Add runtime NullReferenceException validation to foreach null iteration tests by Copilot · Pull Request #80839 · dotnet/roslyn

Copilot · 2025-10-21T18:03:22Z

Identify all tests added/modified in commit d46a551 that verify no diagnostics for foreach on typed null values
Update tests to also execute code and validate NullReferenceException is thrown at runtime
Add .VerifyDiagnostics() to all CompileAndVerify calls
Build and test the changes
Ensure tests follow existing patterns in the repository

Original prompt

This section details on the original issue you should resolve

<issue_title>Consider tests demonstrating a runtime null reference exception when iterating over null.</issue_title>
<issue_description>d46a551 introduced many new tests that demonstrate that it's ok to iterate over a constant null value (though not the null-literal itself). It would be good if the tests that were updated (or added) that have no diagnostics also executed the code and validating that a null-ref exception is thrown. </issue_description>

<agent_instructions>Copilot, can you please take a look at all the tests affected in d46a551 and update those that are reporting no diagnostics to also execute the code and validate that a null-ref exception is thrown at runtime?</agent_instructions>

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

Fixes #80838

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Updated 9 tests to execute code and verify that NullReferenceException is thrown: - ForeachOnDefaultArray - ForeachOnDefaultString - ForeachOnDefaultIEnumerable - ForeachOnNullCastToIEnumerable - ForeachOnNullCastToArray - ForeachOnNullCastToString - ForeachOnNullCastToDynamic - ForeachOnNullCastToMultidimensionalArray - ForeachOnNullCastToConstrainedTypeParameter Co-authored-by: CyrusNajmabadi <4564579+CyrusNajmabadi@users.noreply.github.com>

CyrusNajmabadi · 2025-10-21T18:54:58Z

@dotnet/roslyn-compiler ptal.

jcouv · 2025-10-21T18:57:38Z

src/Compilers/CSharp/Test/Semantic/Semantics/ForEachTests.cs

                """;

-            CreateCompilation(source).VerifyEmitDiagnostics();
+            CompileAndVerify(source, expectedOutput: "NullReferenceException");


@copilot Add .VerifyDiagnostics() to all the CompileAndVerify calls you added. For example: CompileAndVerify(source, expectedOutput: "NullReferenceException").VerifyDiagnostics();

Added .VerifyDiagnostics() to all 9 CompileAndVerify calls in commit 1c2bd78.

Co-authored-by: jcouv <12466233+jcouv@users.noreply.github.com>

jcouv

LGTM Thanks (commit 2)

AlekseyTs · 2025-10-22T13:54:44Z

src/Compilers/CSharp/Test/Semantic/Semantics/ForEachTests.cs

+                        try
+                        {
+                            foreach (int x in default(int[]))
+                            {


{

I think it will be useful to observe that the loop didn't execute, consider printing something from the loop, or throw a different exception.

@CyrusNajmabadi Did you see this comment?

i did. I didn't think it was worthwhile enough, and didn't think the comment was blocking. So i went ahead with merging.

i did. I didn't think it was worthwhile enough, and didn't think the comment was blocking. So i went ahead with merging.

Just making sure you saw it

AlekseyTs

LGTM (commit 3)

* upstream/main: (332 commits) Cache lambdas in analyzer driver (dotnet#80759) Add information for NuGet package version 4.14 (dotnet#80870) Add missing search keywords to VB Advanced options page Fix IDE0031 false positive when preprocessor directives are used in if statements (dotnet#80878) Use core compiler on netfx hosts with toolset package (dotnet#80631) Make string concat assert more precise (dotnet#80619) Extensions: address some diagnostic quality issues (dotnet#80827) Add note on traversal order for bound nodes (dotnet#80872) Ensure that locals at the top level of a constructor have the same safe-context as parameters (dotnet#80807) Fix handling of SymbolDisplayCompilerInternalOptions.UseArityForGenericTypes option for non-native symbol implementations (dotnet#80826) Update src/Analyzers/CSharp/Tests/UseCollectionInitializer/UseCollectionInitializerTests.cs Add IsValidContainingStatement check to prevent collection initializers in using declarations Add back old DocumentSpan constructor (dotnet#80864) Add tests verifying pointer types in type parameters require unsafe context (dotnet#80776) Add regression test for Interlocked.Exchange with nullable types (dotnet#80796) Add regression test for ParseAttributeArgumentList with invalid input (fixes dotnet#8699) (dotnet#80705) Add regression test for compiler crash with syntax error in indexer declaration (dotnet#80772) Add runtime NullReferenceException validation to foreach null iteration tests (dotnet#80839) Update MicrosoftBuildTasksCoreVersionForMetrics to 17.11.48 (dotnet#80812) Mark CS4009 error as a "build only" error. (dotnet#80698) ...

Initial plan

f41fcb4

Copilot AI assigned Copilot and CyrusNajmabadi Oct 21, 2025

Copilot started work on behalf of CyrusNajmabadi October 21, 2025 18:03 View session

github-actions bot added the Area-Infrastructure label Oct 21, 2025

Copilot AI changed the title ~~[WIP] Update tests to validate null reference exception at runtime~~ Add runtime NullReferenceException validation to foreach null iteration tests Oct 21, 2025

Copilot AI requested a review from CyrusNajmabadi October 21, 2025 18:17

Copilot finished work on behalf of CyrusNajmabadi October 21, 2025 18:17

CyrusNajmabadi marked this pull request as ready for review October 21, 2025 18:54

CyrusNajmabadi requested a review from a team as a code owner October 21, 2025 18:54

CyrusNajmabadi approved these changes Oct 21, 2025

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jcouv reviewed Oct 21, 2025

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Copilot started work on behalf of jcouv October 21, 2025 18:57 View session

Add VerifyDiagnostics() to CompileAndVerify calls

4dc5da8

Co-authored-by: jcouv <12466233+jcouv@users.noreply.github.com>

Copilot finished work on behalf of jcouv October 21, 2025 19:06

Copilot AI requested a review from jcouv October 21, 2025 19:06

jcouv approved these changes Oct 21, 2025

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jcouv added Area-Compilers Test Test failures in roslyn-CI and removed Area-Infrastructure labels Oct 21, 2025

jcouv self-assigned this Oct 21, 2025

AlekseyTs reviewed Oct 22, 2025

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AlekseyTs approved these changes Oct 22, 2025

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CyrusNajmabadi merged commit d8fb41b into main Oct 23, 2025
24 checks passed

dotnet-policy-service bot added this to the Next milestone Oct 23, 2025

This was referenced Oct 25, 2025

[Automated] PRs inserted in VS build feature.polytype-11124.148 #80896

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[Automated] PRs inserted in VS build main-11124.32 #80897

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dotnet-bot mentioned this pull request Oct 28, 2025

[Automated] PRs inserted in VS build feature.debugger.main-11127.165 #80926

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dotnet-maestro bot mentioned this pull request Oct 29, 2025

[main] Source code updates from dotnet/roslyn dotnet/dotnet#3147

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CyrusNajmabadi deleted the copilot/update-tests-for-null-ref-exception branch December 2, 2025 11:52

dotnet-maestro bot mentioned this pull request Dec 18, 2025

[main] Source code updates from dotnet/roslyn dotnet/dotnet#3957

Merged

davidwengier modified the milestones: Next, 18.3 Jan 6, 2026

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Add runtime NullReferenceException validation to foreach null iteration tests#80839

Add runtime NullReferenceException validation to foreach null iteration tests#80839
CyrusNajmabadi merged 3 commits intomainfrom
copilot/update-tests-for-null-ref-exception

Copilot AI commented Oct 21, 2025 •

edited

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Copilot AI commented Oct 21, 2025 •

edited

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