1 files changed, 195 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/infer/path.rs b/crates/ra_hir/src/ty/infer/path.rs
new file mode 100644
index 000000000..54aae4f0c
--- /dev/null
+++ b/crates/ra_hir/src/ty/infer/path.rs
@@ -0,0 +1,195 @@
+//! Path expression resolution.
+
+use super::{ExprOrPatId, InferenceContext};
+use crate::{
+    db::HirDatabase,
+    resolve::{ResolveValueResult, Resolver, TypeNs, ValueNs},
+    ty::{Substs, Ty, TypableDef, TypeWalk},
+    AssocItem, HasGenericParams, Namespace, Path,
+};
+
+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 crate::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"),
+                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: TypableDef = 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::Function(it) => it.into(),
+            ValueNs::Const(it) => it.into(),
+            ValueNs::Static(it) => it.into(),
+            ValueNs::Struct(it) => it.into(),
+            ValueNs::EnumVariant(it) => it.into(),
+        };
+
+        let mut ty = self.db.type_for_def(typable, Namespace::Values);
+        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::Trait(_trait), true) => {
+                // FIXME Associated item of trait, e.g. `Default::default`
+                None
+            }
+            (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 segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+
+                self.resolve_ty_assoc_item(ty, segment, id)
+            }
+        }
+    }
+
+    fn resolve_ty_assoc_item(
+        &mut self,
+        ty: Ty,
+        segment: &crate::path::PathSegment,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substs>)> {
+        if let Ty::Unknown = ty {
+            return None;
+        }
+
+        let krate = self.resolver.krate()?;
+
+        // Find impl
+        // FIXME: consider trait candidates
+        let item = ty.clone().iterate_impl_items(self.db, krate, |item| match item {
+            AssocItem::Function(func) => {
+                if segment.name == func.name(self.db) {
+                    Some(AssocItem::Function(func))
+                } else {
+                    None
+                }
+            }
+
+            AssocItem::Const(konst) => {
+                if konst.name(self.db).map_or(false, |n| n == segment.name) {
+                    Some(AssocItem::Const(konst))
+                } else {
+                    None
+                }
+            }
+            AssocItem::TypeAlias(_) => None,
+        })?;
+        let def = match item {
+            AssocItem::Function(f) => ValueNs::Function(f),
+            AssocItem::Const(c) => ValueNs::Const(c),
+            AssocItem::TypeAlias(_) => unreachable!(),
+        };
+        let substs = self.find_self_types(&def, ty);
+
+        self.write_assoc_resolution(id, item);
+        Some((def, substs))
+    }
+
+    fn find_self_types(&self, def: &ValueNs, actual_def_ty: Ty) -> Option<Substs> {
+        if let ValueNs::Function(func) = def {
+            // We only do the infer if parent has generic params
+            let gen = func.generic_params(self.db);
+            if gen.count_parent_params() == 0 {
+                return None;
+            }
+
+            let impl_block = func.impl_block(self.db)?.target_ty(self.db);
+            let impl_block_substs = impl_block.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
+            impl_block_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
+        }
+    }
+}