`ConvertTo-Csv` and `Export-Csv` should unroll (embedded) arrays and lists

Prerequisites

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Steps to reproduce

Knowing that the -InputObject “Specifies the objects that are converted to CSV strings”, I would expect that any embedded array or list to unroll into objects (see also: Suggestion: Add a chunking (partitioning, batching) mechanism to Select-Object, analogous to Get-Content -ReadCount)

$List = 1..5 |ForEach-Object {
    [pscustomobject]@{ id = $_; name = "name$_" }
}

,$List |ConvertTo-Csv

Expected behavior

"id","name"
"1","name1"
"2","name2"
"3","name3"
"4","name4"
"5","name5"

Similar to:

$List |Convert-Csv # Without an unary comma

and to what Add-Content and Set-Content does for:

,(1..5) |Set-Content .\MyFile.txt

Or simply as it is being output:

,$List

id name
-- ----
 1 name1
 2 name2
 3 name3
 4 name4
 5 name5

Actual behavior

"Length","LongLength","Rank","SyncRoot","IsReadOnly","IsFixedSize","IsSynchronized","Count"
"5","5","1","System.Object[]","False","True","False","5"

Error details

No Error

Environment data

Name                           Value
----                           -----
PSVersion                      7.2.6
PSEdition                      Core
GitCommitId                    7.2.6
OS                             Microsoft Windows 10.0.22000
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

[jhoneill]

@mklement0 Yes, I was just reading the comment the 18070, and if for anything which looks at the InputObject parameter generally, the object vs Object[] question should be on the radar.
I wonder, without having checked, if the commands which unroll arrays tend towards having Object[] and the ones which don’t towards Object

When I’m coding in PowerShell I leave InputObject as object (which is implied so I don’t need to have it in the param block), and where a process block would be

Process { 
  Do_stuff_with $InputObject
}

I typically have

Process {
    foreach ($i in  $InputObject ) {
      Do_stuff_with $i
    }
}

I don’t spend enough time in c# to know if that is equally easy to do there - PowerShell is very tolerant of foreach ($i in $ScalarVariable) but this simple change means if the object is an array it unrolls (one level, not nested arrays) and if its scalar it processes as normal.

[jhoneill]

@mklement0 I’m looking at your category C items with a view to taking them to the cmdlet working group

There might be some quibbles about what is truly in category C. With Where-object, someone somewhere is bound to want to use the count of members or even -is [Array] in a where condition. But the list is a helpful place to start from.