Harden attributes_of_types against out-of-scope structs/unions/enums

In rare cases we can end up querying the attributes of a struct, union
or enum type that is no longer in scope and therefore not bound
in the current environment.

Instead of raising an Env.Error_ exception in this case,
this commit treats such structs / unions / enums as having no
attributes attached to their definitions: only the attributes
carried by the type expression are returned.

One example where this occurs is the following, made possible by
the previous commit ("Revised elaboration of function definitions"):

int f(struct s { int a; } * p) { return p-> a; }

int g(void) { return f(NULL); }

"struct s" is scoped within the definition of f.  When we get to
checking the call to f from g, checking that the NULL argument
is compatible with the "struct s *" parameters, we're outside
the scope of "struct s" and its definition is not found in the
current environment.

1 files changed, 12 insertions, 3 deletions

diff --git a/cparser/Cutil.ml b/cparser/Cutil.ml
index f3cd5d14..99b059c0 100644
--- a/cparser/Cutil.ml
+++ b/cparser/Cutil.ml
@@ -175,11 +175,20 @@ let rec attributes_of_type env t =
   | TFun(ty, params, vararg, a) -> a
   | TNamed(s, a) -> attributes_of_type env (unroll env t)
   | TStruct(s, a) ->
-      let ci = Env.find_struct env s in add_attributes ci.ci_attr a
+      begin match Env.find_struct env s with
+      | ci -> add_attributes ci.ci_attr a
+      | exception Env.Error(Env.Unbound_tag _) -> a
+      end
   | TUnion(s, a) ->
-      let ci = Env.find_union env s in add_attributes ci.ci_attr a
+      begin match Env.find_union env s with
+      | ci -> add_attributes ci.ci_attr a
+      | exception Env.Error(Env.Unbound_tag _) -> a
+      end
   | TEnum(s, a) ->
-    let ei = Env.find_enum env s in add_attributes ei.ei_attr a
+      begin match Env.find_enum env s with
+      | ei -> add_attributes ei.ei_attr a
+      | exception Env.Error(Env.Unbound_tag _) -> a
+      end
 
 (* Changing the attributes of a type (at top-level) *)
 (* Same hack as above for array types. *)