From bc2cd1be708c3b376d8cd6c5bee3d91a83d98775 Mon Sep 17 00:00:00 2001
From: Jacob Alexander <haata@kiibohd.com>
Date: Tue, 28 Dec 2021 11:11:20 -0800
Subject: [PATCH 1/2] Relax Vec bounds to allow for zero-length Vecs

Use when building generated code where it's possible to have a zero
length array/vector (e.g. wire-format). See #252

- Added vec::tests::zero_capacity test
- Added sealed::greater_than_eq_0
---
 src/sealed.rs |  6 ++++++
 src/vec.rs    | 23 +++++++++++++++++++++--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/sealed.rs b/src/sealed.rs
index 2efb07f2..53692319 100644
--- a/src/sealed.rs
+++ b/src/sealed.rs
@@ -52,6 +52,12 @@ pub(crate) const fn smaller_than<const N: usize, const MAX: usize>() {
     Assert::<N, MAX>::LESS;
 }
 
+#[allow(dead_code)]
+#[allow(path_statements)]
+pub(crate) const fn greater_than_eq_0<const N: usize>() {
+    Assert::<N, 0>::GREATER_EQ;
+}
+
 #[allow(dead_code)]
 #[allow(path_statements)]
 pub(crate) const fn greater_than_0<const N: usize>() {
diff --git a/src/vec.rs b/src/vec.rs
index 51b4d50c..d458ea45 100644
--- a/src/vec.rs
+++ b/src/vec.rs
@@ -56,8 +56,8 @@ impl<T, const N: usize> Vec<T, N> {
     /// ```
     /// `Vec` `const` constructor; wrap the returned value in [`Vec`](../struct.Vec.html)
     pub const fn new() -> Self {
-        // Const assert N > 0
-        crate::sealed::greater_than_0::<N>();
+        // Const assert N >= 0
+        crate::sealed::greater_than_eq_0::<N>();
 
         Self {
             buffer: [Self::INIT; N],
@@ -1233,4 +1233,23 @@ mod tests {
         assert!(!v.ends_with(b"ba"));
         assert!(!v.ends_with(b"a"));
     }
+
+    #[test]
+    fn zero_capacity() {
+        let mut v: Vec<u8, 0> = Vec::new();
+        // Validate capacity
+        assert_eq!(v.capacity(), 0);
+
+        // Make sure there is no capacity
+        assert!(v.push(1).is_err());
+
+        // Validate length
+        assert_eq!(v.len(), 0);
+
+        // Validate pop
+        assert_eq!(v.pop(), None);
+
+        // Validate slice
+        assert_eq!(v.as_slice(), &[]);
+    }
 }

From 0b92953ef12e93cb51c55759edb73e30625b6806 Mon Sep 17 00:00:00 2001
From: Jacob Alexander <haata@kiibohd.com>
Date: Wed, 29 Dec 2021 12:01:45 -0800
Subject: [PATCH 2/2] Adding is_empty and is_full tests for zero capacity

---
 src/vec.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/vec.rs b/src/vec.rs
index d458ea45..f2866c0c 100644
--- a/src/vec.rs
+++ b/src/vec.rs
@@ -1251,5 +1251,11 @@ mod tests {
 
         // Validate slice
         assert_eq!(v.as_slice(), &[]);
+
+        // Validate empty
+        assert!(v.is_empty());
+
+        // Validate full
+        assert!(v.is_full());
     }
 }