Syntax: Support const functions.

RustEnhanced.sublime-syntax

@@ -106,6 +106,11 @@ contexts:
 
     - include: raw-pointer
 
+    # `const` in a function header has a different scope from `const` values.
+    - match: '\b(const)\s+(?=unsafe|extern|fn)'
+      captures:
+        1: storage.modifier.rust
+
     - match: '\b(const)\s+({{identifier}})'
       captures:
         1: storage.type.rust

tests/syntax-rust/syntax_test_functions.rs

@@ -106,3 +106,21 @@ fn f(self,
 //        ^ punctuation.section.brackets.end
 //         ^ punctuation.separator
 {}
+
+const fn f() {}
+// <- storage.modifier
+//    ^^ meta.function storage.type.function
+//       ^ meta.function entity.name.function
+
+const unsafe fn f() {}
+// <- storage.modifier
+//    ^^^^^^ storage.modifier
+//           ^^ meta.function storage.type.function
+//              ^ meta.function entity.name.function
+
+const extern "C" fn f() {}
+// <- storage.modifier
+//    ^^^^^^ keyword.other
+//           ^^^ string.quoted.double
+//               ^^ meta.function storage.type.function
+//                  ^ meta.function entity.name.function