int]$patch, $unused = $ver.Split(".",4)
+            if ( -not $pre ) {
+                $pre = $unused
+            }
         }
         catch {
             Write-Warning "Cannot convert '$v' to portable version"
@@ -420,6 +431,10 @@ function Test-SuitableDotnet {
 
 # these are mockable functions for testing
 function Get-InstalledCLIVersion {
+    # dotnet might not have been installed _ever_, so just return 0.0.0.0
+    if ( -not $script:DotnetExe ) {
+        return (ConvertTo-PortableVersion 0.0.0)
+    }
     try {
         # earlier versions of dotnet do not support --list-sdks, so we'll check the output
         # and use dotnet --version as a fallback