From 594685b5a2f35e2ff4fc01aca2ae91de92ed0993 Mon Sep 17 00:00:00 2001
From: varkor <github@varkor.com>
Date: Mon, 6 May 2019 17:00:01 +0100
Subject: [PATCH 1/2] `token::LArrow` can begin arguments

`<-` may indicate the start of a negative const argument.
---
 src/libsyntax/parse/parser.rs                             | 3 ++-
 src/test/ui/const-generics/const-expression-parameter.rs  | 2 +-
 .../ui/const-generics/const-expression-parameter.stderr   | 8 +-------
 3 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index d46feeab335..2f7b6f9fa66 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -2319,7 +2319,8 @@ impl<'a> Parser<'a> {
         let ident = self.parse_path_segment_ident()?;
 
         let is_args_start = |token: &token::Token| match *token {
-            token::Lt | token::BinOp(token::Shl) | token::OpenDelim(token::Paren) => true,
+            token::Lt | token::BinOp(token::Shl) | token::OpenDelim(token::Paren)
+            | token::LArrow => true,
             _ => false,
         };
         let check_args_start = |this: &mut Self| {
diff --git a/src/test/ui/const-generics/const-expression-parameter.rs b/src/test/ui/const-generics/const-expression-parameter.rs
index 662c7b767ba..22c6c351622 100644
--- a/src/test/ui/const-generics/const-expression-parameter.rs
+++ b/src/test/ui/const-generics/const-expression-parameter.rs
@@ -6,7 +6,7 @@ fn i32_identity<const X: i32>() -> i32 {
 }
 
 fn foo_a() {
-    i32_identity::<-1>(); //~ ERROR expected identifier, found `<-`
+    i32_identity::<-1>(); // ok
 }
 
 fn foo_b() {
diff --git a/src/test/ui/const-generics/const-expression-parameter.stderr b/src/test/ui/const-generics/const-expression-parameter.stderr
index 2f7a80f0c8f..c255127c280 100644
--- a/src/test/ui/const-generics/const-expression-parameter.stderr
+++ b/src/test/ui/const-generics/const-expression-parameter.stderr
@@ -1,9 +1,3 @@
-error: expected identifier, found `<-`
-  --> $DIR/const-expression-parameter.rs:9:19
-   |
-LL |     i32_identity::<-1>();
-   |                   ^^ expected identifier
-
 error: expected one of `,` or `>`, found `+`
   --> $DIR/const-expression-parameter.rs:13:22
    |
@@ -16,5 +10,5 @@ warning: the feature `const_generics` is incomplete and may cause the compiler t
 LL | #![feature(const_generics)]
    |            ^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 

From e570fe5b220c1c9064587f94a885587b7f910ab1 Mon Sep 17 00:00:00 2001
From: varkor <github@varkor.com>
Date: Mon, 6 May 2019 17:00:34 +0100
Subject: [PATCH 2/2] Remove resolved FIXME

---
 src/libsyntax/parse/parser.rs | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 2f7b6f9fa66..67e3132b2fc 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -6061,8 +6061,6 @@ impl<'a> Parser<'a> {
                         self.fatal("identifiers may currently not be used for const generics")
                     );
                 } else {
-                    // FIXME(const_generics): this currently conflicts with emplacement syntax
-                    // with negative integer literals.
                     self.parse_literal_maybe_minus()?
                 };
                 let value = AnonConst {