C++: Add a skeleton class for requires expressions

Author: jketema

cpp/downgrades/6f5d51e89e762fe4609fd4ac8ee3afb04221e873/exprs.ql

@@ -0,0 +1,15 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class Location extends @location_expr {
+  string toString() { none() }
+}
+
+predicate isExprRequires(Expr expr) { exists(int kind | exprs(expr, kind, _) | kind = 390) }
+
+from Expr expr, int kind, int kind_new, Location location
+where
+  exprs(expr, kind, location) and
+  if isExprRequires(expr) then kind_new = 1 else kind_new = kind
+select expr, kind_new, location