1 files changed, 268 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/infer/path.rs b/crates/ra_hir_ty/src/infer/path.rs
new file mode 100644
index 000000000..14be66836
--- /dev/null
+++ b/crates/ra_hir_ty/src/infer/path.rs
@@ -0,0 +1,268 @@
+//! Path expression resolution.
+
+use hir_def::{
+    path::{Path, PathKind, PathSegment},
+    resolver::{ResolveValueResult, Resolver, TypeNs, ValueNs},
+    AssocItemId, ContainerId, Lookup,
+};
+use hir_expand::name::Name;
+
+use crate::{db::HirDatabase, method_resolution, Substs, Ty, TypeWalk, ValueTyDefId};
+
+use super::{ExprOrPatId, InferenceContext, TraitRef};
+
+impl<'a, D: HirDatabase> InferenceContext<'a, D> {
+    pub(super) fn infer_path(
+        &mut self,
+        resolver: &Resolver,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<Ty> {
+        let ty = self.resolve_value_path(resolver, path, id)?;
+        let ty = self.insert_type_vars(ty);
+        let ty = self.normalize_associated_types_in(ty);
+        Some(ty)
+    }
+
+    fn resolve_value_path(
+        &mut self,
+        resolver: &Resolver,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<Ty> {
+        let (value, self_subst) = if let PathKind::Type(type_ref) = &path.kind {
+            if path.segments.is_empty() {
+                // This can't actually happen syntax-wise
+                return None;
+            }
+            let ty = self.make_ty(type_ref);
+            let remaining_segments_for_ty = &path.segments[..path.segments.len() - 1];
+            let ty = Ty::from_type_relative_path(self.db, resolver, ty, remaining_segments_for_ty);
+            self.resolve_ty_assoc_item(
+                ty,
+                &path.segments.last().expect("path had at least one segment").name,
+                id,
+            )?
+        } else {
+            let value_or_partial = resolver.resolve_path_in_value_ns(self.db, &path)?;
+
+            match value_or_partial {
+                ResolveValueResult::ValueNs(it) => (it, None),
+                ResolveValueResult::Partial(def, remaining_index) => {
+                    self.resolve_assoc_item(def, path, remaining_index, id)?
+                }
+            }
+        };
+
+        let typable: ValueTyDefId = match value {
+            ValueNs::LocalBinding(pat) => {
+                let ty = self.result.type_of_pat.get(pat)?.clone();
+                let ty = self.resolve_ty_as_possible(&mut vec![], ty);
+                return Some(ty);
+            }
+            ValueNs::FunctionId(it) => it.into(),
+            ValueNs::ConstId(it) => it.into(),
+            ValueNs::StaticId(it) => it.into(),
+            ValueNs::StructId(it) => it.into(),
+            ValueNs::EnumVariantId(it) => it.into(),
+        };
+
+        let mut ty = self.db.value_ty(typable);
+        if let Some(self_subst) = self_subst {
+            ty = ty.subst(&self_subst);
+        }
+        let substs = Ty::substs_from_path(self.db, &self.resolver, path, typable);
+        let ty = ty.subst(&substs);
+        Some(ty)
+    }
+
+    fn resolve_assoc_item(
+        &mut self,
+        def: TypeNs,
+        path: &Path,
+        remaining_index: usize,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        assert!(remaining_index < path.segments.len());
+        // there may be more intermediate segments between the resolved one and
+        // the end. Only the last segment needs to be resolved to a value; from
+        // the segments before that, we need to get either a type or a trait ref.
+
+        let resolved_segment = &path.segments[remaining_index - 1];
+        let remaining_segments = &path.segments[remaining_index..];
+        let is_before_last = remaining_segments.len() == 1;
+
+        match (def, is_before_last) {
+            (TypeNs::TraitId(trait_), true) => {
+                let segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+                let trait_ref = TraitRef::from_resolved_path(
+                    self.db,
+                    &self.resolver,
+                    trait_.into(),
+                    resolved_segment,
+                    None,
+                );
+                self.resolve_trait_assoc_item(trait_ref, segment, id)
+            }
+            (def, _) => {
+                // Either we already have a type (e.g. `Vec::new`), or we have a
+                // trait but it's not the last segment, so the next segment
+                // should resolve to an associated type of that trait (e.g. `<T
+                // as Iterator>::Item::default`)
+                let remaining_segments_for_ty = &remaining_segments[..remaining_segments.len() - 1];
+                let ty = Ty::from_partly_resolved_hir_path(
+                    self.db,
+                    &self.resolver,
+                    def,
+                    resolved_segment,
+                    remaining_segments_for_ty,
+                );
+                if let Ty::Unknown = ty {
+                    return None;
+                }
+
+                let ty = self.insert_type_vars(ty);
+                let ty = self.normalize_associated_types_in(ty);
+
+                let segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+
+                self.resolve_ty_assoc_item(ty, &segment.name, id)
+            }
+        }
+    }
+
+    fn resolve_trait_assoc_item(
+        &mut self,
+        trait_ref: TraitRef,
+        segment: &PathSegment,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        let trait_ = trait_ref.trait_;
+        let item = self
+            .db
+            .trait_data(trait_)
+            .items
+            .iter()
+            .map(|(_name, id)| (*id).into())
+            .find_map(|item| match item {
+                AssocItemId::FunctionId(func) => {
+                    if segment.name == self.db.function_data(func).name {
+                        Some(AssocItemId::FunctionId(func))
+                    } else {
+                        None
+                    }
+                }
+
+                AssocItemId::ConstId(konst) => {
+                    if self.db.const_data(konst).name.as_ref().map_or(false, |n| n == &segment.name)
+                    {
+                        Some(AssocItemId::ConstId(konst))
+                    } else {
+                        None
+                    }
+                }
+                AssocItemId::TypeAliasId(_) => None,
+            })?;
+        let def = match item {
+            AssocItemId::FunctionId(f) => ValueNs::FunctionId(f),
+            AssocItemId::ConstId(c) => ValueNs::ConstId(c),
+            AssocItemId::TypeAliasId(_) => unreachable!(),
+        };
+        let substs = Substs::build_for_def(self.db, item)
+            .use_parent_substs(&trait_ref.substs)
+            .fill_with_params()
+            .build();
+
+        self.write_assoc_resolution(id, item);
+        Some((def, Some(substs)))
+    }
+
+    fn resolve_ty_assoc_item(
+        &mut self,
+        ty: Ty,
+        name: &Name,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        if let Ty::Unknown = ty {
+            return None;
+        }
+
+        let canonical_ty = self.canonicalizer().canonicalize_ty(ty.clone());
+
+        method_resolution::iterate_method_candidates(
+            &canonical_ty.value,
+            self.db,
+            &self.resolver.clone(),
+            Some(name),
+            method_resolution::LookupMode::Path,
+            move |_ty, item| {
+                let (def, container) = match item {
+                    AssocItemId::FunctionId(f) => {
+                        (ValueNs::FunctionId(f), f.lookup(self.db).container)
+                    }
+                    AssocItemId::ConstId(c) => (ValueNs::ConstId(c), c.lookup(self.db).container),
+                    AssocItemId::TypeAliasId(_) => unreachable!(),
+                };
+                let substs = match container {
+                    ContainerId::ImplId(_) => self.find_self_types(&def, ty.clone()),
+                    ContainerId::TraitId(trait_) => {
+                        // we're picking this method
+                        let trait_substs = Substs::build_for_def(self.db, trait_)
+                            .push(ty.clone())
+                            .fill(std::iter::repeat_with(|| self.new_type_var()))
+                            .build();
+                        let substs = Substs::build_for_def(self.db, item)
+                            .use_parent_substs(&trait_substs)
+                            .fill_with_params()
+                            .build();
+                        self.obligations.push(super::Obligation::Trait(TraitRef {
+                            trait_,
+                            substs: trait_substs,
+                        }));
+                        Some(substs)
+                    }
+                    ContainerId::ModuleId(_) => None,
+                };
+
+                self.write_assoc_resolution(id, item.into());
+                Some((def, substs))
+            },
+        )
+    }
+
+    fn find_self_types(&self, def: &ValueNs, actual_def_ty: Ty) -> Option<Substs> {
+        if let ValueNs::FunctionId(func) = *def {
+            // We only do the infer if parent has generic params
+            let gen = self.db.generic_params(func.into());
+            if gen.count_parent_params() == 0 {
+                return None;
+            }
+
+            let impl_id = match func.lookup(self.db).container {
+                ContainerId::ImplId(it) => it,
+                _ => return None,
+            };
+            let self_ty = self.db.impl_ty(impl_id).self_type().clone();
+            let self_ty_substs = self_ty.substs()?;
+            let actual_substs = actual_def_ty.substs()?;
+
+            let mut new_substs = vec![Ty::Unknown; gen.count_parent_params()];
+
+            // The following code *link up* the function actual parma type
+            // and impl_block type param index
+            self_ty_substs.iter().zip(actual_substs.iter()).for_each(|(param, pty)| {
+                if let Ty::Param { idx, .. } = param {
+                    if let Some(s) = new_substs.get_mut(*idx as usize) {
+                        *s = pty.clone();
+                    }
+                }
+            });
+
+            Some(Substs(new_substs.into()))
+        } else {
+            None
+        }
+    }
+}