Process.Start() should be supported on MacCatalyst

[chucker]

Description

In MAUI, Mac UI is accomplished through Catalyst (UIKit for macOS) rather than AppKit. As a side-effect, various internals claim to be iOS. For example, OperatingSystem.IsIOS() will return true on a Mac if the app is a Catalyst app.

If you try Process.Start() or Process.Kill(), you get a PlatformNotSupportedException(). I believe this is by mistake, as starting and killing a process should be possible in macOS (but it indeed isn't in iOS).

In short, I believe that line (and the equivalent for Kill()) should read:

if ((OperatingSystem.IsIOS() && !OperatingSystem.IsMacCatalyst()) || OperatingSystem.IsTvOS())

In addition, the annotation [UnsupportedOSPlatform("ios")] appears to be wrong, as it triggers a "unsupported on maccatalyst" warning.

Reproduction Steps

1. Create a project targeting net6.0-maccatalyst, e.g. from the MAUI template.
2. In MacCatalyst-specific code, call:

			var p = System.Diagnostics.Process.Start("/bin/ls");

Expected behavior

No warning should appear, and the process should launch.

Actual behavior

A warning appears, and launching the process throws in StartCore().

Regression?

This is arguably a regression compared to the Xamarin/Mono toolchain, because it targeted Cocoa (AppKit), not Catalyst (UIKit), where this wasn't a problem.

Known Workarounds

No response

Configuration

dotnet --info output:

~> dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.100-rc.2.21505.57
 Commit:    ab39070116

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  12.0
 OS Platform: Darwin
 RID:         osx-x64
 Base Path:   /usr/local/share/dotnet/sdk/6.0.100-rc.2.21505.57/

Host (useful for support):
  Version: 6.0.0-rc.2.21480.5
  Commit:  6b11d64e7e

.NET SDKs installed:
  5.0.402 [/usr/local/share/dotnet/sdk]
  6.0.100-rc.2.21505.57 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.11 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-rc.1.21452.15 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-rc.2.21480.10 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.11 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-rc.1.21451.13 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-rc.2.21480.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

Other information

No response

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Issue Details

---

Description

In MAUI, Mac UI is accomplished through Catalyst (UIKit for macOS) rather than AppKit. As a side-effect, various internals claim to be iOS. For example, OperatingSystem.IsIOS() will return true on a Mac if the app is a Catalyst app.

If you try Process.Start() or Process.Kill(), you get a PlatformNotSupportedException(). I believe this is by mistake, as starting and killing a process should be possible in macOS (but it indeed isn't in iOS).

In short, I believe that line (and the equivalent for Kill()) should read:

if ((OperatingSystem.IsIOS() && !OperatingSystem.IsMacCatalyst()) || OperatingSystem.IsTvOS())

In addition, the annotation [UnsupportedOSPlatform("ios")] appears to be wrong, as it triggers a "unsupported on maccatalyst" warning.

Reproduction Steps

1. Create a project targeting net6.0-maccatalyst, e.g. from the MAUI template.
2. In MacCatalyst-specific code, call:

			var p = System.Diagnostics.Process.Start("/bin/ls");

Expected behavior

No warning should appear, and the process should launch.

Actual behavior

A warning appears, and launching the process throws in StartCore().

Regression?

This is arguably a regression compared to the Xamarin/Mono toolchain, because it targeted Cocoa (AppKit), not Catalyst (UIKit), where this wasn't a problem.

Known Workarounds

No response

Configuration

dotnet --info output:

~> dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.100-rc.2.21505.57
 Commit:    ab39070116

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  12.0
 OS Platform: Darwin
 RID:         osx-x64
 Base Path:   /usr/local/share/dotnet/sdk/6.0.100-rc.2.21505.57/

Host (useful for support):
  Version: 6.0.0-rc.2.21480.5
  Commit:  6b11d64e7e

.NET SDKs installed:
  5.0.402 [/usr/local/share/dotnet/sdk]
  6.0.100-rc.2.21505.57 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.11 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-rc.1.21452.15 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-rc.2.21480.10 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.11 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-rc.1.21451.13 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-rc.2.21480.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

Other information

No response

Author:	chucker
Assignees:	-
Labels:	area-System.Diagnostics.Process, untriaged
Milestone:	-

[teo-tsirpanis]

I am not familiar with Apple's technologies, but is launching arbitrary processes actually supported by Catalyst itself on Mac compiters? My guess is that since Catalyst looks more like iOS it also has some of its constraints, to be able to run on both tablets and computers. If you want to launch another app (not process) then I guess there is an API for that, but again I am not knowledgable at all.

[chucker]

I am not familiar with Apple's technologies, but is launching arbitrary processes actually supported by Catalyst itself on Mac compiters?

I copied the bulk of StartCore() (without the OS check) and it forked a process just fine.

My guess is that since Catalyst looks more like iOS it also has some of its constraints, to be able to run on both tablets and computers.

I don't believe it does. You can use App Sandbox, but I don't think anything about Catalyst forces you into it. Now, since the majority of Catalyst apps will be iOS ports, it's safe to assume many of them won't use a feature that wouldn't also work on iOS. However, since the Xamarin/MAUI team (apparently?) chose to use Catalyst as the new UI toolkit for their Mac apps, I do think this is a relevant issue.

[danmoseley]

@steveisok thoughts? Seems like the fix is easy unless we know of some pitfall.

I wonder whether there are other places where we have OperatingSystem.IsIOS() that block functionality that works fine on Catalyst.

[marek-safar]

Yeah, we marked the process start this way to keep in in sync with other Apple mobile platforms but the restriction could be removed if it makes sense to have it.

@rolfbjarne for more context

[rolfbjarne]

I am not familiar with Apple's technologies, but is launching arbitrary processes actually supported by Catalyst itself on Mac compiters?

I copied the bulk of StartCore() (without the OS check) and it forked a process just fine.

If it works fine (and there are tests that test that it works so that we find out if Apple restricts it somehow), then I think it makes sense (and it's fine) to enable Process.Start for Mac Catalyst.

[filipnavara]

There was originally a problem with the ConfigureTerminalForChildProcess System.Native P/Invoke not being available on the mobile platforms (iOS, tvOS, Mac Catalyst) which propagated all the way up to Process.Start not working and throwing exceptions. This was later resolved in #54273. Omitting the API was intentional at one point in time and not just a fallout from OperatingSystem.IsIOS() == true on Mac Catalyst but the reason for it has passed.

[steveisok]

We can turn the tests on and see what happens. Our motivation for treating this as PNSE was to match iOS/tvOS behavior.

@danmoseley i don't believe there is anything mistakenly platform confused, but we will do a sanity check.