Auto merge of #37676 - eddyb:lazy-7, r=nikomatsakis

[7/n] rustc: desugar UFCS in HIR and don't use DefMap for associated resolutions.

_This is part of a series ([prev](#37412) | [next](#37688)) of patches designed to rework rustc into an out-of-order on-demand pipeline model for both better feature support (e.g. [MIR-based](https://github.com/solson/miri) early constant evaluation) and incremental execution of compiler passes (e.g. type-checking), with beneficial consequences to IDE support as well.
If any motivation is unclear, please ask for additional PR description clarifications or code comments._

<hr>

Previously, a path like `T::Assoc::method`, while equivalent to `<<T>::Assoc>::method`, wasn't desugared in any way at the HIR level and everything inspecting it had to either deal with knowing only `T` (before typeck) or knowing only the definition of `method` (after typeck).
Such a path also had only one `NodeId` and associated resolution during typeck modified `DefMap`, in a way that would be hard for incremental recompilation to track, and inconvenient for partial type conversions from HIR to `Ty`, which are required to break faux-cycles in on-demand type collection.

The desugarings performed by this PR are as follows:
* `use a::{b,c};` is flattened to `use a as _; use a::b; use a::c;`
  * as resolution is complete, `use a as _;` doesn't do anything, except get checked for stability
* `Vec::new` (an expression) becomes `Vec<..>::new<..>`, to distinguish it from `<Vec>::new<..>`
  * the "infer all parameters" `<..>` form is internal and not even pretty-printed
  * used when there are no type parameters at all, in an expression or pattern path segment
* `T::A::B` becomes `<<T>::A>::B` in a type, and `<<T<..>>::A<..>>::B<..>` in an expression/pattern
  * one additional `hir::Ty` node is created for each prefix, starting with the fully-resolved type (`T`) and extending it with each segment (e.g. `<T>::A`)
* fully-resolved paths contain their `Def` in HIR, getting rid of the `DefMap` and absolving incremental recompilation of needing to manually look up nodes to handle that side information

Not keeping the `DefMap` around meant that associated resolutions had to be stored somewhere else:
* expressions and patterns use a new `NodeId -> Def` map in `ty::Tables`
  * compatible with the future per-body (constant / `fn` / closure) `Tables`
* types are accessible via `Ty` and the usual per-item generics / predicates / type
  * `rustdoc` and `save-analysis` are the only situations which insist on mapping syntactical types to semantical ones, or at least understand the resolution of associated types, therefore the type conversion cache, i.e. a `NodeId -> Ty` map, is exposed by typeck for this purpose
  * stability had to be split into a pass that runs on HIR and checks the results of name resolution, and impromptu checks triggered by `typeck` for associated paths, methods, fields, etc.
  * privacy using semantic types results in accurate reachability for `impl Trait`, which fixes #35870, and thorough introspection of associated types, which may allow relaxing private-in-public checking on bounds, while keeping the intended ban on projections with private type parameters

cc @petrochenkov

src/etc/generate-deriving-span-tests.py

@@ -37,8 +37,6 @@
 
 // This file was auto-generated using 'src/etc/generate-deriving-span-tests.py'
 
-extern crate rand;
-
 {error_deriving}
 struct Error;
 {code}
@@ -106,7 +104,6 @@ def write_file(name, string):
 ALL = STRUCT | ENUM
 
 traits = {
-    'Zero': (STRUCT, [], 1),
     'Default': (STRUCT, [], 1),
     'FromPrimitive': (0, [], 0), # only works for C-like enums
 
@@ -116,7 +113,7 @@ def write_file(name, string):
 
 for (trait, supers, errs) in [('Clone', [], 1),
                               ('PartialEq', [], 2),
-                              ('PartialOrd', ['PartialEq'], 8),
+                              ('PartialOrd', ['PartialEq'], 9),
                               ('Eq', ['PartialEq'], 1),
                               ('Ord', ['Eq', 'PartialOrd', 'PartialEq'], 1),
                               ('Debug', [], 1),

src/librustc/cfg/construct.rs

@@ -10,8 +10,6 @@
 
 use rustc_data_structures::graph;
 use cfg::*;
-use hir::def::Def;
-use hir::pat_util;
 use ty::{self, TyCtxt};
 use syntax::ast;
 use syntax::ptr::P;
@@ -100,7 +98,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
     fn pat(&mut self, pat: &hir::Pat, pred: CFGIndex) -> CFGIndex {
         match pat.node {
             PatKind::Binding(.., None) |
-            PatKind::Path(..) |
+            PatKind::Path(_) |
             PatKind::Lit(..) |
             PatKind::Range(..) |
             PatKind::Wild => {
@@ -284,15 +282,15 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
             hir::ExprBreak(label, ref opt_expr) => {
                 let v = self.opt_expr(opt_expr, pred);
-                let loop_scope = self.find_scope(expr, label.map(|l| l.node));
+                let loop_scope = self.find_scope(expr, label);
                 let b = self.add_ast_node(expr.id, &[v]);
                 self.add_exiting_edge(expr, b,
                                       loop_scope, loop_scope.break_index);
                 self.add_unreachable_node()
             }
 
             hir::ExprAgain(label) => {
-                let loop_scope = self.find_scope(expr, label.map(|l| l.node));
+                let loop_scope = self.find_scope(expr, label);
                 let a = self.add_ast_node(expr.id, &[pred]);
                 self.add_exiting_edge(expr, a,
                                       loop_scope, loop_scope.continue_index);
@@ -361,7 +359,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
             hir::ExprClosure(..) |
             hir::ExprLit(..) |
-            hir::ExprPath(..) => {
+            hir::ExprPath(_) => {
                 self.straightline(expr, pred, None::<hir::Expr>.iter())
             }
         }
@@ -457,7 +455,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                     // Visit the guard expression
                     let guard_exit = self.expr(&guard, guard_start);
 
-                    let this_has_bindings = pat_util::pat_contains_bindings_or_wild(&pat);
+                    let this_has_bindings = pat.contains_bindings_or_wild();
 
                     // If both this pattern and the previous pattern
                     // were free of bindings, they must consist only
@@ -570,23 +568,16 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
     fn find_scope(&self,
                   expr: &hir::Expr,
-                  label: Option<ast::Name>) -> LoopScope {
-        if label.is_none() {
-            return *self.loop_scopes.last().unwrap();
-        }
-
-        match self.tcx.expect_def(expr.id) {
-            Def::Label(loop_id) => {
+                  label: Option<hir::Label>) -> LoopScope {
+        match label {
+            None => *self.loop_scopes.last().unwrap(),
+            Some(label) => {
                 for l in &self.loop_scopes {
-                    if l.loop_id == loop_id {
+                    if l.loop_id == label.loop_id {
                         return *l;
                     }
                 }
-                span_bug!(expr.span, "no loop scope for id {}", loop_id);
-            }
-
-            r => {
-                span_bug!(expr.span, "bad entry `{:?}` in def_map for label", r);
+                span_bug!(expr.span, "no loop scope for id {}", label.loop_id);
             }
         }
     }

src/librustc/dep_graph/dep_node.rs

@@ -90,7 +90,7 @@ pub enum DepNode<D: Clone + Debug> {
     RvalueCheck(D),
     Reachability,
     DeadCheck,
-    StabilityCheck,
+    StabilityCheck(D),
     LateLintCheck,
     TransCrate,
     TransCrateItem(D),
@@ -189,7 +189,6 @@ impl<D: Clone + Debug> DepNode<D> {
             Privacy => Some(Privacy),
             Reachability => Some(Reachability),
             DeadCheck => Some(DeadCheck),
-            StabilityCheck => Some(StabilityCheck),
             LateLintCheck => Some(LateLintCheck),
             TransCrate => Some(TransCrate),
             TransWriteMetadata => Some(TransWriteMetadata),
@@ -217,6 +216,7 @@ impl<D: Clone + Debug> DepNode<D> {
             Mir(ref d) => op(d).map(Mir),
             BorrowCheck(ref d) => op(d).map(BorrowCheck),
             RvalueCheck(ref d) => op(d).map(RvalueCheck),
+            StabilityCheck(ref d) => op(d).map(StabilityCheck),
             TransCrateItem(ref d) => op(d).map(TransCrateItem),
             TransInlinedItem(ref d) => op(d).map(TransInlinedItem),
             AssociatedItems(ref d) => op(d).map(AssociatedItems),

src/librustc/hir/def.rs

@@ -83,14 +83,6 @@ impl PathResolution {
         PathResolution { base_def: def, depth: 0 }
     }
 
-    /// Get the definition, if fully resolved, otherwise panic.
-    pub fn full_def(&self) -> Def {
-        if self.depth != 0 {
-            bug!("path not fully resolved: {:?}", self);
-        }
-        self.base_def
-    }
-
     pub fn kind_name(&self) -> &'static str {
         if self.depth != 0 {
             "associated item"

src/librustc/hir/intravisit.rs

@@ -38,6 +38,7 @@ use syntax::ast::{NodeId, CRATE_NODE_ID, Name, Attribute};
 use syntax::codemap::Spanned;
 use syntax_pos::Span;
 use hir::*;
+use hir::def::Def;
 use hir::map::Map;
 use super::itemlikevisit::DeepVisitor;
 
@@ -155,6 +156,9 @@ pub trait Visitor<'v> : Sized {
     fn visit_id(&mut self, _node_id: NodeId) {
         // Nothing to do.
     }
+    fn visit_def_mention(&mut self, _def: Def) {
+        // Nothing to do.
+    }
     fn visit_name(&mut self, _span: Span, _name: Name) {
         // Nothing to do.
     }
@@ -244,12 +248,12 @@ pub trait Visitor<'v> : Sized {
     fn visit_lifetime_def(&mut self, lifetime: &'v LifetimeDef) {
         walk_lifetime_def(self, lifetime)
     }
+    fn visit_qpath(&mut self, qpath: &'v QPath, id: NodeId, span: Span) {
+        walk_qpath(self, qpath, id, span)
+    }
     fn visit_path(&mut self, path: &'v Path, _id: NodeId) {
         walk_path(self, path)
     }
-    fn visit_path_list_item(&mut self, prefix: &'v Path, item: &'v PathListItem) {
-        walk_path_list_item(self, prefix, item)
-    }
     fn visit_path_segment(&mut self, path_span: Span, path_segment: &'v PathSegment) {
         walk_path_segment(self, path_span, path_segment)
     }
@@ -349,23 +353,9 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item) {
             visitor.visit_id(item.id);
             walk_opt_name(visitor, item.span, opt_name)
         }
-        ItemUse(ref vp) => {
+        ItemUse(ref path, _) => {
             visitor.visit_id(item.id);
-            match vp.node {
-                ViewPathSimple(name, ref path) => {
-                    visitor.visit_name(vp.span, name);
-                    visitor.visit_path(path, item.id);
-                }
-                ViewPathGlob(ref path) => {
-                    visitor.visit_path(path, item.id);
-                }
-                ViewPathList(ref prefix, ref list) => {
-                    visitor.visit_path(prefix, item.id);
-                    for item in list {
-                        visitor.visit_path_list_item(prefix, item)
-                    }
-                }
-            }
+            visitor.visit_path(path, item.id);
         }
         ItemStatic(ref typ, _, ref expr) |
         ItemConst(ref typ, ref expr) => {
@@ -481,11 +471,8 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty) {
             walk_fn_decl(visitor, &function_declaration.decl);
             walk_list!(visitor, visit_lifetime_def, &function_declaration.lifetimes);
         }
-        TyPath(ref maybe_qself, ref path) => {
-            if let Some(ref qself) = *maybe_qself {
-                visitor.visit_ty(&qself.ty);
-            }
-            visitor.visit_path(path, typ.id);
+        TyPath(ref qpath) => {
+            visitor.visit_qpath(qpath, typ.id, typ.span);
         }
         TyObjectSum(ref ty, ref bounds) => {
             visitor.visit_ty(ty);
@@ -508,20 +495,28 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty) {
     }
 }
 
+pub fn walk_qpath<'v, V: Visitor<'v>>(visitor: &mut V, qpath: &'v QPath, id: NodeId, span: Span) {
+    match *qpath {
+        QPath::Resolved(ref maybe_qself, ref path) => {
+            if let Some(ref qself) = *maybe_qself {
+                visitor.visit_ty(qself);
+            }
+            visitor.visit_path(path, id)
+        }
+        QPath::TypeRelative(ref qself, ref segment) => {
+            visitor.visit_ty(qself);
+            visitor.visit_path_segment(span, segment);
+        }
+    }
+}
+
 pub fn walk_path<'v, V: Visitor<'v>>(visitor: &mut V, path: &'v Path) {
+    visitor.visit_def_mention(path.def);
     for segment in &path.segments {
         visitor.visit_path_segment(path.span, segment);
     }
 }
 
-pub fn walk_path_list_item<'v, V>(visitor: &mut V, _prefix: &'v Path, item: &'v PathListItem)
-    where V: Visitor<'v>,
-{
-    visitor.visit_id(item.node.id);
-    visitor.visit_name(item.span, item.node.name);
-    walk_opt_name(visitor, item.span, item.node.rename);
-}
-
 pub fn walk_path_segment<'v, V: Visitor<'v>>(visitor: &mut V,
                                              path_span: Span,
                                              segment: &'v PathSegment) {
@@ -555,18 +550,15 @@ pub fn walk_assoc_type_binding<'v, V: Visitor<'v>>(visitor: &mut V,
 pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat) {
     visitor.visit_id(pattern.id);
     match pattern.node {
-        PatKind::TupleStruct(ref path, ref children, _) => {
-            visitor.visit_path(path, pattern.id);
+        PatKind::TupleStruct(ref qpath, ref children, _) => {
+            visitor.visit_qpath(qpath, pattern.id, pattern.span);
             walk_list!(visitor, visit_pat, children);
         }
-        PatKind::Path(ref opt_qself, ref path) => {
-            if let Some(ref qself) = *opt_qself {
-                visitor.visit_ty(&qself.ty);
-            }
-            visitor.visit_path(path, pattern.id)
+        PatKind::Path(ref qpath) => {
+            visitor.visit_qpath(qpath, pattern.id, pattern.span);
         }
-        PatKind::Struct(ref path, ref fields, _) => {
-            visitor.visit_path(path, pattern.id);
+        PatKind::Struct(ref qpath, ref fields, _) => {
+            visitor.visit_qpath(qpath, pattern.id, pattern.span);
             for field in fields {
                 visitor.visit_name(field.span, field.node.name);
                 visitor.visit_pat(&field.node.pat)
@@ -579,7 +571,8 @@ pub fn walk_pat<'v, V: Visitor<'v>>(visitor: &mut V, pattern: &'v Pat) {
         PatKind::Ref(ref subpattern, _) => {
             visitor.visit_pat(subpattern)
         }
-        PatKind::Binding(_, ref pth1, ref optional_subpattern) => {
+        PatKind::Binding(_, def_id, ref pth1, ref optional_subpattern) => {
+            visitor.visit_def_mention(Def::Local(def_id));
             visitor.visit_name(pth1.span, pth1.node);
             walk_list!(visitor, visit_pat, optional_subpattern);
         }
@@ -840,8 +833,8 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
             visitor.visit_expr(element);
             visitor.visit_expr(count)
         }
-        ExprStruct(ref path, ref fields, ref optional_base) => {
-            visitor.visit_path(path, expression.id);
+        ExprStruct(ref qpath, ref fields, ref optional_base) => {
+            visitor.visit_qpath(qpath, expression.id, expression.span);
             for field in fields {
                 visitor.visit_name(field.name.span, field.name.node);
                 visitor.visit_expr(&field.expr)
@@ -917,18 +910,21 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
             visitor.visit_expr(main_expression);
             visitor.visit_expr(index_expression)
         }
-        ExprPath(ref maybe_qself, ref path) => {
-            if let Some(ref qself) = *maybe_qself {
-                visitor.visit_ty(&qself.ty);
-            }
-            visitor.visit_path(path, expression.id)
+        ExprPath(ref qpath) => {
+            visitor.visit_qpath(qpath, expression.id, expression.span);
         }
-        ExprBreak(ref opt_sp_name, ref opt_expr) => {
-            walk_opt_sp_name(visitor, opt_sp_name);
+        ExprBreak(None, ref opt_expr) => {
             walk_list!(visitor, visit_expr, opt_expr);
         }
-        ExprAgain(ref opt_sp_name) => {
-            walk_opt_sp_name(visitor, opt_sp_name);
+        ExprBreak(Some(label), ref opt_expr) => {
+            visitor.visit_def_mention(Def::Label(label.loop_id));
+            visitor.visit_name(label.span, label.name);
+            walk_list!(visitor, visit_expr, opt_expr);
+        }
+        ExprAgain(None) => {}
+        ExprAgain(Some(label)) => {
+            visitor.visit_def_mention(Def::Label(label.loop_id));
+            visitor.visit_name(label.span, label.name);
         }
         ExprRet(ref optional_expression) => {
             walk_list!(visitor, visit_expr, optional_expression);