feat: add is_mutable_raw_ptr and as_raw_ptr to hir::Type

[mehmet-ylcnky]

Summary

Add is_mutable_raw_ptr() and as_raw_ptr() methods to hir::Type, closing an API gap where raw pointer mutability (*mut vs *const) was not queryable through the public API.

Problem

hir::Type provides is_raw_ptr() to check if a type is a raw pointer, but there is no way to distinguish *mut T from *const T. This is asymmetric with references, where both is_mutable_reference() and as_reference() -> Option<(Type, Mutability)> exist:

// References — full mutability API:
pub fn is_reference(&self) -> bool;
pub fn is_mutable_reference(&self) -> bool;
pub fn as_reference(&self) -> Option<(Type, Mutability)>;

// Raw pointers — mutability NOT queryable before this PR:
pub fn is_raw_ptr(&self) -> bool;
pub fn remove_raw_ptr(&self) -> Option<Type>;  // discards mutability

The internal representation (TyKind::RawPtr(Ty, Mutability)) already carries the mutability, but Type.ty is pub(crate) so external consumers cannot access it. The only workaround was parsing the display string:

let is_mut = ty.is_raw_ptr() && ty.display(db).to_string().starts_with("*mut ");

This feature was asked about on StackOverflow (How to determine raw pointer mutability from ra_ap_hir::Type?), where a rust-analyzer team member confirmed this is a gap in the API and encouraged contributing the fix.

Solution Proposal

Add two methods to hir::Type, following the exact same pattern as their reference counterparts:

pub fn is_mutable_raw_ptr(&self) -> bool {
    matches!(self.ty.kind(), TyKind::RawPtr(.., Mutability::Mut))
}

pub fn as_raw_ptr(&self) -> Option<(Type<'db>, Mutability)> {
    let TyKind::RawPtr(ty, m) = self.ty.kind() else { return None };
    let m = Mutability::from_mutable(matches!(m, Mutability::Mut));
    Some((self.derived(ty), m))
}

Test

Snapshot test covers all five type categories side by side, showing the symmetry between the raw pointer and reference APIs:

a (*const u32): is_mutable_raw_ptr: false, as_raw_ptr: Some(Shared)
b (*mut u32):   is_mutable_raw_ptr: true,  as_raw_ptr: Some(Mut)
c (&u32):       is_mutable_reference: false, as_reference: Some(Shared)
d (&mut u32):   is_mutable_reference: true,  as_reference: Some(Mut)
e (u32):        all false/None

AI tools were used in the development of this change.

[ChayimFriedman2]

We don't add tests for API methods.

Also, please add a comment that these methods are used outside r-a, to prevent removing them.

View changes since this review

[mehmet-ylcnky]

Thanks for the review! Removed the tests and added comments noting these methods are used outside rust-analyzer.

[ChayimFriedman2]

Please squash.

View changes since this review

[ChayimFriedman2]

You need to rebase so CI can pass, then I'll merge this.