Fix binding IEnumerable<T> with empty array configuration

[tarekgh]

Fixes #121193

The change is fixing IEnumerable type binding to an empty array configuration. The change also ensures the source generator will behave exactly as the runtime binder.

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[Copilot]

Pull Request Overview

This PR fixes the binding behavior for empty arrays in configuration to nullable IEnumerable<T> properties and the IEnumerable<T> interface type. Previously, empty arrays in configuration would not properly bind to nullable IEnumerable<T> properties, leaving them null instead of assigning an empty array.

Key Changes

• Extended the empty array binding logic to support the IEnumerable<T> interface in addition to arrays
• Added a new helper method IsIEnumerableInterface to detect exact IEnumerable<T> interface types
• Updated both the runtime binder and source generator to handle this case
• Fixed a typo in a comment ("configuation" → "configuration")

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
ConfigurationBinder.cs	Added IsIEnumerableInterface method and updated binding logic to handle empty arrays for IEnumerable<T> properties
TypeSpec.cs	Added IsExactIEnumerableOfT property to identify IEnumerable<T> interface types in source generation
CoreBindingHelpers.cs	Updated source generator to handle empty array assignment for IEnumerable<T> properties
KnownTypeSymbols.cs	Fixed typo in comment: "configuation" → "configuration"
ConfigurationBinderTests.TestClasses.cs	Added test class MyOptionsWithNullableEnumerable with nullable IEnumerable<T> and array properties
ConfigurationBinderTests.cs	Added test case to verify empty array binding to nullable IEnumerable<T> properties

[jeffhandley]

I don't know the context well enough to understand why only T[] and IEnumerable<T> is sufficient to handle.

Could the config have other collection types such as IReadOnlyList<T> where the behavior is the same as IEnumerable<T> and would also have the same unexpected break here?

[tarekgh]

Could the config have other collection types such as IReadOnlyList where the behavior is the same as IEnumerable and would also have the same unexpected break here?

With this change and using other collections like IReadOnlyList<T>, we'll get .NET 9.0 behavior which will bind to null value instead of empty collection. We can consider improving these cases in .NET 11 to limit the risk if we decide to service this change to .NET 10.

[tarekgh]

/ba-g the failures are unrelated and mostly showing in other PRs.

[tarekgh]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0 (link to workflow run)