Ensure :: is treated as a single token in Rust

CHANGELOG.md

@@ -3,9 +3,9 @@
 Diffs are now displayed with unchanged lines aligned to the other side.
 
 Improved Rust parsing to recognise lifetime syntax `'foo`, character
-literals `'x'` and sequences of punctuation.
+literals `'x'` and punctuation.
 
-Improve punctuation parsing for OCaml and JS.
+Improved punctuation parsing for OCaml and JS.
 
 Fixed an issue where the diff calculated may not be minimal.
 

config/syntax.toml

@@ -156,7 +156,9 @@ atom_patterns = [
   "'[a-z_]+",
   # Symbols (e.g. variable names)
   '[a-zA-Z0-9_]+!?',
-  # Operators
+  # Two character operators
+  '(::|&&|\|\|)',
+  # Single character operators
   # | is a delimiter for lambdas, but also used in pattern matching.
   '[.&=<>/*+:;,|#!?-]',
 ]