zcoord: Reject attempt to make range [X,X>

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/base/zcoord.rs b/base/zcoord.rs
index f236ba1d96bd62a0f475d474bd77e89abca7b67c..dbf3749167fc90f73767d618388b0a3ba5367b87 100644 (file)
--- a/base/zcoord.rs
+++ b/base/zcoord.rs
@@ -107,6 +107,8 @@ pub struct ParseError;
 pub enum RangeImpossible {
   #[error("Z coordinate range has end before start, cannot iterate")]
   Backwards,
+  #[error("Z coordinate range has end equal to start, cannot iterate")]
+  Empty,
 }
 
 #[derive(Error,Clone,Copy,Debug,Eq,PartialEq,Serialize,Deserialize)]
@@ -382,7 +384,7 @@ impl Mutable {
     let aso = 'ok: loop { for i in 0.. {
       if i >= a.limbs.len() && i >= b.limbs.len() {
        // Oh actually these numbers are equal!
-       break 'ok ASRD { i: 0, step: ZERO };
+       throw!(RangeImpossible::Empty);
       }
       current.extend_to_limb(i);