Fix explicit empty text defaults (#474)

## Summary
- preserve an explicitly declared empty JSON default during manifest
conversion
- allow a text prompt to accept blank input only when its manifest
explicitly declares a default
- add end-to-end regression coverage for `default: ""`

## Verification
- `pwsh -NoLogo -NoProfile -Command '$cfg = New-PesterConfiguration;
$cfg.Run.Path = "./tests/EmptyDefaultTextParameter.Tests.ps1";
$cfg.Output.Verbosity = "Normal"; $cfg.Run.PassThru = $true; $result =
Invoke-Pester -Configuration $cfg; exit $result.FailedCount'`
- 3 passed, 0 failed

Fixes #473.

Author: HeyItsGilbert

Plaster/Private/ConvertFrom-JsonManifest.ps1

@@ -71,7 +71,7 @@ function ConvertFrom-JsonManifest {
                         $paramElement.SetAttribute('prompt', $param.prompt)
                     }
 
-                    if ($param.default) {
+                    if ($param.PSObject.Properties.Match('default').Count -gt 0) {
                         if ($param.default -is [array]) {
                             $paramElement.SetAttribute('default', ($param.default -join ','))
                         } else {

Plaster/Private/Read-PromptForInput.ps1

@@ -3,15 +3,16 @@ function Read-PromptForInput {
     param(
         $prompt,
         $default,
-        $pattern
+        $pattern,
+        [switch]$AllowEmpty
     )
     if (!$pattern) {
         $patternMatch = $true
     }
 
     do {
         $value = Read-Host -Prompt $prompt
-        if (!$value -and $default) {
+        if (!$value -and ($AllowEmpty -or $default)) {
             $value = $default
             $patternMatch = $true
         } elseif ($value -and $pattern) {
@@ -21,7 +22,7 @@ function Read-PromptForInput {
                 $PSCmdlet.WriteDebug("Value '$value' did not match the pattern '$pattern'")
             }
         }
-    } while (!$value -or !$patternMatch)
+    } while ((!$value -and !$AllowEmpty) -or !$patternMatch)
 
     $value
 }

Plaster/Private/Resolve-ProcessParameter.ps1

@@ -76,7 +76,7 @@ function Resolve-ProcessParameter {
                     }
                 }
                 # Prompt the user for text input.
-                $value = Read-PromptForInput $prompt $default @splat
+                $value = Read-PromptForInput $prompt $default $pattern -AllowEmpty:$Node.HasAttribute('default')
                 $valueToStore = $value
             }
             'user-fullname' {

tests/EmptyDefaultTextParameter.Tests.ps1

@@ -0,0 +1,106 @@
+BeforeDiscovery {
+    if ($null -eq $env:BHProjectPath) {
+        $path = Join-Path -Path $PSScriptRoot -ChildPath '..\build.ps1'
+        . $path -Task Build
+    }
+    $manifest = Import-PowerShellDataFile -Path $env:BHPSModuleManifest
+    $outputDir = Join-Path -Path $env:BHProjectPath -ChildPath 'Output'
+    $outputModDir = Join-Path -Path $outputDir -ChildPath $env:BHProjectName
+    $outputModVerDir = Join-Path -Path $outputModDir -ChildPath $manifest.ModuleVersion
+    $outputModVerManifest = Join-Path $outputModVerDir "$($env:BHProjectName).psd1"
+    Get-Module $env:BHProjectName | Remove-Module -Force -ErrorAction Ignore
+    Import-Module -Name $outputModVerManifest -Verbose:$false -ErrorAction Stop
+}
+
+Describe 'Empty text parameter defaults' -Tag 'Unit' {
+    InModuleScope $env:BHProjectName {
+        It 'preserves an explicit empty JSON default' {
+            $manifest = ConvertFrom-JsonManifest -JsonContent @'
+{
+    "schemaVersion": "2.0",
+    "metadata": {
+        "name": "EmptyDefault",
+        "id": "513d2fdc-3cce-47d9-9531-d85114efb224",
+        "version": "1.0.0",
+        "title": "Empty default",
+        "description": "Tests explicit empty defaults.",
+        "author": "Plaster",
+        "tags": ["Test"]
+    },
+    "parameters": [
+        {
+            "name": "ModuleDesc",
+            "type": "text",
+            "prompt": "Enter a description",
+            "default": ""
+        }
+    ],
+    "content": [
+        {
+            "type": "file",
+            "source": "source.txt",
+            "destination": "source.txt"
+        }
+    ]
+}
+'@
+
+            $parameter = $manifest.plasterManifest.parameters.parameter
+            $parameter.HasAttribute('default') | Should -BeTrue
+            $parameter.default | Should -BeExactly ''
+        }
+
+        It 'accepts blank input when an empty default is explicit' {
+            $script:responses = [System.Collections.Generic.Queue[string]]::new()
+            $script:responses.Enqueue('')
+            $script:responses.Enqueue('unexpected second prompt')
+            Mock Read-Host { $script:responses.Dequeue() }
+
+            $result = Read-PromptForInput -prompt 'Enter a description' -default '' -AllowEmpty
+
+            $result | Should -BeExactly ''
+            Should -Invoke Read-Host -Times 1 -Exactly
+        }
+        It 'completes a JSON template when its text default is empty' {
+            $templatePath = Join-Path $TestDrive 'template'
+            $destinationPath = Join-Path $TestDrive 'output'
+            New-Item -ItemType Directory -Path $templatePath | Out-Null
+            @'
+{
+    "schemaVersion": "2.0",
+    "metadata": {
+        "name": "EmptyDefault",
+        "id": "513d2fdc-3cce-47d9-9531-d85114efb224",
+        "version": "1.0.0",
+        "title": "Empty default",
+        "description": "Tests explicit empty defaults.",
+        "author": "Plaster",
+        "tags": ["Test"]
+    },
+    "parameters": [
+        {
+            "name": "ModuleDesc",
+            "type": "text",
+            "prompt": "Enter a description",
+            "default": ""
+        }
+    ],
+    "content": [
+        {
+            "type": "templateFile",
+            "source": "description.txt",
+            "destination": "description.txt"
+        }
+    ]
+}
+'@ | Set-Content -LiteralPath (Join-Path $templatePath 'plasterManifest.json') -Encoding utf8
+            '<%=$PLASTER_PARAM_ModuleDesc%>' | Set-Content -LiteralPath (Join-Path $templatePath 'description.txt') -Encoding utf8
+            Mock Read-Host { '' }
+
+            Invoke-Plaster -TemplatePath $templatePath -DestinationPath $destinationPath -NoLogo
+
+            (Get-Content -LiteralPath (Join-Path $destinationPath 'description.txt') -Raw).Trim() | Should -BeExactly ''
+            Should -Invoke Read-Host -Times 1 -Exactly
+        }
+    }
+}