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fix(engine): unwrap scalar PSObject during collection binding #27970

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Daksh Goyal (daksh-goyal) wants to merge 1 commit into from
+69 −11
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fix(engine): unwrap scalar PSObject during collection binding #27970

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24 changes: 13 additions & 11 deletions src/System.Management.Automation/engine/ParameterBinderBase.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1795,6 +1795,8 @@ private object EncodeCollection(
"Argument type {0} is not IList, treating this as scalar",
currentValue.GetType().Name);

object currentValueElement = PSObject.Base(currentValue);

@daxian-dbw Dongbo Wang (daxian-dbw) Oct 5, 2026

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This applies to every collection type, and that is too broad. It's better to special case the StringCollection type as the WG comment pointed out in the issue.


if (collectionElementType != null)
{
if (coerceElementTypeIfNeeded)
Expand All @@ -1805,17 +1807,17 @@ private object EncodeCollection(

// Coerce the scalar type into the collection

currentValue =
currentValueElement =
CoerceTypeAsNeeded(
argument,
parameterName,
collectionElementType,
null,
currentValue);
}
else
else if (currentValueElement != null)
{
Type currentValueElementType = currentValue.GetType();
Type currentValueElementType = currentValueElement.GetType();
Type desiredElementType = collectionElementType;

if (currentValueElementType != desiredElementType &&
Expand All @@ -1840,23 +1842,23 @@ private object EncodeCollection(
{
bindingTracer.WriteLine(
"Adding scalar element of type {0} to array position {1}",
(currentValue == null) ? "null" : currentValue.GetType().Name,
(currentValueElement == null) ? "null" : currentValueElement.GetType().Name,
0);
resultAsIList[0] = currentValue;
resultAsIList[0] = currentValueElement;
}
else if (collectionTypeInformation.ParameterCollectionType == ParameterCollectionType.IList)
{
bindingTracer.WriteLine(
"Adding scalar element of type {0} via IList.Add",
(currentValue == null) ? "null" : currentValue.GetType().Name);
resultAsIList.Add(currentValue);
(currentValueElement == null) ? "null" : currentValueElement.GetType().Name);
resultAsIList.Add(currentValueElement);
}
else
{
bindingTracer.WriteLine(
"Adding scalar element of type {0} via ICollection<T>::Add()",
(currentValue == null) ? "null" : currentValue.GetType().Name);
addMethod.Invoke(resultCollection, new object[1] { currentValue });
(currentValueElement == null) ? "null" : currentValueElement.GetType().Name);
addMethod.Invoke(resultCollection, new object[1] { currentValueElement });
}
}
catch (Exception error) // OK, we catch all here by design
Expand All @@ -1877,10 +1879,10 @@ private object EncodeCollection(
GetErrorExtent(argument),
parameterName,
toType,
currentValue?.GetType(),
currentValueElement?.GetType(),
ParameterBinderStrings.CannotConvertArgument,
"CannotConvertArgument",
currentValue ?? "null",
currentValueElement ?? "null",
error.Message);
throw bindingException;
}
Expand Down
56 changes: 56 additions & 0 deletions test/powershell/Language/Parser/ParameterBinding.Tests.ps1
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Expand Up @@ -472,3 +472,59 @@ Describe 'Roundtrippable Conversions for Bare-string Numeric Literals passed to
Invoke-Expression "Test-AdvancedStringValue -Value $Argument" | Should -BeExactly $Argument
}
}

Describe 'Scalar PSObject binding to non-generic IList parameters' -Tags 'CI' {
BeforeAll {
$typeDefinition = @'
using System.Collections.Specialized;
using System.Management.Automation;

namespace ScalarPSObjectCollectionBinding
{
[Cmdlet(VerbsDiagnostic.Test, "ScalarStringCollectionBinding")]
[OutputType(typeof(string))]
public sealed class TestScalarStringCollectionBindingCommand : PSCmdlet
{
[Parameter(Mandatory = true)]
public StringCollection Value { get; set; }

protected override void ProcessRecord()
{
WriteObject(Value[0]);
}
}
}
'@

$types = Add-Type -PassThru -TypeDefinition $typeDefinition
Import-Module $types[0].Assembly
}

It 'binds a scalar PSObject wrapping a string to StringCollection' {
$value = @('expected', 'expected') | Select-Object -Unique

# Confirm that this is the specific problematic input shape.
$value.GetType().FullName | Should -BeExactly 'System.String'
($value -is [System.Management.Automation.PSObject]) |
Should -BeTrue

Test-ScalarStringCollectionBinding -Value $value |
Should -BeExactly 'expected'
}

It 'continues to bind a plain scalar string' {
Test-ScalarStringCollectionBinding -Value 'expected' |
Should -BeExactly 'expected'
}

It 'continues to bind multiple pipeline-produced strings' {
$value = @('first', 'second') | Select-Object -Unique

$result = @(
Test-ScalarStringCollectionBinding -Value $value
)

# The test cmdlet writes Value[0], proving binding succeeded.
$result | Should -BeExactly 'first'
}
}
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