Add Test-PowerShellDataFile function for validation

[MariusStorhaug]

Scripts that load PSD1 content from external sources (config registries, Git blobs, HTTP) need to validate it before parsing. The built-in Import-PowerShellDataFile only reads files and throws on invalid input — there is no string-based or boolean-returning equivalent.

PowerShell's Test-Json sets the established pattern for serialization-format validators: returns [bool], writes parser errors to the error stream when invalid.

Request

Desired capability

Test-PowerShellDataFile -Path module.psd1     # validate a file
$content | Test-PowerShellDataFile             # validate a string
'@{ broken' | Test-PowerShellDataFile          # returns $false, writes error

Parameters

Parameter	Description
-Path	File path to validate (parameter set: Path)
-LiteralPath	Literal path (parameter set: LiteralPath)
-InputObject	String to validate (ValueFromPipeline, default set)
-AllowedTypes	Optional list of allowed value types beyond the PSD1 default subset

Validation rules

• Content parses as a single hashtable expression at the top level
• Only PSD1-allowed types appear (hashtables, arrays, strings, numbers, booleans, null, [datetime], [guid], [char], [scriptblock])
• No command invocations, variable references, or other dynamic constructs (the same safety check Import-PowerShellDataFile performs)

Acceptance criteria

• Returns $true when content is a valid PSD1 expression
• Returns $false when content is invalid; the parser error is written to the error stream
• Accepts pipeline input as a string
• Mirrors Test-Json parameter shape and behavior
• Equivalent to attempting Import-PowerShellDataFile on a temp file but without the file I/O

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Technical decisions

Implementation: Wraps ConvertFrom-PowerShellDataFile (tracked separately) in try/catch. On exception, writes the parser error via Write-Error and returns $false. On success, returns $true.

Function placement: src/functions/public/Test-PowerShellDataFile.ps1.

No new parser logic: Reuses the AST-based parser from ConvertFrom-PowerShellDataFile. This keeps validation behavior consistent with parsing behavior and matches the safety guarantees of the built-in Import-PowerShellDataFile.

Output type: [bool] only.

Alias: Test-Psd1.

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Implementation plan

• Add Test-PowerShellDataFile in src/functions/public/Test-PowerShellDataFile.ps1 with Test-Psd1 alias
• Add Pester tests — valid string, invalid string (syntax error), disallowed type (e.g., command invocation), valid file, invalid file, pipeline input, error-stream contents
• Update README with usage example

Related

• ConvertFrom/ConvertTo-PowerShellDataFile (prerequisite — separate issue)