Merge #2561

2561: Split generic and non-generic paths r=matklad a=matklad



Co-authored-by: Aleksey Kladov <[email protected]>

10 files changed, 385 insertions, 267 deletions

diff --git a/crates/ra_hir_def/src/attr.rs b/crates/ra_hir_def/src/attr.rs
index 5bf82e191..9efa4970c 100644
--- a/crates/ra_hir_def/src/attr.rs
+++ b/crates/ra_hir_def/src/attr.rs
@@ -12,7 +12,7 @@ use ra_syntax::{
 use tt::Subtree;
 
 use crate::{
-    db::DefDatabase, path::Path, src::HasChildSource, src::HasSource, AdtId, AttrDefId, Lookup,
+    db::DefDatabase, path::ModPath, src::HasChildSource, src::HasSource, AdtId, AttrDefId, Lookup,
 };
 
 #[derive(Default, Debug, Clone, PartialEq, Eq)]
@@ -94,7 +94,7 @@ impl Attrs {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Attr {
-    pub(crate) path: Path,
+    pub(crate) path: ModPath,
     pub(crate) input: Option<AttrInput>,
 }
 
@@ -106,7 +106,7 @@ pub enum AttrInput {
 
 impl Attr {
     fn from_src(ast: ast::Attr, hygiene: &Hygiene) -> Option<Attr> {
-        let path = Path::from_src(ast.path()?, hygiene)?;
+        let path = ModPath::from_src(ast.path()?, hygiene)?;
         let input = match ast.input() {
             None => None,
             Some(ast::AttrInput::Literal(lit)) => {
diff --git a/crates/ra_hir_def/src/body.rs b/crates/ra_hir_def/src/body.rs
index b3bc336cf..7787cb87f 100644
--- a/crates/ra_hir_def/src/body.rs
+++ b/crates/ra_hir_def/src/body.rs
@@ -83,7 +83,7 @@ impl Expander {
 
     fn resolve_path_as_macro(&self, db: &impl DefDatabase, path: &Path) -> Option<MacroDefId> {
         self.crate_def_map
-            .resolve_path(db, self.module.local_id, path, BuiltinShadowMode::Other)
+            .resolve_path(db, self.module.local_id, path.mod_path(), BuiltinShadowMode::Other)
             .0
             .take_macros()
     }
diff --git a/crates/ra_hir_def/src/nameres.rs b/crates/ra_hir_def/src/nameres.rs
index bd237a7b3..9aae7e48e 100644
--- a/crates/ra_hir_def/src/nameres.rs
+++ b/crates/ra_hir_def/src/nameres.rs
@@ -74,7 +74,7 @@ use crate::{
     builtin_type::BuiltinType,
     db::DefDatabase,
     nameres::{diagnostics::DefDiagnostic, path_resolution::ResolveMode},
-    path::Path,
+    path::ModPath,
     per_ns::PerNs,
     AstId, FunctionId, ImplId, LocalImportId, LocalModuleId, ModuleDefId, ModuleId, TraitId,
 };
@@ -329,7 +329,7 @@ impl CrateDefMap {
         &self,
         db: &impl DefDatabase,
         original_module: LocalModuleId,
-        path: &Path,
+        path: &ModPath,
         shadow: BuiltinShadowMode,
     ) -> (PerNs, Option<usize>) {
         let res =
diff --git a/crates/ra_hir_def/src/nameres/collector.rs b/crates/ra_hir_def/src/nameres/collector.rs
index 5d7469a6e..912a073ea 100644
--- a/crates/ra_hir_def/src/nameres/collector.rs
+++ b/crates/ra_hir_def/src/nameres/collector.rs
@@ -22,7 +22,7 @@ use crate::{
         diagnostics::DefDiagnostic, mod_resolution::ModDir, path_resolution::ReachedFixedPoint,
         raw, BuiltinShadowMode, CrateDefMap, ModuleData, ModuleOrigin, Resolution, ResolveMode,
     },
-    path::{Path, PathKind},
+    path::{ModPath, PathKind},
     per_ns::PerNs,
     AdtId, AstId, ConstLoc, ContainerId, EnumLoc, EnumVariantId, FunctionLoc, ImplLoc, Intern,
     LocalImportId, LocalModuleId, ModuleDefId, ModuleId, StaticLoc, StructLoc, TraitLoc,
@@ -101,7 +101,7 @@ struct ImportDirective {
 struct MacroDirective {
     module_id: LocalModuleId,
     ast_id: AstId<ast::MacroCall>,
-    path: Path,
+    path: ModPath,
     legacy: Option<MacroCallId>,
 }
 
@@ -113,7 +113,7 @@ struct DefCollector<'a, DB> {
     unresolved_imports: Vec<ImportDirective>,
     resolved_imports: Vec<ImportDirective>,
     unexpanded_macros: Vec<MacroDirective>,
-    unexpanded_attribute_macros: Vec<(LocalModuleId, AstId<ast::ModuleItem>, Path)>,
+    unexpanded_attribute_macros: Vec<(LocalModuleId, AstId<ast::ModuleItem>, ModPath)>,
     mod_dirs: FxHashMap<LocalModuleId, ModDir>,
     cfg_options: &'a CfgOptions,
 }
@@ -428,7 +428,7 @@ where
         } else {
             match import.path.segments.last() {
                 Some(last_segment) => {
-                    let name = import.alias.clone().unwrap_or_else(|| last_segment.name.clone());
+                    let name = import.alias.clone().unwrap_or_else(|| last_segment.clone());
                     log::debug!("resolved import {:?} ({:?}) to {:?}", name, import, def);
 
                     // extern crates in the crate root are special-cased to insert entries into the extern prelude: rust-lang/rust#54658
@@ -565,7 +565,7 @@ where
         res
     }
 
-    fn resolve_attribute_macro(&self, path: &Path) -> Option<MacroDefId> {
+    fn resolve_attribute_macro(&self, path: &ModPath) -> Option<MacroDefId> {
         // FIXME this is currently super hacky, just enough to support the
         // built-in derives
         if let Some(name) = path.as_ident() {
@@ -829,7 +829,7 @@ where
                     tt::TokenTree::Leaf(tt::Leaf::Punct(_)) => continue, // , is ok
                     _ => continue, // anything else would be an error (which we currently ignore)
                 };
-                let path = Path::from_tt_ident(ident);
+                let path = ModPath::from_tt_ident(ident);
 
                 let ast_id = AstId::new(self.file_id, def.kind.ast_id());
                 self.def_collector.unexpanded_attribute_macros.push((self.module_id, ast_id, path));
@@ -917,7 +917,7 @@ where
     }
 }
 
-fn is_macro_rules(path: &Path) -> bool {
+fn is_macro_rules(path: &ModPath) -> bool {
     path.as_ident() == Some(&name![macro_rules])
 }
 
diff --git a/crates/ra_hir_def/src/nameres/path_resolution.rs b/crates/ra_hir_def/src/nameres/path_resolution.rs
index aab4b1dd9..4a249e7e7 100644
--- a/crates/ra_hir_def/src/nameres/path_resolution.rs
+++ b/crates/ra_hir_def/src/nameres/path_resolution.rs
@@ -17,7 +17,7 @@ use test_utils::tested_by;
 use crate::{
     db::DefDatabase,
     nameres::{BuiltinShadowMode, CrateDefMap},
-    path::{Path, PathKind},
+    path::{ModPath, PathKind},
     per_ns::PerNs,
     AdtId, CrateId, EnumVariantId, LocalModuleId, ModuleDefId, ModuleId,
 };
@@ -69,7 +69,7 @@ impl CrateDefMap {
         db: &impl DefDatabase,
         mode: ResolveMode,
         original_module: LocalModuleId,
-        path: &Path,
+        path: &ModPath,
         shadow: BuiltinShadowMode,
     ) -> ResolvePathResult {
         // if it is not the last segment, we prefer the module to the builtin
@@ -113,7 +113,7 @@ impl CrateDefMap {
                     None => return ResolvePathResult::empty(ReachedFixedPoint::Yes),
                 };
                 log::debug!("resolving {:?} in crate root (+ extern prelude)", segment);
-                self.resolve_name_in_crate_root_or_extern_prelude(&segment.name, prefer_module(idx))
+                self.resolve_name_in_crate_root_or_extern_prelude(&segment, prefer_module(idx))
             }
             PathKind::Plain => {
                 let (idx, segment) = match segments.next() {
@@ -121,7 +121,7 @@ impl CrateDefMap {
                     None => return ResolvePathResult::empty(ReachedFixedPoint::Yes),
                 };
                 log::debug!("resolving {:?} in module", segment);
-                self.resolve_name_in_module(db, original_module, &segment.name, prefer_module(idx))
+                self.resolve_name_in_module(db, original_module, &segment, prefer_module(idx))
             }
             PathKind::Super => {
                 if let Some(p) = self.modules[original_module].parent {
@@ -137,7 +137,7 @@ impl CrateDefMap {
                     Some((_, segment)) => segment,
                     None => return ResolvePathResult::empty(ReachedFixedPoint::Yes),
                 };
-                if let Some(def) = self.extern_prelude.get(&segment.name) {
+                if let Some(def) = self.extern_prelude.get(&segment) {
                     log::debug!("absolute path {:?} resolved to crate {:?}", path, def);
                     PerNs::types(*def)
                 } else {
@@ -168,8 +168,10 @@ impl CrateDefMap {
             curr_per_ns = match curr {
                 ModuleDefId::ModuleId(module) => {
                     if module.krate != self.krate {
-                        let path =
-                            Path { segments: path.segments[i..].to_vec(), kind: PathKind::Self_ };
+                        let path = ModPath {
+                            segments: path.segments[i..].to_vec(),
+                            kind: PathKind::Self_,
+                        };
                         log::debug!("resolving {:?} in other crate", path);
                         let defp_map = db.crate_def_map(module.krate);
                         let (def, s) = defp_map.resolve_path(db, module.local_id, &path, shadow);
@@ -182,10 +184,10 @@ impl CrateDefMap {
                     }
 
                     // Since it is a qualified path here, it should not contains legacy macros
-                    match self[module.local_id].scope.get(&segment.name, prefer_module(i)) {
+                    match self[module.local_id].scope.get(&segment, prefer_module(i)) {
                         Some(res) => res.def,
                         _ => {
-                            log::debug!("path segment {:?} not found", segment.name);
+                            log::debug!("path segment {:?} not found", segment);
                             return ResolvePathResult::empty(ReachedFixedPoint::No);
                         }
                     }
@@ -194,7 +196,7 @@ impl CrateDefMap {
                     // enum variant
                     tested_by!(can_import_enum_variant);
                     let enum_data = db.enum_data(e);
-                    match enum_data.variant(&segment.name) {
+                    match enum_data.variant(&segment) {
                         Some(local_id) => {
                             let variant = EnumVariantId { parent: e, local_id };
                             PerNs::both(variant.into(), variant.into())
@@ -214,7 +216,7 @@ impl CrateDefMap {
                     // (`Struct::method`), or some other kind of associated item
                     log::debug!(
                         "path segment {:?} resolved to non-module {:?}, but is not last",
-                        segment.name,
+                        segment,
                         curr,
                     );
 
diff --git a/crates/ra_hir_def/src/nameres/raw.rs b/crates/ra_hir_def/src/nameres/raw.rs
index a2821e1c3..ecb4d7c03 100644
--- a/crates/ra_hir_def/src/nameres/raw.rs
+++ b/crates/ra_hir_def/src/nameres/raw.rs
@@ -22,7 +22,7 @@ use ra_syntax::{
 use test_utils::tested_by;
 
 use crate::{
-    attr::Attrs, db::DefDatabase, path::Path, trace::Trace, FileAstId, HirFileId, InFile,
+    attr::Attrs, db::DefDatabase, path::ModPath, trace::Trace, FileAstId, HirFileId, InFile,
     LocalImportId,
 };
 
@@ -154,7 +154,7 @@ pub(super) enum ModuleData {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ImportData {
-    pub(super) path: Path,
+    pub(super) path: ModPath,
     pub(super) alias: Option<Name>,
     pub(super) is_glob: bool,
     pub(super) is_prelude: bool,
@@ -206,7 +206,7 @@ impl_arena_id!(Macro);
 #[derive(Debug, PartialEq, Eq)]
 pub(super) struct MacroData {
     pub(super) ast_id: FileAstId<ast::MacroCall>,
-    pub(super) path: Path,
+    pub(super) path: ModPath,
     pub(super) name: Option<Name>,
     pub(super) export: bool,
     pub(super) builtin: bool,
@@ -327,7 +327,7 @@ impl RawItemsCollector {
         let attrs = self.parse_attrs(&use_item);
 
         let mut buf = Vec::new();
-        Path::expand_use_item(
+        ModPath::expand_use_item(
             InFile { value: use_item, file_id: self.file_id },
             &self.hygiene,
             |path, use_tree, is_glob, alias| {
@@ -353,7 +353,7 @@ impl RawItemsCollector {
         extern_crate: ast::ExternCrateItem,
     ) {
         if let Some(name_ref) = extern_crate.name_ref() {
-            let path = Path::from_name_ref(&name_ref);
+            let path = ModPath::from_name_ref(&name_ref);
             let alias = extern_crate.alias().and_then(|a| a.name()).map(|it| it.as_name());
             let attrs = self.parse_attrs(&extern_crate);
             // FIXME: cfg_attr
@@ -377,7 +377,7 @@ impl RawItemsCollector {
 
     fn add_macro(&mut self, current_module: Option<Module>, m: ast::MacroCall) {
         let attrs = self.parse_attrs(&m);
-        let path = match m.path().and_then(|path| Path::from_src(path, &self.hygiene)) {
+        let path = match m.path().and_then(|path| ModPath::from_src(path, &self.hygiene)) {
             Some(it) => it,
             _ => return,
         };
diff --git a/crates/ra_hir_def/src/path.rs b/crates/ra_hir_def/src/path.rs
index 1e9eb14ea..20d6d98ea 100644
--- a/crates/ra_hir_def/src/path.rs
+++ b/crates/ra_hir_def/src/path.rs
@@ -1,31 +1,78 @@
 //! A desugared representation of paths like `crate::foo` or `<Type as Trait>::bar`.
-mod lower_use;
+mod lower;
 
 use std::{iter, sync::Arc};
 
-use either::Either;
 use hir_expand::{
     hygiene::Hygiene,
-    name::{name, AsName, Name},
+    name::{AsName, Name},
 };
 use ra_db::CrateId;
-use ra_syntax::{
-    ast::{self, TypeAscriptionOwner},
-    AstNode,
-};
+use ra_syntax::ast;
 
 use crate::{type_ref::TypeRef, InFile};
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct Path {
+pub struct ModPath {
     pub kind: PathKind,
-    pub segments: Vec<PathSegment>,
+    pub segments: Vec<Name>,
+}
+
+impl ModPath {
+    pub fn from_src(path: ast::Path, hygiene: &Hygiene) -> Option<ModPath> {
+        lower::lower_path(path, hygiene).map(|it| it.mod_path)
+    }
+
+    pub fn from_simple_segments(
+        kind: PathKind,
+        segments: impl IntoIterator<Item = Name>,
+    ) -> ModPath {
+        let segments = segments.into_iter().collect::<Vec<_>>();
+        ModPath { kind, segments }
+    }
+
+    pub(crate) fn from_name_ref(name_ref: &ast::NameRef) -> ModPath {
+        name_ref.as_name().into()
+    }
+
+    /// Converts an `tt::Ident` into a single-identifier `Path`.
+    pub(crate) fn from_tt_ident(ident: &tt::Ident) -> ModPath {
+        ident.as_name().into()
+    }
+
+    /// Calls `cb` with all paths, represented by this use item.
+    pub(crate) fn expand_use_item(
+        item_src: InFile<ast::UseItem>,
+        hygiene: &Hygiene,
+        mut cb: impl FnMut(ModPath, &ast::UseTree, /* is_glob */ bool, Option<Name>),
+    ) {
+        if let Some(tree) = item_src.value.use_tree() {
+            lower::lower_use_tree(None, tree, hygiene, &mut cb);
+        }
+    }
+
+    pub fn is_ident(&self) -> bool {
+        self.kind == PathKind::Plain && self.segments.len() == 1
+    }
+
+    pub fn is_self(&self) -> bool {
+        self.kind == PathKind::Self_ && self.segments.is_empty()
+    }
+
+    /// If this path is a single identifier, like `foo`, return its name.
+    pub fn as_ident(&self) -> Option<&Name> {
+        if self.kind != PathKind::Plain || self.segments.len() > 1 {
+            return None;
+        }
+        self.segments.first()
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
-pub struct PathSegment {
-    pub name: Name,
-    pub args_and_bindings: Option<Arc<GenericArgs>>,
+pub struct Path {
+    mod_path: ModPath,
+    /// Invariant: the same len as self.path.segments
+    generic_args: Vec<Option<Arc<GenericArgs>>>,
 }
 
 /// Generic arguments to a path segment (e.g. the `i32` in `Option<i32>`). This
@@ -65,221 +112,110 @@ pub enum PathKind {
 }
 
 impl Path {
-    /// Calls `cb` with all paths, represented by this use item.
-    pub(crate) fn expand_use_item(
-        item_src: InFile<ast::UseItem>,
-        hygiene: &Hygiene,
-        mut cb: impl FnMut(Path, &ast::UseTree, bool, Option<Name>),
-    ) {
-        if let Some(tree) = item_src.value.use_tree() {
-            lower_use::lower_use_tree(None, tree, hygiene, &mut cb);
-        }
-    }
-
-    pub fn from_simple_segments(kind: PathKind, segments: impl IntoIterator<Item = Name>) -> Path {
-        Path {
-            kind,
-            segments: segments
-                .into_iter()
-                .map(|name| PathSegment { name, args_and_bindings: None })
-                .collect(),
-        }
-    }
-
     /// Converts an `ast::Path` to `Path`. Works with use trees.
     /// DEPRECATED: It does not handle `$crate` from macro call.
     pub fn from_ast(path: ast::Path) -> Option<Path> {
-        Path::from_src(path, &Hygiene::new_unhygienic())
+        lower::lower_path(path, &Hygiene::new_unhygienic())
     }
 
     /// Converts an `ast::Path` to `Path`. Works with use trees.
     /// It correctly handles `$crate` based path from macro call.
-    pub fn from_src(mut path: ast::Path, hygiene: &Hygiene) -> Option<Path> {
-        let mut kind = PathKind::Plain;
-        let mut segments = Vec::new();
-        loop {
-            let segment = path.segment()?;
-
-            if segment.has_colon_colon() {
-                kind = PathKind::Abs;
-            }
-
-            match segment.kind()? {
-                ast::PathSegmentKind::Name(name_ref) => {
-                    // FIXME: this should just return name
-                    match hygiene.name_ref_to_name(name_ref) {
-                        Either::Left(name) => {
-                            let args = segment
-                                .type_arg_list()
-                                .and_then(GenericArgs::from_ast)
-                                .or_else(|| {
-                                    GenericArgs::from_fn_like_path_ast(
-                                        segment.param_list(),
-                                        segment.ret_type(),
-                                    )
-                                })
-                                .map(Arc::new);
-                            let segment = PathSegment { name, args_and_bindings: args };
-                            segments.push(segment);
-                        }
-                        Either::Right(crate_id) => {
-                            kind = PathKind::DollarCrate(crate_id);
-                            break;
-                        }
-                    }
-                }
-                ast::PathSegmentKind::Type { type_ref, trait_ref } => {
-                    assert!(path.qualifier().is_none()); // this can only occur at the first segment
-
-                    let self_type = TypeRef::from_ast(type_ref?);
-
-                    match trait_ref {
-                        // <T>::foo
-                        None => {
-                            kind = PathKind::Type(Box::new(self_type));
-                        }
-                        // <T as Trait<A>>::Foo desugars to Trait<Self=T, A>::Foo
-                        Some(trait_ref) => {
-                            let path = Path::from_src(trait_ref.path()?, hygiene)?;
-                            kind = path.kind;
-                            let mut prefix_segments = path.segments;
-                            prefix_segments.reverse();
-                            segments.extend(prefix_segments);
-                            // Insert the type reference (T in the above example) as Self parameter for the trait
-                            let mut last_segment = segments.last_mut()?;
-                            if last_segment.args_and_bindings.is_none() {
-                                last_segment.args_and_bindings =
-                                    Some(Arc::new(GenericArgs::empty()));
-                            };
-                            let args = last_segment.args_and_bindings.as_mut().unwrap();
-                            let mut args_inner = Arc::make_mut(args);
-                            args_inner.has_self_type = true;
-                            args_inner.args.insert(0, GenericArg::Type(self_type));
-                        }
-                    }
-                }
-                ast::PathSegmentKind::CrateKw => {
-                    kind = PathKind::Crate;
-                    break;
-                }
-                ast::PathSegmentKind::SelfKw => {
-                    kind = PathKind::Self_;
-                    break;
-                }
-                ast::PathSegmentKind::SuperKw => {
-                    kind = PathKind::Super;
-                    break;
-                }
-            }
-            path = match qualifier(&path) {
-                Some(it) => it,
-                None => break,
-            };
-        }
-        segments.reverse();
-        return Some(Path { kind, segments });
-
-        fn qualifier(path: &ast::Path) -> Option<ast::Path> {
-            if let Some(q) = path.qualifier() {
-                return Some(q);
-            }
-            // FIXME: this bottom up traversal is not too precise.
-            // Should we handle do a top-down analysis, recording results?
-            let use_tree_list = path.syntax().ancestors().find_map(ast::UseTreeList::cast)?;
-            let use_tree = use_tree_list.parent_use_tree();
-            use_tree.path()
-        }
+    pub fn from_src(path: ast::Path, hygiene: &Hygiene) -> Option<Path> {
+        lower::lower_path(path, hygiene)
     }
 
     /// Converts an `ast::NameRef` into a single-identifier `Path`.
     pub(crate) fn from_name_ref(name_ref: &ast::NameRef) -> Path {
-        name_ref.as_name().into()
+        Path { mod_path: name_ref.as_name().into(), generic_args: vec![None] }
     }
 
-    /// Converts an `tt::Ident` into a single-identifier `Path`.
-    pub(crate) fn from_tt_ident(ident: &tt::Ident) -> Path {
-        ident.as_name().into()
+    /// `true` if this path is just a standalone `self`
+    pub fn is_self(&self) -> bool {
+        self.mod_path.is_self()
     }
 
-    /// `true` is this path is a single identifier, like `foo`
-    pub fn is_ident(&self) -> bool {
-        self.kind == PathKind::Plain && self.segments.len() == 1
+    pub fn kind(&self) -> &PathKind {
+        &self.mod_path.kind
     }
 
-    /// `true` if this path is just a standalone `self`
-    pub fn is_self(&self) -> bool {
-        self.kind == PathKind::Self_ && self.segments.is_empty()
+    pub fn segments(&self) -> PathSegments<'_> {
+        PathSegments {
+            segments: self.mod_path.segments.as_slice(),
+            generic_args: self.generic_args.as_slice(),
+        }
     }
 
-    /// If this path is a single identifier, like `foo`, return its name.
-    pub fn as_ident(&self) -> Option<&Name> {
-        if self.kind != PathKind::Plain || self.segments.len() > 1 {
+    pub fn mod_path(&self) -> &ModPath {
+        &self.mod_path
+    }
+
+    pub fn qualifier(&self) -> Option<Path> {
+        if self.mod_path.is_ident() {
             return None;
         }
-        self.segments.first().map(|s| &s.name)
+        let res = Path {
+            mod_path: ModPath {
+                kind: self.mod_path.kind.clone(),
+                segments: self.mod_path.segments[..self.mod_path.segments.len() - 1].to_vec(),
+            },
+            generic_args: self.generic_args[..self.generic_args.len() - 1].to_vec(),
+        };
+        Some(res)
     }
+}
 
-    pub fn expand_macro_expr(&self) -> Option<Name> {
-        self.as_ident().and_then(|name| Some(name.clone()))
-    }
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct PathSegment<'a> {
+    pub name: &'a Name,
+    pub args_and_bindings: Option<&'a GenericArgs>,
+}
 
-    pub fn is_type_relative(&self) -> bool {
-        match self.kind {
-            PathKind::Type(_) => true,
-            _ => false,
-        }
+pub struct PathSegments<'a> {
+    segments: &'a [Name],
+    generic_args: &'a [Option<Arc<GenericArgs>>],
+}
+
+impl<'a> PathSegments<'a> {
+    pub const EMPTY: PathSegments<'static> = PathSegments { segments: &[], generic_args: &[] };
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+    pub fn len(&self) -> usize {
+        self.segments.len()
+    }
+    pub fn first(&self) -> Option<PathSegment<'a>> {
+        self.get(0)
+    }
+    pub fn last(&self) -> Option<PathSegment<'a>> {
+        self.get(self.len().checked_sub(1)?)
+    }
+    pub fn get(&self, idx: usize) -> Option<PathSegment<'a>> {
+        assert_eq!(self.segments.len(), self.generic_args.len());
+        let res = PathSegment {
+            name: self.segments.get(idx)?,
+            args_and_bindings: self.generic_args.get(idx).unwrap().as_ref().map(|it| &**it),
+        };
+        Some(res)
+    }
+    pub fn skip(&self, len: usize) -> PathSegments<'a> {
+        assert_eq!(self.segments.len(), self.generic_args.len());
+        PathSegments { segments: &self.segments[len..], generic_args: &self.generic_args[len..] }
+    }
+    pub fn take(&self, len: usize) -> PathSegments<'a> {
+        assert_eq!(self.segments.len(), self.generic_args.len());
+        PathSegments { segments: &self.segments[..len], generic_args: &self.generic_args[..len] }
+    }
+    pub fn iter(&self) -> impl Iterator<Item = PathSegment<'a>> {
+        self.segments.iter().zip(self.generic_args.iter()).map(|(name, args)| PathSegment {
+            name,
+            args_and_bindings: args.as_ref().map(|it| &**it),
+        })
     }
 }
 
 impl GenericArgs {
     pub(crate) fn from_ast(node: ast::TypeArgList) -> Option<GenericArgs> {
-        let mut args = Vec::new();
-        for type_arg in node.type_args() {
-            let type_ref = TypeRef::from_ast_opt(type_arg.type_ref());
-            args.push(GenericArg::Type(type_ref));
-        }
-        // lifetimes ignored for now
-        let mut bindings = Vec::new();
-        for assoc_type_arg in node.assoc_type_args() {
-            if let Some(name_ref) = assoc_type_arg.name_ref() {
-                let name = name_ref.as_name();
-                let type_ref = TypeRef::from_ast_opt(assoc_type_arg.type_ref());
-                bindings.push((name, type_ref));
-            }
-        }
-        if args.is_empty() && bindings.is_empty() {
-            None
-        } else {
-            Some(GenericArgs { args, has_self_type: false, bindings })
-        }
-    }
-
-    /// Collect `GenericArgs` from the parts of a fn-like path, i.e. `Fn(X, Y)
-    /// -> Z` (which desugars to `Fn<(X, Y), Output=Z>`).
-    pub(crate) fn from_fn_like_path_ast(
-        params: Option<ast::ParamList>,
-        ret_type: Option<ast::RetType>,
-    ) -> Option<GenericArgs> {
-        let mut args = Vec::new();
-        let mut bindings = Vec::new();
-        if let Some(params) = params {
-            let mut param_types = Vec::new();
-            for param in params.params() {
-                let type_ref = TypeRef::from_ast_opt(param.ascribed_type());
-                param_types.push(type_ref);
-            }
-            let arg = GenericArg::Type(TypeRef::Tuple(param_types));
-            args.push(arg);
-        }
-        if let Some(ret_type) = ret_type {
-            let type_ref = TypeRef::from_ast_opt(ret_type.type_ref());
-            bindings.push((name![Output], type_ref))
-        }
-        if args.is_empty() && bindings.is_empty() {
-            None
-        } else {
-            Some(GenericArgs { args, has_self_type: false, bindings })
-        }
+        lower::lower_generic_args(node)
     }
 
     pub(crate) fn empty() -> GenericArgs {
@@ -289,7 +225,16 @@ impl GenericArgs {
 
 impl From<Name> for Path {
     fn from(name: Name) -> Path {
-        Path::from_simple_segments(PathKind::Plain, iter::once(name))
+        Path {
+            mod_path: ModPath::from_simple_segments(PathKind::Plain, iter::once(name)),
+            generic_args: vec![None],
+        }
+    }
+}
+
+impl From<Name> for ModPath {
+    fn from(name: Name) -> ModPath {
+        ModPath::from_simple_segments(PathKind::Plain, iter::once(name))
     }
 }
 
@@ -319,7 +264,7 @@ macro_rules! __known_path {
 macro_rules! __path {
     ($start:ident $(:: $seg:ident)*) => ({
         $crate::__known_path!($start $(:: $seg)*);
-        $crate::path::Path::from_simple_segments($crate::path::PathKind::Abs, vec![
+        $crate::path::ModPath::from_simple_segments($crate::path::PathKind::Abs, vec![
             $crate::path::__name![$start], $($crate::path::__name![$seg],)*
         ])
     });
diff --git a/crates/ra_hir_def/src/path/lower.rs b/crates/ra_hir_def/src/path/lower.rs
new file mode 100644
index 000000000..a2e995198
--- /dev/null
+++ b/crates/ra_hir_def/src/path/lower.rs
@@ -0,0 +1,176 @@
+//! Transforms syntax into `Path` objects, ideally with accounting for hygiene
+
+mod lower_use;
+
+use std::sync::Arc;
+
+use either::Either;
+use hir_expand::{
+    hygiene::Hygiene,
+    name::{name, AsName},
+};
+use ra_syntax::ast::{self, AstNode, TypeAscriptionOwner};
+
+use crate::{
+    path::{GenericArg, GenericArgs, ModPath, Path, PathKind},
+    type_ref::TypeRef,
+};
+
+pub(super) use lower_use::lower_use_tree;
+
+/// Converts an `ast::Path` to `Path`. Works with use trees.
+/// It correctly handles `$crate` based path from macro call.
+pub(super) fn lower_path(mut path: ast::Path, hygiene: &Hygiene) -> Option<Path> {
+    let mut kind = PathKind::Plain;
+    let mut segments = Vec::new();
+    let mut generic_args = Vec::new();
+    loop {
+        let segment = path.segment()?;
+
+        if segment.has_colon_colon() {
+            kind = PathKind::Abs;
+        }
+
+        match segment.kind()? {
+            ast::PathSegmentKind::Name(name_ref) => {
+                // FIXME: this should just return name
+                match hygiene.name_ref_to_name(name_ref) {
+                    Either::Left(name) => {
+                        let args = segment
+                            .type_arg_list()
+                            .and_then(lower_generic_args)
+                            .or_else(|| {
+                                lower_generic_args_from_fn_path(
+                                    segment.param_list(),
+                                    segment.ret_type(),
+                                )
+                            })
+                            .map(Arc::new);
+                        segments.push(name);
+                        generic_args.push(args)
+                    }
+                    Either::Right(crate_id) => {
+                        kind = PathKind::DollarCrate(crate_id);
+                        break;
+                    }
+                }
+            }
+            ast::PathSegmentKind::Type { type_ref, trait_ref } => {
+                assert!(path.qualifier().is_none()); // this can only occur at the first segment
+
+                let self_type = TypeRef::from_ast(type_ref?);
+
+                match trait_ref {
+                    // <T>::foo
+                    None => {
+                        kind = PathKind::Type(Box::new(self_type));
+                    }
+                    // <T as Trait<A>>::Foo desugars to Trait<Self=T, A>::Foo
+                    Some(trait_ref) => {
+                        let path = Path::from_src(trait_ref.path()?, hygiene)?;
+                        kind = path.mod_path.kind;
+
+                        let mut prefix_segments = path.mod_path.segments;
+                        prefix_segments.reverse();
+                        segments.extend(prefix_segments);
+
+                        let mut prefix_args = path.generic_args;
+                        prefix_args.reverse();
+                        generic_args.extend(prefix_args);
+
+                        // Insert the type reference (T in the above example) as Self parameter for the trait
+                        let last_segment = generic_args.last_mut()?;
+                        if last_segment.is_none() {
+                            *last_segment = Some(Arc::new(GenericArgs::empty()));
+                        };
+                        let args = last_segment.as_mut().unwrap();
+                        let mut args_inner = Arc::make_mut(args);
+                        args_inner.has_self_type = true;
+                        args_inner.args.insert(0, GenericArg::Type(self_type));
+                    }
+                }
+            }
+            ast::PathSegmentKind::CrateKw => {
+                kind = PathKind::Crate;
+                break;
+            }
+            ast::PathSegmentKind::SelfKw => {
+                kind = PathKind::Self_;
+                break;
+            }
+            ast::PathSegmentKind::SuperKw => {
+                kind = PathKind::Super;
+                break;
+            }
+        }
+        path = match qualifier(&path) {
+            Some(it) => it,
+            None => break,
+        };
+    }
+    segments.reverse();
+    generic_args.reverse();
+    let mod_path = ModPath { kind, segments };
+    return Some(Path { mod_path, generic_args });
+
+    fn qualifier(path: &ast::Path) -> Option<ast::Path> {
+        if let Some(q) = path.qualifier() {
+            return Some(q);
+        }
+        // FIXME: this bottom up traversal is not too precise.
+        // Should we handle do a top-down analysis, recording results?
+        let use_tree_list = path.syntax().ancestors().find_map(ast::UseTreeList::cast)?;
+        let use_tree = use_tree_list.parent_use_tree();
+        use_tree.path()
+    }
+}
+
+pub(super) fn lower_generic_args(node: ast::TypeArgList) -> Option<GenericArgs> {
+    let mut args = Vec::new();
+    for type_arg in node.type_args() {
+        let type_ref = TypeRef::from_ast_opt(type_arg.type_ref());
+        args.push(GenericArg::Type(type_ref));
+    }
+    // lifetimes ignored for now
+    let mut bindings = Vec::new();
+    for assoc_type_arg in node.assoc_type_args() {
+        if let Some(name_ref) = assoc_type_arg.name_ref() {
+            let name = name_ref.as_name();
+            let type_ref = TypeRef::from_ast_opt(assoc_type_arg.type_ref());
+            bindings.push((name, type_ref));
+        }
+    }
+    if args.is_empty() && bindings.is_empty() {
+        None
+    } else {
+        Some(GenericArgs { args, has_self_type: false, bindings })
+    }
+}
+
+/// Collect `GenericArgs` from the parts of a fn-like path, i.e. `Fn(X, Y)
+/// -> Z` (which desugars to `Fn<(X, Y), Output=Z>`).
+fn lower_generic_args_from_fn_path(
+    params: Option<ast::ParamList>,
+    ret_type: Option<ast::RetType>,
+) -> Option<GenericArgs> {
+    let mut args = Vec::new();
+    let mut bindings = Vec::new();
+    if let Some(params) = params {
+        let mut param_types = Vec::new();
+        for param in params.params() {
+            let type_ref = TypeRef::from_ast_opt(param.ascribed_type());
+            param_types.push(type_ref);
+        }
+        let arg = GenericArg::Type(TypeRef::Tuple(param_types));
+        args.push(arg);
+    }
+    if let Some(ret_type) = ret_type {
+        let type_ref = TypeRef::from_ast_opt(ret_type.type_ref());
+        bindings.push((name![Output], type_ref))
+    }
+    if args.is_empty() && bindings.is_empty() {
+        None
+    } else {
+        Some(GenericArgs { args, has_self_type: false, bindings })
+    }
+}
diff --git a/crates/ra_hir_def/src/path/lower_use.rs b/crates/ra_hir_def/src/path/lower/lower_use.rs
index e2e1f716d..ea3fdb56c 100644
--- a/crates/ra_hir_def/src/path/lower_use.rs
+++ b/crates/ra_hir_def/src/path/lower/lower_use.rs
@@ -10,13 +10,13 @@ use hir_expand::{
 };
 use ra_syntax::ast::{self, NameOwner};
 
-use crate::path::{Path, PathKind, PathSegment};
+use crate::path::{ModPath, PathKind};
 
 pub(crate) fn lower_use_tree(
-    prefix: Option<Path>,
+    prefix: Option<ModPath>,
     tree: ast::UseTree,
     hygiene: &Hygiene,
-    cb: &mut dyn FnMut(Path, &ast::UseTree, bool, Option<Name>),
+    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<Name>),
 ) {
     if let Some(use_tree_list) = tree.use_tree_list() {
         let prefix = match tree.path() {
@@ -57,7 +57,7 @@ pub(crate) fn lower_use_tree(
     }
 }
 
-fn convert_path(prefix: Option<Path>, path: ast::Path, hygiene: &Hygiene) -> Option<Path> {
+fn convert_path(prefix: Option<ModPath>, path: ast::Path, hygiene: &Hygiene) -> Option<ModPath> {
     let prefix = if let Some(qual) = path.qualifier() {
         Some(convert_path(prefix, qual, hygiene)?)
     } else {
@@ -70,18 +70,15 @@ fn convert_path(prefix: Option<Path>, path: ast::Path, hygiene: &Hygiene) -> Opt
             match hygiene.name_ref_to_name(name_ref) {
                 Either::Left(name) => {
                     // no type args in use
-                    let mut res = prefix.unwrap_or_else(|| Path {
+                    let mut res = prefix.unwrap_or_else(|| ModPath {
                         kind: PathKind::Plain,
                         segments: Vec::with_capacity(1),
                     });
-                    res.segments.push(PathSegment {
-                        name,
-                        args_and_bindings: None, // no type args in use
-                    });
+                    res.segments.push(name);
                     res
                 }
                 Either::Right(crate_id) => {
-                    return Some(Path::from_simple_segments(
+                    return Some(ModPath::from_simple_segments(
                         PathKind::DollarCrate(crate_id),
                         iter::empty(),
                     ))
@@ -92,19 +89,19 @@ fn convert_path(prefix: Option<Path>, path: ast::Path, hygiene: &Hygiene) -> Opt
             if prefix.is_some() {
                 return None;
             }
-            Path::from_simple_segments(PathKind::Crate, iter::empty())
+            ModPath::from_simple_segments(PathKind::Crate, iter::empty())
         }
         ast::PathSegmentKind::SelfKw => {
             if prefix.is_some() {
                 return None;
             }
-            Path::from_simple_segments(PathKind::Self_, iter::empty())
+            ModPath::from_simple_segments(PathKind::Self_, iter::empty())
         }
         ast::PathSegmentKind::SuperKw => {
             if prefix.is_some() {
                 return None;
             }
-            Path::from_simple_segments(PathKind::Super, iter::empty())
+            ModPath::from_simple_segments(PathKind::Super, iter::empty())
         }
         ast::PathSegmentKind::Type { .. } => {
             // not allowed in imports
diff --git a/crates/ra_hir_def/src/resolver.rs b/crates/ra_hir_def/src/resolver.rs
index b6d595a20..2694c0438 100644
--- a/crates/ra_hir_def/src/resolver.rs
+++ b/crates/ra_hir_def/src/resolver.rs
@@ -15,7 +15,7 @@ use crate::{
     expr::{ExprId, PatId},
     generics::GenericParams,
     nameres::{BuiltinShadowMode, CrateDefMap},
-    path::{Path, PathKind},
+    path::{ModPath, PathKind},
     per_ns::PerNs,
     AdtId, ConstId, ContainerId, DefWithBodyId, EnumId, EnumVariantId, FunctionId, GenericDefId,
     HasModule, ImplId, LocalModuleId, Lookup, ModuleDefId, ModuleId, StaticId, StructId, TraitId,
@@ -91,7 +91,7 @@ pub enum ValueNs {
 
 impl Resolver {
     /// Resolve known trait from std, like `std::futures::Future`
-    pub fn resolve_known_trait(&self, db: &impl DefDatabase, path: &Path) -> Option<TraitId> {
+    pub fn resolve_known_trait(&self, db: &impl DefDatabase, path: &ModPath) -> Option<TraitId> {
         let res = self.resolve_module_path(db, path, BuiltinShadowMode::Other).take_types()?;
         match res {
             ModuleDefId::TraitId(it) => Some(it),
@@ -100,7 +100,7 @@ impl Resolver {
     }
 
     /// Resolve known struct from std, like `std::boxed::Box`
-    pub fn resolve_known_struct(&self, db: &impl DefDatabase, path: &Path) -> Option<StructId> {
+    pub fn resolve_known_struct(&self, db: &impl DefDatabase, path: &ModPath) -> Option<StructId> {
         let res = self.resolve_module_path(db, path, BuiltinShadowMode::Other).take_types()?;
         match res {
             ModuleDefId::AdtId(AdtId::StructId(it)) => Some(it),
@@ -109,7 +109,7 @@ impl Resolver {
     }
 
     /// Resolve known enum from std, like `std::result::Result`
-    pub fn resolve_known_enum(&self, db: &impl DefDatabase, path: &Path) -> Option<EnumId> {
+    pub fn resolve_known_enum(&self, db: &impl DefDatabase, path: &ModPath) -> Option<EnumId> {
         let res = self.resolve_module_path(db, path, BuiltinShadowMode::Other).take_types()?;
         match res {
             ModuleDefId::AdtId(AdtId::EnumId(it)) => Some(it),
@@ -120,33 +120,30 @@ impl Resolver {
     fn resolve_module_path(
         &self,
         db: &impl DefDatabase,
-        path: &Path,
+        path: &ModPath,
         shadow: BuiltinShadowMode,
     ) -> PerNs {
         let (item_map, module) = match self.module() {
             Some(it) => it,
             None => return PerNs::none(),
         };
-        let (module_res, segment_index) = item_map.resolve_path(db, module, path, shadow);
+        let (module_res, segment_index) = item_map.resolve_path(db, module, &path, shadow);
         if segment_index.is_some() {
             return PerNs::none();
         }
         module_res
     }
 
-    pub fn resolve_module_path_in_items(&self, db: &impl DefDatabase, path: &Path) -> PerNs {
+    pub fn resolve_module_path_in_items(&self, db: &impl DefDatabase, path: &ModPath) -> PerNs {
         self.resolve_module_path(db, path, BuiltinShadowMode::Module)
     }
 
     pub fn resolve_path_in_type_ns(
         &self,
         db: &impl DefDatabase,
-        path: &Path,
+        path: &ModPath,
     ) -> Option<(TypeNs, Option<usize>)> {
-        if path.is_type_relative() {
-            return None;
-        }
-        let first_name = &path.segments.first()?.name;
+        let first_name = path.segments.first()?;
         let skip_to_mod = path.kind != PathKind::Plain;
         for scope in self.scopes.iter().rev() {
             match scope {
@@ -178,7 +175,7 @@ impl Resolver {
                     let (module_def, idx) = m.crate_def_map.resolve_path(
                         db,
                         m.module_id,
-                        path,
+                        &path,
                         BuiltinShadowMode::Other,
                     );
                     let res = match module_def.take_types()? {
@@ -205,7 +202,7 @@ impl Resolver {
     pub fn resolve_path_in_type_ns_fully(
         &self,
         db: &impl DefDatabase,
-        path: &Path,
+        path: &ModPath,
     ) -> Option<TypeNs> {
         let (res, unresolved) = self.resolve_path_in_type_ns(db, path)?;
         if unresolved.is_some() {
@@ -214,17 +211,14 @@ impl Resolver {
         Some(res)
     }
 
-    pub fn resolve_path_in_value_ns<'p>(
+    pub fn resolve_path_in_value_ns(
         &self,
         db: &impl DefDatabase,
-        path: &'p Path,
+        path: &ModPath,
     ) -> Option<ResolveValueResult> {
-        if path.is_type_relative() {
-            return None;
-        }
         let n_segments = path.segments.len();
         let tmp = name![self];
-        let first_name = if path.is_self() { &tmp } else { &path.segments.first()?.name };
+        let first_name = if path.is_self() { &tmp } else { &path.segments.first()? };
         let skip_to_mod = path.kind != PathKind::Plain && !path.is_self();
         for scope in self.scopes.iter().rev() {
             match scope {
@@ -276,7 +270,7 @@ impl Resolver {
                     let (module_def, idx) = m.crate_def_map.resolve_path(
                         db,
                         m.module_id,
-                        path,
+                        &path,
                         BuiltinShadowMode::Other,
                     );
                     return match idx {
@@ -322,7 +316,7 @@ impl Resolver {
     pub fn resolve_path_in_value_ns_fully(
         &self,
         db: &impl DefDatabase,
-        path: &Path,
+        path: &ModPath,
     ) -> Option<ValueNs> {
         match self.resolve_path_in_value_ns(db, path)? {
             ResolveValueResult::ValueNs(it) => Some(it),
@@ -330,9 +324,13 @@ impl Resolver {
         }
     }
 
-    pub fn resolve_path_as_macro(&self, db: &impl DefDatabase, path: &Path) -> Option<MacroDefId> {
+    pub fn resolve_path_as_macro(
+        &self,
+        db: &impl DefDatabase,
+        path: &ModPath,
+    ) -> Option<MacroDefId> {
         let (item_map, module) = self.module()?;
-        item_map.resolve_path(db, module, path, BuiltinShadowMode::Other).0.take_macros()
+        item_map.resolve_path(db, module, &path, BuiltinShadowMode::Other).0.take_macros()
     }
 
     pub fn process_all_names(&self, db: &impl DefDatabase, f: &mut dyn FnMut(Name, ScopeDef)) {