compiler: Warn if the size of a binary segment is invalid

The compiler would silently accept and Dialyzer would crash on
code like:

  <<X:(2.5)>>

It is never acceptable for Dialyzer to crash. The compiler should
at least generate a warning for such code. It is tempting to let
the compiler generate an error, but that would mean that code like:

  Sz = 42.0,
  <<X:Sz>>.

would be possible to compile with optimizations disabled, but not
with optimizations enabled.

Dialyzer crashes because it calls cerl:bitstr_bitsize/1, which
crashes if the type of size for the segment is invalid. The easiest
way to avoid that crash is to extend the sanity checks in v3_core
to also include the size field of binary segments. That will cause
the compiler to issue a warning and to replace the bad binary
construction with a call to erlang:error/1. (It also means that
Dialyzer will not issue a warning for bad size fields.)

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index 242196c593..01042cc56f 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -823,6 +823,13 @@ bitstr({bin_element,_,E0,Size0,[Type,{unit,Unit}|Flags]}, St0) ->
 	{_,_} ->
 	    throw(bad_binary)
     end,
+    case Size1 of
+	#c_var{} -> ok;
+	#c_literal{val=Sz} when is_integer(Sz), Sz >= 0 -> ok;
+	#c_literal{val=undefined} -> ok;
+	#c_literal{val=all} -> ok;
+	_ -> throw(bad_binary)
+    end,
     {#c_bitstr{val=E1,size=Size1,
 	       unit=#c_literal{val=Unit},
 	       type=#c_literal{val=Type},