This is based on an issue, where Enter-PSHostProcess on a locked down (WDAC enforced) machine allows any admin to connect to any another local hosted PowerShell process and execute commands as that user. This amounts to privilege escalation on the policy locked down machine and something we want to prevent.
Fix is to check for system lock down and disable Enter-PSHostProcess cmdlet with an error message.
- Adds `LanguagePrimitives.IsNullLike()` method to account for `DBNull.Value` and `NullString.Value` so that they can be considered the same as a null value where sensible in PowerShell.
- Updates `-ne` and `-eq` binders to treat `DBNull.Value` and `NullString.Value` as equal to null/AutomationNull.
- Update code paths for comparing objects in LanguagePrimitives to ensure consistency with how the `-eq` and `-ne` binders work when calling LanguagePrimitives methods to do the comparisons.
- Make `LanguagePrimitives.IsNull()` and `LanguagePrimitives.IsNullLike()` public methods.
- Added tests for null behaviours in `NullRepresentatives.Tests.ps1`
.NET Core changes to return "shortest roundtrippable string" by default for the ToString() method of double and float types. This results in ToString() for double/float values sometimes return a string in 17-digit/9-digit precision format. This PR updated the double/float-to-string conversion in PowerShell to continue using the old precision specifier before the change in .NET Core 3.0.
`Read-Host` calls into `$Host.UI.Prompt()`. However, this method is also used when the host prompts for mandatory parameters that aren't provided. The method expects to be called when given a `FieldDescription` and if the input starts with `!` it enters `CommandPromptMode`. In this mode, you can type `!?` to request help, for example. However this mode is not something you can use via `Read-Host` (only if calling `$Host.UI.Prompt()` directly passing in a well constructed `FieldDescription`). When using `Read-Host -Prompt`, the cmdlet creates a `FieldDescription` where the name is the prompt and the rest of the properties are empty.
The fix is that if `Label` is empty, we can assume it's being called from `Read-Host` rather than being called to prompt for a mandatory parameter and thus not enter `CommandPromptMode`.
Expands line continuance for pipelines to allow lines to continue automatically without backticks with the pipe symbol at the start of a line.
This adds to the existing functionality where pipes can be used to continue lines by placing them at the end of a line.
