[release/11.0] Fix confusing exception message in Dictionary.CopyTo when index exceeds array length - #132571
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[release/11.0] Fix confusing exception message in Dictionary.CopyTo when index exceeds array length#132571github-actions[bot] wants to merge 1 commit into
Dictionary.CopyTo when index exceeds array length#132571github-actions[bot] wants to merge 1 commit into
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…eeds array length (#132465) Fixes #131782 ### Description This PR improves the exception message produced by `Dictionary<TKey, TValue>`'s `CopyTo` methods when the provided `index` exceeds the target array's length. Instead of throwing the misleading `Non-negative number required` message, it now utilizes `ThrowHelper.ThrowArgumentOutOfRange_IndexMustBeLessOrEqualException()` to yield a clearer message while maintaining the existing `ArgumentOutOfRangeException` type. ### Customer Impact Prevents confusion when developers encounter unexpected index-related validation errors during collection copy operations.
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Tagging subscribers to this area: @dotnet/area-system-collections |
This was referenced Aug 20, 2026
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/ba-g Failures are #132336 and a BadExit |
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@artl93 This is another customer-reported opportunity to improve an exception message that I recommend we consider for RC2. |
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Backport of #132465 to release/11.0
/cc @jeffhandley @aw0lid
Customer Impact
Customer-reported in #131782. A positive
indexbeyond the destination array length causes genericDictionary<TKey, TValue>.CopyToto throwArgumentOutOfRangeExceptionwith the misleading message "Non-negative number required." This fix keeps the exception type and parameter while using a clearer existing message. The separately reported non-generic path is unchanged.The change in #132465 was also a community contribution to improve the message.
Regression
Testing
Existing tests cover this invalid index and assert the exception type, but not the exception message. No tests were added.
Risk
Low. Only the message resource used for the exception is changed, reusing a different existing resource with a clearer message.