Tweak path parsing logic

src/libsyntax/parse/parser.rs

@@ -3620,7 +3620,7 @@ impl<'a> Parser<'a> {
                 // Parse box pat
                 let subpat = self.parse_pat()?;
                 pat = PatKind::Box(subpat);
-            } else if self.token.is_ident() && self.token.is_path_start() &&
+            } else if self.token.is_ident() && !self.token.is_any_keyword() &&
                       self.look_ahead(1, |t| match *t {
                           token::OpenDelim(token::Paren) | token::OpenDelim(token::Brace) |
                           token::DotDotDot | token::ModSep | token::Not => false,
@@ -3871,6 +3871,11 @@ impl<'a> Parser<'a> {
         })
     }
 
+    fn is_union_item(&mut self) -> bool {
+        self.token.is_keyword(keywords::Union) &&
+        self.look_ahead(1, |t| t.is_ident() && !t.is_any_keyword())
+    }
+
     fn parse_stmt_without_recovery(&mut self,
                                    macro_legacy_warnings: bool)
                                    -> PResult<'a, Option<Stmt>> {
@@ -3885,10 +3890,10 @@ impl<'a> Parser<'a> {
                 node: StmtKind::Local(self.parse_local(attrs.into())?),
                 span: mk_sp(lo, self.prev_span.hi),
             }
-        } else if self.token.is_path_start() && self.token != token::Lt && {
-            !self.check_keyword(keywords::Union) ||
-            self.look_ahead(1, |t| *t == token::Not || *t == token::ModSep)
-        } {
+        // Starts like a simple path, but not a union item.
+        } else if self.token.is_path_start() &&
+                  !self.token.is_qpath_start() &&
+                  !self.is_union_item() {
             let pth = self.parse_path(PathStyle::Expr)?;
 
             if !self.eat(&token::Not) {
@@ -4599,6 +4604,10 @@ impl<'a> Parser<'a> {
             token::Ident(ident) => { this.bump(); codemap::respan(this.prev_span, ident) }
             _ => unreachable!()
         };
+        let isolated_self = |this: &mut Self, n| {
+            this.look_ahead(n, |t| t.is_keyword(keywords::SelfValue)) &&
+            this.look_ahead(n + 1, |t| t != &token::ModSep)
+        };
 
         // Parse optional self parameter of a method.
         // Only a limited set of initial token sequences is considered self parameters, anything
@@ -4611,22 +4620,22 @@ impl<'a> Parser<'a> {
                 // &'lt self
                 // &'lt mut self
                 // &not_self
-                if self.look_ahead(1, |t| t.is_keyword(keywords::SelfValue)) {
+                if isolated_self(self, 1) {
                     self.bump();
                     (SelfKind::Region(None, Mutability::Immutable), expect_ident(self))
                 } else if self.look_ahead(1, |t| t.is_keyword(keywords::Mut)) &&
-                          self.look_ahead(2, |t| t.is_keyword(keywords::SelfValue)) {
+                          isolated_self(self, 2) {
                     self.bump();
                     self.bump();
                     (SelfKind::Region(None, Mutability::Mutable), expect_ident(self))
                 } else if self.look_ahead(1, |t| t.is_lifetime()) &&
-                          self.look_ahead(2, |t| t.is_keyword(keywords::SelfValue)) {
+                          isolated_self(self, 2) {
                     self.bump();
                     let lt = self.parse_lifetime()?;
                     (SelfKind::Region(Some(lt), Mutability::Immutable), expect_ident(self))
                 } else if self.look_ahead(1, |t| t.is_lifetime()) &&
                           self.look_ahead(2, |t| t.is_keyword(keywords::Mut)) &&
-                          self.look_ahead(3, |t| t.is_keyword(keywords::SelfValue)) {
+                          isolated_self(self, 3) {
                     self.bump();
                     let lt = self.parse_lifetime()?;
                     self.bump();
@@ -4641,12 +4650,12 @@ impl<'a> Parser<'a> {
                 // *mut self
                 // *not_self
                 // Emit special error for `self` cases.
-                if self.look_ahead(1, |t| t.is_keyword(keywords::SelfValue)) {
+                if isolated_self(self, 1) {
                     self.bump();
                     self.span_err(self.span, "cannot pass `self` by raw pointer");
                     (SelfKind::Value(Mutability::Immutable), expect_ident(self))
                 } else if self.look_ahead(1, |t| t.is_mutability()) &&
-                          self.look_ahead(2, |t| t.is_keyword(keywords::SelfValue)) {
+                          isolated_self(self, 2) {
                     self.bump();
                     self.bump();
                     self.span_err(self.span, "cannot pass `self` by raw pointer");
@@ -4656,7 +4665,7 @@ impl<'a> Parser<'a> {
                 }
             }
             token::Ident(..) => {
-                if self.token.is_keyword(keywords::SelfValue) {
+                if isolated_self(self, 0) {
                     // self
                     // self: TYPE
                     let eself_ident = expect_ident(self);
@@ -4667,7 +4676,7 @@ impl<'a> Parser<'a> {
                         (SelfKind::Value(Mutability::Immutable), eself_ident)
                     }
                 } else if self.token.is_keyword(keywords::Mut) &&
-                        self.look_ahead(1, |t| t.is_keyword(keywords::SelfValue)) {
+                          isolated_self(self, 1) {
                     // mut self
                     // mut self: TYPE
                     self.bump();
@@ -5958,8 +5967,7 @@ impl<'a> Parser<'a> {
                                     maybe_append(attrs, extra_attrs));
             return Ok(Some(item));
         }
-        if self.check_keyword(keywords::Union) &&
-                self.look_ahead(1, |t| t.is_ident() && !t.is_any_keyword()) {
+        if self.is_union_item() {
             // UNION ITEM
             self.bump();
             let (ident, item_, extra_attrs) = self.parse_item_union()?;

src/libsyntax/parse/token.rs

@@ -159,10 +159,8 @@ impl Token {
     /// Returns `true` if the token can appear at the start of an expression.
     pub fn can_begin_expr(&self) -> bool {
         match *self {
-            OpenDelim(_)                => true,
+            OpenDelim(..)               => true,
             Ident(..)                   => true,
-            Underscore                  => true,
-            Tilde                       => true,
             Literal(..)                 => true,
             Not                         => true,
             BinOp(Minus)                => true,
@@ -172,6 +170,7 @@ impl Token {
             OrOr                        => true, // in lambda syntax
             AndAnd                      => true, // double borrow
             DotDot | DotDotDot          => true, // range notation
+            Lt | BinOp(Shl)             => true, // associated path
             ModSep                      => true,
             Interpolated(NtExpr(..))    => true,
             Interpolated(NtIdent(..))   => true,
@@ -236,8 +235,12 @@ impl Token {
         self.is_keyword(keywords::Const)
     }
 
+    pub fn is_qpath_start(&self) -> bool {
+        self == &Lt || self == &BinOp(Shl)
+    }
+
     pub fn is_path_start(&self) -> bool {
-        self == &ModSep || self == &Lt || self.is_path() ||
+        self == &ModSep || self.is_qpath_start() || self.is_path() ||
         self.is_path_segment_keyword() || self.is_ident() && !self.is_any_keyword()
     }
 

src/test/compile-fail/associated-path-shl.rs

@@ -0,0 +1,20 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Check that associated paths starting with `<<` are successfully parsed.
+
+fn main() {
+    let _: <<A>::B>::C; //~ ERROR type name `A` is undefined or not in scope
+    let _ = <<A>::B>::C; //~ ERROR type name `A` is undefined or not in scope
+    let <<A>::B>::C; //~ ERROR type name `A` is undefined or not in scope
+    let 0 ... <<A>::B>::C; //~ ERROR type name `A` is undefined or not in scope
+                           //~^ ERROR only char and numeric types are allowed in range patterns
+    <<A>::B>::C; //~ ERROR type name `A` is undefined or not in scope
+}

src/test/compile-fail/keyword-self-as-identifier.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z parse-only
-
 fn main() {
-    let Self = "foo"; //~ error: expected identifier, found keyword `Self`
+    let Self = "foo"; //~ ERROR unresolved unit struct/variant or constant `Self`
 }

src/test/compile-fail/keyword-super-as-identifier.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z parse-only
-
 fn main() {
-    let super = "foo"; //~ error: expected identifier, found keyword `super`
+    let super = "foo"; //~ ERROR unresolved unit struct/variant or constant `super`
 }

src/test/compile-fail/keyword-super.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// compile-flags: -Z parse-only
-
 fn main() {
-    let super: isize; //~ ERROR expected identifier, found keyword `super`
+    let super: isize; //~ ERROR unresolved unit struct/variant or constant `super`
 }

src/test/compile-fail/self-vs-path-ambiguity.rs

@@ -0,0 +1,23 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Check that `self::foo` is parsed as a general pattern and not a self argument.
+
+struct S;
+
+impl S {
+    fn f(self::S: S) {}
+    fn g(&self::S: &S) {}
+    fn h(&mut self::S: &mut S) {}
+    fn i(&'a self::S: &S) {} //~ ERROR unexpected lifetime `'a` in pattern
+                             //~^ ERROR expected one of `)` or `mut`, found `'a`
+}
+
+fn main() {}

src/test/compile-fail/self_type_keyword-2.rs

@@ -10,4 +10,14 @@
 
 use self::Self as Foo; //~ ERROR unresolved import `self::Self`
 
-pub fn main() {}
+pub fn main() {
+    let Self = 5;
+    //~^ ERROR unresolved unit struct/variant or constant `Self`
+
+    match 15 {
+        Self => (),
+        //~^ ERROR unresolved unit struct/variant or constant `Self`
+        Foo { x: Self } => (),
+        //~^ ERROR unresolved unit struct/variant or constant `Self`
+    }
+}

src/test/compile-fail/self_type_keyword.rs

@@ -17,12 +17,7 @@ struct Bar<'Self>;
 //~^ ERROR lifetimes cannot use keyword names
 
 pub fn main() {
-    let Self = 5;
-    //~^ ERROR expected identifier, found keyword `Self`
-
     match 15 {
-        Self => (),
-        //~^ ERROR expected identifier, found keyword `Self`
         ref Self => (),
         //~^ ERROR expected identifier, found keyword `Self`
         mut Self => (),
@@ -31,8 +26,6 @@ pub fn main() {
         //~^ ERROR expected identifier, found keyword `Self`
         Self!() => (),
         //~^ ERROR macro undefined: 'Self!'
-        Foo { x: Self } => (),
-        //~^ ERROR expected identifier, found keyword `Self`
         Foo { Self } => (),
         //~^ ERROR expected identifier, found keyword `Self`
     }

src/test/run-pass/union/union-backcomp.rs

@@ -10,6 +10,12 @@
 
 #![feature(untagged_unions)]
 
+macro_rules! union {
+    () => (struct S;)
+}
+
+union!();
+
 fn union() {}
 
 fn main() {