flux_infer/
infer.rs

1use std::{cell::RefCell, fmt, iter};
2
3use flux_common::{bug, dbg, tracked_span_assert_eq, tracked_span_bug, tracked_span_dbg_assert_eq};
4use flux_config::{self as config, InferOpts, OverflowMode};
5use flux_macros::{TypeFoldable, TypeVisitable};
6use flux_middle::{
7    FixpointQueryKind,
8    def_id::MaybeExternId,
9    global_env::GlobalEnv,
10    queries::{QueryErr, QueryResult},
11    query_bug,
12    rty::{
13        self, AliasKind, AliasTy, BaseTy, Binder, BoundVariableKinds, CoroutineObligPredicate,
14        Ctor, ESpan, EVid, EarlyBinder, Expr, ExprKind, FieldProj, GenericArg, HoleKind, InferMode,
15        Lambda, List, Loc, Mutability, Name, Path, PolyVariant, PtrKind, RefineArgs, RefineArgsExt,
16        Region, Sort, Ty, TyCtor, TyKind, Var,
17        canonicalize::{Hoister, HoisterDelegate},
18        fold::TypeFoldable,
19    },
20};
21use itertools::{Itertools, izip};
22use rustc_hir::def_id::{DefId, LocalDefId};
23use rustc_macros::extension;
24use rustc_middle::{
25    mir::BasicBlock,
26    ty::{TyCtxt, Variance},
27};
28use rustc_span::Span;
29
30use crate::{
31    evars::{EVarState, EVarStore},
32    fixpoint_encoding::{FixQueryCache, FixpointCtxt, KVarEncoding, KVarGen},
33    projections::NormalizeExt as _,
34    refine_tree::{Cursor, Marker, RefineTree, Scope},
35};
36
37pub type InferResult<T = ()> = std::result::Result<T, InferErr>;
38
39#[derive(PartialEq, Eq, Clone, Copy, Hash)]
40pub struct Tag {
41    pub reason: ConstrReason,
42    pub src_span: Span,
43    pub dst_span: Option<ESpan>,
44}
45
46impl Tag {
47    pub fn new(reason: ConstrReason, span: Span) -> Self {
48        Self { reason, src_span: span, dst_span: None }
49    }
50
51    pub fn with_dst(self, dst_span: Option<ESpan>) -> Self {
52        Self { dst_span, ..self }
53    }
54}
55
56#[derive(PartialEq, Eq, Clone, Copy, Hash, Debug)]
57pub enum SubtypeReason {
58    Input,
59    Output,
60    Requires,
61    Ensures,
62}
63
64#[derive(PartialEq, Eq, Clone, Copy, Hash, Debug)]
65pub enum ConstrReason {
66    Call,
67    Assign,
68    Ret,
69    Fold,
70    FoldLocal,
71    Predicate,
72    Assert(&'static str),
73    Div,
74    Rem,
75    Goto(BasicBlock),
76    Overflow,
77    Underflow,
78    Subtype(SubtypeReason),
79    Other,
80}
81
82pub struct InferCtxtRoot<'genv, 'tcx> {
83    pub genv: GlobalEnv<'genv, 'tcx>,
84    inner: RefCell<InferCtxtInner>,
85    refine_tree: RefineTree,
86    opts: InferOpts,
87}
88
89pub struct InferCtxtRootBuilder<'a, 'genv, 'tcx> {
90    genv: GlobalEnv<'genv, 'tcx>,
91    opts: InferOpts,
92    params: Vec<(Var, Sort)>,
93    infcx: &'a rustc_infer::infer::InferCtxt<'tcx>,
94    dummy_kvars: bool,
95}
96
97#[extension(pub trait GlobalEnvExt<'genv, 'tcx>)]
98impl<'genv, 'tcx> GlobalEnv<'genv, 'tcx> {
99    fn infcx_root<'a>(
100        self,
101        infcx: &'a rustc_infer::infer::InferCtxt<'tcx>,
102        opts: InferOpts,
103    ) -> InferCtxtRootBuilder<'a, 'genv, 'tcx> {
104        InferCtxtRootBuilder { genv: self, infcx, params: vec![], opts, dummy_kvars: false }
105    }
106}
107
108impl<'genv, 'tcx> InferCtxtRootBuilder<'_, 'genv, 'tcx> {
109    pub fn with_dummy_kvars(mut self) -> Self {
110        self.dummy_kvars = true;
111        self
112    }
113
114    pub fn with_const_generics(mut self, def_id: DefId) -> QueryResult<Self> {
115        self.params.extend(
116            self.genv
117                .generics_of(def_id)?
118                .const_params(self.genv)?
119                .into_iter()
120                .map(|(pcst, sort)| (Var::ConstGeneric(pcst), sort)),
121        );
122        Ok(self)
123    }
124
125    pub fn with_refinement_generics(
126        mut self,
127        def_id: DefId,
128        args: &[GenericArg],
129    ) -> QueryResult<Self> {
130        for (index, param) in self
131            .genv
132            .refinement_generics_of(def_id)?
133            .iter_own_params()
134            .enumerate()
135        {
136            let param = param.instantiate(self.genv.tcx(), args, &[]);
137            let sort = param.sort.normalize_sorts(def_id, self.genv, self.infcx)?;
138
139            let var =
140                Var::EarlyParam(rty::EarlyReftParam { index: index as u32, name: param.name });
141            self.params.push((var, sort));
142        }
143        Ok(self)
144    }
145
146    pub fn identity_for_item(mut self, def_id: DefId) -> QueryResult<Self> {
147        self = self.with_const_generics(def_id)?;
148        let offset = self.params.len();
149        self.genv.refinement_generics_of(def_id)?.fill_item(
150            self.genv,
151            &mut self.params,
152            &mut |param, index| {
153                let index = (index - offset) as u32;
154                let param = param.instantiate_identity();
155                let sort = param.sort.normalize_sorts(def_id, self.genv, self.infcx)?;
156
157                let var = Var::EarlyParam(rty::EarlyReftParam { index, name: param.name });
158                Ok((var, sort))
159            },
160        )?;
161        Ok(self)
162    }
163
164    pub fn build(self) -> QueryResult<InferCtxtRoot<'genv, 'tcx>> {
165        Ok(InferCtxtRoot {
166            genv: self.genv,
167            inner: RefCell::new(InferCtxtInner::new(self.dummy_kvars)),
168            refine_tree: RefineTree::new(self.params),
169            opts: self.opts,
170        })
171    }
172}
173
174impl<'genv, 'tcx> InferCtxtRoot<'genv, 'tcx> {
175    pub fn infcx<'a>(
176        &'a mut self,
177        def_id: DefId,
178        region_infcx: &'a rustc_infer::infer::InferCtxt<'tcx>,
179    ) -> InferCtxt<'a, 'genv, 'tcx> {
180        InferCtxt {
181            genv: self.genv,
182            region_infcx,
183            def_id,
184            cursor: self.refine_tree.cursor_at_root(),
185            inner: &self.inner,
186            check_overflow: self.opts.check_overflow,
187        }
188    }
189
190    pub fn fresh_kvar_in_scope(
191        &self,
192        binders: &[BoundVariableKinds],
193        scope: &Scope,
194        encoding: KVarEncoding,
195    ) -> Expr {
196        let inner = &mut *self.inner.borrow_mut();
197        inner.kvars.fresh(binders, scope.iter(), encoding)
198    }
199
200    pub fn execute_fixpoint_query(
201        self,
202        cache: &mut FixQueryCache,
203        def_id: MaybeExternId,
204        kind: FixpointQueryKind,
205    ) -> QueryResult<Vec<Tag>> {
206        let inner = self.inner.into_inner();
207        let kvars = inner.kvars;
208        let evars = inner.evars;
209
210        let ext = kind.ext();
211
212        let mut refine_tree = self.refine_tree;
213
214        refine_tree.replace_evars(&evars).unwrap();
215
216        if config::dump_constraint() {
217            dbg::dump_item_info(self.genv.tcx(), def_id.resolved_id(), ext, &refine_tree).unwrap();
218        }
219        refine_tree.simplify(self.genv);
220        if config::dump_constraint() {
221            let simp_ext = format!("simp.{ext}");
222            dbg::dump_item_info(self.genv.tcx(), def_id.resolved_id(), simp_ext, &refine_tree)
223                .unwrap();
224        }
225
226        let mut fcx = FixpointCtxt::new(self.genv, def_id, kvars);
227        let cstr = refine_tree.into_fixpoint(&mut fcx)?;
228
229        let backend = match self.opts.solver {
230            flux_config::SmtSolver::Z3 => liquid_fixpoint::SmtSolver::Z3,
231            flux_config::SmtSolver::CVC5 => liquid_fixpoint::SmtSolver::CVC5,
232        };
233
234        fcx.check(cache, cstr, kind, self.opts.scrape_quals, backend)
235    }
236
237    pub fn split(self) -> (RefineTree, KVarGen) {
238        (self.refine_tree, self.inner.into_inner().kvars)
239    }
240}
241
242pub struct InferCtxt<'infcx, 'genv, 'tcx> {
243    pub genv: GlobalEnv<'genv, 'tcx>,
244    pub region_infcx: &'infcx rustc_infer::infer::InferCtxt<'tcx>,
245    pub def_id: DefId,
246    pub check_overflow: OverflowMode,
247    cursor: Cursor<'infcx>,
248    inner: &'infcx RefCell<InferCtxtInner>,
249}
250
251struct InferCtxtInner {
252    kvars: KVarGen,
253    evars: EVarStore,
254}
255
256impl InferCtxtInner {
257    fn new(dummy_kvars: bool) -> Self {
258        Self { kvars: KVarGen::new(dummy_kvars), evars: Default::default() }
259    }
260}
261
262impl<'infcx, 'genv, 'tcx> InferCtxt<'infcx, 'genv, 'tcx> {
263    pub fn at(&mut self, span: Span) -> InferCtxtAt<'_, 'infcx, 'genv, 'tcx> {
264        InferCtxtAt { infcx: self, span }
265    }
266
267    pub fn instantiate_refine_args(
268        &mut self,
269        callee_def_id: DefId,
270        args: &[rty::GenericArg],
271    ) -> InferResult<List<Expr>> {
272        Ok(RefineArgs::for_item(self.genv, callee_def_id, |param, _| {
273            let param = param.instantiate(self.genv.tcx(), args, &[]);
274            Ok(self.fresh_infer_var(&param.sort, param.mode))
275        })?)
276    }
277
278    pub fn instantiate_generic_args(&mut self, args: &[GenericArg]) -> Vec<GenericArg> {
279        args.iter()
280            .map(|a| a.replace_holes(|binders, kind| self.fresh_infer_var_for_hole(binders, kind)))
281            .collect_vec()
282    }
283
284    pub fn fresh_infer_var(&self, sort: &Sort, mode: InferMode) -> Expr {
285        match mode {
286            InferMode::KVar => {
287                let fsort = sort.expect_func().expect_mono();
288                let vars = fsort.inputs().iter().cloned().map_into().collect();
289                let kvar = self.fresh_kvar(&[vars], KVarEncoding::Single);
290                Expr::abs(Lambda::bind_with_fsort(kvar, fsort))
291            }
292            InferMode::EVar => self.fresh_evar(),
293        }
294    }
295
296    pub fn fresh_infer_var_for_hole(
297        &mut self,
298        binders: &[BoundVariableKinds],
299        kind: HoleKind,
300    ) -> Expr {
301        match kind {
302            HoleKind::Pred => self.fresh_kvar(binders, KVarEncoding::Conj),
303            HoleKind::Expr(_) => {
304                // We only use expression holes to infer early param arguments for opaque types
305                // at function calls. These should be well-scoped in the current scope, so we ignore
306                // the extra `binders` around the hole.
307                self.fresh_evar()
308            }
309        }
310    }
311
312    /// Generate a fresh kvar in the _given_ [`Scope`] (similar method in [`InferCtxtRoot`]).
313    pub fn fresh_kvar_in_scope(
314        &self,
315        binders: &[BoundVariableKinds],
316        scope: &Scope,
317        encoding: KVarEncoding,
318    ) -> Expr {
319        let inner = &mut *self.inner.borrow_mut();
320        inner.kvars.fresh(binders, scope.iter(), encoding)
321    }
322
323    /// Generate a fresh kvar in the current scope. See [`KVarGen::fresh`].
324    pub fn fresh_kvar(&self, binders: &[BoundVariableKinds], encoding: KVarEncoding) -> Expr {
325        let inner = &mut *self.inner.borrow_mut();
326        inner.kvars.fresh(binders, self.cursor.vars(), encoding)
327    }
328
329    fn fresh_evar(&self) -> Expr {
330        let evars = &mut self.inner.borrow_mut().evars;
331        Expr::evar(evars.fresh(self.cursor.marker()))
332    }
333
334    pub fn unify_exprs(&self, a: &Expr, b: &Expr) {
335        if a.has_evars() {
336            return;
337        }
338        let evars = &mut self.inner.borrow_mut().evars;
339        if let ExprKind::Var(Var::EVar(evid)) = b.kind()
340            && let EVarState::Unsolved(marker) = evars.get(*evid)
341            && !marker.has_free_vars(a)
342        {
343            evars.solve(*evid, a.clone());
344        }
345    }
346
347    fn enter_exists<T, U>(
348        &mut self,
349        t: &Binder<T>,
350        f: impl FnOnce(&mut InferCtxt<'_, 'genv, 'tcx>, T) -> U,
351    ) -> U
352    where
353        T: TypeFoldable,
354    {
355        self.ensure_resolved_evars(|infcx| {
356            let t = t.replace_bound_refts_with(|sort, mode, _| infcx.fresh_infer_var(sort, mode));
357            Ok(f(infcx, t))
358        })
359        .unwrap()
360    }
361
362    /// Used in conjunction with [`InferCtxt::pop_evar_scope`] to ensure evars are solved at the end
363    /// of some scope, for example, to ensure all evars generated during a function call are solved
364    /// after checking argument subtyping. These functions can be used in a stack-like fashion to
365    /// create nested scopes.
366    pub fn push_evar_scope(&mut self) {
367        self.inner.borrow_mut().evars.push_scope();
368    }
369
370    /// Pop a scope and check all evars have been solved. This only check evars generated from the
371    /// last call to [`InferCtxt::push_evar_scope`].
372    pub fn pop_evar_scope(&mut self) -> InferResult {
373        self.inner
374            .borrow_mut()
375            .evars
376            .pop_scope()
377            .map_err(InferErr::UnsolvedEvar)
378    }
379
380    /// Convenience method pairing [`InferCtxt::push_evar_scope`] and [`InferCtxt::pop_evar_scope`].
381    pub fn ensure_resolved_evars<R>(
382        &mut self,
383        f: impl FnOnce(&mut Self) -> InferResult<R>,
384    ) -> InferResult<R> {
385        self.push_evar_scope();
386        let r = f(self)?;
387        self.pop_evar_scope()?;
388        Ok(r)
389    }
390
391    pub fn fully_resolve_evars<T: TypeFoldable>(&self, t: &T) -> T {
392        self.inner.borrow().evars.replace_evars(t).unwrap()
393    }
394
395    pub fn tcx(&self) -> TyCtxt<'tcx> {
396        self.genv.tcx()
397    }
398
399    pub fn cursor(&self) -> &Cursor<'infcx> {
400        &self.cursor
401    }
402}
403
404/// Methods that interact with the underlying [`Cursor`]
405impl<'infcx, 'genv, 'tcx> InferCtxt<'infcx, 'genv, 'tcx> {
406    pub fn change_item<'a>(
407        &'a mut self,
408        def_id: LocalDefId,
409        region_infcx: &'a rustc_infer::infer::InferCtxt<'tcx>,
410    ) -> InferCtxt<'a, 'genv, 'tcx> {
411        InferCtxt {
412            def_id: def_id.to_def_id(),
413            cursor: self.cursor.branch(),
414            region_infcx,
415            ..*self
416        }
417    }
418
419    pub fn move_to(&mut self, marker: &Marker, clear_children: bool) -> InferCtxt<'_, 'genv, 'tcx> {
420        InferCtxt {
421            cursor: self
422                .cursor
423                .move_to(marker, clear_children)
424                .unwrap_or_else(|| tracked_span_bug!()),
425            ..*self
426        }
427    }
428
429    pub fn branch(&mut self) -> InferCtxt<'_, 'genv, 'tcx> {
430        InferCtxt { cursor: self.cursor.branch(), ..*self }
431    }
432
433    pub fn define_var(&mut self, sort: &Sort) -> Name {
434        self.cursor.define_var(sort)
435    }
436
437    pub fn check_pred(&mut self, pred: impl Into<Expr>, tag: Tag) {
438        self.cursor.check_pred(pred, tag);
439    }
440
441    pub fn assume_pred(&mut self, pred: impl Into<Expr>) {
442        self.cursor.assume_pred(pred);
443    }
444
445    pub fn unpack(&mut self, ty: &Ty) -> Ty {
446        self.hoister(false).hoist(ty)
447    }
448
449    pub fn marker(&self) -> Marker {
450        self.cursor.marker()
451    }
452
453    pub fn hoister(
454        &mut self,
455        assume_invariants: bool,
456    ) -> Hoister<Unpacker<'_, 'infcx, 'genv, 'tcx>> {
457        Hoister::with_delegate(Unpacker { infcx: self, assume_invariants }).transparent()
458    }
459
460    pub fn assume_invariants(&mut self, ty: &Ty) {
461        self.cursor
462            .assume_invariants(self.genv.tcx(), ty, self.check_overflow);
463    }
464
465    fn check_impl(&mut self, pred1: impl Into<Expr>, pred2: impl Into<Expr>, tag: Tag) {
466        self.cursor.check_impl(pred1, pred2, tag);
467    }
468}
469
470pub struct Unpacker<'a, 'infcx, 'genv, 'tcx> {
471    infcx: &'a mut InferCtxt<'infcx, 'genv, 'tcx>,
472    assume_invariants: bool,
473}
474
475impl HoisterDelegate for Unpacker<'_, '_, '_, '_> {
476    fn hoist_exists(&mut self, ty_ctor: &TyCtor) -> Ty {
477        let ty =
478            ty_ctor.replace_bound_refts_with(|sort, _, _| Expr::fvar(self.infcx.define_var(sort)));
479        if self.assume_invariants {
480            self.infcx.assume_invariants(&ty);
481        }
482        ty
483    }
484
485    fn hoist_constr(&mut self, pred: Expr) {
486        self.infcx.assume_pred(pred);
487    }
488}
489
490impl std::fmt::Debug for InferCtxt<'_, '_, '_> {
491    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
492        std::fmt::Debug::fmt(&self.cursor, f)
493    }
494}
495
496#[derive(Debug)]
497pub struct InferCtxtAt<'a, 'infcx, 'genv, 'tcx> {
498    pub infcx: &'a mut InferCtxt<'infcx, 'genv, 'tcx>,
499    pub span: Span,
500}
501
502impl<'genv, 'tcx> InferCtxtAt<'_, '_, 'genv, 'tcx> {
503    fn tag(&self, reason: ConstrReason) -> Tag {
504        Tag::new(reason, self.span)
505    }
506
507    pub fn check_pred(&mut self, pred: impl Into<Expr>, reason: ConstrReason) {
508        let tag = self.tag(reason);
509        self.infcx.check_pred(pred, tag);
510    }
511
512    pub fn check_non_closure_clauses(
513        &mut self,
514        clauses: &[rty::Clause],
515        reason: ConstrReason,
516    ) -> InferResult {
517        for clause in clauses {
518            if let rty::ClauseKind::Projection(projection_pred) = clause.kind_skipping_binder() {
519                let impl_elem = BaseTy::projection(projection_pred.projection_ty)
520                    .to_ty()
521                    .normalize_projections(self)?;
522                let term = projection_pred.term.to_ty().normalize_projections(self)?;
523
524                // TODO: does this really need to be invariant? https://github.com/flux-rs/flux/pull/478#issuecomment-1654035374
525                self.subtyping(&impl_elem, &term, reason)?;
526                self.subtyping(&term, &impl_elem, reason)?;
527            }
528        }
529        Ok(())
530    }
531
532    /// Relate types via subtyping. This is the same as [`InferCtxtAt::subtyping`] except that we
533    /// also require a [`LocEnv`] to handle pointers and strong references
534    pub fn subtyping_with_env(
535        &mut self,
536        env: &mut impl LocEnv,
537        a: &Ty,
538        b: &Ty,
539        reason: ConstrReason,
540    ) -> InferResult {
541        let mut sub = Sub::new(env, reason, self.span);
542        sub.tys(self.infcx, a, b)
543    }
544
545    /// Relate types via subtyping and returns coroutine obligations. This doesn't handle subtyping
546    /// when strong references are involved.
547    ///
548    /// See comment for [`Sub::obligations`].
549    pub fn subtyping(
550        &mut self,
551        a: &Ty,
552        b: &Ty,
553        reason: ConstrReason,
554    ) -> InferResult<Vec<Binder<rty::CoroutineObligPredicate>>> {
555        let mut env = DummyEnv;
556        let mut sub = Sub::new(&mut env, reason, self.span);
557        sub.tys(self.infcx, a, b)?;
558        Ok(sub.obligations)
559    }
560
561    pub fn subtyping_generic_args(
562        &mut self,
563        variance: Variance,
564        a: &GenericArg,
565        b: &GenericArg,
566        reason: ConstrReason,
567    ) -> InferResult<Vec<Binder<rty::CoroutineObligPredicate>>> {
568        let mut env = DummyEnv;
569        let mut sub = Sub::new(&mut env, reason, self.span);
570        sub.generic_args(self.infcx, variance, a, b)?;
571        Ok(sub.obligations)
572    }
573
574    // FIXME(nilehmann) this is similar to `Checker::check_call`, but since is used from
575    // `place_ty::fold` we cannot use that directly. We should try to unify them, because
576    // there are a couple of things missing here (e.g., checking clauses on the struct definition).
577    pub fn check_constructor(
578        &mut self,
579        variant: EarlyBinder<PolyVariant>,
580        generic_args: &[GenericArg],
581        fields: &[Ty],
582        reason: ConstrReason,
583    ) -> InferResult<Ty> {
584        let ret = self.ensure_resolved_evars(|this| {
585            // Replace holes in generic arguments with fresh inference variables
586            let generic_args = this.instantiate_generic_args(generic_args);
587
588            let variant = variant
589                .instantiate(this.tcx(), &generic_args, &[])
590                .replace_bound_refts_with(|sort, mode, _| this.fresh_infer_var(sort, mode));
591
592            // Check arguments
593            for (actual, formal) in iter::zip(fields, variant.fields()) {
594                this.subtyping(actual, formal, reason)?;
595            }
596
597            // Check requires predicates
598            for require in &variant.requires {
599                this.check_pred(require, ConstrReason::Fold);
600            }
601
602            Ok(variant.ret())
603        })?;
604        Ok(self.fully_resolve_evars(&ret))
605    }
606
607    pub fn ensure_resolved_evars<R>(
608        &mut self,
609        f: impl FnOnce(&mut InferCtxtAt<'_, '_, 'genv, 'tcx>) -> InferResult<R>,
610    ) -> InferResult<R> {
611        self.infcx
612            .ensure_resolved_evars(|infcx| f(&mut infcx.at(self.span)))
613    }
614}
615
616impl<'a, 'genv, 'tcx> std::ops::Deref for InferCtxtAt<'_, 'a, 'genv, 'tcx> {
617    type Target = InferCtxt<'a, 'genv, 'tcx>;
618
619    fn deref(&self) -> &Self::Target {
620        self.infcx
621    }
622}
623
624impl std::ops::DerefMut for InferCtxtAt<'_, '_, '_, '_> {
625    fn deref_mut(&mut self) -> &mut Self::Target {
626        self.infcx
627    }
628}
629
630/// Used for debugging to attach a "trace" to the [`RefineTree`] that can be used to print information
631/// to recover the derivation when relating types via subtyping. The code that attaches the trace is
632/// currently commented out because the output is too verbose.
633#[derive(TypeVisitable, TypeFoldable)]
634pub(crate) enum TypeTrace {
635    Types(Ty, Ty),
636    BaseTys(BaseTy, BaseTy),
637}
638
639#[expect(dead_code, reason = "we use this for debugging some time")]
640impl TypeTrace {
641    fn tys(a: &Ty, b: &Ty) -> Self {
642        Self::Types(a.clone(), b.clone())
643    }
644
645    fn btys(a: &BaseTy, b: &BaseTy) -> Self {
646        Self::BaseTys(a.clone(), b.clone())
647    }
648}
649
650impl fmt::Debug for TypeTrace {
651    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
652        match self {
653            TypeTrace::Types(a, b) => write!(f, "{a:?} - {b:?}"),
654            TypeTrace::BaseTys(a, b) => write!(f, "{a:?} - {b:?}"),
655        }
656    }
657}
658
659pub trait LocEnv {
660    fn ptr_to_ref(
661        &mut self,
662        infcx: &mut InferCtxtAt,
663        reason: ConstrReason,
664        re: Region,
665        path: &Path,
666        bound: Ty,
667    ) -> InferResult<Ty>;
668
669    fn unfold_strg_ref(&mut self, infcx: &mut InferCtxt, path: &Path, ty: &Ty) -> InferResult<Loc>;
670
671    fn get(&self, path: &Path) -> Ty;
672}
673
674struct DummyEnv;
675
676impl LocEnv for DummyEnv {
677    fn ptr_to_ref(
678        &mut self,
679        _: &mut InferCtxtAt,
680        _: ConstrReason,
681        _: Region,
682        _: &Path,
683        _: Ty,
684    ) -> InferResult<Ty> {
685        bug!("call to `ptr_to_ref` on `DummyEnv`")
686    }
687
688    fn unfold_strg_ref(&mut self, _: &mut InferCtxt, _: &Path, _: &Ty) -> InferResult<Loc> {
689        bug!("call to `unfold_str_ref` on `DummyEnv`")
690    }
691
692    fn get(&self, _: &Path) -> Ty {
693        bug!("call to `get` on `DummyEnv`")
694    }
695}
696
697/// Context used to relate two types `a` and `b` via subtyping
698struct Sub<'a, E> {
699    /// The environment to lookup locations pointed to by [`TyKind::Ptr`].
700    env: &'a mut E,
701    reason: ConstrReason,
702    span: Span,
703    /// FIXME(nilehmann) This is used to store coroutine obligations generated during subtyping when
704    /// relating an opaque type. Other obligations related to relating opaque types are resolved
705    /// directly here. The implementation is really messy and we may be missing some obligations.
706    obligations: Vec<Binder<rty::CoroutineObligPredicate>>,
707}
708
709impl<'a, E: LocEnv> Sub<'a, E> {
710    fn new(env: &'a mut E, reason: ConstrReason, span: Span) -> Self {
711        Self { env, reason, span, obligations: vec![] }
712    }
713
714    fn tag(&self) -> Tag {
715        Tag::new(self.reason, self.span)
716    }
717
718    fn tys(&mut self, infcx: &mut InferCtxt, a: &Ty, b: &Ty) -> InferResult {
719        let infcx = &mut infcx.branch();
720        // infcx.cursor.push_trace(TypeTrace::tys(a, b));
721
722        // We *fully* unpack the lhs before continuing to be able to prove goals like this
723        // ∃a. (i32[a], ∃b. {i32[b] | a > b})} <: ∃a,b. ({i32[a] | b < a}, i32[b])
724        // See S4.5 in https://arxiv.org/pdf/2209.13000v1.pdf
725        let a = infcx.unpack(a);
726
727        match (a.kind(), b.kind()) {
728            (TyKind::Exists(..), _) => {
729                bug!("existentials should have been removed by the unpacking above");
730            }
731            (TyKind::Constr(..), _) => {
732                bug!("constraint types should have been removed by the unpacking above");
733            }
734
735            (_, TyKind::Exists(ctor_b)) => {
736                infcx.enter_exists(ctor_b, |infcx, ty_b| self.tys(infcx, &a, &ty_b))
737            }
738            (_, TyKind::Constr(pred_b, ty_b)) => {
739                infcx.check_pred(pred_b, self.tag());
740                self.tys(infcx, &a, ty_b)
741            }
742
743            (TyKind::Ptr(PtrKind::Mut(_), path_a), TyKind::StrgRef(_, path_b, ty_b)) => {
744                // We should technically remove `path1` from `env`, but we are assuming that functions
745                // always give back ownership of the location so `path1` is going to be overwritten
746                // after the call anyways.
747                let ty_a = self.env.get(path_a);
748                infcx.unify_exprs(&path_a.to_expr(), &path_b.to_expr());
749                self.tys(infcx, &ty_a, ty_b)
750            }
751            (TyKind::StrgRef(_, path_a, ty_a), TyKind::StrgRef(_, path_b, ty_b)) => {
752                // We have to unfold strong references prior to a subtyping check. Normally, when
753                // checking a function body, a `StrgRef` is automatically unfolded i.e. `x:&strg T`
754                // is turned into a `x:ptr(l); l: T` where `l` is some fresh location. However, we
755                // need the below to do a similar unfolding during function subtyping where we just
756                // have the super-type signature that needs to be unfolded. We also add the binding
757                // to the environment so that we can:
758                // (1) UPDATE the location after the call, and
759                // (2) CHECK the relevant `ensures` clauses of the super-sig.
760                // Same as the `Ptr` case above we should remove the location from the environment
761                // after unfolding to consume it, but we are assuming functions always give back
762                // ownership.
763                self.env.unfold_strg_ref(infcx, path_a, ty_a)?;
764                let ty_a = self.env.get(path_a);
765                infcx.unify_exprs(&path_a.to_expr(), &path_b.to_expr());
766                self.tys(infcx, &ty_a, ty_b)
767            }
768            (
769                TyKind::Ptr(PtrKind::Mut(re), path),
770                TyKind::Indexed(BaseTy::Ref(_, bound, Mutability::Mut), idx),
771            ) => {
772                // We sometimes generate evars for the index of references so we need to make sure
773                // we solve them.
774                self.idxs_eq(infcx, &Expr::unit(), idx);
775
776                self.env.ptr_to_ref(
777                    &mut infcx.at(self.span),
778                    self.reason,
779                    *re,
780                    path,
781                    bound.clone(),
782                )?;
783                Ok(())
784            }
785
786            (TyKind::Indexed(bty_a, idx_a), TyKind::Indexed(bty_b, idx_b)) => {
787                self.btys(infcx, bty_a, bty_b)?;
788                self.idxs_eq(infcx, idx_a, idx_b);
789                Ok(())
790            }
791            (TyKind::Ptr(pk_a, path_a), TyKind::Ptr(pk_b, path_b)) => {
792                debug_assert_eq!(pk_a, pk_b);
793                debug_assert_eq!(path_a, path_b);
794                Ok(())
795            }
796            (TyKind::Param(param_ty_a), TyKind::Param(param_ty_b)) => {
797                debug_assert_eq!(param_ty_a, param_ty_b);
798                Ok(())
799            }
800            (_, TyKind::Uninit) => Ok(()),
801            (TyKind::Downcast(.., fields_a), TyKind::Downcast(.., fields_b)) => {
802                debug_assert_eq!(fields_a.len(), fields_b.len());
803                for (ty_a, ty_b) in iter::zip(fields_a, fields_b) {
804                    self.tys(infcx, ty_a, ty_b)?;
805                }
806                Ok(())
807            }
808            _ => Err(query_bug!("incompatible types: `{a:?}` - `{b:?}`"))?,
809        }
810    }
811
812    fn btys(&mut self, infcx: &mut InferCtxt, a: &BaseTy, b: &BaseTy) -> InferResult {
813        // infcx.push_trace(TypeTrace::btys(a, b));
814
815        match (a, b) {
816            (BaseTy::Int(int_ty_a), BaseTy::Int(int_ty_b)) => {
817                debug_assert_eq!(int_ty_a, int_ty_b);
818                Ok(())
819            }
820            (BaseTy::Uint(uint_ty_a), BaseTy::Uint(uint_ty_b)) => {
821                debug_assert_eq!(uint_ty_a, uint_ty_b);
822                Ok(())
823            }
824            (BaseTy::Adt(a_adt, a_args), BaseTy::Adt(b_adt, b_args)) => {
825                tracked_span_dbg_assert_eq!(a_adt.did(), b_adt.did());
826                tracked_span_dbg_assert_eq!(a_args.len(), b_args.len());
827                let variances = infcx.genv.variances_of(a_adt.did());
828                for (variance, ty_a, ty_b) in izip!(variances, a_args.iter(), b_args.iter()) {
829                    self.generic_args(infcx, *variance, ty_a, ty_b)?;
830                }
831                Ok(())
832            }
833            (BaseTy::FnDef(a_def_id, a_args), BaseTy::FnDef(b_def_id, b_args)) => {
834                debug_assert_eq!(a_def_id, b_def_id);
835                debug_assert_eq!(a_args.len(), b_args.len());
836                // NOTE: we don't check subtyping here because the RHS is *really*
837                // the function type, the LHS is just generated by rustc.
838                // we could generate a subtyping constraint but those would
839                // just be trivial (but might cause useless cycles in fixpoint).
840                // Nico: (This is probably ok because) We never do function
841                // subtyping between `FnDef` *except* when (the def_id) is
842                // passed as an argument to a function.
843                for (arg_a, arg_b) in iter::zip(a_args, b_args) {
844                    match (arg_a, arg_b) {
845                        (GenericArg::Ty(ty_a), GenericArg::Ty(ty_b)) => {
846                            let bty_a = ty_a.as_bty_skipping_existentials();
847                            let bty_b = ty_b.as_bty_skipping_existentials();
848                            tracked_span_dbg_assert_eq!(bty_a, bty_b);
849                        }
850                        (GenericArg::Base(ctor_a), GenericArg::Base(ctor_b)) => {
851                            let bty_a = ctor_a.as_bty_skipping_binder();
852                            let bty_b = ctor_b.as_bty_skipping_binder();
853                            tracked_span_dbg_assert_eq!(bty_a, bty_b);
854                        }
855                        (_, _) => tracked_span_dbg_assert_eq!(arg_a, arg_b),
856                    }
857                }
858                Ok(())
859            }
860            (BaseTy::Float(float_ty_a), BaseTy::Float(float_ty_b)) => {
861                debug_assert_eq!(float_ty_a, float_ty_b);
862                Ok(())
863            }
864            (BaseTy::Slice(ty_a), BaseTy::Slice(ty_b)) => self.tys(infcx, ty_a, ty_b),
865            (BaseTy::Ref(_, ty_a, Mutability::Mut), BaseTy::Ref(_, ty_b, Mutability::Mut)) => {
866                if ty_a.is_slice()
867                    && let TyKind::Indexed(_, idx_a) = ty_a.kind()
868                    && let TyKind::Exists(bty_b) = ty_b.kind()
869                {
870                    // For `&mut [T1][e] <: &mut ∃v[T2][v]`, we can hoist out the existential on the right because we know
871                    // the index is immutable. This means we have to prove `&mut [T1][e] <: ∃v. &mut [T2][v]`
872                    // This will in turn require proving `&mut [T1][e1] <: &mut [T2][?v]` for a fresh evar `?v`.
873                    // We know the evar will solve to `e`, so subtyping simplifies to the bellow.
874                    self.tys(infcx, ty_a, ty_b)?;
875                    self.tys(infcx, &bty_b.replace_bound_reft(idx_a), ty_a)
876                } else {
877                    self.tys(infcx, ty_a, ty_b)?;
878                    self.tys(infcx, ty_b, ty_a)
879                }
880            }
881            (BaseTy::Ref(_, ty_a, Mutability::Not), BaseTy::Ref(_, ty_b, Mutability::Not)) => {
882                self.tys(infcx, ty_a, ty_b)
883            }
884            (BaseTy::Tuple(tys_a), BaseTy::Tuple(tys_b)) => {
885                debug_assert_eq!(tys_a.len(), tys_b.len());
886                for (ty_a, ty_b) in iter::zip(tys_a, tys_b) {
887                    self.tys(infcx, ty_a, ty_b)?;
888                }
889                Ok(())
890            }
891            (_, BaseTy::Alias(AliasKind::Opaque, alias_ty_b)) => {
892                if let BaseTy::Alias(AliasKind::Opaque, alias_ty_a) = a {
893                    debug_assert_eq!(alias_ty_a.refine_args.len(), alias_ty_b.refine_args.len());
894                    iter::zip(alias_ty_a.refine_args.iter(), alias_ty_b.refine_args.iter())
895                        .for_each(|(expr_a, expr_b)| infcx.unify_exprs(expr_a, expr_b));
896                }
897                self.handle_opaque_type(infcx, a, alias_ty_b)
898            }
899            (
900                BaseTy::Alias(AliasKind::Projection, alias_ty_a),
901                BaseTy::Alias(AliasKind::Projection, alias_ty_b),
902            ) => {
903                tracked_span_dbg_assert_eq!(alias_ty_a, alias_ty_b);
904                Ok(())
905            }
906            (BaseTy::Array(ty_a, len_a), BaseTy::Array(ty_b, len_b)) => {
907                tracked_span_dbg_assert_eq!(len_a, len_b);
908                self.tys(infcx, ty_a, ty_b)
909            }
910            (BaseTy::Param(param_a), BaseTy::Param(param_b)) => {
911                debug_assert_eq!(param_a, param_b);
912                Ok(())
913            }
914            (BaseTy::Bool, BaseTy::Bool)
915            | (BaseTy::Str, BaseTy::Str)
916            | (BaseTy::Char, BaseTy::Char)
917            | (BaseTy::RawPtr(_, _), BaseTy::RawPtr(_, _))
918            | (BaseTy::RawPtrMetadata(_), BaseTy::RawPtrMetadata(_)) => Ok(()),
919            (BaseTy::Dynamic(preds_a, _), BaseTy::Dynamic(preds_b, _)) => {
920                tracked_span_assert_eq!(preds_a.erase_regions(), preds_b.erase_regions());
921                Ok(())
922            }
923            (BaseTy::Closure(did1, tys_a, _), BaseTy::Closure(did2, tys_b, _)) if did1 == did2 => {
924                debug_assert_eq!(tys_a.len(), tys_b.len());
925                for (ty_a, ty_b) in iter::zip(tys_a, tys_b) {
926                    self.tys(infcx, ty_a, ty_b)?;
927                }
928                Ok(())
929            }
930            (BaseTy::FnPtr(sig_a), BaseTy::FnPtr(sig_b)) => {
931                tracked_span_assert_eq!(sig_a.erase_regions(), sig_b.erase_regions());
932                Ok(())
933            }
934            (BaseTy::Never, BaseTy::Never) => Ok(()),
935            _ => Err(query_bug!("incompatible base types: `{a:?}` - `{b:?}`"))?,
936        }
937    }
938
939    fn generic_args(
940        &mut self,
941        infcx: &mut InferCtxt,
942        variance: Variance,
943        a: &GenericArg,
944        b: &GenericArg,
945    ) -> InferResult {
946        let (ty_a, ty_b) = match (a, b) {
947            (GenericArg::Ty(ty_a), GenericArg::Ty(ty_b)) => (ty_a.clone(), ty_b.clone()),
948            (GenericArg::Base(ctor_a), GenericArg::Base(ctor_b)) => {
949                tracked_span_dbg_assert_eq!(ctor_a.sort(), ctor_b.sort());
950                (ctor_a.to_ty(), ctor_b.to_ty())
951            }
952            (GenericArg::Lifetime(_), GenericArg::Lifetime(_)) => return Ok(()),
953            (GenericArg::Const(cst_a), GenericArg::Const(cst_b)) => {
954                debug_assert_eq!(cst_a, cst_b);
955                return Ok(());
956            }
957            _ => Err(query_bug!("incompatible generic args: `{a:?}` `{b:?}`"))?,
958        };
959        match variance {
960            Variance::Covariant => self.tys(infcx, &ty_a, &ty_b),
961            Variance::Invariant => {
962                self.tys(infcx, &ty_a, &ty_b)?;
963                self.tys(infcx, &ty_b, &ty_a)
964            }
965            Variance::Contravariant => self.tys(infcx, &ty_b, &ty_a),
966            Variance::Bivariant => Ok(()),
967        }
968    }
969
970    fn idxs_eq(&mut self, infcx: &mut InferCtxt, a: &Expr, b: &Expr) {
971        if a == b {
972            return;
973        }
974        match (a.kind(), b.kind()) {
975            (
976                ExprKind::Ctor(Ctor::Struct(did_a), flds_a),
977                ExprKind::Ctor(Ctor::Struct(did_b), flds_b),
978            ) => {
979                debug_assert_eq!(did_a, did_b);
980                for (a, b) in iter::zip(flds_a, flds_b) {
981                    self.idxs_eq(infcx, a, b);
982                }
983            }
984            (ExprKind::Tuple(flds_a), ExprKind::Tuple(flds_b)) => {
985                for (a, b) in iter::zip(flds_a, flds_b) {
986                    self.idxs_eq(infcx, a, b);
987                }
988            }
989            (_, ExprKind::Tuple(flds_b)) => {
990                for (f, b) in flds_b.iter().enumerate() {
991                    let proj = FieldProj::Tuple { arity: flds_b.len(), field: f as u32 };
992                    let a = a.proj_and_reduce(proj);
993                    self.idxs_eq(infcx, &a, b);
994                }
995            }
996
997            (_, ExprKind::Ctor(Ctor::Struct(def_id), flds_b)) => {
998                for (f, b) in flds_b.iter().enumerate() {
999                    let proj = FieldProj::Adt { def_id: *def_id, field: f as u32 };
1000                    let a = a.proj_and_reduce(proj);
1001                    self.idxs_eq(infcx, &a, b);
1002                }
1003            }
1004
1005            (ExprKind::Tuple(flds_a), _) => {
1006                infcx.unify_exprs(a, b);
1007                for (f, a) in flds_a.iter().enumerate() {
1008                    let proj = FieldProj::Tuple { arity: flds_a.len(), field: f as u32 };
1009                    let b = b.proj_and_reduce(proj);
1010                    self.idxs_eq(infcx, a, &b);
1011                }
1012            }
1013            (ExprKind::Ctor(Ctor::Struct(def_id), flds_a), _) => {
1014                infcx.unify_exprs(a, b);
1015                for (f, a) in flds_a.iter().enumerate() {
1016                    let proj = FieldProj::Adt { def_id: *def_id, field: f as u32 };
1017                    let b = b.proj_and_reduce(proj);
1018                    self.idxs_eq(infcx, a, &b);
1019                }
1020            }
1021            (ExprKind::Abs(lam_a), ExprKind::Abs(lam_b)) => {
1022                self.abs_eq(infcx, lam_a, lam_b);
1023            }
1024            (_, ExprKind::Abs(lam_b)) => {
1025                self.abs_eq(infcx, &a.eta_expand_abs(lam_b.vars(), lam_b.output()), lam_b);
1026            }
1027            (ExprKind::Abs(lam_a), _) => {
1028                infcx.unify_exprs(a, b);
1029                self.abs_eq(infcx, lam_a, &b.eta_expand_abs(lam_a.vars(), lam_a.output()));
1030            }
1031            (ExprKind::KVar(_), _) | (_, ExprKind::KVar(_)) => {
1032                infcx.check_impl(a, b, self.tag());
1033                infcx.check_impl(b, a, self.tag());
1034            }
1035            _ => {
1036                infcx.unify_exprs(a, b);
1037                let span = b.span();
1038                infcx.check_pred(Expr::binary_op(rty::BinOp::Eq, a, b).at_opt(span), self.tag());
1039            }
1040        }
1041    }
1042
1043    fn abs_eq(&mut self, infcx: &mut InferCtxt, a: &Lambda, b: &Lambda) {
1044        debug_assert_eq!(a.vars().len(), b.vars().len());
1045        let vars = a
1046            .vars()
1047            .iter()
1048            .map(|kind| Expr::fvar(infcx.define_var(kind.expect_sort())))
1049            .collect_vec();
1050        let body_a = a.apply(&vars);
1051        let body_b = b.apply(&vars);
1052        self.idxs_eq(infcx, &body_a, &body_b);
1053    }
1054
1055    fn handle_opaque_type(
1056        &mut self,
1057        infcx: &mut InferCtxt,
1058        bty: &BaseTy,
1059        alias_ty: &AliasTy,
1060    ) -> InferResult {
1061        if let BaseTy::Coroutine(def_id, resume_ty, upvar_tys) = bty {
1062            let obligs = mk_coroutine_obligations(
1063                infcx.genv,
1064                def_id,
1065                resume_ty,
1066                upvar_tys,
1067                &alias_ty.def_id,
1068            )?;
1069            self.obligations.extend(obligs);
1070        } else {
1071            let bounds = infcx.genv.item_bounds(alias_ty.def_id)?.instantiate(
1072                infcx.tcx(),
1073                &alias_ty.args,
1074                &alias_ty.refine_args,
1075            );
1076            for clause in &bounds {
1077                if !clause.kind().vars().is_empty() {
1078                    Err(query_bug!("handle_opaque_types: clause with bound vars: `{clause:?}`"))?;
1079                }
1080                if let rty::ClauseKind::Projection(pred) = clause.kind_skipping_binder() {
1081                    let alias_ty = pred.projection_ty.with_self_ty(bty.to_subset_ty_ctor());
1082                    let ty1 = BaseTy::Alias(AliasKind::Projection, alias_ty)
1083                        .to_ty()
1084                        .normalize_projections(&mut infcx.at(self.span))?;
1085                    let ty2 = pred.term.to_ty();
1086                    self.tys(infcx, &ty1, &ty2)?;
1087                }
1088            }
1089        }
1090        Ok(())
1091    }
1092}
1093
1094fn mk_coroutine_obligations(
1095    genv: GlobalEnv,
1096    generator_did: &DefId,
1097    resume_ty: &Ty,
1098    upvar_tys: &List<Ty>,
1099    opaque_def_id: &DefId,
1100) -> InferResult<Vec<Binder<rty::CoroutineObligPredicate>>> {
1101    let bounds = genv.item_bounds(*opaque_def_id)?.skip_binder();
1102    for bound in &bounds {
1103        if let Some(proj_clause) = bound.as_projection_clause() {
1104            return Ok(vec![proj_clause.map(|proj_clause| {
1105                let output = proj_clause.term;
1106                CoroutineObligPredicate {
1107                    def_id: *generator_did,
1108                    resume_ty: resume_ty.clone(),
1109                    upvar_tys: upvar_tys.clone(),
1110                    output: output.to_ty(),
1111                }
1112            })]);
1113        }
1114    }
1115    bug!("no projection predicate")
1116}
1117
1118#[derive(Debug)]
1119pub enum InferErr {
1120    UnsolvedEvar(EVid),
1121    Query(QueryErr),
1122}
1123
1124impl From<QueryErr> for InferErr {
1125    fn from(v: QueryErr) -> Self {
1126        Self::Query(v)
1127    }
1128}
1129
1130mod pretty {
1131    use std::fmt;
1132
1133    use flux_middle::pretty::*;
1134
1135    use super::*;
1136
1137    impl Pretty for Tag {
1138        fn fmt(&self, cx: &PrettyCx, f: &mut fmt::Formatter<'_>) -> fmt::Result {
1139            w!(cx, f, "{:?} at {:?}", ^self.reason, self.src_span)
1140        }
1141    }
1142
1143    impl_debug_with_default_cx!(Tag);
1144}
flux_infer/infer.rs

flux_infer/
infer.rs
