allows any character in the variable name (#1086)

BIL and Core Theory variable literals can contain only a specific
set of valid characters. Thus approach doesn't play nice with various
manglers and non-C languages as well as contradicts with our own
tradition as we generally tend to allow any character in variables,
see our Knowledge variables for example (and which are used underneath
the hood of CT and BIL variables).

One of the real-world examples where bap fails is the new C++ code
with lambdas, that uses `#` for anonymous variables.

In this proposal we allow any string (including the empty one) to be
used as a variable name. First of all, we escape any non-printable or
whitespace characters. We also escape '.' as we use it for variable
versioning. Next, if a prospective variable name starts from a digit,
is empty, or starts with `$` or `#` (which we use to encode de-bruijin
style variables) we prefix them with `_`.

Note, that escaping whitespaces and non-printable characters is really
not necessary, but helps with the textual representation of the
variable name, in case if we hit one.

Author: ivg

lib/bap_core_theory/bap_core_theory_var.ml

@@ -31,33 +31,25 @@ let valid_first_char = function
   | '0'..'9' | '#' | '$' -> false
   | _ -> true
 
-let valid_char c =
-  valid_first_char c || match c with
-  | '0' .. '9' | '\'' | '.' -> true
-  | _ -> false
-
-let non_empty name =
-  if String.length name = 0
-  then invalid_arg "Invalid var literal: a variable can't be empty"
-
-let all_chars_valid name =
-  if not (valid_first_char name.[0])
-  then invalid_argf
-      "Invalid var literal: a variable can't start from %c" name.[0] ();
-  match String.find name ~f:(Fn.non valid_char) with
-  | None -> ()
-  | Some c ->
-    invalid_argf
-      "Invalid var literal: a variable can't contain char %c" c ()
-
-let validate_variable name =
-  non_empty name;
-  all_chars_valid name
+let escapeworthy = Char.all |> List.filter ~f:(function
+    | '.' -> true
+    | c -> Char.is_whitespace c || not (Char.is_print c))
+
+let escape_char = '\\'
+
+let escape =
+  Staged.unstage @@
+  String.Escaping.escape ~escapeworthy ~escape_char
+
+let mangle_if_necessary name =
+  let name = escape name in
+  if String.is_empty name then "_"
+  else if not (valid_first_char name.[0])
+  then "_" ^ name
+  else name
 
 let define sort name : 'a var =
-  validate_variable name;
-  non_empty name;
-  sort, Reg {name; ver=0}
+  sort, Reg {name=mangle_if_necessary name; ver=0}
 
 let create sort ident = sort,ident
 
@@ -118,7 +110,7 @@ module Ident = struct
     failwithf "`%s' is not a valid temporary value" s ()
 
   let split_version s =
-    match String.rfindi s ~f:(fun _ c -> Char.(c = '.')) with
+    match String.Escaping.rindex s ~escape_char '.' with
     | None -> s,0
     | Some n ->
       String.subo ~len:n s,
@@ -134,7 +126,6 @@ module Ident = struct
       let s,ver = split_version s in
       Var {num = num s; ver}
     | _ -> fun _ ->
-      validate_variable x;
       let name,ver = split_version x in
       Reg {name; ver}