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Add CA1812 suppressor for internal classes used as type parameters#116

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copilot/suppress-ca1812-warnings
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Add CA1812 suppressor for internal classes used as type parameters#116
Copilot wants to merge 4 commits intomasterfrom
copilot/suppress-ca1812-warnings

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Copilot AI commented Nov 30, 2025 •
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CA1812 ("Avoid uninstantiated internal classes") produces false positives when internal classes are instantiated via reflection or external code (e.g., JSON deserializers, DI containers). This adds a DiagnosticSuppressor to suppress CA1812 when the class is referenced as a type argument.

Changes

  • CA1812Suppressor.cs: New suppressor (RGS001) that scans for type argument usage in generic invocations, generic types, and typeof expressions
  • CA1812SuppressorTests.cs: Unit tests for suppressor descriptor properties and integration tests that verify actual CA1812 suppression behavior using a mock analyzer
  • README.md: Documentation under new "Suppressions" section

Example

internal class Model { // CA1812 suppressed
    public int Id { get; set; }
}

Model model = JsonConvert.DeserializeObject<Model>(json); // Type argument triggers suppression
Type t = typeof(Model); // Also triggers suppression
Original prompt

This section details on the original issue you should resolve

<issue_title>Suppress CA1812 (internal class never instantiated) if class is referenced as type parameter</issue_title>
<issue_description>```cs
internal class Model { // CA 1812
public int Id { get; set; }
}

Model model = JsonConvert.DeserializeObject(); // suppress CA1812


## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@ronnygunawan</author><body>
You can suppress warnings from other analyzer by using the `DiagnosticSuppressor`</body></comment_new>
</comments>

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Copilot AI and others added 2 commits November 30, 2025 01:45
@ronnygunawan
Add CA1812 suppressor for internal classes used as type parameters
bef7d47 
Co-authored-by: ronnygunawan <3048897+ronnygunawan@users.noreply.github.com>
@ronnygunawan
Address code review: support direct typeof(InternalClass) usage
3d3bfb8 
Co-authored-by: ronnygunawan <3048897+ronnygunawan@users.noreply.github.com>
Copilot AI changed the title [WIP] Suppress CA1812 warning for referenced type parameters Add CA1812 suppressor for internal classes used as type parameters Nov 30, 2025
Copilot AI requested a review from ronnygunawan November 30, 2025 01:51
ronnygunawan
ronnygunawan requested changes Nov 30, 2025
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Add test cases where this suppressor suppresses an actual warning

@ronnygunawan
Add integration tests that verify CA1812 suppression with actual diag…
a0a3f09 
…nostics

Co-authored-by: ronnygunawan <3048897+ronnygunawan@users.noreply.github.com>
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Copilot AI commented Nov 30, 2025

Add test cases where this suppressor suppresses an actual warning

Added integration tests using a mock CA1812 analyzer that verifies actual suppression behavior. The new tests cover:

  • InternalClassUsedAsGenericTypeArgument_CA1812IsSuppressed - Tests List<Model>
  • InternalClassUsedInGenericMethodCall_CA1812IsSuppressed - Tests Deserialize<Model>()
  • InternalClassUsedInTypeOf_CA1812IsSuppressed - Tests typeof(Model)
  • InternalClassNotUsedAsTypeArgument_CA1812IsNotSuppressed - Verifies warning is NOT suppressed when class isn't used as type argument

Commit: a0a3f09

Copilot AI requested a review from ronnygunawan November 30, 2025 15:34
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Suppress CA1812 (internal class never instantiated) if class is referenced as type parameter

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