Unnamed repository; edit this file 'description' to name the repository.
Diffstat (limited to 'crates/hir-ty/src/infer/coerce.rs')
| -rw-r--r-- | crates/hir-ty/src/infer/coerce.rs | 2014 |
1 files changed, 1412 insertions, 602 deletions
diff --git a/crates/hir-ty/src/infer/coerce.rs b/crates/hir-ty/src/infer/coerce.rs index 39bd90849f..78889ccb89 100644 --- a/crates/hir-ty/src/infer/coerce.rs +++ b/crates/hir-ty/src/infer/coerce.rs @@ -1,450 +1,380 @@ -//! Coercion logic. Coercions are certain type conversions that can implicitly -//! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions -//! like going from `&Vec<T>` to `&[T]`. +//! # Type Coercion //! -//! See <https://doc.rust-lang.org/nomicon/coercions.html> and -//! `rustc_hir_analysis/check/coercion.rs`. - -use std::iter; - -use chalk_ir::{BoundVar, Goal, Mutability, TyKind, TyVariableKind, cast::Cast}; -use hir_def::{hir::ExprId, lang_item::LangItem}; -use stdx::always; +//! Under certain circumstances we will coerce from one type to another, +//! for example by auto-borrowing. This occurs in situations where the +//! compiler has a firm 'expected type' that was supplied from the user, +//! and where the actual type is similar to that expected type in purpose +//! but not in representation (so actual subtyping is inappropriate). +//! +//! ## Reborrowing +//! +//! Note that if we are expecting a reference, we will *reborrow* +//! even if the argument provided was already a reference. This is +//! useful for freezing mut things (that is, when the expected type is &T +//! but you have &mut T) and also for avoiding the linearity +//! of mut things (when the expected is &mut T and you have &mut T). See +//! the various `tests/ui/coerce/*.rs` tests for +//! examples of where this is useful. +//! +//! ## Subtle note +//! +//! When inferring the generic arguments of functions, the argument +//! order is relevant, which can lead to the following edge case: +//! +//! ```ignore (illustrative) +//! fn foo<T>(a: T, b: T) { +//! // ... +//! } +//! +//! foo(&7i32, &mut 7i32); +//! // This compiles, as we first infer `T` to be `&i32`, +//! // and then coerce `&mut 7i32` to `&7i32`. +//! +//! foo(&mut 7i32, &7i32); +//! // This does not compile, as we first infer `T` to be `&mut i32` +//! // and are then unable to coerce `&7i32` to `&mut i32`. +//! ``` + +use hir_def::{ + CallableDefId, + hir::{ExprId, ExprOrPatId}, + lang_item::LangItem, + signatures::FunctionSignature, +}; +use intern::sym; +use rustc_ast_ir::Mutability; +use rustc_type_ir::{ + BoundVar, TypeAndMut, + error::TypeError, + inherent::{Const as _, GenericArg as _, IntoKind, Safety, SliceLike, Ty as _}, +}; +use smallvec::{SmallVec, smallvec}; +use tracing::{debug, instrument}; use triomphe::Arc; use crate::{ - Canonical, DomainGoal, FnAbi, FnPointer, FnSig, Guidance, InEnvironment, Interner, Lifetime, - Solution, Substitution, TraitEnvironment, Ty, TyBuilder, TyExt, - autoderef::{Autoderef, AutoderefKind}, - db::HirDatabase, - infer::{ - Adjust, Adjustment, AutoBorrow, InferOk, InferenceContext, OverloadedDeref, PointerCast, - TypeError, TypeMismatch, + Adjust, Adjustment, AutoBorrow, PointerCast, TargetFeatures, TraitEnvironment, + autoderef::Autoderef, + db::{HirDatabase, InternedClosureId}, + infer::{AllowTwoPhase, InferenceContext, TypeMismatch, unify::InferenceTable}, + next_solver::{ + Binder, BoundConst, BoundRegion, BoundRegionKind, BoundTy, BoundTyKind, CallableIdWrapper, + Canonical, ClauseKind, CoercePredicate, Const, ConstKind, DbInterner, ErrorGuaranteed, + GenericArgs, PolyFnSig, PredicateKind, Region, RegionKind, SolverDefId, TraitRef, Ty, + TyKind, + infer::{ + InferCtxt, InferOk, InferResult, + relate::RelateResult, + select::{ImplSource, SelectionError}, + traits::{Obligation, ObligationCause, PredicateObligation, PredicateObligations}, + }, + obligation_ctxt::ObligationCtxt, }, - utils::ClosureSubst, + utils::TargetFeatureIsSafeInTarget, }; -use super::unify::InferenceTable; - -pub(crate) type CoerceResult = Result<InferOk<(Vec<Adjustment>, Ty)>, TypeError>; - -/// Do not require any adjustments, i.e. coerce `x -> x`. -fn identity(_: Ty) -> Vec<Adjustment> { - vec![] -} - -fn simple(kind: Adjust) -> impl FnOnce(Ty) -> Vec<Adjustment> { - move |target| vec![Adjustment { kind, target }] +struct Coerce<'a, 'b, 'db> { + table: &'a mut InferenceTable<'db>, + has_errors: &'a mut bool, + target_features: &'a mut dyn FnMut() -> (&'b TargetFeatures, TargetFeatureIsSafeInTarget), + use_lub: bool, + /// Determines whether or not allow_two_phase_borrow is set on any + /// autoref adjustments we create while coercing. We don't want to + /// allow deref coercions to create two-phase borrows, at least initially, + /// but we do need two-phase borrows for function argument reborrows. + /// See rust#47489 and rust#48598 + /// See docs on the "AllowTwoPhase" type for a more detailed discussion + allow_two_phase: AllowTwoPhase, + /// Whether we allow `NeverToAny` coercions. This is unsound if we're + /// coercing a place expression without it counting as a read in the MIR. + /// This is a side-effect of HIR not really having a great distinction + /// between places and values. + coerce_never: bool, + cause: ObligationCause, } -/// This always returns `Ok(...)`. -fn success( - adj: Vec<Adjustment>, - target: Ty, - goals: Vec<InEnvironment<Goal<Interner>>>, -) -> CoerceResult { - Ok(InferOk { goals, value: (adj, target) }) -} +type CoerceResult<'db> = InferResult<'db, (Vec<Adjustment<'db>>, Ty<'db>)>; -pub(super) enum CoercionCause { - // FIXME: Make better use of this. Right now things like return and break without a value - // use it to point to themselves, causing us to report a mismatch on those expressions even - // though technically they themselves are `!` - Expr(ExprId), +/// Coercing a mutable reference to an immutable works, while +/// coercing `&T` to `&mut T` should be forbidden. +fn coerce_mutbls<'db>(from_mutbl: Mutability, to_mutbl: Mutability) -> RelateResult<'db, ()> { + if from_mutbl >= to_mutbl { Ok(()) } else { Err(TypeError::Mutability) } } -#[derive(Clone, Debug)] -pub(super) struct CoerceMany { - expected_ty: Ty, - final_ty: Option<Ty>, - expressions: Vec<ExprId>, +/// This always returns `Ok(...)`. +fn success<'db>( + adj: Vec<Adjustment<'db>>, + target: Ty<'db>, + obligations: PredicateObligations<'db>, +) -> CoerceResult<'db> { + Ok(InferOk { value: (adj, target), obligations }) } -impl CoerceMany { - pub(super) fn new(expected: Ty) -> Self { - CoerceMany { expected_ty: expected, final_ty: None, expressions: vec![] } - } - - /// Returns the "expected type" with which this coercion was - /// constructed. This represents the "downward propagated" type - /// that was given to us at the start of typing whatever construct - /// we are typing (e.g., the match expression). - /// - /// Typically, this is used as the expected type when - /// type-checking each of the alternative expressions whose types - /// we are trying to merge. - pub(super) fn expected_ty(&self) -> Ty { - self.expected_ty.clone() - } - - /// Returns the current "merged type", representing our best-guess - /// at the LUB of the expressions we've seen so far (if any). This - /// isn't *final* until you call `self.complete()`, which will return - /// the merged type. - pub(super) fn merged_ty(&self) -> Ty { - self.final_ty.clone().unwrap_or_else(|| self.expected_ty.clone()) +impl<'a, 'b, 'db> Coerce<'a, 'b, 'db> { + #[inline] + fn set_tainted_by_errors(&mut self) { + *self.has_errors = true; } - pub(super) fn complete(self, ctx: &mut InferenceContext<'_>) -> Ty { - if let Some(final_ty) = self.final_ty { - final_ty - } else { - ctx.result.standard_types.never.clone() - } + #[inline] + fn interner(&self) -> DbInterner<'db> { + self.table.interner() } - pub(super) fn coerce_forced_unit( - &mut self, - ctx: &mut InferenceContext<'_>, - cause: CoercionCause, - ) { - self.coerce(ctx, None, &ctx.result.standard_types.unit.clone(), cause) + #[inline] + fn infer_ctxt(&self) -> &InferCtxt<'db> { + &self.table.infer_ctxt } - /// Merge two types from different branches, with possible coercion. - /// - /// Mostly this means trying to coerce one to the other, but - /// - if we have two function types for different functions or closures, we need to - /// coerce both to function pointers; - /// - if we were concerned with lifetime subtyping, we'd need to look for a - /// least upper bound. - pub(super) fn coerce( + pub(crate) fn commit_if_ok<T, E>( &mut self, - ctx: &mut InferenceContext<'_>, - expr: Option<ExprId>, - expr_ty: &Ty, - cause: CoercionCause, - ) { - let expr_ty = ctx.resolve_ty_shallow(expr_ty); - self.expected_ty = ctx.resolve_ty_shallow(&self.expected_ty); - - // Special case: two function types. Try to coerce both to - // pointers to have a chance at getting a match. See - // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916 - let sig = match (self.merged_ty().kind(Interner), expr_ty.kind(Interner)) { - (TyKind::FnDef(x, _), TyKind::FnDef(y, _)) - if x == y && ctx.table.unify(&self.merged_ty(), &expr_ty) => - { - None - } - (TyKind::Closure(x, _), TyKind::Closure(y, _)) if x == y => None, - (TyKind::FnDef(..) | TyKind::Closure(..), TyKind::FnDef(..) | TyKind::Closure(..)) => { - // FIXME: we're ignoring safety here. To be more correct, if we have one FnDef and one Closure, - // we should be coercing the closure to a fn pointer of the safety of the FnDef - cov_mark::hit!(coerce_fn_reification); - let sig = - self.merged_ty().callable_sig(ctx.db).expect("FnDef without callable sig"); - Some(sig) - } - _ => None, - }; - if let Some(sig) = sig { - let target_ty = TyKind::Function(sig.to_fn_ptr()).intern(Interner); - let result1 = ctx.table.coerce_inner(self.merged_ty(), &target_ty, CoerceNever::Yes); - let result2 = ctx.table.coerce_inner(expr_ty.clone(), &target_ty, CoerceNever::Yes); - if let (Ok(result1), Ok(result2)) = (result1, result2) { - ctx.table.register_infer_ok(InferOk { value: (), goals: result1.goals }); - for &e in &self.expressions { - ctx.write_expr_adj(e, result1.value.0.clone().into_boxed_slice()); - } - ctx.table.register_infer_ok(InferOk { value: (), goals: result2.goals }); - if let Some(expr) = expr { - ctx.write_expr_adj(expr, result2.value.0.into_boxed_slice()); - self.expressions.push(expr); - } - return self.final_ty = Some(target_ty); + f: impl FnOnce(&mut Self) -> Result<T, E>, + ) -> Result<T, E> { + let snapshot = self.table.snapshot(); + let result = f(self); + match result { + Ok(_) => {} + Err(_) => { + self.table.rollback_to(snapshot); } } + result + } - // It might not seem like it, but order is important here: If the expected - // type is a type variable and the new one is `!`, trying it the other - // way around first would mean we make the type variable `!`, instead of - // just marking it as possibly diverging. - // - // - [Comment from rustc](https://github.com/rust-lang/rust/blob/5ff18d0eaefd1bd9ab8ec33dab2404a44e7631ed/compiler/rustc_hir_typeck/src/coercion.rs#L1334-L1335) - // First try to coerce the new expression to the type of the previous ones, - // but only if the new expression has no coercion already applied to it. - if expr.is_none_or(|expr| !ctx.result.expr_adjustments.contains_key(&expr)) { - if let Ok(res) = ctx.coerce(expr, &expr_ty, &self.merged_ty(), CoerceNever::Yes) { - self.final_ty = Some(res); - if let Some(expr) = expr { - self.expressions.push(expr); - } - return; - } - } + fn unify_raw(&mut self, a: Ty<'db>, b: Ty<'db>) -> InferResult<'db, Ty<'db>> { + debug!("unify(a: {:?}, b: {:?}, use_lub: {})", a, b, self.use_lub); + self.commit_if_ok(|this| { + let at = this.infer_ctxt().at(&this.cause, this.table.trait_env.env); - if let Ok((adjustments, res)) = - ctx.coerce_inner(&self.merged_ty(), &expr_ty, CoerceNever::Yes) - { - self.final_ty = Some(res); - for &e in &self.expressions { - ctx.write_expr_adj(e, adjustments.clone().into_boxed_slice()); - } - } else { - match cause { - CoercionCause::Expr(id) => { - ctx.result.type_mismatches.insert( - id.into(), - TypeMismatch { expected: self.merged_ty(), actual: expr_ty.clone() }, - ); + let res = if this.use_lub { + at.lub(b, a) + } else { + at.sup(b, a) + .map(|InferOk { value: (), obligations }| InferOk { value: b, obligations }) + }; + + // In the new solver, lazy norm may allow us to shallowly equate + // more types, but we emit possibly impossible-to-satisfy obligations. + // Filter these cases out to make sure our coercion is more accurate. + match res { + Ok(InferOk { value, obligations }) => { + let mut ocx = ObligationCtxt::new(this.infer_ctxt()); + ocx.register_obligations(obligations); + if ocx.try_evaluate_obligations().is_empty() { + Ok(InferOk { value, obligations: ocx.into_pending_obligations() }) + } else { + Err(TypeError::Mismatch) + } } + res => res, } - cov_mark::hit!(coerce_merge_fail_fallback); - } - if let Some(expr) = expr { - self.expressions.push(expr); - } + }) } -} - -pub fn could_coerce( - db: &dyn HirDatabase, - env: Arc<TraitEnvironment>, - tys: &Canonical<(Ty, Ty)>, -) -> bool { - coerce(db, env, tys).is_ok() -} - -pub(crate) fn coerce( - db: &dyn HirDatabase, - env: Arc<TraitEnvironment>, - tys: &Canonical<(Ty, Ty)>, -) -> Result<(Vec<Adjustment>, Ty), TypeError> { - let mut table = InferenceTable::new(db, env); - let vars = table.fresh_subst(tys.binders.as_slice(Interner)); - let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner); - let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner); - let (adjustments, ty) = table.coerce(&ty1_with_vars, &ty2_with_vars, CoerceNever::Yes)?; - // default any type vars that weren't unified back to their original bound vars - // (kind of hacky) - let find_var = |iv| { - vars.iter(Interner).position(|v| match v.interned() { - chalk_ir::GenericArgData::Ty(ty) => ty.inference_var(Interner), - chalk_ir::GenericArgData::Lifetime(lt) => lt.inference_var(Interner), - chalk_ir::GenericArgData::Const(c) => c.inference_var(Interner), - } == Some(iv)) - }; - let fallback = |iv, kind, default, binder| match kind { - chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv) - .map_or(default, |i| BoundVar::new(binder, i).to_ty(Interner).cast(Interner)), - chalk_ir::VariableKind::Lifetime => find_var(iv) - .map_or(default, |i| BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner)), - chalk_ir::VariableKind::Const(ty) => find_var(iv) - .map_or(default, |i| BoundVar::new(binder, i).to_const(Interner, ty).cast(Interner)), - }; - // FIXME also map the types in the adjustments - Ok((adjustments, table.resolve_with_fallback(ty, &fallback))) -} -#[derive(Clone, Copy, PartialEq, Eq)] -pub(crate) enum CoerceNever { - Yes, - No, -} - -impl InferenceContext<'_> { - /// Unify two types, but may coerce the first one to the second one - /// using "implicit coercion rules" if needed. - pub(super) fn coerce( - &mut self, - expr: Option<ExprId>, - from_ty: &Ty, - to_ty: &Ty, - // [Comment from rustc](https://github.com/rust-lang/rust/blob/4cc494bbfe9911d24f3ee521f98d5c6bb7e3ffe8/compiler/rustc_hir_typeck/src/coercion.rs#L85-L89) - // Whether we allow `NeverToAny` coercions. This is unsound if we're - // coercing a place expression without it counting as a read in the MIR. - // This is a side-effect of HIR not really having a great distinction - // between places and values. - coerce_never: CoerceNever, - ) -> Result<Ty, TypeError> { - let (adjustments, ty) = self.coerce_inner(from_ty, to_ty, coerce_never)?; - if let Some(expr) = expr { - self.write_expr_adj(expr, adjustments.into_boxed_slice()); - } - Ok(ty) + /// Unify two types (using sub or lub). + fn unify(&mut self, a: Ty<'db>, b: Ty<'db>) -> CoerceResult<'db> { + self.unify_raw(a, b) + .and_then(|InferOk { value: ty, obligations }| success(vec![], ty, obligations)) } - fn coerce_inner( + /// Unify two types (using sub or lub) and produce a specific coercion. + fn unify_and( &mut self, - from_ty: &Ty, - to_ty: &Ty, - coerce_never: CoerceNever, - ) -> Result<(Vec<Adjustment>, Ty), TypeError> { - let from_ty = self.resolve_ty_shallow(from_ty); - let to_ty = self.resolve_ty_shallow(to_ty); - self.table.coerce(&from_ty, &to_ty, coerce_never) + a: Ty<'db>, + b: Ty<'db>, + adjustments: impl IntoIterator<Item = Adjustment<'db>>, + final_adjustment: Adjust<'db>, + ) -> CoerceResult<'db> { + self.unify_raw(a, b).and_then(|InferOk { value: ty, obligations }| { + success( + adjustments + .into_iter() + .chain(std::iter::once(Adjustment { target: ty, kind: final_adjustment })) + .collect(), + ty, + obligations, + ) + }) } -} -impl InferenceTable<'_> { - /// Unify two types, but may coerce the first one to the second one - /// using "implicit coercion rules" if needed. - pub(crate) fn coerce( - &mut self, - from_ty: &Ty, - to_ty: &Ty, - coerce_never: CoerceNever, - ) -> Result<(Vec<Adjustment>, Ty), TypeError> { - let from_ty = self.resolve_ty_shallow(from_ty); - let to_ty = self.resolve_ty_shallow(to_ty); - match self.coerce_inner(from_ty, &to_ty, coerce_never) { - Ok(InferOk { value: (adjustments, ty), goals }) => { - self.register_infer_ok(InferOk { value: (), goals }); - Ok((adjustments, ty)) - } - Err(e) => { - // FIXME deal with error - Err(e) + #[instrument(skip(self))] + fn coerce(&mut self, a: Ty<'db>, b: Ty<'db>) -> CoerceResult<'db> { + // First, remove any resolved type variables (at the top level, at least): + let a = self.table.shallow_resolve(a); + let b = self.table.shallow_resolve(b); + debug!("Coerce.tys({:?} => {:?})", a, b); + + // Coercing from `!` to any type is allowed: + if a.is_never() { + // If we're coercing into an inference var, mark it as possibly diverging. + if b.is_infer() { + self.table.set_diverging(b); } - } - } - fn coerce_inner(&mut self, from_ty: Ty, to_ty: &Ty, coerce_never: CoerceNever) -> CoerceResult { - if from_ty.is_never() { - if let TyKind::InferenceVar(tv, TyVariableKind::General) = to_ty.kind(Interner) { - self.set_diverging(*tv, true); - } - if coerce_never == CoerceNever::Yes { - // Subtle: If we are coercing from `!` to `?T`, where `?T` is an unbound - // type variable, we want `?T` to fallback to `!` if not - // otherwise constrained. An example where this arises: - // - // let _: Option<?T> = Some({ return; }); - // - // here, we would coerce from `!` to `?T`. - return success(simple(Adjust::NeverToAny)(to_ty.clone()), to_ty.clone(), vec![]); + if self.coerce_never { + return success( + vec![Adjustment { kind: Adjust::NeverToAny, target: b }], + b, + PredicateObligations::new(), + ); } else { - return self.unify_and(&from_ty, to_ty, identity); + // Otherwise the only coercion we can do is unification. + return self.unify(a, b); } } // If we are coercing into a TAIT, coerce into its proxy inference var, instead. - let mut to_ty = to_ty; - let _to; - if let Some(tait_table) = &self.tait_coercion_table { - if let TyKind::OpaqueType(opaque_ty_id, _) = to_ty.kind(Interner) { - if !matches!( - from_ty.kind(Interner), - TyKind::InferenceVar(..) | TyKind::OpaqueType(..) - ) { - if let Some(ty) = tait_table.get(opaque_ty_id) { - _to = ty.clone(); - to_ty = &_to; - } - } - } + // FIXME(next-solver): This should not be here. This is not how rustc does thing, and it also not allows us + // to normalize opaques defined in our scopes. Instead, we should properly register + // `TypingMode::Analysis::defining_opaque_types_and_generators`, and rely on the solver to reveal + // them for us (we'll also need some global-like registry for the values, something we cannot + // really implement, therefore we can really support only RPITs and ITIAT or the new `#[define_opaque]` + // TAIT, not the old global TAIT). + let mut b = b; + if let Some(tait_table) = &self.table.tait_coercion_table + && let TyKind::Alias(rustc_type_ir::Opaque, opaque_ty) = b.kind() + && let SolverDefId::InternedOpaqueTyId(opaque_ty_id) = opaque_ty.def_id + && !matches!(a.kind(), TyKind::Infer(..) | TyKind::Alias(rustc_type_ir::Opaque, _)) + && let Some(ty) = tait_table.get(&opaque_ty_id) + { + b = self.table.shallow_resolve(*ty); + } + let b = b; + + // Coercing *from* an unresolved inference variable means that + // we have no information about the source type. This will always + // ultimately fall back to some form of subtyping. + if a.is_infer() { + return self.coerce_from_inference_variable(a, b); } // Consider coercing the subtype to a DST - if let Ok(ret) = self.try_coerce_unsized(&from_ty, to_ty) { - return Ok(ret); + // + // NOTE: this is wrapped in a `commit_if_ok` because it creates + // a "spurious" type variable, and we don't want to have that + // type variable in memory if the coercion fails. + let unsize = self.commit_if_ok(|this| this.coerce_unsized(a, b)); + match unsize { + Ok(_) => { + debug!("coerce: unsize successful"); + return unsize; + } + Err(error) => { + debug!(?error, "coerce: unsize failed"); + } } - // Examine the supertype and consider auto-borrowing. - match to_ty.kind(Interner) { - TyKind::Raw(mt, _) => return self.coerce_ptr(from_ty, to_ty, *mt), - TyKind::Ref(mt, lt, _) => return self.coerce_ref(from_ty, to_ty, *mt, lt), + // Examine the supertype and consider type-specific coercions, such + // as auto-borrowing, coercing pointer mutability, a `dyn*` coercion, + // or pin-ergonomics. + match b.kind() { + TyKind::RawPtr(_, b_mutbl) => { + return self.coerce_raw_ptr(a, b, b_mutbl); + } + TyKind::Ref(r_b, _, mutbl_b) => { + return self.coerce_borrowed_pointer(a, b, r_b, mutbl_b); + } _ => {} } - match from_ty.kind(Interner) { + match a.kind() { TyKind::FnDef(..) => { // Function items are coercible to any closure // type; function pointers are not (that would // require double indirection). // Additionally, we permit coercion of function // items to drop the unsafe qualifier. - self.coerce_from_fn_item(from_ty, to_ty) + self.coerce_from_fn_item(a, b) } - TyKind::Function(from_fn_ptr) => { + TyKind::FnPtr(a_sig_tys, a_hdr) => { // We permit coercion of fn pointers to drop the // unsafe qualifier. - self.coerce_from_fn_pointer(from_ty.clone(), from_fn_ptr, to_ty) + self.coerce_from_fn_pointer(a_sig_tys.with(a_hdr), b) } - TyKind::Closure(_, from_substs) => { + TyKind::Closure(closure_def_id_a, args_a) => { // Non-capturing closures are coercible to // function pointers or unsafe function pointers. // It cannot convert closures that require unsafe. - self.coerce_closure_to_fn(from_ty.clone(), from_substs, to_ty) + self.coerce_closure_to_fn(a, closure_def_id_a.0, args_a, b) } _ => { // Otherwise, just use unification rules. - self.unify_and(&from_ty, to_ty, identity) + self.unify(a, b) } } } - /// Unify two types (using sub or lub) and produce a specific coercion. - fn unify_and<F>(&mut self, t1: &Ty, t2: &Ty, f: F) -> CoerceResult - where - F: FnOnce(Ty) -> Vec<Adjustment>, - { - self.try_unify(t1, t2) - .and_then(|InferOk { goals, .. }| success(f(t1.clone()), t1.clone(), goals)) - } - - fn coerce_ptr(&mut self, from_ty: Ty, to_ty: &Ty, to_mt: Mutability) -> CoerceResult { - let (is_ref, from_mt, from_inner) = match from_ty.kind(Interner) { - TyKind::Ref(mt, _, ty) => (true, mt, ty), - TyKind::Raw(mt, ty) => (false, mt, ty), - _ => return self.unify_and(&from_ty, to_ty, identity), - }; - - coerce_mutabilities(*from_mt, to_mt)?; - - // Check that the types which they point at are compatible. - let from_raw = TyKind::Raw(to_mt, from_inner.clone()).intern(Interner); + /// Coercing *from* an inference variable. In this case, we have no information + /// about the source type, so we can't really do a true coercion and we always + /// fall back to subtyping (`unify_and`). + fn coerce_from_inference_variable(&mut self, a: Ty<'db>, b: Ty<'db>) -> CoerceResult<'db> { + debug!("coerce_from_inference_variable(a={:?}, b={:?})", a, b); + debug_assert!(a.is_infer() && self.table.shallow_resolve(a) == a); + debug_assert!(self.table.shallow_resolve(b) == b); + + if b.is_infer() { + // Two unresolved type variables: create a `Coerce` predicate. + let target_ty = if self.use_lub { self.table.next_ty_var() } else { b }; + + let mut obligations = PredicateObligations::with_capacity(2); + for &source_ty in &[a, b] { + if source_ty != target_ty { + obligations.push(Obligation::new( + self.interner(), + self.cause.clone(), + self.table.trait_env.env, + Binder::dummy(PredicateKind::Coerce(CoercePredicate { + a: source_ty, + b: target_ty, + })), + )); + } + } - // Although references and raw ptrs have the same - // representation, we still register an Adjust::DerefRef so that - // regionck knows that the region for `a` must be valid here. - if is_ref { - self.unify_and(&from_raw, to_ty, |target| { - vec![ - Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() }, - Adjustment { kind: Adjust::Borrow(AutoBorrow::RawPtr(to_mt)), target }, - ] - }) - } else if *from_mt != to_mt { - self.unify_and( - &from_raw, - to_ty, - simple(Adjust::Pointer(PointerCast::MutToConstPointer)), - ) + debug!( + "coerce_from_inference_variable: two inference variables, target_ty={:?}, obligations={:?}", + target_ty, obligations + ); + success(vec![], target_ty, obligations) } else { - self.unify_and(&from_raw, to_ty, identity) + // One unresolved type variable: just apply subtyping, we may be able + // to do something useful. + self.unify(a, b) } } /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`. /// To match `A` with `B`, autoderef will be performed, /// calling `deref`/`deref_mut` where necessary. - fn coerce_ref( + fn coerce_borrowed_pointer( &mut self, - from_ty: Ty, - to_ty: &Ty, - to_mt: Mutability, - to_lt: &Lifetime, - ) -> CoerceResult { - let (_from_lt, from_mt) = match from_ty.kind(Interner) { - TyKind::Ref(mt, lt, _) => { - coerce_mutabilities(*mt, to_mt)?; - (lt.clone(), *mt) // clone is probably not good? - } - _ => return self.unify_and(&from_ty, to_ty, identity), + a: Ty<'db>, + b: Ty<'db>, + r_b: Region<'db>, + mutbl_b: Mutability, + ) -> CoerceResult<'db> { + debug!("coerce_borrowed_pointer(a={:?}, b={:?})", a, b); + debug_assert!(self.table.shallow_resolve(a) == a); + debug_assert!(self.table.shallow_resolve(b) == b); + + // If we have a parameter of type `&M T_a` and the value + // provided is `expr`, we will be adding an implicit borrow, + // meaning that we convert `f(expr)` to `f(&M *expr)`. Therefore, + // to type check, we will construct the type that `&M*expr` would + // yield. + + let (r_a, mt_a) = match a.kind() { + TyKind::Ref(r_a, ty, mutbl) => { + let mt_a = TypeAndMut::<DbInterner<'db>> { ty, mutbl }; + coerce_mutbls(mt_a.mutbl, mutbl_b)?; + (r_a, mt_a) + } + _ => return self.unify(a, b), }; - // NOTE: this code is mostly copied and adapted from rustc, and - // currently more complicated than necessary, carrying errors around - // etc.. This complication will become necessary when we actually track - // details of coercion errors though, so I think it's useful to leave - // the structure like it is. - - let snapshot = self.snapshot(); - - let mut autoderef = Autoderef::new(self, from_ty.clone(), false, false); let mut first_error = None; + let mut r_borrow_var = None; + let mut autoderef = Autoderef::new(self.table, a); let mut found = None; while let Some((referent_ty, autoderefs)) = autoderef.next() { @@ -454,7 +384,7 @@ impl InferenceTable<'_> { continue; } - // At this point, we have deref'd `a` to `referent_ty`. So + // At this point, we have deref'd `a` to `referent_ty`. So // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`. // In the autoderef loop for `&'a mut Vec<T>`, we would get // three callbacks: @@ -476,11 +406,85 @@ impl InferenceTable<'_> { // compare those. Note that this means we use the target // mutability [1], since it may be that we are coercing // from `&mut T` to `&U`. - let lt = to_lt; // FIXME: Involve rustc LUB and SUB flag checks - let derefd_from_ty = TyKind::Ref(to_mt, lt.clone(), referent_ty).intern(Interner); - match autoderef.table.try_unify(&derefd_from_ty, to_ty) { - Ok(result) => { - found = Some(result.map(|()| derefd_from_ty)); + // + // One fine point concerns the region that we use. We + // choose the region such that the region of the final + // type that results from `unify` will be the region we + // want for the autoref: + // + // - if in sub mode, that means we want to use `'b` (the + // region from the target reference) for both + // pointers [2]. This is because sub mode (somewhat + // arbitrarily) returns the subtype region. In the case + // where we are coercing to a target type, we know we + // want to use that target type region (`'b`) because -- + // for the program to type-check -- it must be the + // smaller of the two. + // - One fine point. It may be surprising that we can + // use `'b` without relating `'a` and `'b`. The reason + // that this is ok is that what we produce is + // effectively a `&'b *x` expression (if you could + // annotate the region of a borrow), and regionck has + // code that adds edges from the region of a borrow + // (`'b`, here) into the regions in the borrowed + // expression (`*x`, here). (Search for "link".) + // - if in lub mode, things can get fairly complicated. The + // easiest thing is just to make a fresh + // region variable [4], which effectively means we defer + // the decision to region inference (and regionck, which will add + // some more edges to this variable). However, this can wind up + // creating a crippling number of variables in some cases -- + // e.g., #32278 -- so we optimize one particular case [3]. + // Let me try to explain with some examples: + // - The "running example" above represents the simple case, + // where we have one `&` reference at the outer level and + // ownership all the rest of the way down. In this case, + // we want `LUB('a, 'b)` as the resulting region. + // - However, if there are nested borrows, that region is + // too strong. Consider a coercion from `&'a &'x Rc<T>` to + // `&'b T`. In this case, `'a` is actually irrelevant. + // The pointer we want is `LUB('x, 'b`). If we choose `LUB('a,'b)` + // we get spurious errors (`ui/regions-lub-ref-ref-rc.rs`). + // (The errors actually show up in borrowck, typically, because + // this extra edge causes the region `'a` to be inferred to something + // too big, which then results in borrowck errors.) + // - We could track the innermost shared reference, but there is already + // code in regionck that has the job of creating links between + // the region of a borrow and the regions in the thing being + // borrowed (here, `'a` and `'x`), and it knows how to handle + // all the various cases. So instead we just make a region variable + // and let regionck figure it out. + let r = if !self.use_lub { + r_b // [2] above + } else if autoderefs == 1 { + r_a // [3] above + } else { + if r_borrow_var.is_none() { + // create var lazily, at most once + let r = autoderef.table.next_region_var(); + r_borrow_var = Some(r); // [4] above + } + r_borrow_var.unwrap() + }; + let derefd_ty_a = Ty::new_ref( + autoderef.table.interner(), + r, + referent_ty, + mutbl_b, // [1] above + ); + // We need to construct a new `Coerce` because of lifetimes. + let mut coerce = Coerce { + table: autoderef.table, + has_errors: self.has_errors, + target_features: self.target_features, + use_lub: self.use_lub, + allow_two_phase: self.allow_two_phase, + coerce_never: self.coerce_never, + cause: self.cause.clone(), + }; + match coerce.unify_raw(derefd_ty_a, b) { + Ok(ok) => { + found = Some(ok); break; } Err(err) => { @@ -496,18 +500,24 @@ impl InferenceTable<'_> { // (e.g., in example above, the failure from relating `Vec<T>` // to the target type), since that should be the least // confusing. - let InferOk { value: ty, goals } = match found { - Some(d) => d, - None => { - self.rollback_to(snapshot); - let err = first_error.expect("coerce_borrowed_pointer had no error"); - return Err(err); + let Some(InferOk { value: ty, mut obligations }) = found else { + if let Some(first_error) = first_error { + debug!("coerce_borrowed_pointer: failed with err = {:?}", first_error); + return Err(first_error); + } else { + // This may happen in the new trait solver since autoderef requires + // the pointee to be structurally normalizable, or else it'll just bail. + // So when we have a type like `&<not well formed>`, then we get no + // autoderef steps (even though there should be at least one). That means + // we get no type mismatches, since the loop above just exits early. + return Err(TypeError::Mismatch); } }; - if ty == from_ty && from_mt == Mutability::Not && autoderef.step_count() == 1 { + + if ty == a && mt_a.mutbl.is_not() && autoderef.step_count() == 1 { // As a special case, if we would produce `&'a *x`, that's // a total no-op. We end up with the type `&'a T` just as - // we started with. In that case, just skip it + // we started with. In that case, just skip it // altogether. This is just an optimization. // // Note that for `&mut`, we DO want to reborrow -- @@ -516,285 +526,1085 @@ impl InferenceTable<'_> { // `self.x` both have `&mut `type would be a move of // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`, // which is a borrow. - always!(to_mt == Mutability::Not); // can only coerce &T -> &U - return success(vec![], ty, goals); + assert!(mutbl_b.is_not()); // can only coerce &T -> &U + return success(vec![], ty, obligations); } - let mut adjustments = auto_deref_adjust_steps(&autoderef); + let InferOk { value: mut adjustments, obligations: o } = + autoderef.adjust_steps_as_infer_ok(); + obligations.extend(o); + + // Now apply the autoref. We have to extract the region out of + // the final ref type we got. + let TyKind::Ref(region, _, _) = ty.kind() else { + panic!("expected a ref type, got {:?}", ty); + }; adjustments.push(Adjustment { - kind: Adjust::Borrow(AutoBorrow::Ref(to_lt.clone(), to_mt)), - target: ty.clone(), + kind: Adjust::Borrow(AutoBorrow::Ref(region, mutbl_b)), + target: ty, }); - success(adjustments, ty, goals) + debug!("coerce_borrowed_pointer: succeeded ty={:?} adjustments={:?}", ty, adjustments); + + success(adjustments, ty, obligations) } - /// Attempts to coerce from the type of a Rust function item into a function pointer. - fn coerce_from_fn_item(&mut self, from_ty: Ty, to_ty: &Ty) -> CoerceResult { - match to_ty.kind(Interner) { - TyKind::Function(_) => { - let from_sig = from_ty.callable_sig(self.db).expect("FnDef had no sig"); - - // FIXME check ABI: Intrinsics are not coercible to function pointers - // FIXME Safe `#[target_feature]` functions are not assignable to safe fn pointers (RFC 2396) - - // FIXME rustc normalizes assoc types in the sig here, not sure if necessary - - let from_sig = from_sig.to_fn_ptr(); - let from_fn_pointer = TyKind::Function(from_sig.clone()).intern(Interner); - let ok = self.coerce_from_safe_fn( - from_fn_pointer.clone(), - &from_sig, - to_ty, - |unsafe_ty| { - vec![ - Adjustment { - kind: Adjust::Pointer(PointerCast::ReifyFnPointer), - target: from_fn_pointer, - }, - Adjustment { - kind: Adjust::Pointer(PointerCast::UnsafeFnPointer), - target: unsafe_ty, - }, - ] + /// Performs [unsized coercion] by emulating a fulfillment loop on a + /// `CoerceUnsized` goal until all `CoerceUnsized` and `Unsize` goals + /// are successfully selected. + /// + /// [unsized coercion](https://doc.rust-lang.org/reference/type-coercions.html#unsized-coercions) + #[instrument(skip(self), level = "debug")] + fn coerce_unsized(&mut self, source: Ty<'db>, target: Ty<'db>) -> CoerceResult<'db> { + debug!(?source, ?target); + debug_assert!(self.table.shallow_resolve(source) == source); + debug_assert!(self.table.shallow_resolve(target) == target); + + // We don't apply any coercions incase either the source or target + // aren't sufficiently well known but tend to instead just equate + // them both. + if source.is_infer() { + debug!("coerce_unsized: source is a TyVar, bailing out"); + return Err(TypeError::Mismatch); + } + if target.is_infer() { + debug!("coerce_unsized: target is a TyVar, bailing out"); + return Err(TypeError::Mismatch); + } + + // This is an optimization because coercion is one of the most common + // operations that we do in typeck, since it happens at every assignment + // and call arg (among other positions). + // + // These targets are known to never be RHS in `LHS: CoerceUnsized<RHS>`. + // That's because these are built-in types for which a core-provided impl + // doesn't exist, and for which a user-written impl is invalid. + // + // This is technically incomplete when users write impossible bounds like + // `where T: CoerceUnsized<usize>`, for example, but that trait is unstable + // and coercion is allowed to be incomplete. The only case where this matters + // is impossible bounds. + // + // Note that some of these types implement `LHS: Unsize<RHS>`, but they + // do not implement *`CoerceUnsized`* which is the root obligation of the + // check below. + match target.kind() { + TyKind::Bool + | TyKind::Char + | TyKind::Int(_) + | TyKind::Uint(_) + | TyKind::Float(_) + | TyKind::Infer(rustc_type_ir::IntVar(_) | rustc_type_ir::FloatVar(_)) + | TyKind::Str + | TyKind::Array(_, _) + | TyKind::Slice(_) + | TyKind::FnDef(_, _) + | TyKind::FnPtr(_, _) + | TyKind::Dynamic(_, _) + | TyKind::Closure(_, _) + | TyKind::CoroutineClosure(_, _) + | TyKind::Coroutine(_, _) + | TyKind::CoroutineWitness(_, _) + | TyKind::Never + | TyKind::Tuple(_) => return Err(TypeError::Mismatch), + _ => {} + } + // Additionally, we ignore `&str -> &str` coercions, which happen very + // commonly since strings are one of the most used argument types in Rust, + // we do coercions when type checking call expressions. + if let TyKind::Ref(_, source_pointee, Mutability::Not) = source.kind() + && source_pointee.is_str() + && let TyKind::Ref(_, target_pointee, Mutability::Not) = target.kind() + && target_pointee.is_str() + { + return Err(TypeError::Mismatch); + } + + let traits = ( + LangItem::Unsize.resolve_trait(self.table.db, self.table.trait_env.krate), + LangItem::CoerceUnsized.resolve_trait(self.table.db, self.table.trait_env.krate), + ); + let (Some(unsize_did), Some(coerce_unsized_did)) = traits else { + debug!("missing Unsize or CoerceUnsized traits"); + return Err(TypeError::Mismatch); + }; + + // Note, we want to avoid unnecessary unsizing. We don't want to coerce to + // a DST unless we have to. This currently comes out in the wash since + // we can't unify [T] with U. But to properly support DST, we need to allow + // that, at which point we will need extra checks on the target here. + + // Handle reborrows before selecting `Source: CoerceUnsized<Target>`. + let reborrow = match (source.kind(), target.kind()) { + (TyKind::Ref(_, ty_a, mutbl_a), TyKind::Ref(_, _, mutbl_b)) => { + coerce_mutbls(mutbl_a, mutbl_b)?; + + let r_borrow = self.table.next_region_var(); + + // We don't allow two-phase borrows here, at least for initial + // implementation. If it happens that this coercion is a function argument, + // the reborrow in coerce_borrowed_ptr will pick it up. + // let mutbl = AutoBorrowMutability::new(mutbl_b, AllowTwoPhase::No); + let mutbl = mutbl_b; + + Some(( + Adjustment { kind: Adjust::Deref(None), target: ty_a }, + Adjustment { + kind: Adjust::Borrow(AutoBorrow::Ref(r_borrow, mutbl)), + target: Ty::new_ref(self.interner(), r_borrow, ty_a, mutbl_b), + }, + )) + } + (TyKind::Ref(_, ty_a, mt_a), TyKind::RawPtr(_, mt_b)) => { + coerce_mutbls(mt_a, mt_b)?; + + Some(( + Adjustment { kind: Adjust::Deref(None), target: ty_a }, + Adjustment { + kind: Adjust::Borrow(AutoBorrow::RawPtr(mt_b)), + target: Ty::new_ptr(self.interner(), ty_a, mt_b), }, - simple(Adjust::Pointer(PointerCast::ReifyFnPointer)), - )?; + )) + } + _ => None, + }; + let coerce_source = reborrow.as_ref().map_or(source, |(_, r)| r.target); + + // Setup either a subtyping or a LUB relationship between + // the `CoerceUnsized` target type and the expected type. + // We only have the latter, so we use an inference variable + // for the former and let type inference do the rest. + let coerce_target = self.table.next_ty_var(); - Ok(ok) + let mut coercion = self.unify_and( + coerce_target, + target, + reborrow.into_iter().flat_map(|(deref, autoref)| [deref, autoref]), + Adjust::Pointer(PointerCast::Unsize), + )?; + + // Create an obligation for `Source: CoerceUnsized<Target>`. + let cause = self.cause.clone(); + + // Use a FIFO queue for this custom fulfillment procedure. + // + // A Vec (or SmallVec) is not a natural choice for a queue. However, + // this code path is hot, and this queue usually has a max length of 1 + // and almost never more than 3. By using a SmallVec we avoid an + // allocation, at the (very small) cost of (occasionally) having to + // shift subsequent elements down when removing the front element. + let mut queue: SmallVec<[PredicateObligation<'db>; 4]> = smallvec![Obligation::new( + self.interner(), + cause, + self.table.trait_env.env, + TraitRef::new( + self.interner(), + coerce_unsized_did.into(), + [coerce_source, coerce_target] + ) + )]; + // Keep resolving `CoerceUnsized` and `Unsize` predicates to avoid + // emitting a coercion in cases like `Foo<$1>` -> `Foo<$2>`, where + // inference might unify those two inner type variables later. + let traits = [coerce_unsized_did, unsize_did]; + while !queue.is_empty() { + let obligation = queue.remove(0); + let trait_pred = match obligation.predicate.kind().no_bound_vars() { + Some(PredicateKind::Clause(ClauseKind::Trait(trait_pred))) + if traits.contains(&trait_pred.def_id().0) => + { + self.infer_ctxt().resolve_vars_if_possible(trait_pred) + } + // Eagerly process alias-relate obligations in new trait solver, + // since these can be emitted in the process of solving trait goals, + // but we need to constrain vars before processing goals mentioning + // them. + Some(PredicateKind::AliasRelate(..)) => { + let mut ocx = ObligationCtxt::new(self.infer_ctxt()); + ocx.register_obligation(obligation); + if !ocx.try_evaluate_obligations().is_empty() { + return Err(TypeError::Mismatch); + } + coercion.obligations.extend(ocx.into_pending_obligations()); + continue; + } + _ => { + coercion.obligations.push(obligation); + continue; + } + }; + debug!("coerce_unsized resolve step: {:?}", trait_pred); + match self.infer_ctxt().select(&obligation.with(self.interner(), trait_pred)) { + // Uncertain or unimplemented. + Ok(None) => { + if trait_pred.def_id().0 == unsize_did { + let self_ty = trait_pred.self_ty(); + let unsize_ty = trait_pred.trait_ref.args.inner()[1].expect_ty(); + debug!("coerce_unsized: ambiguous unsize case for {:?}", trait_pred); + match (self_ty.kind(), unsize_ty.kind()) { + (TyKind::Infer(rustc_type_ir::TyVar(v)), TyKind::Dynamic(..)) + if self.table.type_var_is_sized(v) => + { + debug!("coerce_unsized: have sized infer {:?}", v); + coercion.obligations.push(obligation); + // `$0: Unsize<dyn Trait>` where we know that `$0: Sized`, try going + // for unsizing. + } + _ => { + // Some other case for `$0: Unsize<Something>`. Note that we + // hit this case even if `Something` is a sized type, so just + // don't do the coercion. + debug!("coerce_unsized: ambiguous unsize"); + return Err(TypeError::Mismatch); + } + } + } else { + debug!("coerce_unsized: early return - ambiguous"); + if !coerce_source.references_non_lt_error() + && !coerce_target.references_non_lt_error() + { + // rustc always early-returns here, even when the types contains errors. However not bailing + // improves error recovery, and while we don't implement generic consts properly, it also helps + // correct code. + return Err(TypeError::Mismatch); + } + } + } + Err(SelectionError::Unimplemented) => { + debug!("coerce_unsized: early return - can't prove obligation"); + return Err(TypeError::Mismatch); + } + + Err(SelectionError::TraitDynIncompatible(_)) => { + // Dyn compatibility errors in coercion will *always* be due to the + // fact that the RHS of the coercion is a non-dyn compatible `dyn Trait` + // written in source somewhere (otherwise we will never have lowered + // the dyn trait from HIR to middle). + // + // There's no reason to emit yet another dyn compatibility error, + // especially since the span will differ slightly and thus not be + // deduplicated at all! + self.set_tainted_by_errors(); + } + Err(_err) => { + // FIXME: Report an error: + // let guar = self.err_ctxt().report_selection_error( + // obligation.clone(), + // &obligation, + // &err, + // ); + self.set_tainted_by_errors(); + // Treat this like an obligation and follow through + // with the unsizing - the lack of a coercion should + // be silent, as it causes a type mismatch later. + } + + Ok(Some(ImplSource::UserDefined(impl_source))) => { + queue.extend(impl_source.nested); + } + Ok(Some(impl_source)) => queue.extend(impl_source.nested_obligations()), } - _ => self.unify_and(&from_ty, to_ty, identity), } - } - fn coerce_from_fn_pointer( - &mut self, - from_ty: Ty, - from_f: &FnPointer, - to_ty: &Ty, - ) -> CoerceResult { - self.coerce_from_safe_fn( - from_ty, - from_f, - to_ty, - simple(Adjust::Pointer(PointerCast::UnsafeFnPointer)), - identity, - ) + Ok(coercion) } - fn coerce_from_safe_fn<F, G>( + fn coerce_from_safe_fn( &mut self, - from_ty: Ty, - from_fn_ptr: &FnPointer, - to_ty: &Ty, - to_unsafe: F, - normal: G, - ) -> CoerceResult - where - F: FnOnce(Ty) -> Vec<Adjustment>, - G: FnOnce(Ty) -> Vec<Adjustment>, - { - if let TyKind::Function(to_fn_ptr) = to_ty.kind(Interner) { - if let (chalk_ir::Safety::Safe, chalk_ir::Safety::Unsafe) = - (from_fn_ptr.sig.safety, to_fn_ptr.sig.safety) + fn_ty_a: PolyFnSig<'db>, + b: Ty<'db>, + adjustment: Option<Adjust<'db>>, + ) -> CoerceResult<'db> { + debug_assert!(self.table.shallow_resolve(b) == b); + + self.commit_if_ok(|this| { + if let TyKind::FnPtr(_, hdr_b) = b.kind() + && fn_ty_a.safety().is_safe() + && !hdr_b.safety.is_safe() { - let from_unsafe = - TyKind::Function(safe_to_unsafe_fn_ty(from_fn_ptr.clone())).intern(Interner); - return self.unify_and(&from_unsafe, to_ty, to_unsafe); + let unsafe_a = Ty::safe_to_unsafe_fn_ty(this.interner(), fn_ty_a); + this.unify_and( + unsafe_a, + b, + adjustment.map(|kind| Adjustment { + kind, + target: Ty::new_fn_ptr(this.interner(), fn_ty_a), + }), + Adjust::Pointer(PointerCast::UnsafeFnPointer), + ) + } else { + let a = Ty::new_fn_ptr(this.interner(), fn_ty_a); + match adjustment { + Some(adjust) => this.unify_and(a, b, [], adjust), + None => this.unify(a, b), + } } + }) + } + + fn coerce_from_fn_pointer(&mut self, fn_ty_a: PolyFnSig<'db>, b: Ty<'db>) -> CoerceResult<'db> { + debug!(?fn_ty_a, ?b, "coerce_from_fn_pointer"); + debug_assert!(self.table.shallow_resolve(b) == b); + + self.coerce_from_safe_fn(fn_ty_a, b, None) + } + + fn coerce_from_fn_item(&mut self, a: Ty<'db>, b: Ty<'db>) -> CoerceResult<'db> { + debug!("coerce_from_fn_item(a={:?}, b={:?})", a, b); + debug_assert!(self.table.shallow_resolve(a) == a); + debug_assert!(self.table.shallow_resolve(b) == b); + + match b.kind() { + TyKind::FnPtr(_, b_hdr) => { + let a_sig = a.fn_sig(self.interner()); + if let TyKind::FnDef(def_id, _) = a.kind() { + // Intrinsics are not coercible to function pointers + if let CallableDefId::FunctionId(def_id) = def_id.0 { + if FunctionSignature::is_intrinsic(self.table.db, def_id) { + return Err(TypeError::IntrinsicCast); + } + + let attrs = self.table.db.attrs(def_id.into()); + if attrs.by_key(sym::rustc_force_inline).exists() { + return Err(TypeError::ForceInlineCast); + } + + if b_hdr.safety.is_safe() && attrs.by_key(sym::target_feature).exists() { + let fn_target_features = + TargetFeatures::from_attrs_no_implications(&attrs); + // Allow the coercion if the current function has all the features that would be + // needed to call the coercee safely. + let (target_features, target_feature_is_safe) = + (self.target_features)(); + if target_feature_is_safe == TargetFeatureIsSafeInTarget::No + && !target_features.enabled.is_superset(&fn_target_features.enabled) + { + return Err(TypeError::TargetFeatureCast( + CallableIdWrapper(def_id.into()).into(), + )); + } + } + } + } + + self.coerce_from_safe_fn( + a_sig, + b, + Some(Adjust::Pointer(PointerCast::ReifyFnPointer)), + ) + } + _ => self.unify(a, b), } - self.unify_and(&from_ty, to_ty, normal) } - /// Attempts to coerce from the type of a non-capturing closure into a - /// function pointer. + /// Attempts to coerce from the type of a non-capturing closure + /// into a function pointer. fn coerce_closure_to_fn( &mut self, - from_ty: Ty, - from_substs: &Substitution, - to_ty: &Ty, - ) -> CoerceResult { - match to_ty.kind(Interner) { - // if from_substs is non-capturing (FIXME) - TyKind::Function(fn_ty) => { + a: Ty<'db>, + _closure_def_id_a: InternedClosureId, + args_a: GenericArgs<'db>, + b: Ty<'db>, + ) -> CoerceResult<'db> { + debug_assert!(self.table.shallow_resolve(a) == a); + debug_assert!(self.table.shallow_resolve(b) == b); + + match b.kind() { + // FIXME: We need to have an `upvars_mentioned()` query: + // At this point we haven't done capture analysis, which means + // that the ClosureArgs just contains an inference variable instead + // of tuple of captured types. + // + // All we care here is if any variable is being captured and not the exact paths, + // so we check `upvars_mentioned` for root variables being captured. + TyKind::FnPtr(_, hdr) => + // if self + // .db + // .upvars_mentioned(closure_def_id_a.expect_local()) + // .is_none_or(|u| u.is_empty()) => + { // We coerce the closure, which has fn type // `extern "rust-call" fn((arg0,arg1,...)) -> _` // to // `fn(arg0,arg1,...) -> _` // or // `unsafe fn(arg0,arg1,...) -> _` - let safety = fn_ty.sig.safety; - let pointer_ty = coerce_closure_fn_ty(from_substs, safety); + let safety = hdr.safety; + let closure_sig = args_a.closure_sig_untupled().map_bound(|mut sig| { + sig.safety = hdr.safety; + sig + }); + let pointer_ty = Ty::new_fn_ptr(self.interner(), closure_sig); + debug!("coerce_closure_to_fn(a={:?}, b={:?}, pty={:?})", a, b, pointer_ty); self.unify_and( - &pointer_ty, - to_ty, - simple(Adjust::Pointer(PointerCast::ClosureFnPointer(safety))), + pointer_ty, + b, + [], + Adjust::Pointer(PointerCast::ClosureFnPointer(safety)), ) } - _ => self.unify_and(&from_ty, to_ty, identity), + _ => self.unify(a, b), } } - /// Coerce a type using `from_ty: CoerceUnsized<ty_ty>` - /// - /// See: <https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html> - fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> CoerceResult { - // These 'if' statements require some explanation. - // The `CoerceUnsized` trait is special - it is only - // possible to write `impl CoerceUnsized<B> for A` where - // A and B have 'matching' fields. This rules out the following - // two types of blanket impls: - // - // `impl<T> CoerceUnsized<T> for SomeType` - // `impl<T> CoerceUnsized<SomeType> for T` - // - // Both of these trigger a special `CoerceUnsized`-related error (E0376) - // - // We can take advantage of this fact to avoid performing unnecessary work. - // If either `source` or `target` is a type variable, then any applicable impl - // would need to be generic over the self-type (`impl<T> CoerceUnsized<SomeType> for T`) - // or generic over the `CoerceUnsized` type parameter (`impl<T> CoerceUnsized<T> for - // SomeType`). - // - // However, these are exactly the kinds of impls which are forbidden by - // the compiler! Therefore, we can be sure that coercion will always fail - // when either the source or target type is a type variable. This allows us - // to skip performing any trait selection, and immediately bail out. - if from_ty.is_ty_var() { - return Err(TypeError); + fn coerce_raw_ptr(&mut self, a: Ty<'db>, b: Ty<'db>, mutbl_b: Mutability) -> CoerceResult<'db> { + debug!("coerce_raw_ptr(a={:?}, b={:?})", a, b); + debug_assert!(self.table.shallow_resolve(a) == a); + debug_assert!(self.table.shallow_resolve(b) == b); + + let (is_ref, mt_a) = match a.kind() { + TyKind::Ref(_, ty, mutbl) => (true, TypeAndMut::<DbInterner<'db>> { ty, mutbl }), + TyKind::RawPtr(ty, mutbl) => (false, TypeAndMut { ty, mutbl }), + _ => return self.unify(a, b), + }; + coerce_mutbls(mt_a.mutbl, mutbl_b)?; + + // Check that the types which they point at are compatible. + let a_raw = Ty::new_ptr(self.interner(), mt_a.ty, mutbl_b); + // Although references and raw ptrs have the same + // representation, we still register an Adjust::DerefRef so that + // regionck knows that the region for `a` must be valid here. + if is_ref { + self.unify_and( + a_raw, + b, + [Adjustment { kind: Adjust::Deref(None), target: mt_a.ty }], + Adjust::Borrow(AutoBorrow::RawPtr(mutbl_b)), + ) + } else if mt_a.mutbl != mutbl_b { + self.unify_and(a_raw, b, [], Adjust::Pointer(PointerCast::MutToConstPointer)) + } else { + self.unify(a_raw, b) } - if to_ty.is_ty_var() { - return Err(TypeError); + } +} + +#[derive(Debug, Clone, Copy, PartialEq, Eq)] +pub(crate) enum CoerceNever { + No, + Yes, +} + +impl<'db> InferenceContext<'_, 'db> { + /// Attempt to coerce an expression to a type, and return the + /// adjusted type of the expression, if successful. + /// Adjustments are only recorded if the coercion succeeded. + /// The expressions *must not* have any preexisting adjustments. + pub(crate) fn coerce( + &mut self, + expr: ExprOrPatId, + expr_ty: Ty<'db>, + mut target: Ty<'db>, + allow_two_phase: AllowTwoPhase, + coerce_never: CoerceNever, + ) -> RelateResult<'db, Ty<'db>> { + let source = self.table.try_structurally_resolve_type(expr_ty); + target = self.table.try_structurally_resolve_type(target); + debug!("coercion::try({:?}: {:?} -> {:?})", expr, source, target); + + let cause = ObligationCause::new(); + let krate = self.krate(); + let mut coerce = Coerce { + table: &mut self.table, + has_errors: &mut self.result.has_errors, + cause, + allow_two_phase, + coerce_never: matches!(coerce_never, CoerceNever::Yes), + use_lub: false, + target_features: &mut || { + Self::target_features(self.db, &self.target_features, self.owner, krate) + }, + }; + let ok = coerce.commit_if_ok(|coerce| coerce.coerce(source, target))?; + + let (adjustments, _) = self.table.register_infer_ok(ok); + match expr { + ExprOrPatId::ExprId(expr) => self.write_expr_adj(expr, adjustments.into_boxed_slice()), + ExprOrPatId::PatId(pat) => self + .write_pat_adj(pat, adjustments.into_iter().map(|adjust| adjust.target).collect()), } + Ok(target) + } - // Handle reborrows before trying to solve `Source: CoerceUnsized<Target>`. - let reborrow = match (from_ty.kind(Interner), to_ty.kind(Interner)) { - (TyKind::Ref(from_mt, _, from_inner), &TyKind::Ref(to_mt, _, _)) => { - coerce_mutabilities(*from_mt, to_mt)?; + /// Given some expressions, their known unified type and another expression, + /// tries to unify the types, potentially inserting coercions on any of the + /// provided expressions and returns their LUB (aka "common supertype"). + /// + /// This is really an internal helper. From outside the coercion + /// module, you should instantiate a `CoerceMany` instance. + fn try_find_coercion_lub( + &mut self, + exprs: &[ExprId], + prev_ty: Ty<'db>, + new: ExprId, + new_ty: Ty<'db>, + ) -> RelateResult<'db, Ty<'db>> { + let prev_ty = self.table.try_structurally_resolve_type(prev_ty); + let new_ty = self.table.try_structurally_resolve_type(new_ty); + debug!( + "coercion::try_find_coercion_lub({:?}, {:?}, exprs={:?} exprs)", + prev_ty, + new_ty, + exprs.len() + ); + + // The following check fixes #88097, where the compiler erroneously + // attempted to coerce a closure type to itself via a function pointer. + if prev_ty == new_ty { + return Ok(prev_ty); + } - let lt = self.new_lifetime_var(); - Some(( - Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() }, - Adjustment { - kind: Adjust::Borrow(AutoBorrow::Ref(lt.clone(), to_mt)), - target: TyKind::Ref(to_mt, lt, from_inner.clone()).intern(Interner), - }, - )) + let is_force_inline = |ty: Ty<'db>| { + if let TyKind::FnDef(CallableIdWrapper(CallableDefId::FunctionId(did)), _) = ty.kind() { + self.db.attrs(did.into()).by_key(sym::rustc_force_inline).exists() + } else { + false } - (TyKind::Ref(from_mt, _, from_inner), &TyKind::Raw(to_mt, _)) => { - coerce_mutabilities(*from_mt, to_mt)?; + }; + if is_force_inline(prev_ty) || is_force_inline(new_ty) { + return Err(TypeError::ForceInlineCast); + } - Some(( - Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() }, - Adjustment { - kind: Adjust::Borrow(AutoBorrow::RawPtr(to_mt)), - target: TyKind::Raw(to_mt, from_inner.clone()).intern(Interner), - }, - )) + // Special-case that coercion alone cannot handle: + // Function items or non-capturing closures of differing IDs or GenericArgs. + let (a_sig, b_sig) = { + let is_capturing_closure = |_ty: Ty<'db>| { + // FIXME: + // if let TyKind::Closure(closure_def_id, _args) = ty.kind() { + // self.db.upvars_mentioned(closure_def_id.expect_local()).is_some() + // } else { + // false + // } + false + }; + if is_capturing_closure(prev_ty) || is_capturing_closure(new_ty) { + (None, None) + } else { + match (prev_ty.kind(), new_ty.kind()) { + (TyKind::FnDef(..), TyKind::FnDef(..)) => { + // Don't reify if the function types have a LUB, i.e., they + // are the same function and their parameters have a LUB. + match self.table.commit_if_ok(|table| { + // We need to eagerly handle nested obligations due to lazy norm. + let mut ocx = ObligationCtxt::new(&table.infer_ctxt); + let value = ocx.lub( + &ObligationCause::new(), + table.trait_env.env, + prev_ty, + new_ty, + )?; + if ocx.try_evaluate_obligations().is_empty() { + Ok(InferOk { value, obligations: ocx.into_pending_obligations() }) + } else { + Err(TypeError::Mismatch) + } + }) { + // We have a LUB of prev_ty and new_ty, just return it. + Ok(ok) => return Ok(self.table.register_infer_ok(ok)), + Err(_) => ( + Some(prev_ty.fn_sig(self.table.interner())), + Some(new_ty.fn_sig(self.table.interner())), + ), + } + } + (TyKind::Closure(_, args), TyKind::FnDef(..)) => { + let b_sig = new_ty.fn_sig(self.table.interner()); + let a_sig = args.closure_sig_untupled().map_bound(|mut sig| { + sig.safety = b_sig.safety(); + sig + }); + (Some(a_sig), Some(b_sig)) + } + (TyKind::FnDef(..), TyKind::Closure(_, args)) => { + let a_sig = prev_ty.fn_sig(self.table.interner()); + let b_sig = args.closure_sig_untupled().map_bound(|mut sig| { + sig.safety = a_sig.safety(); + sig + }); + (Some(a_sig), Some(b_sig)) + } + (TyKind::Closure(_, args_a), TyKind::Closure(_, args_b)) => { + (Some(args_a.closure_sig_untupled()), Some(args_b.closure_sig_untupled())) + } + _ => (None, None), + } } - _ => None, }; - let coerce_from = - reborrow.as_ref().map_or_else(|| from_ty.clone(), |(_, adj)| adj.target.clone()); + if let (Some(a_sig), Some(b_sig)) = (a_sig, b_sig) { + // The signature must match. + let sig = self + .table + .infer_ctxt + .at(&ObligationCause::new(), self.table.trait_env.env) + .lub(a_sig, b_sig) + .map(|ok| self.table.register_infer_ok(ok))?; + + // Reify both sides and return the reified fn pointer type. + let fn_ptr = Ty::new_fn_ptr(self.table.interner(), sig); + let prev_adjustment = match prev_ty.kind() { + TyKind::Closure(..) => { + Adjust::Pointer(PointerCast::ClosureFnPointer(a_sig.safety())) + } + TyKind::FnDef(..) => Adjust::Pointer(PointerCast::ReifyFnPointer), + _ => panic!("should not try to coerce a {prev_ty:?} to a fn pointer"), + }; + let next_adjustment = match new_ty.kind() { + TyKind::Closure(..) => { + Adjust::Pointer(PointerCast::ClosureFnPointer(b_sig.safety())) + } + TyKind::FnDef(..) => Adjust::Pointer(PointerCast::ReifyFnPointer), + _ => panic!("should not try to coerce a {new_ty:?} to a fn pointer"), + }; + for &expr in exprs { + self.write_expr_adj( + expr, + Box::new([Adjustment { kind: prev_adjustment.clone(), target: fn_ptr }]), + ); + } + self.write_expr_adj( + new, + Box::new([Adjustment { kind: next_adjustment, target: fn_ptr }]), + ); + return Ok(fn_ptr); + } - let krate = self.trait_env.krate; - let coerce_unsized_trait = match LangItem::CoerceUnsized.resolve_trait(self.db, krate) { - Some(trait_) => trait_, - _ => return Err(TypeError), + // Configure a Coerce instance to compute the LUB. + // We don't allow two-phase borrows on any autorefs this creates since we + // probably aren't processing function arguments here and even if we were, + // they're going to get autorefed again anyway and we can apply 2-phase borrows + // at that time. + // + // NOTE: we set `coerce_never` to `true` here because coercion LUBs only + // operate on values and not places, so a never coercion is valid. + let krate = self.krate(); + let mut coerce = Coerce { + table: &mut self.table, + has_errors: &mut self.result.has_errors, + cause: ObligationCause::new(), + allow_two_phase: AllowTwoPhase::No, + coerce_never: true, + use_lub: true, + target_features: &mut || { + Self::target_features(self.db, &self.target_features, self.owner, krate) + }, }; - let coerce_unsized_tref = { - let b = TyBuilder::trait_ref(self.db, coerce_unsized_trait); - if b.remaining() != 2 { - // The CoerceUnsized trait should have two generic params: Self and T. - return Err(TypeError); + // First try to coerce the new expression to the type of the previous ones, + // but only if the new expression has no coercion already applied to it. + let mut first_error = None; + if !self.result.expr_adjustments.contains_key(&new) { + let result = coerce.commit_if_ok(|coerce| coerce.coerce(new_ty, prev_ty)); + match result { + Ok(ok) => { + let (adjustments, target) = self.table.register_infer_ok(ok); + self.write_expr_adj(new, adjustments.into_boxed_slice()); + debug!( + "coercion::try_find_coercion_lub: was able to coerce from new type {:?} to previous type {:?} ({:?})", + new_ty, prev_ty, target + ); + return Ok(target); + } + Err(e) => first_error = Some(e), } - b.push(coerce_from).push(to_ty.clone()).build() - }; + } - let goal: InEnvironment<DomainGoal> = - InEnvironment::new(&self.trait_env.env, coerce_unsized_tref.cast(Interner)); - - let canonicalized = self.canonicalize_with_free_vars(goal); - - // FIXME: rustc's coerce_unsized is more specialized -- it only tries to - // solve `CoerceUnsized` and `Unsize` goals at this point and leaves the - // rest for later. Also, there's some logic about sized type variables. - // Need to find out in what cases this is necessary - let solution = self - .db - .trait_solve(krate, self.trait_env.block, canonicalized.value.clone().cast(Interner)) - .ok_or(TypeError)?; - - match solution { - Solution::Unique(v) => { - canonicalized.apply_solution( - self, - Canonical { - binders: v.binders, - // FIXME handle constraints - value: v.value.subst, - }, - ); + match coerce.commit_if_ok(|coerce| coerce.coerce(prev_ty, new_ty)) { + Err(_) => { + // Avoid giving strange errors on failed attempts. + if let Some(e) = first_error { + Err(e) + } else { + Err(self + .table + .commit_if_ok(|table| { + table + .infer_ctxt + .at(&ObligationCause::new(), table.trait_env.env) + .lub(prev_ty, new_ty) + }) + .unwrap_err()) + } } - Solution::Ambig(Guidance::Definite(subst)) => { - // FIXME need to record an obligation here - canonicalized.apply_solution(self, subst) + Ok(ok) => { + let (adjustments, target) = self.table.register_infer_ok(ok); + for &expr in exprs { + self.write_expr_adj(expr, adjustments.as_slice().into()); + } + debug!( + "coercion::try_find_coercion_lub: was able to coerce previous type {:?} to new type {:?} ({:?})", + prev_ty, new_ty, target + ); + Ok(target) } - // FIXME actually we maybe should also accept unknown guidance here - _ => return Err(TypeError), - }; - let unsize = - Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target: to_ty.clone() }; - let adjustments = match reborrow { - None => vec![unsize], - Some((deref, autoref)) => vec![deref, autoref, unsize], - }; - success(adjustments, to_ty.clone(), vec![]) + } } } -fn coerce_closure_fn_ty(closure_substs: &Substitution, safety: chalk_ir::Safety) -> Ty { - let closure_sig = ClosureSubst(closure_substs).sig_ty().clone(); - match closure_sig.kind(Interner) { - TyKind::Function(fn_ty) => TyKind::Function(FnPointer { - num_binders: fn_ty.num_binders, - sig: FnSig { safety, abi: FnAbi::Rust, variadic: fn_ty.sig.variadic }, - substitution: fn_ty.substitution.clone(), - }) - .intern(Interner), - _ => TyKind::Error.intern(Interner), - } +/// CoerceMany encapsulates the pattern you should use when you have +/// many expressions that are all getting coerced to a common +/// type. This arises, for example, when you have a match (the result +/// of each arm is coerced to a common type). It also arises in less +/// obvious places, such as when you have many `break foo` expressions +/// that target the same loop, or the various `return` expressions in +/// a function. +/// +/// The basic protocol is as follows: +/// +/// - Instantiate the `CoerceMany` with an initial `expected_ty`. +/// This will also serve as the "starting LUB". The expectation is +/// that this type is something which all of the expressions *must* +/// be coercible to. Use a fresh type variable if needed. +/// - For each expression whose result is to be coerced, invoke `coerce()` with. +/// - In some cases we wish to coerce "non-expressions" whose types are implicitly +/// unit. This happens for example if you have a `break` with no expression, +/// or an `if` with no `else`. In that case, invoke `coerce_forced_unit()`. +/// - `coerce()` and `coerce_forced_unit()` may report errors. They hide this +/// from you so that you don't have to worry your pretty head about it. +/// But if an error is reported, the final type will be `err`. +/// - Invoking `coerce()` may cause us to go and adjust the "adjustments" on +/// previously coerced expressions. +/// - When all done, invoke `complete()`. This will return the LUB of +/// all your expressions. +/// - WARNING: I don't believe this final type is guaranteed to be +/// related to your initial `expected_ty` in any particular way, +/// although it will typically be a subtype, so you should check it. +/// - Invoking `complete()` may cause us to go and adjust the "adjustments" on +/// previously coerced expressions. +/// +/// Example: +/// +/// ```ignore (illustrative) +/// let mut coerce = CoerceMany::new(expected_ty); +/// for expr in exprs { +/// let expr_ty = fcx.check_expr_with_expectation(expr, expected); +/// coerce.coerce(fcx, &cause, expr, expr_ty); +/// } +/// let final_ty = coerce.complete(fcx); +/// ``` +#[derive(Debug, Clone)] +pub(crate) struct CoerceMany<'db, 'exprs> { + expected_ty: Ty<'db>, + final_ty: Option<Ty<'db>>, + expressions: Expressions<'exprs>, + pushed: usize, } -fn safe_to_unsafe_fn_ty(fn_ty: FnPointer) -> FnPointer { - FnPointer { - num_binders: fn_ty.num_binders, - sig: FnSig { safety: chalk_ir::Safety::Unsafe, ..fn_ty.sig }, - substitution: fn_ty.substitution, - } +/// The type of a `CoerceMany` that is storing up the expressions into +/// a buffer. We use this for things like `break`. +pub(crate) type DynamicCoerceMany<'db> = CoerceMany<'db, 'db>; + +#[derive(Debug, Clone)] +enum Expressions<'exprs> { + Dynamic(SmallVec<[ExprId; 4]>), + UpFront(&'exprs [ExprId]), } -fn coerce_mutabilities(from: Mutability, to: Mutability) -> Result<(), TypeError> { - match (from, to) { - (Mutability::Mut, Mutability::Mut | Mutability::Not) - | (Mutability::Not, Mutability::Not) => Ok(()), - (Mutability::Not, Mutability::Mut) => Err(TypeError), +impl<'db, 'exprs> CoerceMany<'db, 'exprs> { + /// The usual case; collect the set of expressions dynamically. + /// If the full set of coercion sites is known before hand, + /// consider `with_coercion_sites()` instead to avoid allocation. + pub(crate) fn new(expected_ty: Ty<'db>) -> Self { + Self::make(expected_ty, Expressions::Dynamic(SmallVec::new())) + } + + /// As an optimization, you can create a `CoerceMany` with a + /// preexisting slice of expressions. In this case, you are + /// expected to pass each element in the slice to `coerce(...)` in + /// order. This is used with arrays in particular to avoid + /// needlessly cloning the slice. + pub(crate) fn with_coercion_sites( + expected_ty: Ty<'db>, + coercion_sites: &'exprs [ExprId], + ) -> Self { + Self::make(expected_ty, Expressions::UpFront(coercion_sites)) + } + + fn make(expected_ty: Ty<'db>, expressions: Expressions<'exprs>) -> Self { + CoerceMany { expected_ty, final_ty: None, expressions, pushed: 0 } + } + + /// Returns the "expected type" with which this coercion was + /// constructed. This represents the "downward propagated" type + /// that was given to us at the start of typing whatever construct + /// we are typing (e.g., the match expression). + /// + /// Typically, this is used as the expected type when + /// type-checking each of the alternative expressions whose types + /// we are trying to merge. + pub(crate) fn expected_ty(&self) -> Ty<'db> { + self.expected_ty + } + + /// Returns the current "merged type", representing our best-guess + /// at the LUB of the expressions we've seen so far (if any). This + /// isn't *final* until you call `self.complete()`, which will return + /// the merged type. + pub(crate) fn merged_ty(&self) -> Ty<'db> { + self.final_ty.unwrap_or(self.expected_ty) + } + + /// Indicates that the value generated by `expression`, which is + /// of type `expression_ty`, is one of the possibilities that we + /// could coerce from. This will record `expression`, and later + /// calls to `coerce` may come back and add adjustments and things + /// if necessary. + pub(crate) fn coerce( + &mut self, + icx: &mut InferenceContext<'_, 'db>, + cause: &ObligationCause, + expression: ExprId, + expression_ty: Ty<'db>, + ) { + self.coerce_inner(icx, cause, expression, expression_ty, false, false) + } + + /// Indicates that one of the inputs is a "forced unit". This + /// occurs in a case like `if foo { ... };`, where the missing else + /// generates a "forced unit". Another example is a `loop { break; + /// }`, where the `break` has no argument expression. We treat + /// these cases slightly differently for error-reporting + /// purposes. Note that these tend to correspond to cases where + /// the `()` expression is implicit in the source, and hence we do + /// not take an expression argument. + /// + /// The `augment_error` gives you a chance to extend the error + /// message, in case any results (e.g., we use this to suggest + /// removing a `;`). + pub(crate) fn coerce_forced_unit( + &mut self, + icx: &mut InferenceContext<'_, 'db>, + expr: ExprId, + cause: &ObligationCause, + label_unit_as_expected: bool, + ) { + self.coerce_inner(icx, cause, expr, icx.types.unit, true, label_unit_as_expected) + } + + /// The inner coercion "engine". If `expression` is `None`, this + /// is a forced-unit case, and hence `expression_ty` must be + /// `Nil`. + pub(crate) fn coerce_inner( + &mut self, + icx: &mut InferenceContext<'_, 'db>, + cause: &ObligationCause, + expression: ExprId, + mut expression_ty: Ty<'db>, + force_unit: bool, + label_expression_as_expected: bool, + ) { + // Incorporate whatever type inference information we have + // until now; in principle we might also want to process + // pending obligations, but doing so should only improve + // compatibility (hopefully that is true) by helping us + // uncover never types better. + if expression_ty.is_ty_var() { + expression_ty = icx.shallow_resolve(expression_ty); + } + + let (expected, found) = if label_expression_as_expected { + // In the case where this is a "forced unit", like + // `break`, we want to call the `()` "expected" + // since it is implied by the syntax. + // (Note: not all force-units work this way.)" + (expression_ty, self.merged_ty()) + } else { + // Otherwise, the "expected" type for error + // reporting is the current unification type, + // which is basically the LUB of the expressions + // we've seen so far (combined with the expected + // type) + (self.merged_ty(), expression_ty) + }; + + // Handle the actual type unification etc. + let result = if !force_unit { + if self.pushed == 0 { + // Special-case the first expression we are coercing. + // To be honest, I'm not entirely sure why we do this. + // We don't allow two-phase borrows, see comment in try_find_coercion_lub for why + icx.coerce( + expression.into(), + expression_ty, + self.expected_ty, + AllowTwoPhase::No, + CoerceNever::Yes, + ) + } else { + match self.expressions { + Expressions::Dynamic(ref exprs) => icx.try_find_coercion_lub( + exprs, + self.merged_ty(), + expression, + expression_ty, + ), + Expressions::UpFront(coercion_sites) => icx.try_find_coercion_lub( + &coercion_sites[0..self.pushed], + self.merged_ty(), + expression, + expression_ty, + ), + } + } + } else { + // this is a hack for cases where we default to `()` because + // the expression etc has been omitted from the source. An + // example is an `if let` without an else: + // + // if let Some(x) = ... { } + // + // we wind up with a second match arm that is like `_ => + // ()`. That is the case we are considering here. We take + // a different path to get the right "expected, found" + // message and so forth (and because we know that + // `expression_ty` will be unit). + // + // Another example is `break` with no argument expression. + assert!(expression_ty.is_unit(), "if let hack without unit type"); + icx.table.infer_ctxt.at(cause, icx.table.trait_env.env).eq(expected, found).map( + |infer_ok| { + icx.table.register_infer_ok(infer_ok); + expression_ty + }, + ) + }; + + debug!(?result); + match result { + Ok(v) => { + self.final_ty = Some(v); + match self.expressions { + Expressions::Dynamic(ref mut buffer) => buffer.push(expression), + Expressions::UpFront(coercion_sites) => { + // if the user gave us an array to validate, check that we got + // the next expression in the list, as expected + assert_eq!(coercion_sites[self.pushed], expression); + } + } + } + Err(_coercion_error) => { + // Mark that we've failed to coerce the types here to suppress + // any superfluous errors we might encounter while trying to + // emit or provide suggestions on how to fix the initial error. + icx.set_tainted_by_errors(); + + self.final_ty = Some(icx.types.error); + + icx.result.type_mismatches.insert( + expression.into(), + if label_expression_as_expected { + TypeMismatch { expected: found, actual: expected } + } else { + TypeMismatch { expected, actual: found } + }, + ); + } + } + + self.pushed += 1; + } + + pub(crate) fn complete(self, icx: &mut InferenceContext<'_, 'db>) -> Ty<'db> { + if let Some(final_ty) = self.final_ty { + final_ty + } else { + // If we only had inputs that were of type `!` (or no + // inputs at all), then the final type is `!`. + assert_eq!(self.pushed, 0); + icx.types.never + } } } -pub(super) fn auto_deref_adjust_steps(autoderef: &Autoderef<'_, '_>) -> Vec<Adjustment> { - let steps = autoderef.steps(); - let targets = - steps.iter().skip(1).map(|(_, ty)| ty.clone()).chain(iter::once(autoderef.final_ty())); - steps - .iter() - .map(|(kind, _source)| match kind { - // We do not know what kind of deref we require at this point yet - AutoderefKind::Overloaded => Some(OverloadedDeref(None)), - AutoderefKind::Builtin => None, - }) - .zip(targets) - .map(|(autoderef, target)| Adjustment { kind: Adjust::Deref(autoderef), target }) - .collect() +pub fn could_coerce<'db>( + db: &'db dyn HirDatabase, + env: Arc<TraitEnvironment<'db>>, + tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>, +) -> bool { + coerce(db, env, tys).is_ok() +} + +fn coerce<'db>( + db: &'db dyn HirDatabase, + env: Arc<TraitEnvironment<'db>>, + tys: &Canonical<'db, (Ty<'db>, Ty<'db>)>, +) -> Result<(Vec<Adjustment<'db>>, Ty<'db>), TypeError<DbInterner<'db>>> { + let mut table = InferenceTable::new(db, env); + let interner = table.interner(); + let ((ty1_with_vars, ty2_with_vars), vars) = table.infer_ctxt.instantiate_canonical(tys); + + let cause = ObligationCause::new(); + // FIXME: Target features. + let target_features = TargetFeatures::default(); + let mut coerce = Coerce { + table: &mut table, + has_errors: &mut false, + cause, + allow_two_phase: AllowTwoPhase::No, + coerce_never: true, + use_lub: false, + target_features: &mut || (&target_features, TargetFeatureIsSafeInTarget::No), + }; + let InferOk { value: (adjustments, ty), obligations } = + coerce.coerce(ty1_with_vars, ty2_with_vars)?; + table.register_predicates(obligations); + + // default any type vars that weren't unified back to their original bound vars + // (kind of hacky) + let mut fallback_ty = |debruijn, infer| { + let var = vars.var_values.iter().position(|arg| { + arg.as_type().is_some_and(|ty| match ty.kind() { + TyKind::Infer(it) => infer == it, + _ => false, + }) + }); + var.map_or_else( + || Ty::new_error(interner, ErrorGuaranteed), + |i| { + Ty::new_bound( + interner, + debruijn, + BoundTy { kind: BoundTyKind::Anon, var: BoundVar::from_usize(i) }, + ) + }, + ) + }; + let mut fallback_const = |debruijn, infer| { + let var = vars.var_values.iter().position(|arg| { + arg.as_const().is_some_and(|ty| match ty.kind() { + ConstKind::Infer(it) => infer == it, + _ => false, + }) + }); + var.map_or_else( + || Const::new_error(interner, ErrorGuaranteed), + |i| Const::new_bound(interner, debruijn, BoundConst { var: BoundVar::from_usize(i) }), + ) + }; + let mut fallback_region = |debruijn, infer| { + let var = vars.var_values.iter().position(|arg| { + arg.as_region().is_some_and(|ty| match ty.kind() { + RegionKind::ReVar(it) => infer == it, + _ => false, + }) + }); + var.map_or_else( + || Region::error(interner), + |i| { + Region::new_bound( + interner, + debruijn, + BoundRegion { kind: BoundRegionKind::Anon, var: BoundVar::from_usize(i) }, + ) + }, + ) + }; + // FIXME also map the types in the adjustments + // FIXME: We don't fallback correctly since this is done on `InferenceContext` and we only have `InferenceTable`. + let ty = table.resolve_with_fallback( + ty, + &mut fallback_ty, + &mut fallback_const, + &mut fallback_region, + ); + Ok((adjustments, ty)) } |