From 2b27c6235b4feb1e2aaac2dde5c5c67a29470127 Mon Sep 17 00:00:00 2001
From: varkor <github@varkor.com>
Date: Fri, 31 May 2019 21:18:43 +0100
Subject: [PATCH] Allow `true` and `false` in const generic arguments

---
 src/libsyntax/parse/parser.rs                          | 10 +++++++---
 .../ui/const-generics/condition-in-trait-const-arg.rs  |  2 ++
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 746e9cad4962..a562d2a1d2b4 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -5250,9 +5250,13 @@ impl<'a> Parser<'a> {
                     // FIXME(const_generics): to distinguish between idents for types and consts,
                     // we should introduce a GenericArg::Ident in the AST and distinguish when
                     // lowering to the HIR. For now, idents for const args are not permitted.
-                    return Err(
-                        self.fatal("identifiers may currently not be used for const generics")
-                    );
+                    if self.token.is_keyword(kw::True) || self.token.is_keyword(kw::False) {
+                        self.parse_literal_maybe_minus()?
+                    } else {
+                        return Err(
+                            self.fatal("identifiers may currently not be used for const generics")
+                        );
+                    }
                 } else {
                     self.parse_literal_maybe_minus()?
                 };
diff --git a/src/test/ui/const-generics/condition-in-trait-const-arg.rs b/src/test/ui/const-generics/condition-in-trait-const-arg.rs
index 18105eb7a75f..091fe904826d 100644
--- a/src/test/ui/const-generics/condition-in-trait-const-arg.rs
+++ b/src/test/ui/const-generics/condition-in-trait-const-arg.rs
@@ -7,4 +7,6 @@ trait IsZeroTrait<const IS_ZERO: bool>{}
 
 impl IsZeroTrait<{0u8 == 0u8}> for () {}
 
+impl IsZeroTrait<true> for ((),) {}
+
 fn main() {}