From a81bdc960dd2d9007089e8ca0ff878a3d7c34d9e Mon Sep 17 00:00:00 2001
From: Ben Bridle <ben@derelict.engineering>
Date: Fri, 17 Oct 2025 21:20:05 +1300
Subject: Restrict variable names to lower-case characters and hyphens

This is so that the characters < and > can be used in patterns without
over-zealously interpreting rules as variable names.
---
 src/highlighter.rs | 32 +++++++++++++++++++-------------
 1 file changed, 19 insertions(+), 13 deletions(-)

diff --git a/src/highlighter.rs b/src/highlighter.rs
index 40e618e..fe40160 100644
--- a/src/highlighter.rs
+++ b/src/highlighter.rs
@@ -105,22 +105,28 @@ impl Highlighter {
 
 fn replace_variables(pattern: &str, variables: &HashMap<String, String>) -> String {
     let mut output = String::new();
-    let mut chars = pattern.chars();
-    while let Some(c) = chars.next() {
-        if c == '<' {
-            let mut name = String::from('<');
-            loop {
-                match chars.next() {
-                    Some('>') => { name.push('>'); break; }
-                    Some(c)   => name.push(c),
-                    None      => panic!("Missing '>' character"),
+    let chars: Vec<char> = pattern.chars().collect();
+    let mut i = 0;
+    'outer: while let Some(c) = chars.get(i) {
+        if *c == '<' {
+            let mut name = String::from(*c);
+            let mut j = i+1;
+            while let Some(d) = chars.get(j) {
+                name.push(*d);
+                if *d == '>' {
+                    let pattern = variables.get(&name).expect(&format!("Missing definition for {name:?}"));
+                    output.push_str(&format!("(?:{pattern})"));
+                    i = j+1;
+                    continue 'outer;
                 }
+                if !d.is_lowercase() && *d != '-' {
+                    break;
+                }
+                j += 1;
             }
-            let pattern = variables.get(&name).expect(&format!("Missing definition for {name:?}"));
-            output.push_str(&format!("(?:{pattern})"));
-        } else {
-            output.push(c);
         }
+        output.push(*c);
+        i += 1;
     }
     return output;
 }
-- 
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