3 files changed, 1174 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/infer/coerce.rs b/crates/ra_hir/src/ty/infer/coerce.rs
new file mode 100644
index 000000000..0429a9866
--- /dev/null
+++ b/crates/ra_hir/src/ty/infer/coerce.rs
@@ -0,0 +1,336 @@
+//! Coercion logic. Coercions are certain type conversions that can implicitly
+//! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions
+//! like going from `&Vec<T>` to `&[T]`.
+//!
+//! See: https://doc.rust-lang.org/nomicon/coercions.html
+
+use rustc_hash::FxHashMap;
+
+use test_utils::tested_by;
+
+use super::{InferTy, InferenceContext, TypeVarValue};
+use crate::{
+    db::HirDatabase,
+    lang_item::LangItemTarget,
+    resolve::Resolver,
+    ty::{autoderef, Substs, Ty, TypeCtor, TypeWalk},
+    type_ref::Mutability,
+    Adt,
+};
+
+impl<'a, D: HirDatabase> InferenceContext<'a, D> {
+    /// Unify two types, but may coerce the first one to the second one
+    /// using "implicit coercion rules" if needed.
+    pub(super) fn coerce(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool {
+        let from_ty = self.resolve_ty_shallow(from_ty).into_owned();
+        let to_ty = self.resolve_ty_shallow(to_ty);
+        self.coerce_inner(from_ty, &to_ty)
+    }
+
+    /// Merge two types from different branches, with possible implicit coerce.
+    ///
+    /// Note that it is only possible that one type are coerced to another.
+    /// Coercing both types to another least upper bound type is not possible in rustc,
+    /// which will simply result in "incompatible types" error.
+    pub(super) fn coerce_merge_branch<'t>(&mut self, ty1: &Ty, ty2: &Ty) -> Ty {
+        if self.coerce(ty1, ty2) {
+            ty2.clone()
+        } else if self.coerce(ty2, ty1) {
+            ty1.clone()
+        } else {
+            tested_by!(coerce_merge_fail_fallback);
+            // For incompatible types, we use the latter one as result
+            // to be better recovery for `if` without `else`.
+            ty2.clone()
+        }
+    }
+
+    pub(super) fn init_coerce_unsized_map(
+        db: &'a D,
+        resolver: &Resolver,
+    ) -> FxHashMap<(TypeCtor, TypeCtor), usize> {
+        let krate = resolver.krate().unwrap();
+        let impls = match db.lang_item(krate, "coerce_unsized".into()) {
+            Some(LangItemTarget::Trait(trait_)) => db.impls_for_trait(krate, trait_),
+            _ => return FxHashMap::default(),
+        };
+
+        impls
+            .iter()
+            .filter_map(|impl_block| {
+                // `CoerseUnsized` has one generic parameter for the target type.
+                let trait_ref = impl_block.target_trait_ref(db)?;
+                let cur_from_ty = trait_ref.substs.0.get(0)?;
+                let cur_to_ty = trait_ref.substs.0.get(1)?;
+
+                match (&cur_from_ty, cur_to_ty) {
+                    (ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => {
+                        // FIXME: We return the first non-equal bound as the type parameter to coerce to unsized type.
+                        // This works for smart-pointer-like coercion, which covers all impls from std.
+                        st1.iter().zip(st2.iter()).enumerate().find_map(|(i, (ty1, ty2))| {
+                            match (ty1, ty2) {
+                                (Ty::Param { idx: p1, .. }, Ty::Param { idx: p2, .. })
+                                    if p1 != p2 =>
+                                {
+                                    Some(((*ctor1, *ctor2), i))
+                                }
+                                _ => None,
+                            }
+                        })
+                    }
+                    _ => None,
+                }
+            })
+            .collect()
+    }
+
+    fn coerce_inner(&mut self, mut from_ty: Ty, to_ty: &Ty) -> bool {
+        match (&from_ty, to_ty) {
+            // Never type will make type variable to fallback to Never Type instead of Unknown.
+            (ty_app!(TypeCtor::Never), Ty::Infer(InferTy::TypeVar(tv))) => {
+                let var = self.new_maybe_never_type_var();
+                self.var_unification_table.union_value(*tv, TypeVarValue::Known(var));
+                return true;
+            }
+            (ty_app!(TypeCtor::Never), _) => return true,
+
+            // Trivial cases, this should go after `never` check to
+            // avoid infer result type to be never
+            _ => {
+                if self.unify_inner_trivial(&from_ty, &to_ty) {
+                    return true;
+                }
+            }
+        }
+
+        // Pointer weakening and function to pointer
+        match (&mut from_ty, to_ty) {
+            // `*mut T`, `&mut T, `&T`` -> `*const T`
+            // `&mut T` -> `&T`
+            // `&mut T` -> `*mut T`
+            (ty_app!(c1@TypeCtor::RawPtr(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared)))
+            | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::RawPtr(Mutability::Shared)))
+            | (ty_app!(c1@TypeCtor::Ref(_)), ty_app!(c2@TypeCtor::Ref(Mutability::Shared)))
+            | (ty_app!(c1@TypeCtor::Ref(Mutability::Mut)), ty_app!(c2@TypeCtor::RawPtr(_))) => {
+                *c1 = *c2;
+            }
+
+            // Illegal mutablity conversion
+            (
+                ty_app!(TypeCtor::RawPtr(Mutability::Shared)),
+                ty_app!(TypeCtor::RawPtr(Mutability::Mut)),
+            )
+            | (
+                ty_app!(TypeCtor::Ref(Mutability::Shared)),
+                ty_app!(TypeCtor::Ref(Mutability::Mut)),
+            ) => return false,
+
+            // `{function_type}` -> `fn()`
+            (ty_app!(TypeCtor::FnDef(_)), ty_app!(TypeCtor::FnPtr { .. })) => {
+                match from_ty.callable_sig(self.db) {
+                    None => return false,
+                    Some(sig) => {
+                        let num_args = sig.params_and_return.len() as u16 - 1;
+                        from_ty =
+                            Ty::apply(TypeCtor::FnPtr { num_args }, Substs(sig.params_and_return));
+                    }
+                }
+            }
+
+            _ => {}
+        }
+
+        if let Some(ret) = self.try_coerce_unsized(&from_ty, &to_ty) {
+            return ret;
+        }
+
+        // Auto Deref if cannot coerce
+        match (&from_ty, to_ty) {
+            // FIXME: DerefMut
+            (ty_app!(TypeCtor::Ref(_), st1), ty_app!(TypeCtor::Ref(_), st2)) => {
+                self.unify_autoderef_behind_ref(&st1[0], &st2[0])
+            }
+
+            // Otherwise, normal unify
+            _ => self.unify(&from_ty, to_ty),
+        }
+    }
+
+    /// Coerce a type using `from_ty: CoerceUnsized<ty_ty>`
+    ///
+    /// See: https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html
+    fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> Option<bool> {
+        let (ctor1, st1, ctor2, st2) = match (from_ty, to_ty) {
+            (ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => (ctor1, st1, ctor2, st2),
+            _ => return None,
+        };
+
+        let coerce_generic_index = *self.coerce_unsized_map.get(&(*ctor1, *ctor2))?;
+
+        // Check `Unsize` first
+        match self.check_unsize_and_coerce(
+            st1.0.get(coerce_generic_index)?,
+            st2.0.get(coerce_generic_index)?,
+            0,
+        ) {
+            Some(true) => {}
+            ret => return ret,
+        }
+
+        let ret = st1
+            .iter()
+            .zip(st2.iter())
+            .enumerate()
+            .filter(|&(idx, _)| idx != coerce_generic_index)
+            .all(|(_, (ty1, ty2))| self.unify(ty1, ty2));
+
+        Some(ret)
+    }
+
+    /// Check if `from_ty: Unsize<to_ty>`, and coerce to `to_ty` if it holds.
+    ///
+    /// It should not be directly called. It is only used by `try_coerce_unsized`.
+    ///
+    /// See: https://doc.rust-lang.org/nightly/std/marker/trait.Unsize.html
+    fn check_unsize_and_coerce(&mut self, from_ty: &Ty, to_ty: &Ty, depth: usize) -> Option<bool> {
+        if depth > 1000 {
+            panic!("Infinite recursion in coercion");
+        }
+
+        match (&from_ty, &to_ty) {
+            // `[T; N]` -> `[T]`
+            (ty_app!(TypeCtor::Array, st1), ty_app!(TypeCtor::Slice, st2)) => {
+                Some(self.unify(&st1[0], &st2[0]))
+            }
+
+            // `T` -> `dyn Trait` when `T: Trait`
+            (_, Ty::Dyn(_)) => {
+                // FIXME: Check predicates
+                Some(true)
+            }
+
+            // `(..., T)` -> `(..., U)` when `T: Unsize<U>`
+            (
+                ty_app!(TypeCtor::Tuple { cardinality: len1 }, st1),
+                ty_app!(TypeCtor::Tuple { cardinality: len2 }, st2),
+            ) => {
+                if len1 != len2 || *len1 == 0 {
+                    return None;
+                }
+
+                match self.check_unsize_and_coerce(
+                    st1.last().unwrap(),
+                    st2.last().unwrap(),
+                    depth + 1,
+                ) {
+                    Some(true) => {}
+                    ret => return ret,
+                }
+
+                let ret = st1[..st1.len() - 1]
+                    .iter()
+                    .zip(&st2[..st2.len() - 1])
+                    .all(|(ty1, ty2)| self.unify(ty1, ty2));
+
+                Some(ret)
+            }
+
+            // Foo<..., T, ...> is Unsize<Foo<..., U, ...>> if:
+            // - T: Unsize<U>
+            // - Foo is a struct
+            // - Only the last field of Foo has a type involving T
+            // - T is not part of the type of any other fields
+            // - Bar<T>: Unsize<Bar<U>>, if the last field of Foo has type Bar<T>
+            (
+                ty_app!(TypeCtor::Adt(Adt::Struct(struct1)), st1),
+                ty_app!(TypeCtor::Adt(Adt::Struct(struct2)), st2),
+            ) if struct1 == struct2 => {
+                let fields = struct1.fields(self.db);
+                let (last_field, prev_fields) = fields.split_last()?;
+
+                // Get the generic parameter involved in the last field.
+                let unsize_generic_index = {
+                    let mut index = None;
+                    let mut multiple_param = false;
+                    last_field.ty(self.db).walk(&mut |ty| match ty {
+                        &Ty::Param { idx, .. } => {
+                            if index.is_none() {
+                                index = Some(idx);
+                            } else if Some(idx) != index {
+                                multiple_param = true;
+                            }
+                        }
+                        _ => {}
+                    });
+
+                    if multiple_param {
+                        return None;
+                    }
+                    index?
+                };
+
+                // Check other fields do not involve it.
+                let mut multiple_used = false;
+                prev_fields.iter().for_each(|field| {
+                    field.ty(self.db).walk(&mut |ty| match ty {
+                        &Ty::Param { idx, .. } if idx == unsize_generic_index => {
+                            multiple_used = true
+                        }
+                        _ => {}
+                    })
+                });
+                if multiple_used {
+                    return None;
+                }
+
+                let unsize_generic_index = unsize_generic_index as usize;
+
+                // Check `Unsize` first
+                match self.check_unsize_and_coerce(
+                    st1.get(unsize_generic_index)?,
+                    st2.get(unsize_generic_index)?,
+                    depth + 1,
+                ) {
+                    Some(true) => {}
+                    ret => return ret,
+                }
+
+                // Then unify other parameters
+                let ret = st1
+                    .iter()
+                    .zip(st2.iter())
+                    .enumerate()
+                    .filter(|&(idx, _)| idx != unsize_generic_index)
+                    .all(|(_, (ty1, ty2))| self.unify(ty1, ty2));
+
+                Some(ret)
+            }
+
+            _ => None,
+        }
+    }
+
+    /// Unify `from_ty` to `to_ty` with optional auto Deref
+    ///
+    /// Note that the parameters are already stripped the outer reference.
+    fn unify_autoderef_behind_ref(&mut self, from_ty: &Ty, to_ty: &Ty) -> bool {
+        let canonicalized = self.canonicalizer().canonicalize_ty(from_ty.clone());
+        let to_ty = self.resolve_ty_shallow(&to_ty);
+        // FIXME: Auto DerefMut
+        for derefed_ty in
+            autoderef::autoderef(self.db, &self.resolver.clone(), canonicalized.value.clone())
+        {
+            let derefed_ty = canonicalized.decanonicalize_ty(derefed_ty.value);
+            match (&*self.resolve_ty_shallow(&derefed_ty), &*to_ty) {
+                // Stop when constructor matches.
+                (ty_app!(from_ctor, st1), ty_app!(to_ctor, st2)) if from_ctor == to_ctor => {
+                    // It will not recurse to `coerce`.
+                    return self.unify_substs(st1, st2, 0);
+                }
+                _ => {}
+            }
+        }
+
+        false
+    }
+}
diff --git a/crates/ra_hir/src/ty/infer/expr.rs b/crates/ra_hir/src/ty/infer/expr.rs
new file mode 100644
index 000000000..f8807c742
--- /dev/null
+++ b/crates/ra_hir/src/ty/infer/expr.rs
@@ -0,0 +1,658 @@
+//! Type inference for expressions.
+
+use std::iter::{repeat, repeat_with};
+use std::sync::Arc;
+
+use super::{BindingMode, Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch};
+use crate::{
+    db::HirDatabase,
+    expr::{self, Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
+    generics::{GenericParams, HasGenericParams},
+    name,
+    nameres::Namespace,
+    path::{GenericArg, GenericArgs},
+    ty::{
+        autoderef, method_resolution, op, primitive, CallableDef, InferTy, Mutability, Obligation,
+        ProjectionPredicate, ProjectionTy, Substs, TraitRef, Ty, TypeCtor, TypeWalk,
+    },
+    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.body.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, &param_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.body.clone(), self.db, 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(primitive::UncertainIntTy::Unknown)
+                                | TypeCtor::Int(primitive::UncertainIntTy::Known(
+                                    primitive::IntTy {
+                                        signedness: primitive::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(
+                                primitive::UncertainIntTy::Known(primitive::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(primitive::UncertainIntTy::Known(
+                        primitive::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)),
+                Literal::Float(_v, ty) => Ty::simple(TypeCtor::Float(*ty)),
+            },
+        };
+        // 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, &param_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(_) => {}
+                }
+            }
+        }
+    }
+}
diff --git a/crates/ra_hir/src/ty/infer/pat.rs b/crates/ra_hir/src/ty/infer/pat.rs
new file mode 100644
index 000000000..c125ddfbc
--- /dev/null
+++ b/crates/ra_hir/src/ty/infer/pat.rs
@@ -0,0 +1,180 @@
+//! Type inference for patterns.
+
+use std::iter::repeat;
+use std::sync::Arc;
+
+use test_utils::tested_by;
+
+use super::{BindingMode, InferenceContext};
+use crate::{
+    db::HirDatabase,
+    expr::{BindingAnnotation, Pat, PatId, RecordFieldPat},
+    ty::{Mutability, Substs, Ty, TypeCtor, TypeWalk},
+    Name, Path,
+};
+
+impl<'a, D: HirDatabase> InferenceContext<'a, D> {
+    fn infer_tuple_struct_pat(
+        &mut self,
+        path: Option<&Path>,
+        subpats: &[PatId],
+        expected: &Ty,
+        default_bm: BindingMode,
+    ) -> 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::new_tuple_field(i)))
+                .map_or(Ty::Unknown, |field| field.ty(self.db))
+                .subst(&substs);
+            let expected_ty = self.normalize_associated_types_in(expected_ty);
+            self.infer_pat(subpat, &expected_ty, default_bm);
+        }
+
+        ty
+    }
+
+    fn infer_record_pat(
+        &mut self,
+        path: Option<&Path>,
+        subpats: &[RecordFieldPat],
+        expected: &Ty,
+        default_bm: BindingMode,
+        id: PatId,
+    ) -> Ty {
+        let (ty, def) = self.resolve_variant(path);
+        if let Some(variant) = def {
+            self.write_variant_resolution(id.into(), variant);
+        }
+
+        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);
+            let expected_ty = self.normalize_associated_types_in(expected_ty);
+            self.infer_pat(subpat.pat, &expected_ty, default_bm);
+        }
+
+        ty
+    }
+
+    pub(super) fn infer_pat(
+        &mut self,
+        pat: PatId,
+        mut expected: &Ty,
+        mut default_bm: BindingMode,
+    ) -> Ty {
+        let body = Arc::clone(&self.body); // avoid borrow checker problem
+
+        let is_non_ref_pat = match &body[pat] {
+            Pat::Tuple(..)
+            | Pat::TupleStruct { .. }
+            | Pat::Record { .. }
+            | Pat::Range { .. }
+            | Pat::Slice { .. } => true,
+            // FIXME: Path/Lit might actually evaluate to ref, but inference is unimplemented.
+            Pat::Path(..) | Pat::Lit(..) => true,
+            Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Missing => false,
+        };
+        if is_non_ref_pat {
+            while let Some((inner, mutability)) = expected.as_reference() {
+                expected = inner;
+                default_bm = match default_bm {
+                    BindingMode::Move => BindingMode::Ref(mutability),
+                    BindingMode::Ref(Mutability::Shared) => BindingMode::Ref(Mutability::Shared),
+                    BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
+                }
+            }
+        } else if let Pat::Ref { .. } = &body[pat] {
+            tested_by!(match_ergonomics_ref);
+            // When you encounter a `&pat` pattern, reset to Move.
+            // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
+            default_bm = BindingMode::Move;
+        }
+
+        // Lose mutability.
+        let default_bm = default_bm;
+        let expected = expected;
+
+        let ty = match &body[pat] {
+            Pat::Tuple(ref args) => {
+                let expectations = match expected.as_tuple() {
+                    Some(parameters) => &*parameters.0,
+                    _ => &[],
+                };
+                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, default_bm))
+                    .collect();
+
+                Ty::apply(TypeCtor::Tuple { cardinality: args.len() as u16 }, Substs(inner_tys))
+            }
+            Pat::Ref { pat, mutability } => {
+                let expectation = match expected.as_reference() {
+                    Some((inner_ty, exp_mut)) => {
+                        if *mutability != exp_mut {
+                            // FIXME: emit type error?
+                        }
+                        inner_ty
+                    }
+                    _ => &Ty::Unknown,
+                };
+                let subty = self.infer_pat(*pat, expectation, default_bm);
+                Ty::apply_one(TypeCtor::Ref(*mutability), subty)
+            }
+            Pat::TupleStruct { path: p, args: subpats } => {
+                self.infer_tuple_struct_pat(p.as_ref(), subpats, expected, default_bm)
+            }
+            Pat::Record { path: p, args: fields } => {
+                self.infer_record_pat(p.as_ref(), fields, expected, default_bm, pat)
+            }
+            Pat::Path(path) => {
+                // FIXME use correct resolver for the surrounding expression
+                let resolver = self.resolver.clone();
+                self.infer_path(&resolver, &path, pat.into()).unwrap_or(Ty::Unknown)
+            }
+            Pat::Bind { mode, name: _, subpat } => {
+                let mode = if mode == &BindingAnnotation::Unannotated {
+                    default_bm
+                } else {
+                    BindingMode::convert(*mode)
+                };
+                let inner_ty = if let Some(subpat) = subpat {
+                    self.infer_pat(*subpat, expected, default_bm)
+                } else {
+                    expected.clone()
+                };
+                let inner_ty = self.insert_type_vars_shallow(inner_ty);
+
+                let bound_ty = match mode {
+                    BindingMode::Ref(mutability) => {
+                        Ty::apply_one(TypeCtor::Ref(mutability), inner_ty.clone())
+                    }
+                    BindingMode::Move => 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
+    }
+}