From ce3beb609f75fb690d6980c9e6a62c6efa6f3d97 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Sun, 23 Jul 2017 19:32:36 +0300
Subject: Discern between `Path` and `Path<>` in AST

---
 src/libsyntax/ast.rs       | 14 ++++++--------
 src/libsyntax/ext/build.rs | 20 ++++++++------------
 2 files changed, 14 insertions(+), 20 deletions(-)

(limited to 'src/libsyntax')

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index b8e371a4e76..544afc5d6f6 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -120,12 +120,11 @@ pub struct PathSegment {
     pub span: Span,
 
     /// Type/lifetime parameters attached to this path. They come in
-    /// two flavors: `Path<A,B,C>` and `Path(A,B) -> C`. Note that
-    /// this is more than just simple syntactic sugar; the use of
-    /// parens affects the region binding rules, so we preserve the
-    /// distinction.
-    /// The `Option<P<..>>` wrapper is purely a size optimization;
-    /// `None` is used to represent both `Path` and `Path<>`.
+    /// two flavors: `Path<A,B,C>` and `Path(A,B) -> C`.
+    /// `None` means that no parameter list is supplied (`Path`),
+    /// `Some` means that parameter list is supplied (`Path<X, Y>`)
+    /// but it can be empty (`Path<>`).
+    /// `P` is used as a size optimization for the common case with no parameters.
     pub parameters: Option<P<PathParameters>>,
 }
 
@@ -181,8 +180,7 @@ pub struct AngleBracketedParameterData {
 
 impl Into<Option<P<PathParameters>>> for AngleBracketedParameterData {
     fn into(self) -> Option<P<PathParameters>> {
-        let empty = self.lifetimes.is_empty() && self.types.is_empty() && self.bindings.is_empty();
-        if empty { None } else { Some(P(PathParameters::AngleBracketed(self))) }
+        Some(P(PathParameters::AngleBracketed(self)))
     }
 }
 
diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index d8140417214..af9143eadbc 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -326,14 +326,10 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
         }
 
         segments.extend(idents.into_iter().map(|i| ast::PathSegment::from_ident(i, sp)));
-        let parameters = if lifetimes.is_empty() && types.is_empty() && bindings.is_empty() {
-            None
+        let parameters = if !lifetimes.is_empty() || !types.is_empty() || !bindings.is_empty() {
+            ast::AngleBracketedParameterData { lifetimes, types, bindings }.into()
         } else {
-            Some(P(ast::PathParameters::AngleBracketed(ast::AngleBracketedParameterData {
-                lifetimes: lifetimes,
-                types: types,
-                bindings: bindings,
-            })))
+            None
         };
         segments.push(ast::PathSegment {
             identifier: last_identifier,
@@ -369,15 +365,15 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                  bindings: Vec<ast::TypeBinding>)
                  -> (ast::QSelf, ast::Path) {
         let mut path = trait_path;
-        let parameters = ast::AngleBracketedParameterData {
-            lifetimes: lifetimes,
-            types: types,
-            bindings: bindings,
+        let parameters = if !lifetimes.is_empty() || !types.is_empty() || !bindings.is_empty() {
+            ast::AngleBracketedParameterData { lifetimes, types, bindings }.into()
+        } else {
+            None
         };
         path.segments.push(ast::PathSegment {
             identifier: ident.node,
             span: ident.span,
-            parameters: Some(P(ast::PathParameters::AngleBracketed(parameters))),
+            parameters: parameters,
         });
 
         (ast::QSelf {
-- 
cgit 1.4.1-3-g733a5