From c36c0fdc154bed5563b73497532242404e736231 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 18 Feb 2022 17:21:16 -0800
Subject: [PATCH 1/2] Add test of negative literal

---
 tests/test_ensure.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tests/test_ensure.rs b/tests/test_ensure.rs
index c75edc5..411983d 100644
--- a/tests/test_ensure.rs
+++ b/tests/test_ensure.rs
@@ -327,10 +327,14 @@ fn test_path() {
     fn f<const I: isize>() {}
     let test = || Ok(ensure!(f::<1>() != ()));
     assert_err(test, "Condition failed: `f::<1>() != ()` (() vs ())");
+    let test = || Ok(ensure!(f::<-1>() != ()));
+    assert_err(test, "Condition failed: `f::<-1>() != ()`"); // FIXME
 
     fn g<T, const I: isize>() {}
     let test = || Ok(ensure!(g::<u8, 1>() != ()));
     assert_err(test, "Condition failed: `g::<u8, 1>() != ()` (() vs ())");
+    let test = || Ok(ensure!(g::<u8, -1>() != ()));
+    assert_err(test, "Condition failed: `g::<u8, -1>() != ()` (() vs ())");
 
     #[derive(PartialOrd, PartialEq, Debug)]
     enum E<'a, T> {

From c38e117db2f87147806dfb3fb359e7dcbcbcaa28 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 18 Feb 2022 17:26:49 -0800
Subject: [PATCH 2/2] Handle negative literal const generic argument after left
 arrow

---
 src/ensure.rs        | 16 ++++++++++++++++
 tests/test_ensure.rs |  2 +-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/ensure.rs b/src/ensure.rs
index dcb9b09..96a810a 100644
--- a/src/ensure.rs
+++ b/src/ensure.rs
@@ -257,6 +257,10 @@ macro_rules! __parse_ensure {
         $crate::__parse_ensure!(generic (epath $stack) $bail ($($fuel)*) {($($buf)* $colons <) $($parse)*} (< $($rest)*) < $($rest)*)
     };
 
+    (epath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $($dup:tt)*) :: <- $($rest:tt)*) => {
+        $crate::__parse_ensure!(generic (epath $stack) $bail ($($fuel)*) {($($buf)* $colons <) $($parse)*} (- $($rest)*) - $($rest)*)
+    };
+
     (epath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $($dup:tt)*) :: $ident:ident $($rest:tt)*) => {
         $crate::__parse_ensure!(epath $stack $bail ($($fuel)*) {($($buf)* $colons $ident) $($parse)*} ($($rest)*) $($rest)*)
     };
@@ -303,6 +307,10 @@ macro_rules! __parse_ensure {
         $crate::__parse_ensure!(generic (atom $stack) $bail ($($fuel)*) {($($buf)* $dot $ident $colons <) $($parse)*} (< $($rest)*) < $($rest)*)
     };
 
+    (atom $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($dot:tt $ident:tt $colons:tt $($dup:tt)*) . $i:ident :: <- $($rest:tt)*) => {
+        $crate::__parse_ensure!(generic (atom $stack) $bail ($($fuel)*) {($($buf)* $dot $ident $colons <) $($parse)*} (- $($rest)*) - $($rest)*)
+    };
+
     (atom $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($dot:tt $($dup:tt)*) . $field:ident $($rest:tt)*) => {
         $crate::__parse_ensure!(atom $stack $bail ($($fuel)*) {($($buf)* $dot $field) $($parse)*} ($($rest)*) $($rest)*)
     };
@@ -427,6 +435,10 @@ macro_rules! __parse_ensure {
         $crate::__parse_ensure!(generic (tpath $stack) $bail ($($fuel)*) {($($buf)* <) $($parse)*} (< $($rest)*) < $($rest)*)
     };
 
+    (tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} $dup:tt <- $($rest:tt)*) => {
+        $crate::__parse_ensure!(generic (tpath $stack) $bail ($($fuel)*) {($($buf)* <) $($parse)*} (- $($rest)*) - $($rest)*)
+    };
+
     (tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $langle:tt $($dup:tt)*) :: < $($rest:tt)*) => {
         $crate::__parse_ensure!(generic (tpath $stack) $bail ($($fuel)*) {($($buf)* $colons $langle) $($parse)*} ($($rest)*) $($rest)*)
     };
@@ -435,6 +447,10 @@ macro_rules! __parse_ensure {
         $crate::__parse_ensure!(generic (tpath $stack) $bail ($($fuel)*) {($($buf)* $colons <) $($parse)*} (< $($rest)*) < $($rest)*)
     };
 
+    (tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $($dup:tt)*) :: <- $($rest:tt)*) => {
+        $crate::__parse_ensure!(generic (tpath $stack) $bail ($($fuel)*) {($($buf)* $colons <) $($parse)*} (- $($rest)*) - $($rest)*)
+    };
+
     (tpath $stack:tt $bail:tt (~$($fuel:tt)*) {($($buf:tt)*) $($parse:tt)*} ($colons:tt $($dup:tt)*) :: $ident:ident $($rest:tt)*) => {
         $crate::__parse_ensure!(tpath $stack $bail ($($fuel)*) {($($buf)* $colons $ident) $($parse)*} ($($rest)*) $($rest)*)
     };
diff --git a/tests/test_ensure.rs b/tests/test_ensure.rs
index 411983d..4bb12f9 100644
--- a/tests/test_ensure.rs
+++ b/tests/test_ensure.rs
@@ -328,7 +328,7 @@ fn test_path() {
     let test = || Ok(ensure!(f::<1>() != ()));
     assert_err(test, "Condition failed: `f::<1>() != ()` (() vs ())");
     let test = || Ok(ensure!(f::<-1>() != ()));
-    assert_err(test, "Condition failed: `f::<-1>() != ()`"); // FIXME
+    assert_err(test, "Condition failed: `f::<-1>() != ()` (() vs ())");
 
     fn g<T, const I: isize>() {}
     let test = || Ok(ensure!(g::<u8, 1>() != ()));