[soareschen]

Overview

[deepseek-v4.1-flash] A mutable Option<&mut str> #[implicit] argument compiles again. The &str borrowing change made every Option<&str> read go through OptionAsRef, which borrows the field shared, but it applied the same field type to the mutable form too, so the generated bound became HasFieldMut<_, Value = str> and the read called as_deref_mut on a &mut str.

Motivation

A #[cgp_fn] or #[cgp_impl] with #[implicit] nickname: Option<&mut str> failed with E0308, expected &mut Option<_>, found &mut str. The form worked before that change, and the reference documentation describes it as reading an Option<String> field with .as_deref_mut().

Impact

A mutable read keeps the Option<String> field and reads it with .as_deref_mut(), which is the read a &mut self getter already uses; the shared Option<&str> keeps the allocator-free OptionAsRef read, and a &mut str implicit is unchanged. The new test pins the expansion and runs the provider against a Some and a None field.

Areas needing attention

The fix keeps the mutable option form on an Option<String> field rather than generalizing it to any Option<U> whose U derefs to str. A general form needs a mutable counterpart to OptionAsRef, and the getter macros use the same Option<String> read, so the two families agree.