Rollup merge of #42886 - durka:pplmm-mwe, r=petrochenkov

syntax: allow negative integer literal expression to be interpolated as pattern

Fixes #42820.

r? @jseyfried

src/test/compile-fail/patkind-litrange-no-expr.rs

@@ -0,0 +1,36 @@
+// Copyright 2017 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.
+
+macro_rules! enum_number {
+    ($name:ident { $($variant:ident = $value:expr, )* }) => {
+        enum $name {
+            $($variant = $value,)*
+        }
+
+        fn foo(value: i32) -> Option<$name> {
+            match value {
+                $( $value => Some($name::$variant), )* // PatKind::Lit
+                $( $value ... 42 => Some($name::$variant), )* // PatKind::Range
+                _ => None
+            }
+        }
+    }
+}
+
+enum_number!(Change {
+    Pos = 1,
+    Neg = -1,
+    Arith = 1 + 1, //~ ERROR arbitrary expressions aren't allowed in patterns
+                   //~^ ERROR arbitrary expressions aren't allowed in patterns
+                   //~^^ ERROR only char and numeric types are allowed in range patterns
+});
+
+fn main() {}
+

src/test/run-pass/macro-pat-neg-lit.rs

@@ -0,0 +1,35 @@
+// Copyright 2017 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.
+
+macro_rules! enum_number {
+    ($name:ident { $($variant:ident = $value:expr, )* }) => {
+        enum $name {
+            $($variant = $value,)*
+        }
+
+        fn foo(value: i32) -> Option<$name> {
+            match value {
+                $( $value => Some($name::$variant), )*
+                _ => None
+            }
+        }
+    }
+}
+
+enum_number!(Change {
+    Down = -1,
+    None = 0,
+    Up = 1,
+});
+
+fn main() {
+    if let Some(Change::Down) = foo(-1) {} else { panic!() }
+}
+