Fix mapping key parsing: preserve raw text without type resolution, use [pscustomobject] cast to handle member name collisions

- Keys like true/false/null/~ are now preserved as literal strings instead of being
  type-resolved then cast back (which changed true->True, null->empty string)
- Quoted keys still have their escapes expanded correctly
- Replace Add-Member loop with [pscustomobject]$map cast to avoid errors when
  keys collide with built-in member names like ToString/GetType
- Add 3 tests: YAML-special keys, quoted key escapes, member name collision keys

Author: MariusStorhaug

src/functions/private/ConvertFrom-YamlMapping.ps1

@@ -30,42 +30,45 @@
             throw "ConvertFrom-Yaml: expected mapping key at line $($line.Number): '$($line.Content)'."
         }
 
-        $key = ConvertFrom-YamlScalar -Raw $line.Content.Substring(0, $colonIdx).Trim()
+        $rawKey = $line.Content.Substring(0, $colonIdx).Trim()
+        if ($rawKey.Length -ge 2 -and $rawKey[0] -eq "'" -and $rawKey[-1] -eq "'") {
+            $key = ($rawKey.Substring(1, $rawKey.Length - 2)) -replace "''", "'"
+        } elseif ($rawKey.Length -ge 2 -and $rawKey[0] -eq '"' -and $rawKey[-1] -eq '"') {
+            $key = Expand-YamlDoubleQuoted -Text ($rawKey.Substring(1, $rawKey.Length - 2))
+        } else {
+            $key = $rawKey
+        }
         $rest = $line.Content.Substring($colonIdx + 1).Trim()
 
         $Context.Index++
 
         if ($rest.Length -gt 0) {
-            $map[[string]$key] = ConvertFrom-YamlScalar -Raw $rest
+            $map[$key] = ConvertFrom-YamlScalar -Raw $rest
             continue
         }
 
         # Value on subsequent indented lines (mapping or sequence) or null.
         if ($Context.Index -ge $lines.Count) {
-            $map[[string]$key] = $null
+            $map[$key] = $null
             continue
         }
 
         $next = $lines[$Context.Index]
         if ($next.Indent -le $Indent) {
-            $map[[string]$key] = $null
+            $map[$key] = $null
             continue
         }
 
         # Sequences are allowed to start at the same indent as the parent key in YAML.
         # We require the child to be indented strictly greater than the key here for clarity.
         $childIndent = $next.Indent
         $value = ConvertFrom-YamlNode -Context $Context -Indent $childIndent -Depth ($Depth + 1)
-        $map[[string]$key] = $value
+        $map[$key] = $value
     }
 
     if ($Context.AsHashtable) {
         return $map
     }
 
-    $obj = [pscustomobject]@{}
-    foreach ($k in $map.Keys) {
-        Add-Member -InputObject $obj -MemberType NoteProperty -Name $k -Value $map[$k]
-    }
-    return $obj
+    return [pscustomobject]$map
 }

tests/ConvertFrom-Yaml.Tests.ps1

@@ -131,6 +131,46 @@ mango: 3
             $names[1] | Should -Be 'apple'
             $names[2] | Should -Be 'mango'
         }
+
+        It 'Preserves raw text of YAML-special keys without type resolution' {
+            $yaml = @'
+true: a
+false: b
+null: c
+~: d
+'@
+            $result = $yaml | ConvertFrom-Yaml -AsHashtable
+            $result.Keys | Should -Contain 'true'
+            $result.Keys | Should -Contain 'false'
+            $result.Keys | Should -Contain 'null'
+            $result.Keys | Should -Contain '~'
+            $result['true'] | Should -Be 'a'
+            $result['false'] | Should -Be 'b'
+            $result['null'] | Should -Be 'c'
+            $result['~'] | Should -Be 'd'
+        }
+
+        It 'Handles quoted mapping keys with escapes' {
+            $yaml = @'
+"key\nwith": value1
+'single''s': value2
+'@
+            $result = $yaml | ConvertFrom-Yaml -AsHashtable
+            $result.Keys | Should -Contain "key`nwith"
+            $result["key`nwith"] | Should -Be 'value1'
+            $result.Keys | Should -Contain "single's"
+            $result["single's"] | Should -Be 'value2'
+        }
+
+        It 'Parses keys that collide with built-in member names' {
+            $yaml = @'
+ToString: hello
+GetType: world
+'@
+            $result = $yaml | ConvertFrom-Yaml
+            $result.PSObject.Properties['ToString'].Value | Should -Be 'hello'
+            $result.PSObject.Properties['GetType'].Value | Should -Be 'world'
+        }
     }
 
     Context 'Sequences' {