Fix null indentation in ConvertTo-YamlNode, reject tabs in indentation, strengthen empty-array and unsigned-enum test assertions

Author: MariusStorhaug

src/functions/private/ConvertFrom-YamlLineStream.ps1

@@ -8,7 +8,7 @@
         - Lines that are empty or whitespace-only are skipped.
         - Lines whose first non-whitespace character is `#` are skipped.
         - Inline comments (` #...` outside quotes) are stripped from the content.
-        - Tabs in indentation are not allowed (YAML spec); they are treated as one space here.
+        - Tabs in indentation are not allowed (YAML spec); a terminating error is thrown if one is found.
     #>
     [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseOutputTypeCorrectly', '',
         Justification = 'Comma-unary operator preserves List type; PSScriptAnalyzer misdetects as Object[].')]
@@ -31,9 +31,12 @@
             continue
         }
 
-        # Compute indent (spaces before first non-space).
+        # Compute indent (spaces before first non-space). Tabs are invalid per YAML spec.
         $indent = 0
         while ($indent -lt $raw.Length -and ($raw[$indent] -eq ' ' -or $raw[$indent] -eq "`t")) {
+            if ($raw[$indent] -eq "`t") {
+                throw "YAML forbids tab characters in indentation (line $($i + 1)). Use spaces instead."
+            }
             $indent++
         }
 

src/functions/private/ConvertTo-YamlNode.ps1

@@ -30,7 +30,8 @@
     }
 
     if ($null -eq $Value) {
-        $null = $Builder.Append('null').AppendLine()
+        $indent = ' ' * ($Level * $Options.Indent)
+        $null = $Builder.Append($indent).Append('null').AppendLine()
         return
     }
 

tests/ConvertFrom-Yaml.Tests.ps1

@@ -636,8 +636,9 @@ a:
         }
 
         It 'Parses [] as an empty array' {
-            $result = 'items: []' | ConvertFrom-Yaml
-            $result.items | Should -BeNullOrEmpty
+            $result = 'items: []' | ConvertFrom-Yaml -AsHashtable
+            $result['items'].GetType().Name | Should -Be 'Object[]'
+            $result['items'].Count | Should -Be 0
             # Verify via round-trip that ConvertTo-Yaml emits []
             $yaml = [ordered]@{ items = @() } | ConvertTo-Yaml
             $yaml | Should -Match '\[\]'
@@ -663,5 +664,10 @@ key: value
 '@
             { $yaml | ConvertFrom-Yaml } | Should -Throw '*unexpected content*'
         }
+
+        It 'Throws on tab characters in indentation' {
+            $yaml = "key:`n`tvalue: 1"
+            { $yaml | ConvertFrom-Yaml } | Should -Throw '*tab*'
+        }
     }
 }

tests/ConvertTo-Yaml.Tests.ps1

@@ -293,7 +293,9 @@ Describe 'ConvertTo-Yaml' {
             $val = [System.Security.AccessControl.FileSystemRights]::FullControl
             $obj = [ordered]@{ rights = $val }
             $yaml = $obj | ConvertTo-Yaml
-            $expected = [int]$val
+            $underlyingType = [System.Enum]::GetUnderlyingType($val.GetType())
+            $numeric = [System.Convert]::ChangeType($val, $underlyingType)
+            $expected = ([System.IConvertible]$numeric).ToString([cultureinfo]::InvariantCulture)
             $yaml.Trim() | Should -Be "rights: $expected"
         }
     }