Add test for GH 2684

rakudo/rakudo#2684

S10-packages/precompilation.t

@@ -3,7 +3,7 @@ use Test;
 use lib $?FILE.IO.parent(2).add("packages/Test-Helpers");
 use Test::Util;
 
-plan 49;
+plan 51;
 
 my @*MODULES; # needed for calling CompUnit::Repository::need directly
 
@@ -289,3 +289,16 @@ with make-temp-dir() -> $dir {
 	     'no funny business with precompiled string strands (\qq[$_])';
     }
 }
+
+# GH 2684
+with make-temp-dir() -> $dir {
+    $dir.add('GH2684.pm6').spurt: ｢
+        my $x; BEGIN { $x = -> { "foo".subst(/o/, 'a', :g) } }; $x();
+    ｣;
+
+    for ^2 {
+        is_run 'use lib \qq[$dir.absolute().perl()]; use GH2684;',
+            {:out(''), :err(''), :0status},
+	    "Dyncomp lexical lookup plays well with BEGIN blocks ($_)";
+    }
+}