Fixed codegen for IEnumerable<T> binding (#123422)

[dmitry-kandiner]

Binding of an IEnumerable in a nested positional record resulted in throwing of an InvalidOperationException from source generated code. The condition for emitting the code throwing the exception only worked with Arrays, and this fix applies the same logic for IEnumerable as well.

Fix #123422

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[dmitry-kandiner]

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[Copilot]

Pull request overview

This pull request fixes a regression in the configuration binder's source generator where binding IEnumerable<T> in nested positional records incorrectly threw an InvalidOperationException. The issue occurred because the code generation logic for handling empty collections and error conditions only checked for ArraySpec types, but not for IEnumerable<T> types.

Changes:

• Updated the condition for emitting exception-throwing code to handle both ArraySpec and types with IsExactIEnumerableOfT property
• Added a test case to verify that nested IEnumerable<T> in positional records can be bound successfully

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Emitter/CoreBindingHelpers.cs	Fixed the condition that determines when to emit if (member is null) vs else for exception throwing, now including IEnumerable<T> types alongside arrays
src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.cs	Added test case TestBindingNestedIEnumerable to verify the fix works for the reported scenario
src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.TestClasses.cs	Added test classes ContainingIEnumerable and NestedWithIEnumerable to support the new test case

[tarekgh]

@dmitry-kandiner please don't force push again because this reset the review. Thanks!

[dmitry-kandiner]

@dmitry-kandiner please don't force push again because this reset the review. Thanks!

Oops! I assumed not being lined up to the target branch will prevent merging. My mistake.

[tarekgh]

Oops! I assumed not being lined up to the target branch will prevent merging. My mistake.

No worries. We don't have to do that except if there is a merge conflict. Otherwise, every change in the PR will reset the CI run and takes longer to finish.