Auto merge of #22172 - eddyb:almost-there, r=nikomatsakis

Adds `<module::Type>::method` support and makes `module::Type::method` a shorthand for it.
This is most of #16293, except that chaining multiple associated types is not yet supported.
It also fixes #22563 as `impl`s are no longer treated as modules in resolve.

Unfortunately, this is still a *[breaking-change]*:
* If you used a global path to a primitive type, i.e. `::bool`, `::i32` etc. - that was a bug I had to fix.
Solution: remove the leading `::`.
* If you passed explicit `impl`-side type parameters to an inherent method, e.g.:
```rust
struct Foo<T>(T);
impl<A, B> Foo<(A, B)> {
    fn pair(a: A, b: B) -> Foo<(A, B)> { Foo((a, b)) }
}
Foo::<A, B>::pair(a, b)
// Now that is sugar for:
<Foo<A, B>>::pair(a, b)
// Which isn't valid because `Foo` has only one type parameter.
// Solution: replace with:
Foo::<(A, B)>::pair(a, b)
// And, if possible, remove the explicit type param entirely:
Foo::pair(a, b)
```
* If you used the `QPath`-related `AstBuilder` methods @hugwijst added in #21943.
The methods still exist, but `QPath` was replaced by `QSelf`, with the actual path stored separately.
Solution: unpack the pair returned by `cx.qpath` to get the two arguments for `cx.expr_qpath`.

2 files changed, 70 insertions, 39 deletions

diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index 43dfcbae57e..4d099529cb4 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -774,7 +774,7 @@ mod test {
         assert!(string_to_expr("a".to_string()) ==
                    P(ast::Expr{
                     id: ast::DUMMY_NODE_ID,
-                    node: ast::ExprPath(ast::Path {
+                    node: ast::ExprPath(None, ast::Path {
                         span: sp(0, 1),
                         global: false,
                         segments: vec!(
@@ -792,7 +792,7 @@ mod test {
         assert!(string_to_expr("::a::b".to_string()) ==
                    P(ast::Expr {
                     id: ast::DUMMY_NODE_ID,
-                    node: ast::ExprPath(ast::Path {
+                    node: ast::ExprPath(None, ast::Path {
                             span: sp(0, 6),
                             global: true,
                             segments: vec!(
@@ -974,7 +974,7 @@ mod test {
                     id: ast::DUMMY_NODE_ID,
                     node:ast::ExprRet(Some(P(ast::Expr{
                         id: ast::DUMMY_NODE_ID,
-                        node:ast::ExprPath(ast::Path{
+                        node:ast::ExprPath(None, ast::Path{
                             span: sp(7, 8),
                             global: false,
                             segments: vec!(
@@ -995,7 +995,7 @@ mod test {
                    P(Spanned{
                        node: ast::StmtExpr(P(ast::Expr {
                            id: ast::DUMMY_NODE_ID,
-                           node: ast::ExprPath(ast::Path {
+                           node: ast::ExprPath(None, ast::Path {
                                span:sp(0,1),
                                global:false,
                                segments: vec!(
@@ -1041,7 +1041,7 @@ mod test {
                             node: ast::ItemFn(P(ast::FnDecl {
                                 inputs: vec!(ast::Arg{
                                     ty: P(ast::Ty{id: ast::DUMMY_NODE_ID,
-                                                  node: ast::TyPath(ast::Path{
+                                                  node: ast::TyPath(None, ast::Path{
                                         span:sp(10,13),
                                         global:false,
                                         segments: vec!(
@@ -1051,7 +1051,7 @@ mod test {
                                                 parameters: ast::PathParameters::none(),
                                             }
                                         ),
-                                        }, ast::DUMMY_NODE_ID),
+                                        }),
                                         span:sp(10,13)
                                     }),
                                     pat: P(ast::Pat {
@@ -1084,7 +1084,7 @@ mod test {
                                         stmts: vec!(P(Spanned{
                                             node: ast::StmtSemi(P(ast::Expr{
                                                 id: ast::DUMMY_NODE_ID,
-                                                node: ast::ExprPath(
+                                                node: ast::ExprPath(None,
                                                       ast::Path{
                                                         span:sp(17,18),
                                                         global:false,
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index fec33eddb91..f171e8279f4 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -25,7 +25,7 @@ use ast::{ExprAssign, ExprAssignOp, ExprBinary, ExprBlock, ExprBox};
 use ast::{ExprBreak, ExprCall, ExprCast};
 use ast::{ExprField, ExprTupField, ExprClosure, ExprIf, ExprIfLet, ExprIndex};
 use ast::{ExprLit, ExprLoop, ExprMac, ExprRange};
-use ast::{ExprMethodCall, ExprParen, ExprPath, ExprQPath};
+use ast::{ExprMethodCall, ExprParen, ExprPath};
 use ast::{ExprRepeat, ExprRet, ExprStruct, ExprTup, ExprUnary};
 use ast::{ExprVec, ExprWhile, ExprWhileLet, ExprForLoop, Field, FnDecl};
 use ast::{ForeignItem, ForeignItemStatic, ForeignItemFn, ForeignMod, FunctionRetTy};
@@ -43,7 +43,7 @@ use ast::{MethodImplItem, NamedField, UnNeg, NoReturn, NodeId, UnNot};
 use ast::{Pat, PatEnum, PatIdent, PatLit, PatRange, PatRegion, PatStruct};
 use ast::{PatTup, PatBox, PatWild, PatWildMulti, PatWildSingle};
 use ast::{PolyTraitRef};
-use ast::{QPath, RequiredMethod};
+use ast::{QSelf, RequiredMethod};
 use ast::{Return, BiShl, BiShr, Stmt, StmtDecl};
 use ast::{StmtExpr, StmtSemi, StmtMac, StructDef, StructField};
 use ast::{StructVariantKind, BiSub, StrStyle};
@@ -53,7 +53,7 @@ use ast::{TtDelimited, TtSequence, TtToken};
 use ast::{TupleVariantKind, Ty, Ty_, TypeBinding};
 use ast::{TyFixedLengthVec, TyBareFn};
 use ast::{TyTypeof, TyInfer, TypeMethod};
-use ast::{TyParam, TyParamBound, TyParen, TyPath, TyPolyTraitRef, TyPtr, TyQPath};
+use ast::{TyParam, TyParamBound, TyParen, TyPath, TyPolyTraitRef, TyPtr};
 use ast::{TyRptr, TyTup, TyU32, TyVec, UnUniq};
 use ast::{TypeImplItem, TypeTraitItem, Typedef,};
 use ast::{UnnamedField, UnsafeBlock};
@@ -143,7 +143,7 @@ macro_rules! maybe_whole_expr {
                         _ => unreachable!()
                     };
                     let span = $p.span;
-                    Some($p.mk_expr(span.lo, span.hi, ExprPath(pt)))
+                    Some($p.mk_expr(span.lo, span.hi, ExprPath(None, pt)))
                 }
                 token::Interpolated(token::NtBlock(_)) => {
                     // FIXME: The following avoids an issue with lexical borrowck scopes,
@@ -1076,8 +1076,7 @@ impl<'a> Parser<'a> {
     }
 
     pub fn parse_ty_path(&mut self) -> Ty_ {
-        let path = self.parse_path(LifetimeAndTypesWithoutColons);
-        TyPath(path, ast::DUMMY_NODE_ID)
+        TyPath(None, self.parse_path(LifetimeAndTypesWithoutColons))
     }
 
     /// parse a TyBareFn type:
@@ -1525,19 +1524,36 @@ impl<'a> Parser<'a> {
         } else if self.eat_lt() {
             // QUALIFIED PATH `<TYPE as TRAIT_REF>::item`
             let self_type = self.parse_ty_sum();
-            self.expect_keyword(keywords::As);
-            let trait_ref = self.parse_trait_ref();
+
+            let mut path = if self.eat_keyword(keywords::As) {
+                self.parse_path(LifetimeAndTypesWithoutColons)
+            } else {
+                ast::Path {
+                    span: self.span,
+                    global: false,
+                    segments: vec![]
+                }
+            };
+
+            let qself = QSelf {
+                ty: self_type,
+                position: path.segments.len()
+            };
+
             self.expect(&token::Gt);
             self.expect(&token::ModSep);
-            let item_name = self.parse_ident();
-            TyQPath(P(QPath {
-                self_type: self_type,
-                trait_ref: P(trait_ref),
-                item_path: ast::PathSegment {
-                    identifier: item_name,
-                    parameters: ast::PathParameters::none()
-                }
-            }))
+
+            path.segments.push(ast::PathSegment {
+                identifier: self.parse_ident(),
+                parameters: ast::PathParameters::none()
+            });
+
+            if path.segments.len() == 1 {
+                path.span.lo = self.last_span.lo;
+            }
+            path.span.hi = self.last_span.hi;
+
+            TyPath(Some(qself), path)
         } else if self.check(&token::ModSep) ||
                   self.token.is_ident() ||
                   self.token.is_path() {
@@ -2178,7 +2194,7 @@ impl<'a> Parser<'a> {
                          }, token::Plain) => {
                 self.bump();
                 let path = ast_util::ident_to_path(mk_sp(lo, hi), id);
-                ex = ExprPath(path);
+                ex = ExprPath(None, path);
                 hi = self.last_span.hi;
             }
             token::OpenDelim(token::Bracket) => {
@@ -2220,10 +2236,22 @@ impl<'a> Parser<'a> {
                 if self.eat_lt() {
                     // QUALIFIED PATH `<TYPE as TRAIT_REF>::item::<'a, T>`
                     let self_type = self.parse_ty_sum();
-                    self.expect_keyword(keywords::As);
-                    let trait_ref = self.parse_trait_ref();
+                    let mut path = if self.eat_keyword(keywords::As) {
+                        self.parse_path(LifetimeAndTypesWithoutColons)
+                    } else {
+                        ast::Path {
+                            span: self.span,
+                            global: false,
+                            segments: vec![]
+                        }
+                    };
+                    let qself = QSelf {
+                        ty: self_type,
+                        position: path.segments.len()
+                    };
                     self.expect(&token::Gt);
                     self.expect(&token::ModSep);
+
                     let item_name = self.parse_ident();
                     let parameters = if self.eat(&token::ModSep) {
                         self.expect_lt();
@@ -2238,15 +2266,18 @@ impl<'a> Parser<'a> {
                     } else {
                         ast::PathParameters::none()
                     };
+                    path.segments.push(ast::PathSegment {
+                        identifier: item_name,
+                        parameters: parameters
+                    });
+
+                    if path.segments.len() == 1 {
+                        path.span.lo = self.last_span.lo;
+                    }
+                    path.span.hi = self.last_span.hi;
+
                     let hi = self.span.hi;
-                    return self.mk_expr(lo, hi, ExprQPath(P(QPath {
-                        self_type: self_type,
-                        trait_ref: P(trait_ref),
-                        item_path: ast::PathSegment {
-                            identifier: item_name,
-                            parameters: parameters
-                        }
-                    })));
+                    return self.mk_expr(lo, hi, ExprPath(Some(qself), path));
                 }
                 if self.eat_keyword(keywords::Move) {
                     return self.parse_lambda_expr(CaptureByValue);
@@ -2386,7 +2417,7 @@ impl<'a> Parser<'a> {
                     }
 
                     hi = pth.span.hi;
-                    ex = ExprPath(pth);
+                    ex = ExprPath(None, pth);
                 } else {
                     // other literal expression
                     let lit = self.parse_lit();
@@ -3428,7 +3459,7 @@ impl<'a> Parser<'a> {
                 let end = if self.token.is_ident() || self.token.is_path() {
                     let path = self.parse_path(LifetimeAndTypesWithColons);
                     let hi = self.span.hi;
-                    self.mk_expr(lo, hi, ExprPath(path))
+                    self.mk_expr(lo, hi, ExprPath(None, path))
                 } else {
                     self.parse_literal_maybe_minus()
                 };
@@ -4815,10 +4846,10 @@ impl<'a> Parser<'a> {
         let opt_trait = if could_be_trait && self.eat_keyword(keywords::For) {
             // New-style trait. Reinterpret the type as a trait.
             match ty.node {
-                TyPath(ref path, node_id) => {
+                TyPath(None, ref path) => {
                     Some(TraitRef {
                         path: (*path).clone(),
-                        ref_id: node_id,
+                        ref_id: ty.id,
                     })
                 }
                 _ => {