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Document some builtin impls in the next solver #122238

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merged 2 commits into from
Mar 14, 2024
Merged

Document some builtin impls in the next solver #122238

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4b76fac
Document some builtin impls in the next solver
fee1-dead Mar 9, 2024
69d781a
move impl documentation to their actual locations
fee1-dead Mar 14, 2024
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1 change: 1 addition & 0 deletions compiler/rustc_target/src/abi/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -121,6 +121,7 @@ impl<'a> Layout<'a> {
///
/// Currently, that means that the type is pointer-sized, pointer-aligned,
/// and has a initialized (non-union), scalar ABI.
// Please also update compiler/rustc_trait_selection/src/solve/trait_goals.rs if the criteria changes
pub fn is_pointer_like(self, data_layout: &TargetDataLayout) -> bool {
self.size() == data_layout.pointer_size
&& self.align().abi == data_layout.pointer_align.abi
Expand Down
39 changes: 39 additions & 0 deletions compiler/rustc_trait_selection/src/solve/trait_goals.rs
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Expand Up @@ -188,6 +188,16 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
})
}

/// ```rust,ignore (not valid rust syntax)
/// impl Sized for u*, i*, bool, f*, FnPtr, FnDef, *(const/mut) T, char, &mut? T, [T; N], dyn* Trait, !
///
/// impl Sized for (T1, T2, .., Tn) where T1: Sized, T2: Sized, .. Tn: Sized
///
/// impl Sized for Adt where T: Sized forall T in field types
/// ```
///
/// note that `[T; N]` is unconditionally sized since `T: Sized` is required for the array type to be
/// well-formed.
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My initial reaction was that I would prefer moving the comment for each builtin impl to the most specific place possible, having only a single impl per comment. This would mostly correspond to commenting the match arms on the self_ty matches in most cases.

I worry that these comments here can easily get out of date. E.g. When changing instantiate_constituent_tys_for_sized_trait we likely won't remember updating this function 🤔 E.g. this function currently diverges from the old solver by checking that all tuple fields are sized, not only the last one

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Sure, that would work. I will move these.

fn consider_builtin_sized_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
Expand All @@ -202,6 +212,20 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
)
}

/// ```rust,ignore (not valid rust syntax)
/// impl Copy/Clone for FnDef, FnPtr
///
/// impl Copy/Clone for (T1, T2, .., Tn) where T1: Copy/Clone, T2: Copy/Clone, .. Tn: Copy/Clone
///
/// impl Copy/Clone for Closure where T: Copy/Clone forall T in upvars
///
/// // only when `coroutine_clone` is enabled and the coroutine is movable
/// impl Copy/Clone for Coroutine where T: Copy/Clone forall T in (upvars, witnesses)
///
/// impl Copy/Clone for CoroutineWitness where T: Copy/Clone forall T in coroutine_hidden_types
/// ```
///
/// Some built-in types don't have built-in impls because they can be implemented within the standard library.
fn consider_builtin_copy_clone_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
Expand All @@ -216,6 +240,9 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
)
}

/// Implements `PointerLike` for types that are pointer-sized, pointer-aligned,
/// and have a initialized (non-union), scalar ABI.
// Please also update compiler/rustc_target/src/abi/mod.rs if the criteria changes
fn consider_builtin_pointer_like_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
Expand Down Expand Up @@ -245,6 +272,12 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
}
}

/// ```rust,ignore (not valid rust syntax)
/// impl FnPtr for FnPtr {}
/// impl !FnPtr for T where T != FnPtr && T is rigid {}
/// ```
///
/// Note: see [`Ty::is_known_rigid`] for what it means for the type to be rigid.
fn consider_builtin_fn_ptr_trait_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
Expand Down Expand Up @@ -375,6 +408,12 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
}
}

/// ```rust, ignore (not valid rust syntax)
/// impl Tuple for () {}
/// impl Tuple for (T1,) {}
/// impl Tuple for (T1, T2) {}
/// impl Tuple for (T1, .., Tn) {}
/// ```
fn consider_builtin_tuple_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
Expand Down
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