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Recursive TypeVariable resolution results in ClassCastException when type var is referenced multiple times #1390

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mcumings opened this issue Sep 25, 2018 · 0 comments · Fixed by #1391

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@mcumings
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@mcumings mcumings commented Sep 25, 2018

The recursive type variable resolution protections put into place in Gson 2.8.2 to fix #1128 does not work if a TypeVariable is referenced multiple times.

Example failing code:

    enum TestEnum { ONE, TWO, THREE }

    private static class TestEnumSetCollection extends SetCollection<TestEnum> {}

    private static class SetCollection<T> extends BaseCollection<T, Set<T>> {}

    private static class BaseCollection<U, C extends Collection<U>>
    {
        public C collection;
    }

When used with the following code to unmarshal

TestEnumSetCollection withSet = gson.fromJson("{\"collection\":[\"ONE\",\"THREE\"]}", TestEnumSetCollection.class);

The enum values are unmarshaled as String instances instead of as TestEnum instances, causing ClassCastException to be raised at runtime. This is due to the fact that the visitedTypeVariables map receives an entry for T, resolves it properly, and then upon subsequent attempt to resolve T fails, since the visitedTypeVariables set indicates that T has already been resolved.

mcumings added a commit to mcumings/gson that referenced this issue Sep 25, 2018
When a type variable is referenced multiple times it needs to resolve
to the same value.  Previously, the second attempt would abort
resolution early in order to protect against infinite recursion.
mcumings added a commit to mcumings/gson that referenced this issue Sep 25, 2018
When a type variable is referenced multiple times it needs to resolve
to the same value.  Previously, the second attempt would abort
resolution early in order to protect against infinite recursion.
eamonnmcmanus added a commit that referenced this issue Aug 2, 2021
Fix issue with recursive type variable protections to fix #1390
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