2921 added the `?` operator to allow filters to have expressions like `?foo & foo = "foo"`, where `?foo` is true if and only if `foo` is a defined variable (or an expression where all the variables have been successfully resolved).

However, it doesn't seem to have been working, which I'd spotted in the ocaml-system updates in https://github.com/ocaml/opam-repository/pull/25861. Unfortunately, the failure means that the repository can't be used with --strict.

The fundamental problem is that the warning about undefined variables is displayed when the variables are being resolved, which sadly includes the moment they are being tested with the ? operator. However, when a filter is partially evaluated, the resulting filter will only contain undefined variables (and the post variable), which allows the check added in #5141 to be co-opted to display the unresolved variables after the filter has been reduced, rather than during the reducing.

ocaml / opam

Don't display undefined variable warnings when evaluating the `?` operator #5983

2921 added the `?` operator to allow filters to have expressions like `?foo & foo = "foo"`, where `?foo` is true if and only if `foo` is a defined variable (or an expression where all the variables have been successfully resolved).

ocaml / opam

Don't display undefined variable warnings when evaluating the `?` operator #5983

2921 added the ? operator to allow filters to have expressions like ?foo & foo = "foo", where ?foo is true if and only if foo is a defined variable (or an expression where all the variables have been successfully resolved).

2921 added the `?` operator to allow filters to have expressions like `?foo & foo = "foo"`, where `?foo` is true if and only if `foo` is a defined variable (or an expression where all the variables have been successfully resolved).