From eee27611404dfc38f19a61197931c9bfccc81aee Mon Sep 17 00:00:00 2001 From: Lukas Wirth Date: Sat, 28 Dec 2024 15:08:26 +0100 Subject: [PATCH] Implement parameter variance inference --- crates/hir-ty/src/chalk_db.rs | 21 +- crates/hir-ty/src/db.rs | 4 + crates/hir-ty/src/generics.rs | 8 + crates/hir-ty/src/lib.rs | 1 + crates/hir-ty/src/tests.rs | 78 +- crates/hir-ty/src/tests/closure_captures.rs | 7 + crates/hir-ty/src/tests/incremental.rs | 17 +- crates/hir-ty/src/variance.rs | 1172 +++++++++++++++++++ 8 files changed, 1271 insertions(+), 37 deletions(-) create mode 100644 crates/hir-ty/src/variance.rs diff --git a/crates/hir-ty/src/chalk_db.rs b/crates/hir-ty/src/chalk_db.rs index 55d0edd5e0..0a2612219a 100644 --- a/crates/hir-ty/src/chalk_db.rs +++ b/crates/hir-ty/src/chalk_db.rs @@ -950,11 +950,18 @@ pub(crate) fn fn_def_datum_query(db: &dyn HirDatabase, fn_def_id: FnDefId) -> Ar pub(crate) fn fn_def_variance_query(db: &dyn HirDatabase, fn_def_id: FnDefId) -> Variances { let callable_def: CallableDefId = from_chalk(db, fn_def_id); - let generic_params = - generics(db.upcast(), GenericDefId::from_callable(db.upcast(), callable_def)); Variances::from_iter( Interner, - std::iter::repeat(chalk_ir::Variance::Invariant).take(generic_params.len()), + db.variances_of(GenericDefId::from_callable(db.upcast(), callable_def)) + .as_deref() + .unwrap_or_default() + .iter() + .map(|v| match v { + crate::variance::Variance::Covariant => chalk_ir::Variance::Covariant, + crate::variance::Variance::Invariant => chalk_ir::Variance::Invariant, + crate::variance::Variance::Contravariant => chalk_ir::Variance::Contravariant, + crate::variance::Variance::Bivariant => chalk_ir::Variance::Invariant, + }), ) } @@ -962,10 +969,14 @@ pub(crate) fn adt_variance_query( db: &dyn HirDatabase, chalk_ir::AdtId(adt_id): AdtId, ) -> Variances { - let generic_params = generics(db.upcast(), adt_id.into()); Variances::from_iter( Interner, - std::iter::repeat(chalk_ir::Variance::Invariant).take(generic_params.len()), + db.variances_of(adt_id.into()).as_deref().unwrap_or_default().iter().map(|v| match v { + crate::variance::Variance::Covariant => chalk_ir::Variance::Covariant, + crate::variance::Variance::Invariant => chalk_ir::Variance::Invariant, + crate::variance::Variance::Contravariant => chalk_ir::Variance::Contravariant, + crate::variance::Variance::Bivariant => chalk_ir::Variance::Invariant, + }), ) } diff --git a/crates/hir-ty/src/db.rs b/crates/hir-ty/src/db.rs index 6856eaa3e0..6b05682667 100644 --- a/crates/hir-ty/src/db.rs +++ b/crates/hir-ty/src/db.rs @@ -271,6 +271,10 @@ pub trait HirDatabase: DefDatabase + Upcast { #[ra_salsa::invoke(chalk_db::adt_variance_query)] fn adt_variance(&self, adt_id: chalk_db::AdtId) -> chalk_db::Variances; + #[ra_salsa::invoke(crate::variance::variances_of)] + #[ra_salsa::cycle(crate::variance::variances_of_cycle)] + fn variances_of(&self, def: GenericDefId) -> Option>; + #[ra_salsa::invoke(chalk_db::associated_ty_value_query)] fn associated_ty_value( &self, diff --git a/crates/hir-ty/src/generics.rs b/crates/hir-ty/src/generics.rs index fe7541d237..e7a2721afe 100644 --- a/crates/hir-ty/src/generics.rs +++ b/crates/hir-ty/src/generics.rs @@ -132,6 +132,14 @@ impl Generics { self.params.len() } + pub(crate) fn len_self_lifetimes(&self) -> usize { + self.params.len_lifetimes() + } + + pub(crate) fn has_trait_self(&self) -> bool { + self.params.trait_self_param().is_some() + } + /// (parent total, self param, type params, const params, impl trait list, lifetimes) pub(crate) fn provenance_split(&self) -> (usize, bool, usize, usize, usize, usize) { let mut self_param = false; diff --git a/crates/hir-ty/src/lib.rs b/crates/hir-ty/src/lib.rs index 224fcf313a..88134f564c 100644 --- a/crates/hir-ty/src/lib.rs +++ b/crates/hir-ty/src/lib.rs @@ -50,6 +50,7 @@ pub mod traits; mod test_db; #[cfg(test)] mod tests; +mod variance; use std::hash::Hash; diff --git a/crates/hir-ty/src/tests.rs b/crates/hir-ty/src/tests.rs index cabeeea2bd..b7607b5f63 100644 --- a/crates/hir-ty/src/tests.rs +++ b/crates/hir-ty/src/tests.rs @@ -127,7 +127,15 @@ fn check_impl(ra_fixture: &str, allow_none: bool, only_types: bool, display_sour None => continue, }; let def_map = module.def_map(&db); - visit_module(&db, &def_map, module.local_id, &mut |it| defs.push(it)); + visit_module(&db, &def_map, module.local_id, &mut |it| { + defs.push(match it { + ModuleDefId::FunctionId(it) => it.into(), + ModuleDefId::EnumVariantId(it) => it.into(), + ModuleDefId::ConstId(it) => it.into(), + ModuleDefId::StaticId(it) => it.into(), + _ => return, + }) + }); } defs.sort_by_key(|def| match def { DefWithBodyId::FunctionId(it) => { @@ -375,7 +383,15 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String { let def_map = module.def_map(&db); let mut defs: Vec = Vec::new(); - visit_module(&db, &def_map, module.local_id, &mut |it| defs.push(it)); + visit_module(&db, &def_map, module.local_id, &mut |it| { + defs.push(match it { + ModuleDefId::FunctionId(it) => it.into(), + ModuleDefId::EnumVariantId(it) => it.into(), + ModuleDefId::ConstId(it) => it.into(), + ModuleDefId::StaticId(it) => it.into(), + _ => return, + }) + }); defs.sort_by_key(|def| match def { DefWithBodyId::FunctionId(it) => { let loc = it.lookup(&db); @@ -405,11 +421,11 @@ fn infer_with_mismatches(content: &str, include_mismatches: bool) -> String { buf } -fn visit_module( +pub(crate) fn visit_module( db: &TestDB, crate_def_map: &DefMap, module_id: LocalModuleId, - cb: &mut dyn FnMut(DefWithBodyId), + cb: &mut dyn FnMut(ModuleDefId), ) { visit_scope(db, crate_def_map, &crate_def_map[module_id].scope, cb); for impl_id in crate_def_map[module_id].scope.impls() { @@ -417,18 +433,18 @@ fn visit_module( for &item in impl_data.items.iter() { match item { AssocItemId::FunctionId(it) => { - let def = it.into(); - cb(def); - let body = db.body(def); + let body = db.body(it.into()); + cb(it.into()); visit_body(db, &body, cb); } AssocItemId::ConstId(it) => { - let def = it.into(); - cb(def); - let body = db.body(def); + let body = db.body(it.into()); + cb(it.into()); visit_body(db, &body, cb); } - AssocItemId::TypeAliasId(_) => (), + AssocItemId::TypeAliasId(it) => { + cb(it.into()); + } } } } @@ -437,33 +453,27 @@ fn visit_module( db: &TestDB, crate_def_map: &DefMap, scope: &ItemScope, - cb: &mut dyn FnMut(DefWithBodyId), + cb: &mut dyn FnMut(ModuleDefId), ) { for decl in scope.declarations() { + cb(decl); match decl { ModuleDefId::FunctionId(it) => { - let def = it.into(); - cb(def); - let body = db.body(def); + let body = db.body(it.into()); visit_body(db, &body, cb); } ModuleDefId::ConstId(it) => { - let def = it.into(); - cb(def); - let body = db.body(def); + let body = db.body(it.into()); visit_body(db, &body, cb); } ModuleDefId::StaticId(it) => { - let def = it.into(); - cb(def); - let body = db.body(def); + let body = db.body(it.into()); visit_body(db, &body, cb); } ModuleDefId::AdtId(hir_def::AdtId::EnumId(it)) => { db.enum_data(it).variants.iter().for_each(|&(it, _)| { - let def = it.into(); - cb(def); - let body = db.body(def); + let body = db.body(it.into()); + cb(it.into()); visit_body(db, &body, cb); }); } @@ -473,7 +483,7 @@ fn visit_module( match item { AssocItemId::FunctionId(it) => cb(it.into()), AssocItemId::ConstId(it) => cb(it.into()), - AssocItemId::TypeAliasId(_) => (), + AssocItemId::TypeAliasId(it) => cb(it.into()), } } } @@ -483,7 +493,7 @@ fn visit_module( } } - fn visit_body(db: &TestDB, body: &Body, cb: &mut dyn FnMut(DefWithBodyId)) { + fn visit_body(db: &TestDB, body: &Body, cb: &mut dyn FnMut(ModuleDefId)) { for (_, def_map) in body.blocks(db) { for (mod_id, _) in def_map.modules() { visit_module(db, &def_map, mod_id, cb); @@ -553,7 +563,13 @@ fn salsa_bug() { let module = db.module_for_file(pos.file_id); let crate_def_map = module.def_map(&db); visit_module(&db, &crate_def_map, module.local_id, &mut |def| { - db.infer(def); + db.infer(match def { + ModuleDefId::FunctionId(it) => it.into(), + ModuleDefId::EnumVariantId(it) => it.into(), + ModuleDefId::ConstId(it) => it.into(), + ModuleDefId::StaticId(it) => it.into(), + _ => return, + }); }); let new_text = " @@ -586,6 +602,12 @@ fn salsa_bug() { let module = db.module_for_file(pos.file_id); let crate_def_map = module.def_map(&db); visit_module(&db, &crate_def_map, module.local_id, &mut |def| { - db.infer(def); + db.infer(match def { + ModuleDefId::FunctionId(it) => it.into(), + ModuleDefId::EnumVariantId(it) => it.into(), + ModuleDefId::ConstId(it) => it.into(), + ModuleDefId::StaticId(it) => it.into(), + _ => return, + }); }); } diff --git a/crates/hir-ty/src/tests/closure_captures.rs b/crates/hir-ty/src/tests/closure_captures.rs index b63d632dd2..7de92d6b16 100644 --- a/crates/hir-ty/src/tests/closure_captures.rs +++ b/crates/hir-ty/src/tests/closure_captures.rs @@ -24,6 +24,13 @@ fn check_closure_captures(ra_fixture: &str, expect: Expect) { let mut captures_info = Vec::new(); for def in defs { + let def = match def { + hir_def::ModuleDefId::FunctionId(it) => it.into(), + hir_def::ModuleDefId::EnumVariantId(it) => it.into(), + hir_def::ModuleDefId::ConstId(it) => it.into(), + hir_def::ModuleDefId::StaticId(it) => it.into(), + _ => continue, + }; let infer = db.infer(def); let db = &db; captures_info.extend(infer.closure_info.iter().flat_map(|(closure_id, (captures, _))| { diff --git a/crates/hir-ty/src/tests/incremental.rs b/crates/hir-ty/src/tests/incremental.rs index 0a24eeb1fe..3757d722ac 100644 --- a/crates/hir-ty/src/tests/incremental.rs +++ b/crates/hir-ty/src/tests/incremental.rs @@ -1,4 +1,5 @@ use base_db::SourceDatabaseFileInputExt as _; +use hir_def::ModuleDefId; use test_fixture::WithFixture; use crate::{db::HirDatabase, test_db::TestDB}; @@ -19,7 +20,9 @@ fn foo() -> i32 { let module = db.module_for_file(pos.file_id.file_id()); let crate_def_map = module.def_map(&db); visit_module(&db, &crate_def_map, module.local_id, &mut |def| { - db.infer(def); + if let ModuleDefId::FunctionId(it) = def { + db.infer(it.into()); + } }); }); assert!(format!("{events:?}").contains("infer")) @@ -39,7 +42,9 @@ fn foo() -> i32 { let module = db.module_for_file(pos.file_id.file_id()); let crate_def_map = module.def_map(&db); visit_module(&db, &crate_def_map, module.local_id, &mut |def| { - db.infer(def); + if let ModuleDefId::FunctionId(it) = def { + db.infer(it.into()); + } }); }); assert!(!format!("{events:?}").contains("infer"), "{events:#?}") @@ -66,7 +71,9 @@ fn baz() -> i32 { let module = db.module_for_file(pos.file_id.file_id()); let crate_def_map = module.def_map(&db); visit_module(&db, &crate_def_map, module.local_id, &mut |def| { - db.infer(def); + if let ModuleDefId::FunctionId(it) = def { + db.infer(it.into()); + } }); }); assert!(format!("{events:?}").contains("infer")) @@ -91,7 +98,9 @@ fn baz() -> i32 { let module = db.module_for_file(pos.file_id.file_id()); let crate_def_map = module.def_map(&db); visit_module(&db, &crate_def_map, module.local_id, &mut |def| { - db.infer(def); + if let ModuleDefId::FunctionId(it) = def { + db.infer(it.into()); + } }); }); assert!(format!("{events:?}").matches("infer").count() == 1, "{events:#?}") diff --git a/crates/hir-ty/src/variance.rs b/crates/hir-ty/src/variance.rs new file mode 100644 index 0000000000..2339e37fa1 --- /dev/null +++ b/crates/hir-ty/src/variance.rs @@ -0,0 +1,1172 @@ +//! Module for inferring the variance of type and lifetime parameters. See the [rustc dev guide] +//! chapter for more info. +//! +//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/variance.html + +use crate::db::HirDatabase; +use crate::generics::{generics, Generics}; +use crate::{ + AliasTy, Const, ConstScalar, DynTyExt, FnPointer, GenericArg, GenericArgData, Interner, + Lifetime, LifetimeData, Ty, TyKind, +}; +use base_db::ra_salsa::Cycle; +use chalk_ir::Mutability; +use hir_def::data::adt::StructFlags; +use hir_def::{AdtId, GenericDefId, GenericParamId, VariantId}; +use std::fmt; +use std::ops::Not; +use triomphe::Arc; + +pub(crate) fn variances_of(db: &dyn HirDatabase, def: GenericDefId) -> Option> { + tracing::debug!("variances_of(def={:?})", def); + match def { + GenericDefId::FunctionId(_) => (), + GenericDefId::AdtId(adt) => { + if let AdtId::StructId(id) = adt { + let flags = &db.struct_data(id).flags; + if flags.contains(StructFlags::IS_UNSAFE_CELL) { + return Some(Arc::from_iter(vec![Variance::Invariant; 1])); + } else if flags.contains(StructFlags::IS_PHANTOM_DATA) { + return Some(Arc::from_iter(vec![Variance::Covariant; 1])); + } + } + } + _ => return None, + } + + let generics = generics(db.upcast(), def); + let count = generics.len(); + if count == 0 { + return None; + } + let mut ctxt = Context { + def, + has_trait_self: generics.parent_generics().map_or(false, |it| it.has_trait_self()), + len_self: generics.len_self(), + len_self_lifetimes: generics.len_self_lifetimes(), + generics, + constraints: Vec::new(), + db, + }; + + ctxt.build_constraints_for_item(); + let res = ctxt.solve(); + res.is_empty().not().then(|| Arc::from_iter(res)) +} + +pub(crate) fn variances_of_cycle( + db: &dyn HirDatabase, + _cycle: &Cycle, + def: &GenericDefId, +) -> Option> { + let generics = generics(db.upcast(), *def); + let count = generics.len(); + + if count == 0 { + return None; + } + Some(Arc::from(vec![Variance::Bivariant; count])) +} + +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)] +pub enum Variance { + Covariant, // T <: T iff A <: B -- e.g., function return type + Invariant, // T <: T iff B == A -- e.g., type of mutable cell + Contravariant, // T <: T iff B <: A -- e.g., function param type + Bivariant, // T <: T -- e.g., unused type parameter +} + +impl fmt::Display for Variance { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self { + Variance::Covariant => write!(f, "covariant"), + Variance::Invariant => write!(f, "invariant"), + Variance::Contravariant => write!(f, "contravariant"), + Variance::Bivariant => write!(f, "bivariant"), + } + } +} + +impl Variance { + /// `a.xform(b)` combines the variance of a context with the + /// variance of a type with the following meaning. If we are in a + /// context with variance `a`, and we encounter a type argument in + /// a position with variance `b`, then `a.xform(b)` is the new + /// variance with which the argument appears. + /// + /// Example 1: + /// ```ignore (illustrative) + /// *mut Vec + /// ``` + /// Here, the "ambient" variance starts as covariant. `*mut T` is + /// invariant with respect to `T`, so the variance in which the + /// `Vec` appears is `Covariant.xform(Invariant)`, which + /// yields `Invariant`. Now, the type `Vec` is covariant with + /// respect to its type argument `T`, and hence the variance of + /// the `i32` here is `Invariant.xform(Covariant)`, which results + /// (again) in `Invariant`. + /// + /// Example 2: + /// ```ignore (illustrative) + /// fn(*const Vec, *mut Vec` appears is + /// `Contravariant.xform(Covariant)` or `Contravariant`. The same + /// is true for its `i32` argument. In the `*mut T` case, the + /// variance of `Vec` is `Contravariant.xform(Invariant)`, + /// and hence the outermost type is `Invariant` with respect to + /// `Vec` (and its `i32` argument). + /// + /// Source: Figure 1 of "Taming the Wildcards: + /// Combining Definition- and Use-Site Variance" published in PLDI'11. + fn xform(self, v: Variance) -> Variance { + match (self, v) { + // Figure 1, column 1. + (Variance::Covariant, Variance::Covariant) => Variance::Covariant, + (Variance::Covariant, Variance::Contravariant) => Variance::Contravariant, + (Variance::Covariant, Variance::Invariant) => Variance::Invariant, + (Variance::Covariant, Variance::Bivariant) => Variance::Bivariant, + + // Figure 1, column 2. + (Variance::Contravariant, Variance::Covariant) => Variance::Contravariant, + (Variance::Contravariant, Variance::Contravariant) => Variance::Covariant, + (Variance::Contravariant, Variance::Invariant) => Variance::Invariant, + (Variance::Contravariant, Variance::Bivariant) => Variance::Bivariant, + + // Figure 1, column 3. + (Variance::Invariant, _) => Variance::Invariant, + + // Figure 1, column 4. + (Variance::Bivariant, _) => Variance::Bivariant, + } + } + + fn glb(self, v: Variance) -> Variance { + // Greatest lower bound of the variance lattice as + // defined in The Paper: + // + // * + // - + + // o + match (self, v) { + (Variance::Invariant, _) | (_, Variance::Invariant) => Variance::Invariant, + + (Variance::Covariant, Variance::Contravariant) => Variance::Invariant, + (Variance::Contravariant, Variance::Covariant) => Variance::Invariant, + + (Variance::Covariant, Variance::Covariant) => Variance::Covariant, + + (Variance::Contravariant, Variance::Contravariant) => Variance::Contravariant, + + (x, Variance::Bivariant) | (Variance::Bivariant, x) => x, + } + } +} +#[derive(Copy, Clone, Debug)] +struct InferredIndex(usize); + +#[derive(Clone)] +enum VarianceTerm { + ConstantTerm(Variance), + TransformTerm(Box, Box), +} + +impl fmt::Debug for VarianceTerm { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self { + VarianceTerm::ConstantTerm(c1) => write!(f, "{c1:?}"), + VarianceTerm::TransformTerm(v1, v2) => write!(f, "({v1:?} \u{00D7} {v2:?})"), + } + } +} + +struct Context<'db> { + db: &'db dyn HirDatabase, + def: GenericDefId, + has_trait_self: bool, + len_self: usize, + len_self_lifetimes: usize, + generics: Generics, + constraints: Vec, +} + +/// Declares that the variable `decl_id` appears in a location with +/// variance `variance`. +#[derive(Clone)] +struct Constraint { + inferred: InferredIndex, + variance: VarianceTerm, +} + +impl Context<'_> { + fn build_constraints_for_item(&mut self) { + match self.def { + GenericDefId::AdtId(adt) => { + let db = self.db; + let mut add_constraints_from_variant = |variant| { + let subst = self.generics.placeholder_subst(db); + for (_, field) in db.field_types(variant).iter() { + self.add_constraints_from_ty( + &field.clone().substitute(Interner, &subst), + &VarianceTerm::ConstantTerm(Variance::Covariant), + ); + } + }; + match adt { + AdtId::StructId(s) => add_constraints_from_variant(VariantId::StructId(s)), + AdtId::UnionId(u) => add_constraints_from_variant(VariantId::UnionId(u)), + AdtId::EnumId(e) => { + db.enum_data(e).variants.iter().for_each(|&(variant, _)| { + add_constraints_from_variant(VariantId::EnumVariantId(variant)) + }); + } + } + } + GenericDefId::FunctionId(f) => { + let subst = self.generics.placeholder_subst(self.db); + self.add_constraints_from_sig2( + &self + .db + .callable_item_signature(f.into()) + .substitute(Interner, &subst) + .params_and_return, + &VarianceTerm::ConstantTerm(Variance::Covariant), + ); + } + _ => {} + } + } + + fn contravariant(&mut self, variance: &VarianceTerm) -> VarianceTerm { + self.xform(variance, &VarianceTerm::ConstantTerm(Variance::Contravariant)) + } + + fn invariant(&mut self, variance: &VarianceTerm) -> VarianceTerm { + self.xform(variance, &VarianceTerm::ConstantTerm(Variance::Invariant)) + } + + fn xform(&mut self, v1: &VarianceTerm, v2: &VarianceTerm) -> VarianceTerm { + match (v1, v2) { + // Applying a "covariant" transform is always a no-op + (_, VarianceTerm::ConstantTerm(Variance::Covariant)) => v1.clone(), + (VarianceTerm::ConstantTerm(c1), VarianceTerm::ConstantTerm(c2)) => { + VarianceTerm::ConstantTerm(c1.xform(*c2)) + } + _ => VarianceTerm::TransformTerm(Box::new(v1.clone()), Box::new(v2.clone())), + } + } + + fn add_constraints_from_invariant_args( + &mut self, + args: &[GenericArg], + variance: &VarianceTerm, + ) { + tracing::debug!( + "add_constraints_from_invariant_args(args={:?}, variance={:?})", + args, + variance + ); + let variance_i = self.invariant(variance); + + for k in args { + match k.data(Interner) { + GenericArgData::Lifetime(lt) => self.add_constraints_from_region(lt, &variance_i), + GenericArgData::Ty(ty) => self.add_constraints_from_ty(ty, &variance_i), + GenericArgData::Const(val) => self.add_constraints_from_const(val, &variance_i), + } + } + } + + /// Adds constraints appropriate for an instance of `ty` appearing + /// in a context with the generics defined in `generics` and + /// ambient variance `variance` + fn add_constraints_from_ty(&mut self, ty: &Ty, variance: &VarianceTerm) { + tracing::debug!("add_constraints_from_ty(ty={:?}, variance={:?})", ty, variance); + match ty.kind(Interner) { + TyKind::Scalar(_) | TyKind::Never | TyKind::Str | TyKind::Foreign(..) => { + // leaf type -- noop + } + + TyKind::FnDef(..) | TyKind::Coroutine(..) | TyKind::Closure(..) => { + panic!("Unexpected unnameable type in variance computation: {ty:?}"); + } + + TyKind::Ref(mutbl, lifetime, ty) => { + self.add_constraints_from_region(lifetime, variance); + self.add_constraints_from_mt(ty, *mutbl, variance); + } + + TyKind::Array(typ, len) => { + self.add_constraints_from_const(len, variance); + self.add_constraints_from_ty(typ, variance); + } + + TyKind::Slice(typ) => { + self.add_constraints_from_ty(typ, variance); + } + + TyKind::Raw(mutbl, ty) => { + self.add_constraints_from_mt(ty, *mutbl, variance); + } + + TyKind::Tuple(_, subtys) => { + for subty in subtys.type_parameters(Interner) { + self.add_constraints_from_ty(&subty, variance); + } + } + + TyKind::Adt(def, args) => { + self.add_constraints_from_args(def.0.into(), args.as_slice(Interner), variance); + } + + TyKind::Alias(AliasTy::Opaque(opaque)) => { + self.add_constraints_from_invariant_args( + opaque.substitution.as_slice(Interner), + variance, + ); + } + TyKind::Alias(AliasTy::Projection(proj)) => { + self.add_constraints_from_invariant_args( + proj.substitution.as_slice(Interner), + variance, + ); + } + // FIXME: check this + TyKind::AssociatedType(_, subst) => { + self.add_constraints_from_invariant_args(subst.as_slice(Interner), variance); + } + // FIXME: check this + TyKind::OpaqueType(_, subst) => { + self.add_constraints_from_invariant_args(subst.as_slice(Interner), variance); + } + + TyKind::Dyn(it) => { + // The type `dyn Trait +'a` is covariant w/r/t `'a`: + self.add_constraints_from_region(&it.lifetime, variance); + + if let Some(trait_ref) = it.principal() { + // Trait are always invariant so we can take advantage of that. + self.add_constraints_from_invariant_args( + trait_ref + .map(|it| it.map(|it| it.substitution.clone())) + .substitute( + Interner, + &[GenericArg::new( + Interner, + chalk_ir::GenericArgData::Ty(TyKind::Error.intern(Interner)), + )], + ) + .skip_binders() + .as_slice(Interner), + variance, + ); + } + + // FIXME + // for projection in data.projection_bounds() { + // match projection.skip_binder().term.unpack() { + // TyKind::TermKind::Ty(ty) => { + // self.add_constraints_from_ty( ty, self.invariant); + // } + // TyKind::TermKind::Const(c) => { + // self.add_constraints_from_const( c, self.invariant) + // } + // } + // } + } + + // Chalk has no params, so use placeholders for now? + TyKind::Placeholder(index) => { + let idx = crate::from_placeholder_idx(self.db, *index); + let index = idx.local_id.into_raw().into_u32() as usize + self.len_self_lifetimes; + let inferred = if idx.parent == self.def { + InferredIndex(self.has_trait_self as usize + index) + } else { + InferredIndex(self.len_self + index) + }; + tracing::debug!("add_constraint(index={:?}, variance={:?})", inferred, variance); + self.constraints.push(Constraint { inferred, variance: variance.clone() }); + } + TyKind::Function(f) => { + self.add_constraints_from_sig(f, variance); + } + + TyKind::Error => { + // we encounter this when walking the trait references for object + // types, where we use Error as the Self type + } + + TyKind::CoroutineWitness(..) | TyKind::BoundVar(..) | TyKind::InferenceVar(..) => { + panic!("unexpected type encountered in variance inference: {:?}", ty); + } + } + } + + /// Adds constraints appropriate for a nominal type (enum, struct, + /// object, etc) appearing in a context with ambient variance `variance` + fn add_constraints_from_args( + &mut self, + def_id: GenericDefId, + args: &[GenericArg], + variance: &VarianceTerm, + ) { + tracing::debug!( + "add_constraints_from_args(def_id={:?}, args={:?}, variance={:?})", + def_id, + args, + variance + ); + + // We don't record `inferred_starts` entries for empty generics. + if args.is_empty() { + return; + } + if def_id == self.def { + // HACK: Workaround for the trivial cycle salsa case (see + // recursive_one_bivariant_more_non_bivariant_params test) + let variance_i = self.xform(variance, &VarianceTerm::ConstantTerm(Variance::Bivariant)); + for k in args { + match k.data(Interner) { + GenericArgData::Lifetime(lt) => { + self.add_constraints_from_region(lt, &variance_i) + } + GenericArgData::Ty(ty) => self.add_constraints_from_ty(ty, &variance_i), + GenericArgData::Const(val) => self.add_constraints_from_const(val, variance), + } + } + } else { + let Some(variances) = self.db.variances_of(def_id) else { + return; + }; + + for (i, k) in args.iter().enumerate() { + let variance_decl = &VarianceTerm::ConstantTerm(variances[i]); + let variance_i = self.xform(variance, variance_decl); + match k.data(Interner) { + GenericArgData::Lifetime(lt) => { + self.add_constraints_from_region(lt, &variance_i) + } + GenericArgData::Ty(ty) => self.add_constraints_from_ty(ty, &variance_i), + GenericArgData::Const(val) => self.add_constraints_from_const(val, variance), + } + } + } + } + + /// Adds constraints appropriate for a const expression `val` + /// in a context with ambient variance `variance` + fn add_constraints_from_const(&mut self, c: &Const, variance: &VarianceTerm) { + match &c.data(Interner).value { + chalk_ir::ConstValue::Concrete(c) => { + if let ConstScalar::UnevaluatedConst(_, subst) = &c.interned { + self.add_constraints_from_invariant_args(subst.as_slice(Interner), variance); + } + } + _ => {} + } + } + + /// Adds constraints appropriate for a function with signature + /// `sig` appearing in a context with ambient variance `variance` + fn add_constraints_from_sig(&mut self, sig: &FnPointer, variance: &VarianceTerm) { + let contra = self.contravariant(variance); + let mut tys = sig.substitution.0.iter(Interner).filter_map(move |p| p.ty(Interner)); + self.add_constraints_from_ty(tys.next_back().unwrap(), variance); + for input in tys { + self.add_constraints_from_ty(input, &contra); + } + } + + fn add_constraints_from_sig2(&mut self, sig: &[Ty], variance: &VarianceTerm) { + let contra = self.contravariant(variance); + let mut tys = sig.iter(); + self.add_constraints_from_ty(tys.next_back().unwrap(), variance); + for input in tys { + self.add_constraints_from_ty(input, &contra); + } + } + + /// Adds constraints appropriate for a region appearing in a + /// context with ambient variance `variance` + fn add_constraints_from_region(&mut self, region: &Lifetime, variance: &VarianceTerm) { + match region.data(Interner) { + // FIXME: chalk has no params? + LifetimeData::Placeholder(index) => { + let idx = crate::lt_from_placeholder_idx(self.db, *index); + let index = idx.local_id.into_raw().into_u32() as usize; + let inferred = if idx.parent == self.def { + InferredIndex(index) + } else { + InferredIndex(self.has_trait_self as usize + self.len_self + index) + }; + tracing::debug!("add_constraint(index={:?}, variance={:?})", inferred, variance); + self.constraints.push(Constraint { inferred, variance: variance.clone() }); + } + LifetimeData::Static => {} + + LifetimeData::BoundVar(..) => { + // Either a higher-ranked region inside of a type or a + // late-bound function parameter. + // + // We do not compute constraints for either of these. + } + + LifetimeData::Error => {} + + LifetimeData::Phantom(..) | LifetimeData::InferenceVar(..) | LifetimeData::Erased => { + // We don't expect to see anything but 'static or bound + // regions when visiting member types or method types. + panic!( + "unexpected region encountered in variance \ + inference: {:?}", + region + ); + } + } + } + + /// Adds constraints appropriate for a mutability-type pair + /// appearing in a context with ambient variance `variance` + fn add_constraints_from_mt(&mut self, ty: &Ty, mt: Mutability, variance: &VarianceTerm) { + match mt { + Mutability::Mut => { + let invar = self.invariant(variance); + self.add_constraints_from_ty(ty, &invar); + } + + Mutability::Not => { + self.add_constraints_from_ty(ty, variance); + } + } + } +} + +impl Context<'_> { + fn solve(self) -> Vec { + let mut solutions = vec![Variance::Bivariant; self.generics.len()]; + // Propagate constraints until a fixed point is reached. Note + // that the maximum number of iterations is 2C where C is the + // number of constraints (each variable can change values at most + // twice). Since number of constraints is linear in size of the + // input, so is the inference process. + let mut changed = true; + while changed { + changed = false; + + for constraint in &self.constraints { + let Constraint { inferred, variance: term } = constraint; + let InferredIndex(inferred) = inferred; + let variance = Self::evaluate(term); + let old_value = solutions[*inferred]; + let new_value = variance.glb(old_value); + if old_value != new_value { + solutions[*inferred] = new_value; + changed = true; + } + } + } + + // Const parameters are always invariant. + // Make all const parameters invariant. + for (idx, param) in self.generics.iter_id().enumerate() { + if let GenericParamId::ConstParamId(_) = param { + solutions[idx] = Variance::Invariant; + } + } + + // Functions are permitted to have unused generic parameters: make those invariant. + if let GenericDefId::FunctionId(_) = self.def { + for variance in &mut solutions { + if *variance == Variance::Bivariant { + *variance = Variance::Invariant; + } + } + } + + solutions + } + + fn evaluate(term: &VarianceTerm) -> Variance { + match term { + VarianceTerm::ConstantTerm(v) => *v, + VarianceTerm::TransformTerm(t1, t2) => { + let v1 = Self::evaluate(t1); + let v2 = Self::evaluate(t2); + v1.xform(v2) + } + } + } +} + +#[cfg(test)] +mod tests { + use expect_test::{expect, Expect}; + use hir_def::{ + generics::GenericParamDataRef, src::HasSource, AdtId, GenericDefId, ModuleDefId, + }; + use itertools::Itertools; + use stdx::format_to; + use syntax::{ast::HasName, AstNode}; + use test_fixture::WithFixture; + + use hir_def::Lookup; + + use crate::{db::HirDatabase, test_db::TestDB, variance::generics}; + + #[test] + fn phantom_data() { + check( + r#" +//- minicore: phantom_data + +struct Covariant { + t: core::marker::PhantomData +} +"#, + expect![[r#" + Covariant[A: covariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_types() { + check( + r#" +//- minicore: cell + +use core::cell::UnsafeCell; + +struct InvariantMut<'a,A:'a,B:'a> { //~ ERROR ['a: +, A: o, B: o] + t: &'a mut (A,B) +} + +struct InvariantCell { //~ ERROR [A: o] + t: UnsafeCell +} + +struct InvariantIndirect { //~ ERROR [A: o] + t: InvariantCell +} + +struct Covariant { //~ ERROR [A: +] + t: A, u: fn() -> A +} + +struct Contravariant { //~ ERROR [A: -] + t: fn(A) +} + +enum Enum { //~ ERROR [A: +, B: -, C: o] + Foo(Covariant), + Bar(Contravariant),` + Zed(Covariant,Contravariant) +} +"#, + expect![[r#" + InvariantMut['a: covariant, A: invariant, B: invariant] + InvariantCell[A: invariant] + InvariantIndirect[A: invariant] + Covariant[A: covariant] + Contravariant[A: contravariant] + Enum[A: covariant, B: contravariant, C: invariant] + "#]], + ); + } + + #[test] + fn type_resolve_error_two_structs_deep() { + check( + r#" +struct Hello<'a> { + missing: Missing<'a>, +} + +struct Other<'a> { + hello: Hello<'a>, +} +"#, + expect![[r#" + Hello['a: bivariant] + Other['a: bivariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_associated_consts() { + // FIXME: Should be invariant + check( + r#" +trait Trait { + const Const: usize; +} + +struct Foo { //~ ERROR [T: o] + field: [u8; ::Const] +} +"#, + expect![[r#" + Foo[T: bivariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_associated_types() { + check( + r#" +trait Trait<'a> { + type Type; + + fn method(&'a self) { } +} + +struct Foo<'a, T : Trait<'a>> { //~ ERROR ['a: +, T: +] + field: (T, &'a ()) +} + +struct Bar<'a, T : Trait<'a>> { //~ ERROR ['a: o, T: o] + field: >::Type +} + +"#, + expect![[r#" + method[Self: contravariant, 'a: contravariant] + Foo['a: covariant, T: covariant] + Bar['a: invariant, T: invariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_associated_types2() { + // FIXME: RPITs have variance, but we can't treat them as their own thing right now + check( + r#" +trait Foo { + type Bar; +} + +fn make() -> *const dyn Foo {} +"#, + expect![""], + ); + } + + #[test] + fn rustc_test_variance_trait_bounds() { + check( + r#" +trait Getter { + fn get(&self) -> T; +} + +trait Setter { + fn get(&self, _: T); +} + +struct TestStruct> { //~ ERROR [U: +, T: +] + t: T, u: U +} + +enum TestEnum> { //~ ERROR [U: *, T: +] + //~^ ERROR: `U` is never used + Foo(T) +} + +struct TestContraStruct> { //~ ERROR [U: *, T: +] + //~^ ERROR: `U` is never used + t: T +} + +struct TestBox+Setter> { //~ ERROR [U: *, T: +] + //~^ ERROR: `U` is never used + t: T +} +"#, + expect![[r#" + get[Self: contravariant, T: covariant] + get[Self: contravariant, T: contravariant] + TestStruct[U: covariant, T: covariant] + TestEnum[U: bivariant, T: covariant] + TestContraStruct[U: bivariant, T: covariant] + TestBox[U: bivariant, T: covariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_trait_matching() { + check( + r#" + +trait Get { + fn get(&self) -> T; +} + +struct Cloner { + t: T +} + +impl Get for Cloner { + fn get(&self) -> T {} +} + +fn get<'a, G>(get: &G) -> i32 + where G : Get<&'a i32> +{} + +fn pick<'b, G>(get: &'b G, if_odd: &'b i32) -> i32 + where G : Get<&'b i32> +{} +"#, + expect![[r#" + get[Self: contravariant, T: covariant] + Cloner[T: covariant] + get[T: invariant] + get['a: invariant, G: contravariant] + pick['b: contravariant, G: contravariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_trait_object_bound() { + check( + r#" +enum Option { + Some(T), + None +} +trait T { fn foo(&self); } + +struct TOption<'a> { //~ ERROR ['a: +] + v: Option<*const (dyn T + 'a)>, +} +"#, + expect![[r#" + Option[T: covariant] + foo[Self: contravariant] + TOption['a: covariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_types_bounds() { + check( + r#" +//- minicore: send +struct TestImm { //~ ERROR [A: +, B: +] + x: A, + y: B, +} + +struct TestMut { //~ ERROR [A: +, B: o] + x: A, + y: &'static mut B, +} + +struct TestIndirect { //~ ERROR [A: +, B: o] + m: TestMut +} + +struct TestIndirect2 { //~ ERROR [A: o, B: o] + n: TestMut, + m: TestMut +} + +trait Getter { + fn get(&self) -> A; +} + +trait Setter { + fn set(&mut self, a: A); +} + +struct TestObject { //~ ERROR [A: o, R: o] + n: *const (dyn Setter + Send), + m: *const (dyn Getter + Send), +} +"#, + expect![[r#" + TestImm[A: covariant, B: covariant] + TestMut[A: covariant, B: invariant] + TestIndirect[A: covariant, B: invariant] + TestIndirect2[A: invariant, B: invariant] + get[Self: contravariant, A: covariant] + set[Self: invariant, A: contravariant] + TestObject[A: invariant, R: invariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_unused_region_param() { + check( + r#" +struct SomeStruct<'a> { x: u32 } //~ ERROR parameter `'a` is never used +enum SomeEnum<'a> { Nothing } //~ ERROR parameter `'a` is never used +trait SomeTrait<'a> { fn foo(&self); } // OK on traits. +"#, + expect![[r#" + SomeStruct['a: bivariant] + SomeEnum['a: bivariant] + foo[Self: contravariant, 'a: invariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_unused_type_param() { + check( + r#" +//- minicore: sized +struct SomeStruct { x: u32 } +enum SomeEnum { Nothing } +enum ListCell { + Cons(*const ListCell), + Nil +} + +struct SelfTyAlias(*const Self); +struct WithBounds {} +struct WithWhereBounds where T: Sized {} +struct WithOutlivesBounds {} +struct DoubleNothing { + s: SomeStruct, +} + +"#, + expect![[r#" + SomeStruct[A: bivariant] + SomeEnum[A: bivariant] + ListCell[T: bivariant] + SelfTyAlias[T: bivariant] + WithBounds[T: bivariant] + WithWhereBounds[T: bivariant] + WithOutlivesBounds[T: bivariant] + DoubleNothing[T: bivariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_use_contravariant_struct1() { + check( + r#" +struct SomeStruct(fn(T)); + +fn foo<'min,'max>(v: SomeStruct<&'max ()>) + -> SomeStruct<&'min ()> + where 'max : 'min +{} +"#, + expect![[r#" + SomeStruct[T: contravariant] + foo['min: contravariant, 'max: covariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_use_contravariant_struct2() { + check( + r#" +struct SomeStruct(fn(T)); + +fn bar<'min,'max>(v: SomeStruct<&'min ()>) + -> SomeStruct<&'max ()> + where 'max : 'min +{} +"#, + expect![[r#" + SomeStruct[T: contravariant] + bar['min: covariant, 'max: contravariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_use_covariant_struct1() { + check( + r#" +struct SomeStruct(T); + +fn foo<'min,'max>(v: SomeStruct<&'min ()>) + -> SomeStruct<&'max ()> + where 'max : 'min +{} +"#, + expect![[r#" + SomeStruct[T: covariant] + foo['min: contravariant, 'max: covariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_use_covariant_struct2() { + check( + r#" +struct SomeStruct(T); + +fn foo<'min,'max>(v: SomeStruct<&'max ()>) + -> SomeStruct<&'min ()> + where 'max : 'min +{} +"#, + expect![[r#" + SomeStruct[T: covariant] + foo['min: covariant, 'max: contravariant] + "#]], + ); + } + + #[test] + fn rustc_test_variance_use_invariant_struct1() { + check( + r#" +struct SomeStruct(*mut T); + +fn foo<'min,'max>(v: SomeStruct<&'max ()>) + -> SomeStruct<&'min ()> + where 'max : 'min +{} + +fn bar<'min,'max>(v: SomeStruct<&'min ()>) + -> SomeStruct<&'max ()> + where 'max : 'min +{} +"#, + expect![[r#" + SomeStruct[T: invariant] + foo['min: invariant, 'max: invariant] + bar['min: invariant, 'max: invariant] + "#]], + ); + } + + #[test] + fn recursive_one_bivariant_more_non_bivariant_params() { + // FIXME: This is wrong, this should be `BivariantPartialIndirect[T: bivariant, U: covariant]` (likewise for Wrapper) + // This is a limitation of current salsa where a cycle may only set a fallback value to the + // query result which is not what we want! We want to treat the cycle call as fallback + // without setting the query result to the fallback. + // `BivariantPartial` works as we workaround for the trivial case of being self-referential + check( + r#" +struct BivariantPartial(*const BivariantPartial, U); +struct Wrapper(BivariantPartialIndirect); +struct BivariantPartialIndirect(*const Wrapper, U); +"#, + expect![[r#" + BivariantPartial[T: bivariant, U: covariant] + Wrapper[T: bivariant, U: bivariant] + BivariantPartialIndirect[T: bivariant, U: bivariant] + "#]], + ); + } + + #[track_caller] + fn check(ra_fixture: &str, expected: Expect) { + // use tracing_subscriber::{layer::SubscriberExt, Layer}; + // let my_layer = tracing_subscriber::fmt::layer(); + // let _g = tracing::subscriber::set_default(tracing_subscriber::registry().with( + // my_layer.with_filter(tracing_subscriber::filter::filter_fn(|metadata| { + // metadata.target().starts_with("hir_ty::variance") + // })), + // )); + let (db, file_id) = TestDB::with_single_file(ra_fixture); + + let mut defs: Vec = Vec::new(); + let module = db.module_for_file_opt(file_id).unwrap(); + let def_map = module.def_map(&db); + crate::tests::visit_module(&db, &def_map, module.local_id, &mut |it| { + defs.push(match it { + ModuleDefId::FunctionId(it) => it.into(), + ModuleDefId::AdtId(it) => it.into(), + ModuleDefId::ConstId(it) => it.into(), + ModuleDefId::TraitId(it) => it.into(), + ModuleDefId::TraitAliasId(it) => it.into(), + ModuleDefId::TypeAliasId(it) => it.into(), + _ => return, + }) + }); + let defs = defs + .into_iter() + .filter_map(|def| { + Some(( + def, + match def { + GenericDefId::FunctionId(it) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::AdtId(AdtId::EnumId(it)) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::AdtId(AdtId::StructId(it)) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::AdtId(AdtId::UnionId(it)) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::TraitId(it) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::TraitAliasId(it) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::TypeAliasId(it) => { + let loc = it.lookup(&db); + loc.source(&db).value.name().unwrap() + } + GenericDefId::ImplId(_) => return None, + GenericDefId::ConstId(_) => return None, + }, + )) + }) + .sorted_by_key(|(_, n)| n.syntax().text_range().start()); + let mut res = String::new(); + for (def, name) in defs { + let Some(variances) = db.variances_of(def) else { + continue; + }; + format_to!( + res, + "{name}[{}]\n", + generics(&db, def) + .iter() + .map(|(_, param)| match param { + GenericParamDataRef::TypeParamData(type_param_data) => { + type_param_data.name.as_ref().unwrap() + } + GenericParamDataRef::ConstParamData(const_param_data) => + &const_param_data.name, + GenericParamDataRef::LifetimeParamData(lifetime_param_data) => { + &lifetime_param_data.name + } + }) + .zip_eq(&*variances) + .format_with(", ", |(name, var), f| f(&format_args!( + "{}: {var}", + name.as_str() + ))) + ); + } + + expected.assert_eq(&res); + } +}