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|
//! Type inference, i.e. the process of walking through the code and determining
//! the type of each expression and pattern.
//!
//! For type inference, compare the implementations in rustc (the various
//! check_* methods in librustc_typeck/check/mod.rs are a good entry point) and
//! IntelliJ-Rust (org.rust.lang.core.types.infer). Our entry point for
//! inference here is the `infer` function, which infers the types of all
//! expressions in a given function.
//!
//! During inference, types (i.e. the `Ty` struct) can contain type 'variables'
//! which represent currently unknown types; as we walk through the expressions,
//! we might determine that certain variables need to be equal to each other, or
//! to certain types. To record this, we use the union-find implementation from
//! the `ena` crate, which is extracted from rustc.
use std::borrow::Cow;
use std::iter::repeat;
use std::ops::Index;
use std::sync::Arc;
use std::mem;
use ena::unify::{InPlaceUnificationTable, UnifyKey, UnifyValue, NoError};
use ra_arena::map::ArenaMap;
use rustc_hash::FxHashMap;
use test_utils::tested_by;
use crate::{
Function, StructField, Path, Name,
FnSignature, AdtDef,
HirDatabase,
ImplItem,
type_ref::{TypeRef, Mutability},
expr::{Body, Expr, BindingAnnotation, Literal, ExprId, Pat, PatId, UnaryOp, BinaryOp, Statement, FieldPat, self},
generics::GenericParams,
path::{GenericArgs, GenericArg},
adt::VariantDef,
resolve::{Resolver, Resolution},
nameres::Namespace
};
use super::{Ty, TypableDef, Substs, primitive, op};
/// The entry point of type inference.
pub fn infer(db: &impl HirDatabase, func: Function) -> Arc<InferenceResult> {
db.check_canceled();
let body = func.body(db);
let resolver = func.resolver(db);
let mut ctx = InferenceContext::new(db, body, resolver);
let signature = func.signature(db);
ctx.collect_fn_signature(&signature);
ctx.infer_body();
Arc::new(ctx.resolve_all())
}
#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub enum ExprOrPatId {
Expr(ExprId),
Pat(PatId),
}
impl From<ExprId> for ExprOrPatId {
fn from(id: ExprId) -> Self {
ExprOrPatId::Expr(id)
}
}
impl From<PatId> for ExprOrPatId {
fn from(id: PatId) -> Self {
ExprOrPatId::Pat(id)
}
}
/// The result of type inference: A mapping from expressions and patterns to types.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct InferenceResult {
/// For each method call expr, records the function it resolves to.
method_resolutions: FxHashMap<ExprId, Function>,
/// For each field access expr, records the field it resolves to.
field_resolutions: FxHashMap<ExprId, StructField>,
/// For each associated item record what it resolves to
assoc_resolutions: FxHashMap<ExprOrPatId, ImplItem>,
pub(super) type_of_expr: ArenaMap<ExprId, Ty>,
pub(super) type_of_pat: ArenaMap<PatId, Ty>,
}
impl InferenceResult {
pub fn method_resolution(&self, expr: ExprId) -> Option<Function> {
self.method_resolutions.get(&expr).map(|it| *it)
}
pub fn field_resolution(&self, expr: ExprId) -> Option<StructField> {
self.field_resolutions.get(&expr).map(|it| *it)
}
pub fn assoc_resolutions(&self, id: ExprOrPatId) -> Option<ImplItem> {
self.assoc_resolutions.get(&id).map(|it| *it)
}
}
impl Index<ExprId> for InferenceResult {
type Output = Ty;
fn index(&self, expr: ExprId) -> &Ty {
self.type_of_expr.get(expr).unwrap_or(&Ty::Unknown)
}
}
impl Index<PatId> for InferenceResult {
type Output = Ty;
fn index(&self, pat: PatId) -> &Ty {
self.type_of_pat.get(pat).unwrap_or(&Ty::Unknown)
}
}
/// The inference context contains all information needed during type inference.
#[derive(Clone, Debug)]
struct InferenceContext<'a, D: HirDatabase> {
db: &'a D,
body: Arc<Body>,
resolver: Resolver,
var_unification_table: InPlaceUnificationTable<TypeVarId>,
method_resolutions: FxHashMap<ExprId, Function>,
field_resolutions: FxHashMap<ExprId, StructField>,
assoc_resolutions: FxHashMap<ExprOrPatId, ImplItem>,
type_of_expr: ArenaMap<ExprId, Ty>,
type_of_pat: ArenaMap<PatId, Ty>,
/// The return type of the function being inferred.
return_ty: Ty,
}
impl<'a, D: HirDatabase> InferenceContext<'a, D> {
fn new(db: &'a D, body: Arc<Body>, resolver: Resolver) -> Self {
InferenceContext {
method_resolutions: FxHashMap::default(),
field_resolutions: FxHashMap::default(),
assoc_resolutions: FxHashMap::default(),
type_of_expr: ArenaMap::default(),
type_of_pat: ArenaMap::default(),
var_unification_table: InPlaceUnificationTable::new(),
return_ty: Ty::Unknown, // set in collect_fn_signature
db,
body,
resolver,
}
}
fn resolve_all(mut self) -> InferenceResult {
let mut tv_stack = Vec::new();
let mut expr_types = mem::replace(&mut self.type_of_expr, ArenaMap::default());
for ty in expr_types.values_mut() {
let resolved = self.resolve_ty_completely(&mut tv_stack, mem::replace(ty, Ty::Unknown));
*ty = resolved;
}
let mut pat_types = mem::replace(&mut self.type_of_pat, ArenaMap::default());
for ty in pat_types.values_mut() {
let resolved = self.resolve_ty_completely(&mut tv_stack, mem::replace(ty, Ty::Unknown));
*ty = resolved;
}
InferenceResult {
method_resolutions: self.method_resolutions,
field_resolutions: self.field_resolutions,
assoc_resolutions: self.assoc_resolutions,
type_of_expr: expr_types,
type_of_pat: pat_types,
}
}
fn write_expr_ty(&mut self, expr: ExprId, ty: Ty) {
self.type_of_expr.insert(expr, ty);
}
fn write_method_resolution(&mut self, expr: ExprId, func: Function) {
self.method_resolutions.insert(expr, func);
}
fn write_field_resolution(&mut self, expr: ExprId, field: StructField) {
self.field_resolutions.insert(expr, field);
}
fn write_assoc_resolution(&mut self, id: ExprOrPatId, item: ImplItem) {
self.assoc_resolutions.insert(id, item);
}
fn write_pat_ty(&mut self, pat: PatId, ty: Ty) {
self.type_of_pat.insert(pat, ty);
}
fn make_ty(&mut self, type_ref: &TypeRef) -> Ty {
let ty = Ty::from_hir(
self.db,
// TODO use right resolver for block
&self.resolver,
type_ref,
);
let ty = self.insert_type_vars(ty);
ty
}
fn unify_substs(&mut self, substs1: &Substs, substs2: &Substs, depth: usize) -> bool {
substs1.0.iter().zip(substs2.0.iter()).all(|(t1, t2)| self.unify_inner(t1, t2, depth))
}
fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
self.unify_inner(ty1, ty2, 0)
}
fn unify_inner(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
if depth > 1000 {
// prevent stackoverflows
panic!("infinite recursion in unification");
}
if ty1 == ty2 {
return true;
}
// try to resolve type vars first
let ty1 = self.resolve_ty_shallow(ty1);
let ty2 = self.resolve_ty_shallow(ty2);
match (&*ty1, &*ty2) {
(Ty::Unknown, ..) => true,
(.., Ty::Unknown) => true,
(Ty::Int(t1), Ty::Int(t2)) => match (t1, t2) {
(primitive::UncertainIntTy::Unknown, _)
| (_, primitive::UncertainIntTy::Unknown) => true,
_ => t1 == t2,
},
(Ty::Float(t1), Ty::Float(t2)) => match (t1, t2) {
(primitive::UncertainFloatTy::Unknown, _)
| (_, primitive::UncertainFloatTy::Unknown) => true,
_ => t1 == t2,
},
(Ty::Bool, _) | (Ty::Str, _) | (Ty::Never, _) | (Ty::Char, _) => ty1 == ty2,
(
Ty::Adt { def_id: def_id1, substs: substs1, .. },
Ty::Adt { def_id: def_id2, substs: substs2, .. },
) if def_id1 == def_id2 => self.unify_substs(substs1, substs2, depth + 1),
(Ty::Slice(t1), Ty::Slice(t2)) => self.unify_inner(t1, t2, depth + 1),
(Ty::RawPtr(t1, m1), Ty::RawPtr(t2, m2)) if m1 == m2 => {
self.unify_inner(t1, t2, depth + 1)
}
(Ty::Ref(t1, m1), Ty::Ref(t2, m2)) if m1 == m2 => self.unify_inner(t1, t2, depth + 1),
(Ty::FnPtr(sig1), Ty::FnPtr(sig2)) if sig1 == sig2 => true,
(Ty::Tuple(ts1), Ty::Tuple(ts2)) if ts1.len() == ts2.len() => {
ts1.iter().zip(ts2.iter()).all(|(t1, t2)| self.unify_inner(t1, t2, depth + 1))
}
(Ty::Infer(InferTy::TypeVar(tv1)), Ty::Infer(InferTy::TypeVar(tv2)))
| (Ty::Infer(InferTy::IntVar(tv1)), Ty::Infer(InferTy::IntVar(tv2)))
| (Ty::Infer(InferTy::FloatVar(tv1)), Ty::Infer(InferTy::FloatVar(tv2))) => {
// both type vars are unknown since we tried to resolve them
self.var_unification_table.union(*tv1, *tv2);
true
}
(Ty::Infer(InferTy::TypeVar(tv)), other)
| (other, Ty::Infer(InferTy::TypeVar(tv)))
| (Ty::Infer(InferTy::IntVar(tv)), other)
| (other, Ty::Infer(InferTy::IntVar(tv)))
| (Ty::Infer(InferTy::FloatVar(tv)), other)
| (other, Ty::Infer(InferTy::FloatVar(tv))) => {
// the type var is unknown since we tried to resolve it
self.var_unification_table.union_value(*tv, TypeVarValue::Known(other.clone()));
true
}
_ => false,
}
}
fn new_type_var(&mut self) -> Ty {
Ty::Infer(InferTy::TypeVar(self.var_unification_table.new_key(TypeVarValue::Unknown)))
}
fn new_integer_var(&mut self) -> Ty {
Ty::Infer(InferTy::IntVar(self.var_unification_table.new_key(TypeVarValue::Unknown)))
}
fn new_float_var(&mut self) -> Ty {
Ty::Infer(InferTy::FloatVar(self.var_unification_table.new_key(TypeVarValue::Unknown)))
}
/// Replaces Ty::Unknown by a new type var, so we can maybe still infer it.
fn insert_type_vars_shallow(&mut self, ty: Ty) -> Ty {
match ty {
Ty::Unknown => self.new_type_var(),
Ty::Int(primitive::UncertainIntTy::Unknown) => self.new_integer_var(),
Ty::Float(primitive::UncertainFloatTy::Unknown) => self.new_float_var(),
_ => ty,
}
}
fn insert_type_vars(&mut self, ty: Ty) -> Ty {
ty.fold(&mut |ty| self.insert_type_vars_shallow(ty))
}
/// Resolves the type as far as currently possible, replacing type variables
/// by their known types. All types returned by the infer_* functions should
/// be resolved as far as possible, i.e. contain no type variables with
/// known type.
fn resolve_ty_as_possible(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
ty.fold(&mut |ty| match ty {
Ty::Infer(tv) => {
let inner = tv.to_inner();
if tv_stack.contains(&inner) {
tested_by!(type_var_cycles_resolve_as_possible);
// recursive type
return tv.fallback_value();
}
if let Some(known_ty) = self.var_unification_table.probe_value(inner).known() {
// known_ty may contain other variables that are known by now
tv_stack.push(inner);
let result = self.resolve_ty_as_possible(tv_stack, known_ty.clone());
tv_stack.pop();
result
} else {
ty
}
}
_ => ty,
})
}
/// If `ty` is a type variable with known type, returns that type;
/// otherwise, return ty.
fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
let mut ty = Cow::Borrowed(ty);
// The type variable could resolve to a int/float variable. Hence try
// resolving up to three times; each type of variable shouldn't occur
// more than once
for i in 0..3 {
if i > 0 {
tested_by!(type_var_resolves_to_int_var);
}
match &*ty {
Ty::Infer(tv) => {
let inner = tv.to_inner();
match self.var_unification_table.probe_value(inner).known() {
Some(known_ty) => {
// The known_ty can't be a type var itself
ty = Cow::Owned(known_ty.clone());
}
_ => return ty,
}
}
_ => return ty,
}
}
log::error!("Inference variable still not resolved: {:?}", ty);
ty
}
/// Resolves the type completely; type variables without known type are
/// replaced by Ty::Unknown.
fn resolve_ty_completely(&mut self, tv_stack: &mut Vec<TypeVarId>, ty: Ty) -> Ty {
ty.fold(&mut |ty| match ty {
Ty::Infer(tv) => {
let inner = tv.to_inner();
if tv_stack.contains(&inner) {
tested_by!(type_var_cycles_resolve_completely);
// recursive type
return tv.fallback_value();
}
if let Some(known_ty) = self.var_unification_table.probe_value(inner).known() {
// known_ty may contain other variables that are known by now
tv_stack.push(inner);
let result = self.resolve_ty_completely(tv_stack, known_ty.clone());
tv_stack.pop();
result
} else {
tv.fallback_value()
}
}
_ => ty,
})
}
fn infer_path_expr(&mut self, resolver: &Resolver, path: &Path, id: ExprOrPatId) -> Option<Ty> {
let resolved = resolver.resolve_path_segments(self.db, &path);
let (def, remaining_index) = resolved.into_inner();
log::debug!(
"path {:?} resolved to {:?} with remaining index {:?}",
path,
def,
remaining_index
);
// if the remaining_index is None, we expect the path
// to be fully resolved, in this case we continue with
// the default by attempting to `take_values´ from the resolution.
// Otherwise the path was partially resolved, which means
// we might have resolved into a type for which
// we may find some associated item starting at the
// path.segment pointed to by `remaining_index´
let mut resolved =
if remaining_index.is_none() { def.take_values()? } else { def.take_types()? };
let remaining_index = remaining_index.unwrap_or(path.segments.len());
// resolve intermediate segments
for segment in &path.segments[remaining_index..] {
let ty = match resolved {
Resolution::Def(def) => {
let typable: Option<TypableDef> = def.into();
let typable = typable?;
let substs =
Ty::substs_from_path_segment(self.db, &self.resolver, segment, typable);
self.db.type_for_def(typable, Namespace::Types).apply_substs(substs)
}
Resolution::LocalBinding(_) => {
// can't have a local binding in an associated item path
return None;
}
Resolution::GenericParam(..) => {
// TODO associated item of generic param
return None;
}
Resolution::SelfType(_) => {
// TODO associated item of self type
return None;
}
};
// Attempt to find an impl_item for the type which has a name matching
// the current segment
log::debug!("looking for path segment: {:?}", segment);
let item: crate::ModuleDef = ty.iterate_impl_items(self.db, |item| {
let matching_def: Option<crate::ModuleDef> = match item {
crate::ImplItem::Method(func) => {
let sig = func.signature(self.db);
if segment.name == *sig.name() {
Some(func.into())
} else {
None
}
}
crate::ImplItem::Const(konst) => {
let sig = konst.signature(self.db);
if segment.name == *sig.name() {
Some(konst.into())
} else {
None
}
}
// TODO: Resolve associated types
crate::ImplItem::TypeAlias(_) => None,
};
match matching_def {
Some(_) => {
self.write_assoc_resolution(id, item);
return matching_def;
}
None => None,
}
})?;
resolved = Resolution::Def(item.into());
}
match resolved {
Resolution::Def(def) => {
let typable: Option<TypableDef> = def.into();
let typable = typable?;
let substs = Ty::substs_from_path(self.db, &self.resolver, path, typable);
let ty = self.db.type_for_def(typable, Namespace::Values).apply_substs(substs);
let ty = self.insert_type_vars(ty);
Some(ty)
}
Resolution::LocalBinding(pat) => {
let ty = self.type_of_pat.get(pat)?;
let ty = self.resolve_ty_as_possible(&mut vec![], ty.clone());
Some(ty)
}
Resolution::GenericParam(..) => {
// generic params can't refer to values... yet
None
}
Resolution::SelfType(_) => {
log::error!("path expr {:?} resolved to Self type in values ns", path);
None
}
}
}
fn resolve_variant(&mut self, path: Option<&Path>) -> (Ty, Option<VariantDef>) {
let path = match path {
Some(path) => path,
None => return (Ty::Unknown, None),
};
let resolver = &self.resolver;
let typable: Option<TypableDef> = match resolver.resolve_path(self.db, &path).take_types() {
Some(Resolution::Def(def)) => def.into(),
Some(Resolution::LocalBinding(..)) => {
// this cannot happen
log::error!("path resolved to local binding in type ns");
return (Ty::Unknown, None);
}
Some(Resolution::GenericParam(..)) => {
// generic params can't be used in struct literals
return (Ty::Unknown, None);
}
Some(Resolution::SelfType(..)) => {
// TODO this is allowed in an impl for a struct, handle this
return (Ty::Unknown, None);
}
None => return (Ty::Unknown, None),
};
let def = match typable {
None => return (Ty::Unknown, None),
Some(it) => it,
};
// TODO remove the duplication between here and `Ty::from_path`?
let substs = Ty::substs_from_path(self.db, resolver, path, def);
match def {
TypableDef::Struct(s) => {
let ty = s.ty(self.db);
let ty = self.insert_type_vars(ty.apply_substs(substs));
(ty, Some(s.into()))
}
TypableDef::EnumVariant(var) => {
let ty = var.parent_enum(self.db).ty(self.db);
let ty = self.insert_type_vars(ty.apply_substs(substs));
(ty, Some(var.into()))
}
TypableDef::TypeAlias(_)
| TypableDef::Function(_)
| TypableDef::Enum(_)
| TypableDef::Const(_)
| TypableDef::Static(_) => (Ty::Unknown, None),
}
}
fn infer_tuple_struct_pat(
&mut self,
path: Option<&Path>,
subpats: &[PatId],
expected: &Ty,
) -> Ty {
let (ty, def) = self.resolve_variant(path);
self.unify(&ty, expected);
let substs = ty.substs().unwrap_or_else(Substs::empty);
for (i, &subpat) in subpats.iter().enumerate() {
let expected_ty = def
.and_then(|d| d.field(self.db, &Name::tuple_field_name(i)))
.map_or(Ty::Unknown, |field| field.ty(self.db))
.subst(&substs);
self.infer_pat(subpat, &expected_ty);
}
ty
}
fn infer_struct_pat(&mut self, path: Option<&Path>, subpats: &[FieldPat], expected: &Ty) -> Ty {
let (ty, def) = self.resolve_variant(path);
self.unify(&ty, expected);
let substs = ty.substs().unwrap_or_else(Substs::empty);
for subpat in subpats {
let matching_field = def.and_then(|it| it.field(self.db, &subpat.name));
let expected_ty =
matching_field.map_or(Ty::Unknown, |field| field.ty(self.db)).subst(&substs);
self.infer_pat(subpat.pat, &expected_ty);
}
ty
}
fn infer_pat(&mut self, pat: PatId, expected: &Ty) -> Ty {
let body = Arc::clone(&self.body); // avoid borrow checker problem
let ty = match &body[pat] {
Pat::Tuple(ref args) => {
let expectations = match *expected {
Ty::Tuple(ref tuple_args) => &**tuple_args,
_ => &[],
};
let expectations_iter = expectations.iter().chain(repeat(&Ty::Unknown));
let inner_tys = args
.iter()
.zip(expectations_iter)
.map(|(&pat, ty)| self.infer_pat(pat, ty))
.collect::<Vec<_>>()
.into();
Ty::Tuple(inner_tys)
}
Pat::Ref { pat, mutability } => {
let expectation = match *expected {
Ty::Ref(ref sub_ty, exp_mut) => {
if *mutability != exp_mut {
// TODO: emit type error?
}
&**sub_ty
}
_ => &Ty::Unknown,
};
let subty = self.infer_pat(*pat, expectation);
Ty::Ref(subty.into(), *mutability)
}
Pat::TupleStruct { path: ref p, args: ref subpats } => {
self.infer_tuple_struct_pat(p.as_ref(), subpats, expected)
}
Pat::Struct { path: ref p, args: ref fields } => {
self.infer_struct_pat(p.as_ref(), fields, expected)
}
Pat::Path(path) => {
// TODO use correct resolver for the surrounding expression
let resolver = self.resolver.clone();
self.infer_path_expr(&resolver, &path, pat.into()).unwrap_or(Ty::Unknown)
}
Pat::Bind { mode, name: _name, subpat } => {
let inner_ty = if let Some(subpat) = subpat {
self.infer_pat(*subpat, expected)
} else {
expected.clone()
};
let inner_ty = self.insert_type_vars_shallow(inner_ty);
let bound_ty = match mode {
BindingAnnotation::Ref => Ty::Ref(inner_ty.clone().into(), Mutability::Shared),
BindingAnnotation::RefMut => Ty::Ref(inner_ty.clone().into(), Mutability::Mut),
BindingAnnotation::Mutable | BindingAnnotation::Unannotated => inner_ty.clone(),
};
let bound_ty = self.resolve_ty_as_possible(&mut vec![], bound_ty);
self.write_pat_ty(pat, bound_ty);
return inner_ty;
}
_ => Ty::Unknown,
};
// use a new type variable if we got Ty::Unknown here
let ty = self.insert_type_vars_shallow(ty);
self.unify(&ty, expected);
let ty = self.resolve_ty_as_possible(&mut vec![], ty);
self.write_pat_ty(pat, ty.clone());
ty
}
fn substs_for_method_call(
&mut self,
def_generics: Option<Arc<GenericParams>>,
generic_args: &Option<GenericArgs>,
) -> Substs {
let (parent_param_count, param_count) =
def_generics.map_or((0, 0), |g| (g.count_parent_params(), g.params.len()));
let mut substs = Vec::with_capacity(parent_param_count + param_count);
for _ in 0..parent_param_count {
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 infer_expr(&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::Bool));
let then_ty = self.infer_expr(*then_branch, expected);
match else_branch {
Some(else_branch) => {
self.infer_expr(*else_branch, expected);
}
None => {
// no else branch -> unit
self.unify(&then_ty, &Ty::unit()); // actually coerce
}
};
then_ty
}
Expr::Block { statements, tail } => self.infer_block(statements, *tail, expected),
Expr::Loop { body } => {
self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
// TODO handle break with value
Ty::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::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());
self.infer_pat(*pat, &Ty::Unknown);
self.infer_expr(*body, &Expectation::has_type(Ty::unit()));
Ty::unit()
}
Expr::Lambda { body, args, arg_types } => {
assert_eq!(args.len(), arg_types.len());
for (arg_pat, arg_type) in args.iter().zip(arg_types.iter()) {
let expected = if let Some(type_ref) = arg_type {
let ty = self.make_ty(type_ref);
ty
} else {
Ty::Unknown
};
self.infer_pat(*arg_pat, &expected);
}
// TODO: infer lambda type etc.
let _body_ty = self.infer_expr(*body, &Expectation::none());
Ty::Unknown
}
Expr::Call { callee, args } => {
let callee_ty = self.infer_expr(*callee, &Expectation::none());
let (param_tys, ret_ty) = match &callee_ty {
Ty::FnPtr(sig) => (sig.input.clone(), sig.output.clone()),
Ty::FnDef { substs, sig, .. } => {
let ret_ty = sig.output.clone().subst(&substs);
let param_tys =
sig.input.iter().map(|ty| ty.clone().subst(&substs)).collect();
(param_tys, ret_ty)
}
_ => {
// not callable
// TODO report an error?
(Vec::new(), Ty::Unknown)
}
};
let param_iter = param_tys.into_iter().chain(repeat(Ty::Unknown));
for (arg, param) in args.iter().zip(param_iter) {
self.infer_expr(*arg, &Expectation::has_type(param));
}
ret_ty
}
Expr::MethodCall { receiver, args, method_name, generic_args } => {
let receiver_ty = self.infer_expr(*receiver, &Expectation::none());
let resolved = receiver_ty.clone().lookup_method(self.db, method_name);
let (derefed_receiver_ty, method_ty, def_generics) = match resolved {
Some((ty, func)) => {
self.write_method_resolution(tgt_expr, func);
(
ty,
self.db.type_for_def(func.into(), Namespace::Values),
Some(func.generic_params(self.db)),
)
}
None => (Ty::Unknown, receiver_ty, None),
};
let substs = self.substs_for_method_call(def_generics, generic_args);
let method_ty = method_ty.apply_substs(substs);
let method_ty = self.insert_type_vars(method_ty);
let (expected_receiver_ty, param_tys, ret_ty) = match &method_ty {
Ty::FnPtr(sig) => {
if !sig.input.is_empty() {
(sig.input[0].clone(), sig.input[1..].to_vec(), sig.output.clone())
} else {
(Ty::Unknown, Vec::new(), sig.output.clone())
}
}
Ty::FnDef { substs, sig, .. } => {
let ret_ty = sig.output.clone().subst(&substs);
if !sig.input.is_empty() {
let mut arg_iter = sig.input.iter().map(|ty| ty.clone().subst(&substs));
let receiver_ty = arg_iter.next().unwrap();
(receiver_ty, arg_iter.collect(), ret_ty)
} else {
(Ty::Unknown, Vec::new(), ret_ty)
}
}
_ => (Ty::Unknown, Vec::new(), Ty::Unknown),
};
// Apply autoref so the below unification works correctly
let actual_receiver_ty = match expected_receiver_ty {
Ty::Ref(_, mutability) => Ty::Ref(Arc::new(derefed_receiver_ty), mutability),
_ => derefed_receiver_ty,
};
self.unify(&expected_receiver_ty, &actual_receiver_ty);
let param_iter = param_tys.into_iter().chain(repeat(Ty::Unknown));
for (arg, param) in args.iter().zip(param_iter) {
self.infer_expr(*arg, &Expectation::has_type(param));
}
ret_ty
}
Expr::Match { expr, arms } => {
let expected = if expected.ty == Ty::Unknown {
Expectation::has_type(self.new_type_var())
} else {
expected.clone()
};
let input_ty = self.infer_expr(*expr, &Expectation::none());
for arm in arms {
for &pat in &arm.pats {
let _pat_ty = self.infer_pat(pat, &input_ty);
}
if let Some(guard_expr) = arm.guard {
self.infer_expr(guard_expr, &Expectation::has_type(Ty::Bool));
}
self.infer_expr(arm.expr, &expected);
}
expected.ty
}
Expr::Path(p) => {
// TODO this could be more efficient...
let resolver = expr::resolver_for_expr(self.body.clone(), self.db, tgt_expr);
self.infer_path_expr(&resolver, p, tgt_expr.into()).unwrap_or(Ty::Unknown)
}
Expr::Continue => Ty::Never,
Expr::Break { expr } => {
if let Some(expr) = expr {
// TODO handle break with value
self.infer_expr(*expr, &Expectation::none());
}
Ty::Never
}
Expr::Return { expr } => {
if let Some(expr) = expr {
self.infer_expr(*expr, &Expectation::has_type(self.return_ty.clone()));
}
Ty::Never
}
Expr::StructLit { path, fields, spread } => {
let (ty, def_id) = self.resolve_variant(path.as_ref());
let substs = ty.substs().unwrap_or_else(Substs::empty);
for field in fields {
let field_ty = def_id
.and_then(|it| it.field(self.db, &field.name))
.map_or(Ty::Unknown, |field| field.ty(self.db))
.subst(&substs);
self.infer_expr(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 ty = receiver_ty
.autoderef(self.db)
.find_map(|derefed_ty| match derefed_ty {
Ty::Tuple(fields) => {
let i = name.to_string().parse::<usize>().ok();
i.and_then(|i| fields.get(i).cloned())
}
Ty::Adt { def_id: AdtDef::Struct(s), ref substs, .. } => {
s.field(self.db, name).map(|field| {
self.write_field_resolution(tgt_expr, field);
field.ty(self.db).subst(substs)
})
}
_ => None,
})
.unwrap_or(Ty::Unknown);
self.insert_type_vars(ty)
}
Expr::Try { expr } => {
let _inner_ty = self.infer_expr(*expr, &Expectation::none());
Ty::Unknown
}
Expr::Cast { expr, type_ref } => {
let _inner_ty = self.infer_expr(*expr, &Expectation::none());
let cast_ty = self.make_ty(type_ref);
// TODO check the cast...
cast_ty
}
Expr::Ref { expr, mutability } => {
let expectation = if let Ty::Ref(ref subty, expected_mutability) = expected.ty {
if expected_mutability == Mutability::Mut && *mutability == Mutability::Shared {
// TODO: throw type error - expected mut reference but found shared ref,
// which cannot be coerced
}
Expectation::has_type((**subty).clone())
} else {
Expectation::none()
};
// TODO reference coercions etc.
let inner_ty = self.infer_expr(*expr, &expectation);
Ty::Ref(Arc::new(inner_ty), *mutability)
}
Expr::UnaryOp { expr, op } => {
let inner_ty = self.infer_expr(*expr, &Expectation::none());
match op {
UnaryOp::Deref => {
if let Some(derefed_ty) = inner_ty.builtin_deref() {
derefed_ty
} else {
// TODO Deref::deref
Ty::Unknown
}
}
UnaryOp::Neg => {
match inner_ty {
Ty::Int(primitive::UncertainIntTy::Unknown)
| Ty::Int(primitive::UncertainIntTy::Signed(..))
| Ty::Infer(InferTy::IntVar(..))
| Ty::Infer(InferTy::FloatVar(..))
| Ty::Float(..) => inner_ty,
// TODO: resolve ops::Neg trait
_ => Ty::Unknown,
}
}
UnaryOp::Not => {
match inner_ty {
Ty::Bool | Ty::Int(_) | Ty::Infer(InferTy::IntVar(..)) => inner_ty,
// TODO: resolve ops::Not trait for inner_ty
_ => Ty::Unknown,
}
}
}
}
Expr::BinaryOp { lhs, rhs, op } => match op {
Some(op) => {
let lhs_expectation = match op {
BinaryOp::BooleanAnd | BinaryOp::BooleanOr => {
Expectation::has_type(Ty::Bool)
}
_ => Expectation::none(),
};
let lhs_ty = self.infer_expr(*lhs, &lhs_expectation);
// TODO: 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));
// TODO: similar as above, return ty is often associated trait type
op::binary_op_return_ty(*op, rhs_ty)
}
_ => Ty::Unknown,
},
Expr::Tuple { exprs } => {
let mut ty_vec = Vec::with_capacity(exprs.len());
for arg in exprs.iter() {
ty_vec.push(self.infer_expr(*arg, &Expectation::none()));
}
Ty::Tuple(Arc::from(ty_vec))
}
Expr::Array { exprs } => {
let elem_ty = match &expected.ty {
Ty::Slice(inner) | Ty::Array(inner) => Ty::clone(&inner),
_ => self.new_type_var(),
};
for expr in exprs.iter() {
self.infer_expr(*expr, &Expectation::has_type(elem_ty.clone()));
}
Ty::Array(Arc::new(elem_ty))
}
Expr::Literal(lit) => match lit {
Literal::Bool(..) => Ty::Bool,
Literal::String(..) => Ty::Ref(Arc::new(Ty::Str), Mutability::Shared),
Literal::ByteString(..) => {
let byte_type = Arc::new(Ty::Int(primitive::UncertainIntTy::Unsigned(
primitive::UintTy::U8,
)));
let slice_type = Arc::new(Ty::Slice(byte_type));
Ty::Ref(slice_type, Mutability::Shared)
}
Literal::Char(..) => Ty::Char,
Literal::Int(_v, ty) => Ty::Int(*ty),
Literal::Float(_v, ty) => Ty::Float(*ty),
},
};
// use a new type variable if we got Ty::Unknown here
let ty = self.insert_type_vars_shallow(ty);
self.unify(&ty, &expected.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 {
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);
let decl_ty = self.insert_type_vars(decl_ty);
let ty = if let Some(expr) = initializer {
let expr_ty = self.infer_expr(*expr, &Expectation::has_type(decl_ty));
expr_ty
} else {
decl_ty
};
self.infer_pat(*pat, &ty);
}
Statement::Expr(expr) => {
self.infer_expr(*expr, &Expectation::none());
}
}
}
let ty = if let Some(expr) = tail { self.infer_expr(expr, expected) } else { Ty::unit() };
ty
}
fn collect_fn_signature(&mut self, signature: &FnSignature) {
let body = Arc::clone(&self.body); // avoid borrow checker problem
for (type_ref, pat) in signature.params().iter().zip(body.params()) {
let ty = self.make_ty(type_ref);
self.infer_pat(*pat, &ty);
}
self.return_ty = self.make_ty(signature.ret_type());
}
fn infer_body(&mut self) {
self.infer_expr(self.body.body_expr(), &Expectation::has_type(self.return_ty.clone()));
}
}
/// The ID of a type variable.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
pub struct TypeVarId(u32);
impl UnifyKey for TypeVarId {
type Value = TypeVarValue;
fn index(&self) -> u32 {
self.0
}
fn from_index(i: u32) -> Self {
TypeVarId(i)
}
fn tag() -> &'static str {
"TypeVarId"
}
}
/// The value of a type variable: either we already know the type, or we don't
/// know it yet.
#[derive(Clone, PartialEq, Eq, Debug)]
pub enum TypeVarValue {
Known(Ty),
Unknown,
}
impl TypeVarValue {
fn known(&self) -> Option<&Ty> {
match self {
TypeVarValue::Known(ty) => Some(ty),
TypeVarValue::Unknown => None,
}
}
}
impl UnifyValue for TypeVarValue {
type Error = NoError;
fn unify_values(value1: &Self, value2: &Self) -> Result<Self, NoError> {
match (value1, value2) {
// We should never equate two type variables, both of which have
// known types. Instead, we recursively equate those types.
(TypeVarValue::Known(t1), TypeVarValue::Known(t2)) => panic!(
"equating two type variables, both of which have known types: {:?} and {:?}",
t1, t2
),
// If one side is known, prefer that one.
(TypeVarValue::Known(..), TypeVarValue::Unknown) => Ok(value1.clone()),
(TypeVarValue::Unknown, TypeVarValue::Known(..)) => Ok(value2.clone()),
(TypeVarValue::Unknown, TypeVarValue::Unknown) => Ok(TypeVarValue::Unknown),
}
}
}
/// The kinds of placeholders we need during type inference. There's separate
/// values for general types, and for integer and float variables. The latter
/// two are used for inference of literal values (e.g. `100` could be one of
/// several integer types).
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
pub enum InferTy {
TypeVar(TypeVarId),
IntVar(TypeVarId),
FloatVar(TypeVarId),
}
impl InferTy {
fn to_inner(self) -> TypeVarId {
match self {
InferTy::TypeVar(ty) | InferTy::IntVar(ty) | InferTy::FloatVar(ty) => ty,
}
}
fn fallback_value(self) -> Ty {
match self {
InferTy::TypeVar(..) => Ty::Unknown,
InferTy::IntVar(..) => {
Ty::Int(primitive::UncertainIntTy::Signed(primitive::IntTy::I32))
}
InferTy::FloatVar(..) => {
Ty::Float(primitive::UncertainFloatTy::Known(primitive::FloatTy::F64))
}
}
}
}
/// When inferring an expression, we propagate downward whatever type hint we
/// are able in the form of an `Expectation`.
#[derive(Clone, PartialEq, Eq, Debug)]
struct Expectation {
ty: Ty,
// TODO: In some cases, we need to be aware whether the expectation is that
// the type match exactly what we passed, or whether it just needs to be
// coercible to the expected type. See Expectation::rvalue_hint in rustc.
}
impl Expectation {
/// The expectation that the type of the expression needs to equal the given
/// type.
fn has_type(ty: Ty) -> Self {
Expectation { ty }
}
/// This expresses no expectation on the type.
fn none() -> Self {
Expectation { ty: Ty::Unknown }
}
}
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