//! Type inference for expressions.
use std::iter::{repeat, repeat_with};
use std::sync::Arc;
use hir_def::{
builtin_type::Signedness,
path::{GenericArg, GenericArgs},
};
use hir_expand::name;
use super::{BindingMode, Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch};
use crate::{
db::HirDatabase,
expr::{self, Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
generics::{GenericParams, HasGenericParams},
ty::{
autoderef, method_resolution, op, CallableDef, InferTy, IntTy, Mutability, Namespace,
Obligation, ProjectionPredicate, ProjectionTy, Substs, TraitRef, Ty, TypeCtor, TypeWalk,
Uncertain,
},
Adt, Name,
};
impl<'a, D: HirDatabase> InferenceContext<'a, D> {
pub(super) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
let ty = self.infer_expr_inner(tgt_expr, expected);
let could_unify = self.unify(&ty, &expected.ty);
if !could_unify {
self.result.type_mismatches.insert(
tgt_expr,
TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() },
);
}
let ty = self.resolve_ty_as_possible(&mut vec![], ty);
ty
}
/// Infer type of expression with possibly implicit coerce to the expected type.
/// Return the type after possible coercion.
fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
let ty = self.infer_expr_inner(expr, &expected);
let ty = if !self.coerce(&ty, &expected.ty) {
self.result
.type_mismatches
.insert(expr, TypeMismatch { expected: expected.ty.clone(), actual: ty.clone() });
// Return actual type when type mismatch.
// This is needed for diagnostic when return type mismatch.
ty
} else if expected.ty == Ty::Unknown {
ty
} else {
expected.ty.clone()
};
self.resolve_ty_as_possible(&mut vec![], ty)
}
fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
let body = Arc::clone(&self.body); // avoid borrow checker problem
let ty = match &body[tgt_expr] {
Expr::Missing => Ty::Unknown,
Expr::If { condition, then_branch, else_branch } => {
// if let is desugared to match, so this is always simple if
self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
let then_ty = self.infer_expr_inner(*then_branch, &expected);
let else_ty = match else_branch {
Some(else_branch) => self.infer_expr_inner(*else_branch, &expected),
None => Ty::unit(),
};
self.coerce_merge_branch(&then_ty, &else_ty)
}
Expr::Block { statements, tail } => self.infer_block(statements, *tail, expected),
Expr::TryBlock { body } => {
let _inner = self.infer_expr(*body, expected);
// FIXME should be std::result::Result<{inner}, _>
Ty::Unknown
}
Expr::Loop { body } => {
self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
// FIXME handle break with value
Ty::simple(TypeCtor::Never)
}
Expr::While { condition, body } => {
// while let is desugared to a match loop, so this is always simple while
self.infer_expr(*condition, &Expectation::has_type(Ty::simple(TypeCtor::Bool)));
self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
Ty::unit()
}
Expr::For { iterable, body, pat } => {
let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
let pat_ty = match self.resolve_into_iter_item() {
Some(into_iter_item_alias) => {
let pat_ty = self.new_type_var();
let projection = ProjectionPredicate {
ty: pat_ty.clone(),
projection_ty: ProjectionTy {
associated_ty: into_iter_item_alias,
parameters: Substs::single(iterable_ty),
},
};
self.obligations.push(Obligation::Projection(projection));
self.resolve_ty_as_possible(&mut vec![], pat_ty)
}
None => Ty::Unknown,
};
self.infer_pat(*pat, &pat_ty, BindingMode::default());
self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
Ty::unit()
}
Expr::Lambda { body, args, arg_types } => {
assert_eq!(args.len(), arg_types.len());
let mut sig_tys = Vec::new();
for (arg_pat, arg_type) in args.iter().zip(arg_types.iter()) {
let expected = if let Some(type_ref) = arg_type {
self.make_ty(type_ref)
} else {
Ty::Unknown
};
let arg_ty = self.infer_pat(*arg_pat, &expected, BindingMode::default());
sig_tys.push(arg_ty);
}
// add return type
let ret_ty = self.new_type_var();
sig_tys.push(ret_ty.clone());
let sig_ty = Ty::apply(
TypeCtor::FnPtr { num_args: sig_tys.len() as u16 - 1 },
Substs(sig_tys.into()),
);
let closure_ty =
Ty::apply_one(TypeCtor::Closure { def: self.owner, expr: tgt_expr }, sig_ty);
// Eagerly try to relate the closure type with the expected
// type, otherwise we often won't have enough information to
// infer the body.
self.coerce(&closure_ty, &expected.ty);
self.infer_expr(*body, &Expectation::has_type(ret_ty));
closure_ty
}
Expr::Call { callee, args } => {
let callee_ty = self.infer_expr(*callee, &Expectation::none());
let (param_tys, ret_ty) = match callee_ty.callable_sig(self.db) {
Some(sig) => (sig.params().to_vec(), sig.ret().clone()),
None => {
// Not callable
// FIXME: report an error
(Vec::new(), Ty::Unknown)
}
};
self.register_obligations_for_call(&callee_ty);
self.check_call_arguments(args, ¶m_tys);
let ret_ty = self.normalize_associated_types_in(ret_ty);
ret_ty
}
Expr::MethodCall { receiver, args, method_name, generic_args } => self
.infer_method_call(tgt_expr, *receiver, &args, &method_name, generic_args.as_ref()),
Expr::Match { expr, arms } => {
let input_ty = self.infer_expr(*expr, &Expectation::none());
let mut result_ty = self.new_maybe_never_type_var();
for arm in arms {
for &pat in &arm.pats {
let _pat_ty = self.infer_pat(pat, &input_ty, BindingMode::default());
}
if let Some(guard_expr) = arm.guard {
self.infer_expr(
guard_expr,
&Expectation::has_type(Ty::simple(TypeCtor::Bool)),
);
}
let arm_ty = self.infer_expr_inner(arm.expr, &expected);
result_ty = self.coerce_merge_branch(&result_ty, &arm_ty);
}
result_ty
}
Expr::Path(p) => {
// FIXME this could be more efficient...
let resolver = expr::resolver_for_expr(self.db, self.owner, tgt_expr);
self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
}
Expr::Continue => Ty::simple(TypeCtor::Never),
Expr::Break { expr } => {
if let Some(expr) = expr {
// FIXME handle break with value
self.infer_expr(*expr, &Expectation::none());
}
Ty::simple(TypeCtor::Never)
}
Expr::Return { expr } => {
if let Some(expr) = expr {
self.infer_expr(*expr, &Expectation::has_type(self.return_ty.clone()));
}
Ty::simple(TypeCtor::Never)
}
Expr::RecordLit { path, fields, spread } => {
let (ty, def_id) = self.resolve_variant(path.as_ref());
if let Some(variant) = def_id {
self.write_variant_resolution(tgt_expr.into(), variant);
}
self.unify(&ty, &expected.ty);
let substs = ty.substs().unwrap_or_else(Substs::empty);
for (field_idx, field) in fields.iter().enumerate() {
let field_ty = def_id
.and_then(|it| match it.field(self.db, &field.name) {
Some(field) => Some(field),
None => {
self.push_diagnostic(InferenceDiagnostic::NoSuchField {
expr: tgt_expr,
field: field_idx,
});
None
}
})
.map_or(Ty::Unknown, |field| field.ty(self.db))
.subst(&substs);
self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
}
if let Some(expr) = spread {
self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
}
ty
}
Expr::Field { expr, name } => {
let receiver_ty = self.infer_expr(*expr, &Expectation::none());
let canonicalized = self.canonicalizer().canonicalize_ty(receiver_ty);
let ty = autoderef::autoderef(
self.db,
&self.resolver.clone(),
canonicalized.value.clone(),
)
.find_map(|derefed_ty| match canonicalized.decanonicalize_ty(derefed_ty.value) {
Ty::Apply(a_ty) => match a_ty.ctor {
TypeCtor::Tuple { .. } => name
.as_tuple_index()
.and_then(|idx| a_ty.parameters.0.get(idx).cloned()),
TypeCtor::Adt(Adt::Struct(s)) => s.field(self.db, name).map(|field| {
self.write_field_resolution(tgt_expr, field);
field.ty(self.db).subst(&a_ty.parameters)
}),
_ => None,
},
_ => None,
})
.unwrap_or(Ty::Unknown);
let ty = self.insert_type_vars(ty);
self.normalize_associated_types_in(ty)
}
Expr::Await { expr } => {
let inner_ty = self.infer_expr(*expr, &Expectation::none());
let ty = match self.resolve_future_future_output() {
Some(future_future_output_alias) => {
let ty = self.new_type_var();
let projection = ProjectionPredicate {
ty: ty.clone(),
projection_ty: ProjectionTy {
associated_ty: future_future_output_alias,
parameters: Substs::single(inner_ty),
},
};
self.obligations.push(Obligation::Projection(projection));
self.resolve_ty_as_possible(&mut vec![], ty)
}
None => Ty::Unknown,
};
ty
}
Expr::Try { expr } => {
let inner_ty = self.infer_expr(*expr, &Expectation::none());
let ty = match self.resolve_ops_try_ok() {
Some(ops_try_ok_alias) => {
let ty = self.new_type_var();
let projection = ProjectionPredicate {
ty: ty.clone(),
projection_ty: ProjectionTy {
associated_ty: ops_try_ok_alias,
parameters: Substs::single(inner_ty),
},
};
self.obligations.push(Obligation::Projection(projection));
self.resolve_ty_as_possible(&mut vec![], ty)
}
None => Ty::Unknown,
};
ty
}
Expr::Cast { expr, type_ref } => {
let _inner_ty = self.infer_expr(*expr, &Expectation::none());
let cast_ty = self.make_ty(type_ref);
// FIXME check the cast...
cast_ty
}
Expr::Ref { expr, mutability } => {
let expectation =
if let Some((exp_inner, exp_mutability)) = &expected.ty.as_reference() {
if *exp_mutability == Mutability::Mut && *mutability == Mutability::Shared {
// FIXME: throw type error - expected mut reference but found shared ref,
// which cannot be coerced
}
Expectation::has_type(Ty::clone(exp_inner))
} else {
Expectation::none()
};
// FIXME reference coercions etc.
let inner_ty = self.infer_expr(*expr, &expectation);
Ty::apply_one(TypeCtor::Ref(*mutability), inner_ty)
}
Expr::Box { expr } => {
let inner_ty = self.infer_expr(*expr, &Expectation::none());
if let Some(box_) = self.resolve_boxed_box() {
Ty::apply_one(TypeCtor::Adt(box_), inner_ty)
} else {
Ty::Unknown
}
}
Expr::UnaryOp { expr, op } => {
let inner_ty = self.infer_expr(*expr, &Expectation::none());
match op {
UnaryOp::Deref => {
let canonicalized = self.canonicalizer().canonicalize_ty(inner_ty);
if let Some(derefed_ty) =
autoderef::deref(self.db, &self.resolver, &canonicalized.value)
{
canonicalized.decanonicalize_ty(derefed_ty.value)
} else {
Ty::Unknown
}
}
UnaryOp::Neg => {
match &inner_ty {
Ty::Apply(a_ty) => match a_ty.ctor {
TypeCtor::Int(Uncertain::Unknown)
| TypeCtor::Int(Uncertain::Known(IntTy {
signedness: Signedness::Signed,
..
}))
| TypeCtor::Float(..) => inner_ty,
_ => Ty::Unknown,
},
Ty::Infer(InferTy::IntVar(..)) | Ty::Infer(InferTy::FloatVar(..)) => {
inner_ty
}
// FIXME: resolve ops::Neg trait
_ => Ty::Unknown,
}
}
UnaryOp::Not => {
match &inner_ty {
Ty::Apply(a_ty) => match a_ty.ctor {
TypeCtor::Bool | TypeCtor::Int(_) => inner_ty,
_ => Ty::Unknown,
},
Ty::Infer(InferTy::IntVar(..)) => inner_ty,
// FIXME: resolve ops::Not trait for inner_ty
_ => Ty::Unknown,
}
}
}
}
Expr::BinaryOp { lhs, rhs, op } => match op {
Some(op) => {
let lhs_expectation = match op {
BinaryOp::LogicOp(..) => Expectation::has_type(Ty::simple(TypeCtor::Bool)),
_ => Expectation::none(),
};
let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
// FIXME: find implementation of trait corresponding to operation
// symbol and resolve associated `Output` type
let rhs_expectation = op::binary_op_rhs_expectation(*op, lhs_ty);
let rhs_ty = self.infer_expr(*rhs, &Expectation::has_type(rhs_expectation));
// FIXME: similar as above, return ty is often associated trait type
op::binary_op_return_ty(*op, rhs_ty)
}
_ => Ty::Unknown,
},
Expr::Index { base, index } => {
let _base_ty = self.infer_expr(*base, &Expectation::none());
let _index_ty = self.infer_expr(*index, &Expectation::none());
// FIXME: use `std::ops::Index::Output` to figure out the real return type
Ty::Unknown
}
Expr::Tuple { exprs } => {
let mut tys = match &expected.ty {
ty_app!(TypeCtor::Tuple { .. }, st) => st
.iter()
.cloned()
.chain(repeat_with(|| self.new_type_var()))
.take(exprs.len())
.collect::<Vec<_>>(),
_ => (0..exprs.len()).map(|_| self.new_type_var()).collect(),
};
for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
}
Ty::apply(TypeCtor::Tuple { cardinality: tys.len() as u16 }, Substs(tys.into()))
}
Expr::Array(array) => {
let elem_ty = match &expected.ty {
ty_app!(TypeCtor::Array, st) | ty_app!(TypeCtor::Slice, st) => {
st.as_single().clone()
}
_ => self.new_type_var(),
};
match array {
Array::ElementList(items) => {
for expr in items.iter() {
self.infer_expr_coerce(*expr, &Expectation::has_type(elem_ty.clone()));
}
}
Array::Repeat { initializer, repeat } => {
self.infer_expr_coerce(
*initializer,
&Expectation::has_type(elem_ty.clone()),
);
self.infer_expr(
*repeat,
&Expectation::has_type(Ty::simple(TypeCtor::Int(Uncertain::Known(
IntTy::usize(),
)))),
);
}
}
Ty::apply_one(TypeCtor::Array, elem_ty)
}
Expr::Literal(lit) => match lit {
Literal::Bool(..) => Ty::simple(TypeCtor::Bool),
Literal::String(..) => {
Ty::apply_one(TypeCtor::Ref(Mutability::Shared), Ty::simple(TypeCtor::Str))
}
Literal::ByteString(..) => {
let byte_type = Ty::simple(TypeCtor::Int(Uncertain::Known(IntTy::u8())));
let slice_type = Ty::apply_one(TypeCtor::Slice, byte_type);
Ty::apply_one(TypeCtor::Ref(Mutability::Shared), slice_type)
}
Literal::Char(..) => Ty::simple(TypeCtor::Char),
Literal::Int(_v, ty) => Ty::simple(TypeCtor::Int((*ty).into())),
Literal::Float(_v, ty) => Ty::simple(TypeCtor::Float((*ty).into())),
},
};
// use a new type variable if we got Ty::Unknown here
let ty = self.insert_type_vars_shallow(ty);
let ty = self.resolve_ty_as_possible(&mut vec![], ty);
self.write_expr_ty(tgt_expr, ty.clone());
ty
}
fn infer_block(
&mut self,
statements: &[Statement],
tail: Option<ExprId>,
expected: &Expectation,
) -> Ty {
let mut diverges = false;
for stmt in statements {
match stmt {
Statement::Let { pat, type_ref, initializer } => {
let decl_ty =
type_ref.as_ref().map(|tr| self.make_ty(tr)).unwrap_or(Ty::Unknown);
// Always use the declared type when specified
let mut ty = decl_ty.clone();
if let Some(expr) = initializer {
let actual_ty =
self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
if decl_ty == Ty::Unknown {
ty = actual_ty;
}
}
let ty = self.resolve_ty_as_possible(&mut vec![], ty);
self.infer_pat(*pat, &ty, BindingMode::default());
}
Statement::Expr(expr) => {
if let ty_app!(TypeCtor::Never) = self.infer_expr(*expr, &Expectation::none()) {
diverges = true;
}
}
}
}
let ty = if let Some(expr) = tail {
self.infer_expr_coerce(expr, expected)
} else {
self.coerce(&Ty::unit(), &expected.ty);
Ty::unit()
};
if diverges {
Ty::simple(TypeCtor::Never)
} else {
ty
}
}
fn infer_method_call(
&mut self,
tgt_expr: ExprId,
receiver: ExprId,
args: &[ExprId],
method_name: &Name,
generic_args: Option<&GenericArgs>,
) -> Ty {
let receiver_ty = self.infer_expr(receiver, &Expectation::none());
let canonicalized_receiver = self.canonicalizer().canonicalize_ty(receiver_ty.clone());
let resolved = method_resolution::lookup_method(
&canonicalized_receiver.value,
self.db,
method_name,
&self.resolver,
);
let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
Some((ty, func)) => {
let ty = canonicalized_receiver.decanonicalize_ty(ty);
self.write_method_resolution(tgt_expr, func);
(
ty,
self.db.type_for_def(func.into(), Namespace::Values),
Some(func.generic_params(self.db)),
)
}
None => (receiver_ty, Ty::Unknown, None),
};
let substs = self.substs_for_method_call(def_generics, generic_args, &derefed_receiver_ty);
let method_ty = method_ty.apply_substs(substs);
let method_ty = self.insert_type_vars(method_ty);
self.register_obligations_for_call(&method_ty);
let (expected_receiver_ty, param_tys, ret_ty) = match method_ty.callable_sig(self.db) {
Some(sig) => {
if !sig.params().is_empty() {
(sig.params()[0].clone(), sig.params()[1..].to_vec(), sig.ret().clone())
} else {
(Ty::Unknown, Vec::new(), sig.ret().clone())
}
}
None => (Ty::Unknown, Vec::new(), Ty::Unknown),
};
// Apply autoref so the below unification works correctly
// FIXME: return correct autorefs from lookup_method
let actual_receiver_ty = match expected_receiver_ty.as_reference() {
Some((_, mutability)) => Ty::apply_one(TypeCtor::Ref(mutability), derefed_receiver_ty),
_ => derefed_receiver_ty,
};
self.unify(&expected_receiver_ty, &actual_receiver_ty);
self.check_call_arguments(args, ¶m_tys);
let ret_ty = self.normalize_associated_types_in(ret_ty);
ret_ty
}
fn check_call_arguments(&mut self, args: &[ExprId], param_tys: &[Ty]) {
// Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
// We do this in a pretty awful way: first we type-check any arguments
// that are not closures, then we type-check the closures. This is so
// that we have more information about the types of arguments when we
// type-check the functions. This isn't really the right way to do this.
for &check_closures in &[false, true] {
let param_iter = param_tys.iter().cloned().chain(repeat(Ty::Unknown));
for (&arg, param_ty) in args.iter().zip(param_iter) {
let is_closure = match &self.body[arg] {
Expr::Lambda { .. } => true,
_ => false,
};
if is_closure != check_closures {
continue;
}
let param_ty = self.normalize_associated_types_in(param_ty);
self.infer_expr_coerce(arg, &Expectation::has_type(param_ty.clone()));
}
}
}
fn substs_for_method_call(
&mut self,
def_generics: Option<Arc<GenericParams>>,
generic_args: Option<&GenericArgs>,
receiver_ty: &Ty,
) -> Substs {
let (parent_param_count, param_count) =
def_generics.as_ref().map_or((0, 0), |g| (g.count_parent_params(), g.params.len()));
let mut substs = Vec::with_capacity(parent_param_count + param_count);
// Parent arguments are unknown, except for the receiver type
if let Some(parent_generics) = def_generics.and_then(|p| p.parent_params.clone()) {
for param in &parent_generics.params {
if param.name == name::SELF_TYPE {
substs.push(receiver_ty.clone());
} else {
substs.push(Ty::Unknown);
}
}
}
// handle provided type arguments
if let Some(generic_args) = generic_args {
// if args are provided, it should be all of them, but we can't rely on that
for arg in generic_args.args.iter().take(param_count) {
match arg {
GenericArg::Type(type_ref) => {
let ty = self.make_ty(type_ref);
substs.push(ty);
}
}
}
};
let supplied_params = substs.len();
for _ in supplied_params..parent_param_count + param_count {
substs.push(Ty::Unknown);
}
assert_eq!(substs.len(), parent_param_count + param_count);
Substs(substs.into())
}
fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
if let Ty::Apply(a_ty) = callable_ty {
if let TypeCtor::FnDef(def) = a_ty.ctor {
let generic_predicates = self.db.generic_predicates(def.into());
for predicate in generic_predicates.iter() {
let predicate = predicate.clone().subst(&a_ty.parameters);
if let Some(obligation) = Obligation::from_predicate(predicate) {
self.obligations.push(obligation);
}
}
// add obligation for trait implementation, if this is a trait method
match def {
CallableDef::Function(f) => {
if let Some(trait_) = f.parent_trait(self.db) {
// construct a TraitDef
let substs = a_ty.parameters.prefix(
trait_.generic_params(self.db).count_params_including_parent(),
);
self.obligations.push(Obligation::Trait(TraitRef { trait_, substs }));
}
}
CallableDef::Struct(_) | CallableDef::EnumVariant(_) => {}
}
}
}
}
}