Ruby: exclude 'require' and 'require_relative' definitions from call graph

The syntax_suggest library redefines Kernel.require/require_relative.
Somehow this causes performance issues on ruby/ruby. As a workaround
we exclude 'require' and 'require_relative'.

Author: aibaars

ruby/ql/lib/codeql/ruby/ast/internal/Module.qll

@@ -137,7 +137,14 @@ private module Cached {
   }
 
   cached
-  Method lookupMethod(Module m, string name) { TMethod(result) = lookupMethodOrConst(m, name) }
+  Method lookupMethod(Module m, string name) {
+    // The syntax_suggest library redefines Kernel.require/require_relative.
+    // Somehow this causes performance issues on ruby/ruby. As a workaround
+    // we exclude 'require' and 'require_relative'.
+    // TODO: find the actual cause of the slowdown and fix things properly.
+    not name = ["require", "require_relative"] and
+    TMethod(result) = lookupMethodOrConst(m, name)
+  }
 
   cached
   Expr lookupConst(Module m, string name) {