Fix empty collection serialization, depth-exceeded indent, and [] / {} round-tripping

MariusStorhaug · MariusStorhaug · commit 7ce8fd0f6dfb · 2026-05-03T02:19:40.000+02:00
- Fix if/else expressions that collapsed empty arrays to $null (PowerShell
  unrolls @() to nothing in expression output). Converted to statement form
  in ConvertTo-YamlMapping, ConvertTo-YamlSequence, ConvertTo-YamlNode,
  Get-YamlMappingPair, and ConvertTo-Yaml.
- Add indentation to empty {} and [] output in ConvertTo-YamlMapping and
  ConvertTo-YamlSequence so nested empty collections serialize correctly.
- Add indentation to depth-exceeded branch in ConvertTo-YamlNode.
- Add inline empty-collection checks in ConvertTo-YamlSequence for nested
  mapping/sequence values within sequence-item-mappings.
- Recognize {} and [] inline literals in ConvertFrom-YamlMapping and
  ConvertFrom-YamlSequence to restore round-trip fidelity.
- Add 17 new tests: empty collection rendering, depth-exceeded indentation,
  {} / [] parsing, and round-trip preservation of empty collections.
diff --git a/src/functions/private/ConvertFrom-YamlMapping.ps1 b/src/functions/private/ConvertFrom-YamlMapping.ps1
@@ -43,7 +43,13 @@
         $Context.Index++
 
         if ($rest.Length -gt 0) {
-            $map[$key] = ConvertFrom-YamlScalar -Raw $rest
+            if ($rest -ceq '{}') {
+                $map[$key] = if ($Context.AsHashtable) { [ordered]@{} } else { [pscustomobject][ordered]@{} }
+            } elseif ($rest -ceq '[]') {
+                $map[$key] = @()
+            } else {
+                $map[$key] = ConvertFrom-YamlScalar -Raw $rest
+            }
             continue
         }
 
diff --git a/src/functions/private/ConvertFrom-YamlSequence.ps1 b/src/functions/private/ConvertFrom-YamlSequence.ps1
@@ -64,6 +64,19 @@
             continue
         }
 
+        # Empty collection literals (flow-style shorthand).
+        if ($afterDash -ceq '{}') {
+            $val = if ($Context.AsHashtable) { [ordered]@{} } else { [pscustomobject][ordered]@{} }
+            $list.Add($val)
+            $Context.Index++
+            continue
+        }
+        if ($afterDash -ceq '[]') {
+            $list.Add(@())
+            $Context.Index++
+            continue
+        }
+
         # Plain scalar element.
         $list.Add((ConvertFrom-YamlScalar -Raw $afterDash))
         $Context.Index++
diff --git a/src/functions/private/ConvertTo-YamlMapping.ps1 b/src/functions/private/ConvertTo-YamlMapping.ps1
@@ -14,7 +14,8 @@
 
     $pairs = Get-YamlMappingPair -Value $Value
     if ($pairs.Count -eq 0) {
-        $null = $Builder.Append('{}').AppendLine()
+        $indent = ' ' * ($Level * $Options.Indent)
+        $null = $Builder.Append($indent).Append('{}').AppendLine()
         return
     }
 
@@ -29,10 +30,10 @@
             continue
         }
 
-        $rawVal = if ($val -is [psobject] -and $null -ne $val.PSObject -and $null -ne $val.PSObject.BaseObject) {
-            $val.PSObject.BaseObject
+        if ($val -is [psobject] -and $null -ne $val.PSObject -and $null -ne $val.PSObject.BaseObject) {
+            $rawVal = $val.PSObject.BaseObject
         } else {
-            $val
+            $rawVal = $val
         }
 
         if (Test-YamlMappingType -Value $rawVal) {
diff --git a/src/functions/private/ConvertTo-YamlNode.ps1 b/src/functions/private/ConvertTo-YamlNode.ps1
@@ -24,7 +24,8 @@
 
     if ($CurrentDepth -gt $Options.Depth) {
         $repr = if ($null -eq $Value) { 'null' } else { Format-YamlScalar -Value $Value.ToString() -Options $Options }
-        $null = $Builder.Append($repr).AppendLine()
+        $indent = ' ' * ($Level * $Options.Indent)
+        $null = $Builder.Append($indent).Append($repr).AppendLine()
         return
     }
 
@@ -34,10 +35,10 @@
     }
 
     # Unwrap PSObject for type tests.
-    $raw = if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {
-        $Value.PSObject.BaseObject
+    if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {
+        $raw = $Value.PSObject.BaseObject
     } else {
-        $Value
+        $raw = $Value
     }
 
     if (Test-YamlMappingType -Value $raw) {
diff --git a/src/functions/private/ConvertTo-YamlSequence.ps1 b/src/functions/private/ConvertTo-YamlSequence.ps1
@@ -14,17 +14,18 @@
 
     $items = @($Value)
     if ($items.Count -eq 0) {
-        $null = $Builder.Append('[]').AppendLine()
+        $indent = ' ' * ($Level * $Options.Indent)
+        $null = $Builder.Append($indent).Append('[]').AppendLine()
         return
     }
 
     $indent = ' ' * ($Level * $Options.Indent)
 
     foreach ($item in $items) {
-        $rawItem = if ($item -is [psobject] -and $null -ne $item.PSObject -and $null -ne $item.PSObject.BaseObject) {
-            $item.PSObject.BaseObject
+        if ($item -is [psobject] -and $null -ne $item.PSObject -and $null -ne $item.PSObject.BaseObject) {
+            $rawItem = $item.PSObject.BaseObject
         } else {
-            $item
+            $rawItem = $item
         }
 
         if ($null -eq $item) {
@@ -46,10 +47,10 @@
                 $first = $false
 
                 $val = $pair.Value
-                $rawVal = if ($val -is [psobject] -and $null -ne $val.PSObject -and $null -ne $val.PSObject.BaseObject) {
-                    $val.PSObject.BaseObject
+                if ($val -is [psobject] -and $null -ne $val.PSObject -and $null -ne $val.PSObject.BaseObject) {
+                    $rawVal = $val.PSObject.BaseObject
                 } else {
-                    $val
+                    $rawVal = $val
                 }
 
                 if ($null -eq $val) {
@@ -58,14 +59,24 @@
                 }
 
                 if (Test-YamlMappingType -Value $rawVal) {
-                    $null = $Builder.Append($prefix).Append($keyText).Append(':').AppendLine()
-                    ConvertTo-YamlNode -Value $val -Builder $Builder -Level ($Level + 2) -CurrentDepth ($CurrentDepth + 1) -Options $Options
+                    $childPairs = Get-YamlMappingPair -Value $val
+                    if ($childPairs.Count -eq 0) {
+                        $null = $Builder.Append($prefix).Append($keyText).Append(': {}').AppendLine()
+                    } else {
+                        $null = $Builder.Append($prefix).Append($keyText).Append(':').AppendLine()
+                        ConvertTo-YamlNode -Value $val -Builder $Builder -Level ($Level + 2) -CurrentDepth ($CurrentDepth + 1) -Options $Options
+                    }
                     continue
                 }
 
                 if (Test-YamlSequenceType -Value $rawVal) {
-                    $null = $Builder.Append($prefix).Append($keyText).Append(':').AppendLine()
-                    ConvertTo-YamlSequence -Value $rawVal -Builder $Builder -Level ($Level + 2) -CurrentDepth ($CurrentDepth + 1) -Options $Options
+                    $arr = @($rawVal)
+                    if ($arr.Count -eq 0) {
+                        $null = $Builder.Append($prefix).Append($keyText).Append(': []').AppendLine()
+                    } else {
+                        $null = $Builder.Append($prefix).Append($keyText).Append(':').AppendLine()
+                        ConvertTo-YamlSequence -Value $rawVal -Builder $Builder -Level ($Level + 2) -CurrentDepth ($CurrentDepth + 1) -Options $Options
+                    }
                     continue
                 }
 
@@ -76,8 +87,13 @@
         }
 
         if (Test-YamlSequenceType -Value $rawItem) {
-            $null = $Builder.Append($indent).Append('-').AppendLine()
-            ConvertTo-YamlSequence -Value $rawItem -Builder $Builder -Level ($Level + 1) -CurrentDepth ($CurrentDepth + 1) -Options $Options
+            $arr = @($rawItem)
+            if ($arr.Count -eq 0) {
+                $null = $Builder.Append($indent).Append('- []').AppendLine()
+            } else {
+                $null = $Builder.Append($indent).Append('-').AppendLine()
+                ConvertTo-YamlSequence -Value $rawItem -Builder $Builder -Level ($Level + 1) -CurrentDepth ($CurrentDepth + 1) -Options $Options
+            }
             continue
         }
 
diff --git a/src/functions/private/Get-YamlMappingPair.ps1 b/src/functions/private/Get-YamlMappingPair.ps1
@@ -13,10 +13,10 @@
     )
 
     $pairs = [System.Collections.Generic.List[pscustomobject]]::new()
-    $raw = if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {
-        $Value.PSObject.BaseObject
+    if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {
+        $raw = $Value.PSObject.BaseObject
     } else {
-        $Value
+        $raw = $Value
     }
 
     if ($raw -is [System.Collections.IDictionary]) {
diff --git a/src/functions/public/ConvertTo-Yaml.ps1 b/src/functions/public/ConvertTo-Yaml.ps1
@@ -83,7 +83,11 @@
         if ($AsArray) {
             ConvertTo-YamlSequence -Value $items.ToArray() -Builder $sb -Level 0 -CurrentDepth 0 -Options $options
         } else {
-            $root = if ($items.Count -eq 1) { $items[0] } else { $items.ToArray() }
+            if ($items.Count -eq 1) {
+                $root = $items[0]
+            } else {
+                $root = $items.ToArray()
+            }
             ConvertTo-YamlNode -Value $root -Builder $sb -Level 0 -CurrentDepth 0 -Options $options
         }
         return $sb.ToString().TrimEnd("`r", "`n")
diff --git a/tests/ConvertFrom-Yaml.Tests.ps1 b/tests/ConvertFrom-Yaml.Tests.ps1
@@ -329,4 +329,39 @@ a:
                 Should -Be 'ConvertFrom-Yaml'
         }
     }
+
+    Context 'Empty collection literals' {
+        It 'Parses {} as an empty mapping (PSCustomObject by default)' {
+            $result = 'data: {}' | ConvertFrom-Yaml
+            $result.data | Should -BeOfType [PSCustomObject]
+            @($result.data.PSObject.Properties).Count | Should -Be 0
+        }
+
+        It 'Parses {} as an empty OrderedDictionary with -AsHashtable' {
+            $result = 'data: {}' | ConvertFrom-Yaml -AsHashtable
+            $result['data'] | Should -BeOfType [System.Collections.Specialized.OrderedDictionary]
+            $result['data'].Count | Should -Be 0
+        }
+
+        It 'Parses [] as an empty array' {
+            $result = 'items: []' | ConvertFrom-Yaml
+            $result.items | Should -BeNullOrEmpty
+            # Verify via round-trip that ConvertTo-Yaml emits []
+            $yaml = [ordered]@{ items = @() } | ConvertTo-Yaml
+            $yaml | Should -Match '\[\]'
+        }
+
+        It 'Parses sequence items {} and [] correctly' {
+            $yaml = @'
+- {}
+- []
+- hello
+'@
+            $result = $yaml | ConvertFrom-Yaml -NoEnumerate -AsHashtable
+            $result[0] | Should -BeOfType [System.Collections.Specialized.OrderedDictionary]
+            $result[0].Count | Should -Be 0
+            $result[1].Count | Should -Be 0
+            $result[2] | Should -Be 'hello'
+        }
+    }
 }
diff --git a/tests/ConvertTo-Yaml.Tests.ps1 b/tests/ConvertTo-Yaml.Tests.ps1
@@ -178,6 +178,69 @@ Describe 'ConvertTo-Yaml' {
             $yaml = $obj | ConvertTo-Yaml -Depth 5
             $yaml | Should -Match 'b: value'
         }
+
+        It 'Indents depth-exceeded values correctly under a mapping key' {
+            $obj = [ordered]@{
+                a = [ordered]@{
+                    b = [ordered]@{
+                        c = 'value'
+                    }
+                }
+            }
+            $yaml = $obj | ConvertTo-Yaml -Depth 1 -WarningAction SilentlyContinue
+            $lines = $yaml.TrimEnd("`r", "`n") -split "`r?`n"
+            # The depth-exceeded line should be indented under 'b:'
+            $bLine = $lines | Where-Object { $_ -match '^\s+b:' }
+            $bLine | Should -Not -BeNullOrEmpty
+            $depthLine = $lines[($lines.IndexOf($bLine) + 1)]
+            $depthLine | Should -Match '^\s{4}'
+        }
+    }
+
+    Context 'Empty collections' {
+        It 'Renders an empty hashtable as {}' {
+            $yaml = [ordered]@{} | ConvertTo-Yaml
+            $yaml.Trim() | Should -Be '{}'
+        }
+
+        It 'Renders an empty array as []' {
+            $yaml = ConvertTo-Yaml -InputObject @()
+            $yaml.Trim() | Should -Be '[]'
+        }
+
+        It 'Renders a nested empty mapping inline' {
+            $obj = [ordered]@{ key = [ordered]@{} }
+            $yaml = $obj | ConvertTo-Yaml
+            $yaml.Trim() | Should -Be 'key: {}'
+        }
+
+        It 'Renders a nested empty array inline' {
+            $obj = [ordered]@{ key = @() }
+            $yaml = $obj | ConvertTo-Yaml
+            $yaml.Trim() | Should -Be 'key: []'
+        }
+
+        It 'Renders an empty mapping value in a sequence-of-mappings inline' {
+            $obj = @(
+                [ordered]@{ name = 'Alice'; data = [ordered]@{} }
+            )
+            $yaml = ConvertTo-Yaml -InputObject $obj
+            $yaml | Should -Match 'data: \{\}'
+        }
+
+        It 'Renders an empty array value in a sequence-of-mappings inline' {
+            $obj = @(
+                [ordered]@{ name = 'Alice'; items = @() }
+            )
+            $yaml = ConvertTo-Yaml -InputObject $obj
+            $yaml | Should -Match 'items: \[\]'
+        }
+
+        It 'Renders an empty sequence item in a sequence as - []' {
+            $obj = @( @(), @('a') )
+            $yaml = ConvertTo-Yaml -InputObject $obj
+            $yaml | Should -Match '(?m)^- \[\]'
+        }
     }
 
     Context 'Aliases' {
@@ -244,4 +307,17 @@ Describe 'Round-trip ConvertTo-Yaml | ConvertFrom-Yaml' {
         $result['c'] | Should -Be 'null'
         $result['c'] | Should -BeOfType [string]
     }
+
+    It 'Preserves an empty mapping under a key' {
+        $obj = [ordered]@{ data = [ordered]@{} }
+        $result = $obj | ConvertTo-Yaml | ConvertFrom-Yaml -AsHashtable
+        $result['data'] | Should -BeOfType [System.Collections.Specialized.OrderedDictionary]
+        $result['data'].Count | Should -Be 0
+    }
+
+    It 'Preserves an empty array under a key' {
+        $obj = [ordered]@{ items = @() }
+        $result = $obj | ConvertTo-Yaml | ConvertFrom-Yaml -AsHashtable
+        $result['items'].Count | Should -Be 0
+    }
 }

Original file line number	Diff line number	Diff line change
`@@ -14,7 +14,8 @@`
`14`	`14`
`15`	`15`	`$pairs = Get-YamlMappingPair -Value $Value`
`16`	`16`	`if ($pairs.Count -eq 0) {`
`17`		`- $null = $Builder.Append('{}').AppendLine()`
	`17`	`+ $indent = ' ' * ($Level * $Options.Indent)`
	`18`	`+ $null = $Builder.Append($indent).Append('{}').AppendLine()`
`18`	`19`	`return`
`19`	`20`	`}`
`20`	`21`
`@@ -29,10 +30,10 @@`
`29`	`30`	`continue`
`30`	`31`	`}`
`31`	`32`
`32`		`- $rawVal = if ($val -is [psobject] -and $null -ne $val.PSObject -and $null -ne $val.PSObject.BaseObject) {`
`33`		`- $val.PSObject.BaseObject`
	`33`	`+ if ($val -is [psobject] -and $null -ne $val.PSObject -and $null -ne $val.PSObject.BaseObject) {`
	`34`	`+ $rawVal = $val.PSObject.BaseObject`
`34`	`35`	`} else {`
`35`		`- $val`
	`36`	`+ $rawVal = $val`
`36`	`37`	`}`
`37`	`38`
`38`	`39`	`if (Test-YamlMappingType -Value $rawVal) {`
Original file line number	Diff line number	Diff line change
`@@ -24,7 +24,8 @@`
`24`	`24`
`25`	`25`	`if ($CurrentDepth -gt $Options.Depth) {`
`26`	`26`	`$repr = if ($null -eq $Value) { 'null' } else { Format-YamlScalar -Value $Value.ToString() -Options $Options }`
`27`		`- $null = $Builder.Append($repr).AppendLine()`
	`27`	`+ $indent = ' ' * ($Level * $Options.Indent)`
	`28`	`+ $null = $Builder.Append($indent).Append($repr).AppendLine()`
`28`	`29`	`return`
`29`	`30`	`}`
`30`	`31`
`@@ -34,10 +35,10 @@`
`34`	`35`	`}`
`35`	`36`
`36`	`37`	`# Unwrap PSObject for type tests.`
`37`		`- $raw = if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {`
`38`		`- $Value.PSObject.BaseObject`
	`38`	`+ if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {`
	`39`	`+ $raw = $Value.PSObject.BaseObject`
`39`	`40`	`} else {`
`40`		`- $Value`
	`41`	`+ $raw = $Value`
`41`	`42`	`}`
`42`	`43`
`43`	`44`	`if (Test-YamlMappingType -Value $raw) {`
Original file line number	Diff line number	Diff line change
`@@ -13,10 +13,10 @@`
`13`	`13`	`)`
`14`	`14`
`15`	`15`	`$pairs = [System.Collections.Generic.List[pscustomobject]]::new()`
`16`		`- $raw = if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {`
`17`		`- $Value.PSObject.BaseObject`
	`16`	`+ if ($Value -is [psobject] -and $null -ne $Value.PSObject -and $null -ne $Value.PSObject.BaseObject) {`
	`17`	`+ $raw = $Value.PSObject.BaseObject`
`18`	`18`	`} else {`
`19`		`- $Value`
	`19`	`+ $raw = $Value`
`20`	`20`	`}`
`21`	`21`
`22`	`22`	`if ($raw -is [System.Collections.IDictionary]) {`