Emit explicit overlong mapping keys

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug

src/functions/private/ConvertTo-YamlFlowText.ps1

@@ -132,7 +132,13 @@ function ConvertTo-YamlFlowText {
             continue
         }
         if ($frame.State -eq 'MappingValue') {
-            $frame.Parts.Add("$($frame.KeyText)`: $($frame.Child.Value)")
+            $keyNode = $frame.Node.Entries[$frame.Index].Key
+            $explicitKey = (
+                Get-YamlEmissionImplicitKeyLength -Node $keyNode `
+                    -RenderedText $frame.KeyText
+            ) -gt 1024
+            $keyPrefix = if ($explicitKey) { '? ' } else { '' }
+            $frame.Parts.Add("$keyPrefix$($frame.KeyText)`: $($frame.Child.Value)")
             $frame.Index++
             $frame.State = 'MappingKey'
         }

src/functions/private/Get-YamlEmissionImplicitKeyLength.ps1

@@ -0,0 +1,20 @@
+function Get-YamlEmissionImplicitKeyLength {
+    <#
+        .SYNOPSIS
+        Gets an emitted implicit key length in Unicode scalar values.
+    #>
+    [CmdletBinding()]
+    [OutputType([int])]
+    param (
+        [Parameter(Mandatory)]
+        [pscustomobject] $Node,
+
+        [Parameter(Mandatory)]
+        [string] $RenderedText
+    )
+
+    if ($Node.Kind.Equals('Scalar', [System.StringComparison]::Ordinal)) {
+        return Get-YamlRuneCount -Text ([string] $Node.Value)
+    }
+    return Get-YamlRuneCount -Text $RenderedText
+}

src/functions/private/Write-YamlNodeText.ps1

@@ -45,12 +45,20 @@ function Write-YamlNodeText {
         if ($task.Type -eq 'Entry') {
             $keyText = ConvertTo-YamlFlowText -Node $task.Entry.Key `
                 -EmittedReferences $EmittedReferences
+            $explicitKey = (
+                Get-YamlEmissionImplicitKeyLength -Node $task.Entry.Key `
+                    -RenderedText $keyText
+            ) -gt 1024
+            if ($explicitKey) {
+                $spaces = ' ' * ($task.Level * $Indent)
+                [void] $Builder.Append($spaces).Append('? ').Append($keyText).Append("`n")
+            }
             $stack.Push([pscustomobject]@{
                     Type        = 'Node'
                     Node        = $task.Entry.Value
                     Entry       = $null
                     Level       = $task.Level
-                    LeadingText = "$keyText`: "
+                    LeadingText = if ($explicitKey) { ': ' } else { "$keyText`: " }
                 })
             continue
         }

tests/ConvertTo-Yaml.Tests.ps1

@@ -261,6 +261,53 @@ Describe 'ConvertTo-Yaml' {
             $enumerator.Value | Should -Be 'value'
         }
 
+        It 'uses explicit keys when scalar keys exceed 1024 Unicode values' {
+            $atLimit = [System.Collections.Specialized.OrderedDictionary]::new()
+            $atLimit.Add(('x' * 1024), 'value')
+            $overLimit = [System.Collections.Specialized.OrderedDictionary]::new()
+            $overLimit.Add(('😀' * 1025), [ordered]@{ nested = 'value' })
+
+            $atLimitYaml = ConvertTo-Yaml -InputObject $atLimit
+            $overLimitYaml = ConvertTo-Yaml -InputObject $overLimit
+            $roundTrip = $overLimitYaml | ConvertFrom-Yaml -AsHashtable
+
+            $atLimitYaml | Should -Not -Match '^\? '
+            $overLimitYaml | Should -Match '^\? '
+            $overLimitYaml | Should -Match '(?m)^: $'
+            ($overLimitYaml | Test-Yaml) | Should -BeTrue
+            $roundTrip.Contains(('😀' * 1025)) | Should -BeTrue
+            $roundTrip[('😀' * 1025)]['nested'] | Should -Be 'value'
+        }
+
+        It 'uses explicit keys when rendered collection keys exceed 1024 values' {
+            $dictionary = [System.Collections.Specialized.OrderedDictionary]::new()
+            $key = [object[]] (0..299)
+            $dictionary.Add($key, 'value')
+
+            $yaml = ConvertTo-Yaml -InputObject $dictionary
+            $roundTrip = $yaml | ConvertFrom-Yaml -AsHashtable
+            $enumerator = $roundTrip.GetEnumerator()
+            $null = $enumerator.MoveNext()
+
+            $yaml | Should -Match '^\? \['
+            ($yaml | Test-Yaml) | Should -BeTrue
+            $enumerator.Key | Should -Be $key
+            $enumerator.Value | Should -Be 'value'
+        }
+
+        It 'uses explicit keys inside flow-rendered complex keys' {
+            $innerKey = [System.Collections.Specialized.OrderedDictionary]::new()
+            $innerKey.Add(('x' * 1025), 'inner')
+            $dictionary = [System.Collections.Specialized.OrderedDictionary]::new()
+            $dictionary.Add($innerKey, 'outer')
+
+            $yaml = ConvertTo-Yaml -InputObject $dictionary
+
+            $yaml | Should -Match '\{\? '
+            ($yaml | Test-Yaml) | Should -BeTrue
+            { $yaml | ConvertFrom-Yaml -AsHashtable } | Should -Not -Throw
+        }
+
         It 'rejects dictionary keys that normalize to the same YAML value' {
             $dictionary = [System.Collections.Specialized.OrderedDictionary]::new()
             $dictionary.Add([int] 1, 'int')