Add ImportModuleManifest to wrap Get-Module

I thought Get-Module would error if it could not parse the manifest. Instead it returns an empty ModuleInfo object. This wrapper will correct that while preserving the old error handling...
PoshCode · Jaykul · Feb 10, 2020 · Dec 19, 2019 · Jan 11, 2020 · Jan 11, 2020
commit 59dd957da0153c42b9bc0c5626b05481c08c9edb
diff --git a/Source/Private/ImportModuleManifest.ps1 b/Source/Private/ImportModuleManifest.ps1
@@ -0,0 +1,36 @@
+function ImportModuleManifest {
+    [CmdletBinding()]
+    param(
+        [Alias("PSPath")]
+        [Parameter(Mandatory, ValueFromPipelineByPropertyName)]
+        [string]$Path
+    )
+    process {
+        # Get all the information in the module manifest
+        $ModuleInfo = Get-Module $Path -ListAvailable -WarningAction SilentlyContinue -ErrorAction SilentlyContinue -ErrorVariable Problems
+
+        # Some versions fails silently. If the GUID is empty, we didn't get anything at all
+        if ($ModuleInfo.Guid -eq [Guid]::Empty) {
+            Write-Error "Cannot parse '$Path' as a module manifest, try Test-ModuleManifest for details"
+            return
+        }
+
+        # Some versions show errors are when the psm1 doesn't exist (yet), but we don't care
+        $ErrorsWeIgnore = "^" + (@(
+            "Modules_InvalidRequiredModulesinModuleManifest"
+            "Modules_InvalidRootModuleInModuleManifest"
+        ) -join "|^")
+
+        # If there are any OTHER problems we'll fail
+        if ($Problems = $Problems.Where({ $_.FullyQualifiedErrorId -notmatch $ErrorsWeIgnore })) {
+            foreach ($problem in $Problems) {
+                Write-Error $problem
+            }
+            # Short circuit - don't output the ModuleInfo if there were errors
+            return
+        }
+
+        # Workaround the fact that Get-Module returns the DefaultCommandPrefix as Prefix
+        Update-Object -InputObject $ModuleInfo -UpdateObject @{ DefaultCommandPrefix = $ModuleInfo.Prefix; Prefix = "" }
+    }
+}
diff --git a/Tests/Private/ImportModuleManifest.Tests.ps1 b/Tests/Private/ImportModuleManifest.Tests.ps1
@@ -0,0 +1,59 @@
+#requires -Module ModuleBuilder
+Describe "ImportModuleManifest" {
+
+    Context "Mandatory Parameter" {
+        $CommandInfo = InModuleScope ModuleBuilder { Get-Command ImportModuleManifest }
+
+        It 'has a mandatory Path parameter for the PSPath by pipeline' {
+            $Path = $CommandInfo.Parameters['Path']
+            $Path | Should -Not -BeNullOrEmpty
+            $Path.ParameterType | Should -Be ([string])
+            $Path.Aliases | Should -Be ("PSPath")
+            $Path.Attributes.Where{ $_ -is [Parameter] }.Mandatory | Should -Be $true
+            $Path.Attributes.Where{ $_ -is [Parameter] }.ValueFromPipelineByPropertyName | Should -Be $true
+        }
+
+    }
+
+    Context "Parsing Manifests" {
+        It "Does not cause errors for non-existent root modules" {
+            New-ModuleManifest -Path TestDrive:\BadRoot.psd1 -Author TestName -RootModule NoSuchFile
+
+            InModuleScope ModuleBuilder {
+                ImportModuleManifest -Path TestDrive:\BadRoot.psd1 -ErrorAction Stop
+            }
+        }
+
+        It "Returns the ModuleInfo with DefaultCommandPrefix instead of Prefix" {
+            New-ModuleManifest -Path TestDrive:\TestPrefix.psd1 -Author TestName -DefaultCommandPrefix PrePre
+
+            $Prefix = InModuleScope ModuleBuilder {
+                $DebugPreference = "Continue"
+                Get-ChildItem TestDrive:\TestPrefix.psd1 | ImportModuleManifest
+                $DebugPreference = "SilentlyContinue"
+            }
+
+            $Prefix.Prefix | Should -BeNullOrEmpty
+            $Prefix.DefaultCommandPrefix | Should -Be "PrePre"
+        }
+
+        It "Does cause errors for manifests that are invalid" {
+            New-ModuleManifest -Path TestDrive:\Invalid.psd1 -Author TestName -ModuleVersion "1.0.0"
+            Set-Content TestDrive:\Invalid.psd1 (
+                (Get-Content -Path TestDrive:\Invalid.psd1 -Raw) -replace "1.0.0"
+            )
+
+            {
+                InModuleScope ModuleBuilder {
+                    ImportModuleManifest -Path TestDrive:\Invalid.psd1 -ErrorAction Stop -WarningAction Stop
+                }
+            } | Should -Throw
+        }
+    }
+
+    Context "Invalid module manifest" {
+        # In the current PowerShell 5.1 and 6.1
+        # We can't make Get-Module -ListAvailable throw on a manifest
+        # So I can't test the if($Problems = ... code
+    }
+}