[DllImportGenerator] Warn/fail when passing by reference a SafeHandle without an accessible parameterless constructor.

[teo-tsirpanis]

When passing SafeHandles by reference, the DllImportGenerator needs their types to have an accessible parameterless constructor. If they don't, it tries to create them by generating a call to Activator.CreateInstance(typeof(MySafeHandle), nonPublic: true). If they don't have a parameterless constructor at all, the P/Invoke fails at runtime.

An analyzer should be added that helps with this situation. If the SafeHandle descendant in question does not have an accessible parameterless constructor. If it is in the same assembly with the P/Invoke, it should cause an error, directing the user to add one (or even helping them with a fixer). If it is in a different assembly, it should warn the user that the P/Invoke is not guaranteed to work, and suggest them to contact the SafeHandle in question's author.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[jkoritzinsky]

cc: @AaronRobinsonMSFT @elinor-fung @stephentoub this would be a proposal to add back part of the analyzer/code-fix removed in dotnet/roslyn-analyzers#5308 for being too noisy for SafeHandle-derived types used in non-P/Invoke scenarios. As part of #63085, we hit the exact scenario that the removed functionality was designed to assist.

[stephentoub]

I'm fine with an analyzer that warns on faulty P/Invokes in general: if we can detect a problem in a DllImport at compile time, a warning makes sense. And a SafeHandle returned from a p/invoke but lacking a ctor that makes that feasible is one such case. My pushback on the previous analyzer was that it was triggered for any SafeHandle, regardless of how it was consumed, regardless of whether it was used in P/Invokes.

[ghost]

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Issue Details

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When passing SafeHandles by reference, the DllImportGenerator needs their types to have an accessible parameterless constructor. If they don't, it tries to create them by generating a call to Activator.CreateInstance(typeof(MySafeHandle), nonPublic: true). If they don't have a parameterless constructor at all, the P/Invoke fails at runtime.

An analyzer should be added that helps with this situation. If the SafeHandle descendant in question does not have an accessible parameterless constructor. If it is in the same assembly with the P/Invoke, it should cause an error, directing the user to add one (or even helping them with a fixer). If it is in a different assembly, it should warn the user that the P/Invoke is not guaranteed to work, and suggest them to contact the SafeHandle in question's author.

Author:	teo-tsirpanis
Assignees:	-
Labels:	area-System.Runtime.InteropServices, source-generator
Milestone:	Future