1 files changed, 180 insertions, 0 deletions

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
+    }
+}