ConvertTo-Json behaviour with array with single element inconsistent when piping

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Steps to reproduce

Single element

PS> $arr = @(1)
PS> ConvertTo-Json -InputObject $arr -Compress # [1]
PS> $arr | ConvertTo-Json -Compress # 1

Multiple elements

PS> $arr = @(1,2)
PS> ConvertTo-Json -InputObject $arr -Compress # [1,2]
PS> $arr | ConvertTo-Json -Compress # [1,2]

Expected behavior

I expected the same behaviour from both of these lines when an array contains one item:

PS> $arr = @(1)
PS> ConvertTo-Json -InputObject $arr -Compress # [1]
PS> $arr | ConvertTo-Json -Compress # [1]

Actual behavior

ConvertTo-Json with piped input converts a single element array to a string without array characters ([]).

Error details

No response

Environment data

Name                           Value
----                           -----
PSVersion                      7.2.6
PSEdition                      Core
GitCommitId                    7.2.6
OS                             Darwin 21.6.0 Darwin Kernel Version 21.6.0: Mon Aug 22 20:19:52 PDT 2022; root:xnu-8020.140.49~2/RELEASE_ARM64_T6000
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

[nosalan]

This is quite error-prone behavior of ConvertTo-Json for single element arrays, I wish it was fixed.

[johanredeploy]

@jhoneill makes sense when you explain it.

So this is a workaround I guess?

$arr = @(1)
,$arr | ConvertTo-Json -Compress # [1]

I will either way restort to using InputObject in the future because this confused me for a fair while.

Still seems a bit inconsistent that multiple elements yields proper output when piping.