[release/8.0-staging] Fix problem in ReadyToRun_TypeGenericInfoMap::HasConstraints#105728
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ivdiazsa wants to merge 1 commit intodotnet:release/8.0-stagingfrom
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[release/8.0-staging] Fix problem in ReadyToRun_TypeGenericInfoMap::HasConstraints#105728ivdiazsa wants to merge 1 commit intodotnet:release/8.0-stagingfrom ivdiazsa:pr-96358-backport
ivdiazsa wants to merge 1 commit intodotnet:release/8.0-stagingfrom
ivdiazsa:pr-96358-backport
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jeffschwMSFT
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lgtm. we will take for consideration in 8.0.x
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@ivdiazsa Did you mean to close this? |
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Oh no certainly not! This was a big mistake! |
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@jeffschwMSFT I was housekeeping and forgot I had this pending. Would it be possible to open a new PR and get the approval right away? |
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Customer Impact
Backport of PR #96358 to release/8.0. This bug came to light as reported by a customer in issue #96225. Since it reproduces on .NET 8 but was gone by .NET 9 preview 1, some further bisecting was done to figure out the fix.
The problem was that the code in the VM that is supposed to check for whether a generic type had (a) constraining clause(s), actually checked for whether said type was either covariant or contravariant. This completely different and therefore erroneous behavior broke some scenarios with generics and made them crash, like the one hindering our customer in this case.
Regression
This is a regression as the same scenario works properly in .NET 7 and .NET 6 versions. For context, it was accidentally introduced in this PR: #85743
Testing
This was validated using the customer's failing repro scenarios.
Risk
This PR poses little to no risk to the product. Since it's a small and simple one, we decided it would be a convenient and easy backport. The failure is well understood and has a well defined scope.