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is_prefix/is_suffix on absent fields

The change​

Before: Enforcing is_prefix or is_suffix on an absent field was silently skipped.

After: Enforcing is_prefix or is_suffix on an absent field now causes an enforcement failure.

Do I need to migrate?​

Consider a rule like this:

(rule
 (enforce (dune (library (public_name (is_prefix "mylib."))))))

Case 1: You intended to enforce the field's presence

If your intent was that all libraries must have a public_name with this prefix, then no migration is needed. The new behavior is a bug fix: previously, libraries without public_name would silently pass when they should have failed. Now they correctly trigger an enforcement failure.

Case 2: You intended conditional enforcement

If your intent was to only check the prefix when public_name exists (and allow libraries without it), you need to migrate. Wrap the constraint with if_present:

(rule
 (enforce (dune (library (if_present (public_name (is_prefix "mylib.")))))))

The if_present wrapper applies the constraint only when the field exists. When the field is absent, the condition is satisfied and no enforcement failure occurs.

Alternative: For more complex conditions, you can use the explicit if_ construct with has_field:

(rule
 (enforce
  (dune
   (library
    (if_ (has_field public_name)
         (public_name (is_prefix "mylib."))
         true_)))))