Fix derive bounds for fully-qualified field types by djkoloski · Pull Request #139272 · rust-lang/rust (original) (raw)
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Builtin traits like Clone, Debug, and PartialEq which can be
derived look for uses of generics when adding type bounds. However, the
procedure for adding these trait bounds did not account for
fully-qualified type paths. This causes code which does not
fully-qualify paths to generate correct derive bounds, while
fully-qualified paths do not receive correct bounds. For example:
struct Foo<T: MyTrait>(T::MyType);Will receive the correct T::MyType: Clone bound, but:
struct Foo<T: MyTrait>(<T>::MyType);Does not. This change modifies generic parameter detection to walk up
the chain of QSelfs in path types when looking for type parameters,
rather than only looking at the outermost type.
Status: Awaiting review from the assignee but also interested parties.
Relevant to the compiler team, which will review and decide on the PR/issue.
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Relevant to the types team, which will review and decide on the PR/issue.
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bors added a commit to rust-lang-ci/rust that referenced this pull request
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Fix derive bounds for fully-qualified field types
Builtin traits like Clone, Debug, and PartialEq which can be derived look for uses of generics when adding type bounds. However, the procedure for adding these trait bounds did not account for fully-qualified type paths. This causes code which does not fully-qualify paths to generate correct derive bounds, while fully-qualified paths do not receive correct bounds. For example:
#[derive(Clone)]
struct Foo<T: MyTrait>(T::MyType);Will receive the correct T::MyType: Clone bound, but:
#[derive(Clone)]
struct Foo<T: MyTrait>(<T>::MyType);Does not. This change modifies generic parameter detection to walk up the chain of QSelfs in path types when looking for type parameters, rather than only looking at the outermost type.
Related issues:
Note that there are existing tests for this behavior. However, the existing tests accidentally include fields with the working syntax (T::MyType) alongside fields with the broken syntax (<T>::MyType) and so this issue has gone undiscovered.
This is a conservative fix; it aims only to make previously-invalid code valid. It does not attempt to move the builtin derive macros closer to a perfect derive.
Status: This is awaiting some action (such as code changes or more information) from the author.
and removed S-waiting-on-review
Status: Awaiting review from the assignee but also interested parties.
labels