Extend ~ts to handle binaries with characters coded in ISO-latin-1

Make sure io_lib:fwrite() with a format string including "~ts" does
not crash when given binaries that cannot be interpreted as
UTF-8-encoded strings.

We want to avoid crashes caused by excessive use of the 't' modifier.

2 files changed, 29 insertions, 4 deletions

diff --git a/lib/stdlib/src/io_lib_format.erl b/lib/stdlib/src/io_lib_format.erl
index 6a06d9448b..64d19ccf48 100644
--- a/lib/stdlib/src/io_lib_format.erl
+++ b/lib/stdlib/src/io_lib_format.erl
@@ -185,8 +185,7 @@ control($s, [L0], F, Adj, P, Pad, latin1, _I) ->
     L = iolist_to_chars(L0),
     string(L, F, Adj, P, Pad);
 control($s, [L0], F, Adj, P, Pad, unicode, _I) ->
-    L = unicode:characters_to_list(L0),
-    true = is_list(L),
+    L = cdata_to_chars(L0),
     uniconv(string(L, F, Adj, P, Pad));
 control($e, [A], F, Adj, P, Pad, _Enc, _I) when is_float(A) ->
     fwrite_e(A, F, Adj, P, Pad);
@@ -558,6 +557,25 @@ iolist_to_chars([]) ->
 iolist_to_chars(B) when is_binary(B) ->
     binary_to_list(B).
 
+%% cdata() :: clist() | cbinary()
+%% clist() ::  maybe_improper_list(char() | cbinary() | clist(),
+%%                                 cbinary() | nil())
+%% cbinary() :: unicode:unicode_binary() | unicode:latin1_binary()
+
+%% cdata_to_chars(cdata()) -> io_lib:deep_char_list()
+
+cdata_to_chars([C|Cs]) when is_integer(C), C >= $\000 ->
+    [C | cdata_to_chars(Cs)];
+cdata_to_chars([I|Cs]) ->
+    [cdata_to_chars(I) | cdata_to_chars(Cs)];
+cdata_to_chars([]) ->
+    [];
+cdata_to_chars(B) when is_binary(B) ->
+    case catch unicode:characters_to_list(B) of
+        L when is_list(L) -> L;
+        _ -> binary_to_list(B)
+    end.
+
 %% string(String, Field, Adjust, Precision, PadChar)
 
 string(S, none, _Adj, none, _Pad) -> S;
diff --git a/lib/stdlib/test/io_SUITE.erl b/lib/stdlib/test/io_SUITE.erl
index 05009fa570..65a112c966 100644
--- a/lib/stdlib/test/io_SUITE.erl
+++ b/lib/stdlib/test/io_SUITE.erl
@@ -29,7 +29,7 @@
          manpage/1, otp_6708/1, otp_7084/1, otp_7421/1,
 	 io_lib_collect_line_3_wb/1, cr_whitespace_in_string/1,
 	 io_fread_newlines/1, otp_8989/1, io_lib_fread_literal/1,
-	 io_lib_print_binary_depth_one/1, otp_10302/1]).
+	 io_lib_print_binary_depth_one/1, otp_10302/1, otp_10836/1]).
 
 %-define(debug, true).
 
@@ -65,7 +65,7 @@ all() ->
      manpage, otp_6708, otp_7084, otp_7421,
      io_lib_collect_line_3_wb, cr_whitespace_in_string,
      io_fread_newlines, otp_8989, io_lib_fread_literal,
-     io_lib_print_binary_depth_one, otp_10302].
+     io_lib_print_binary_depth_one, otp_10302, otp_10836].
 
 groups() -> 
     [].
@@ -2078,3 +2078,10 @@ pretty(Term, Opts) when is_list(Opts) ->
 
 is_latin1(S) ->
     S >= 0 andalso S =< 255.
+
+otp_10836(doc) ->
+    "OTP-10836. ~ts extended to latin1";
+otp_10836(Suite) when is_list(Suite) ->
+    S = io_lib:format("~ts", [[<<"äpple"/utf8>>, <<"äpple">>]]),
+    "äppleäpple" = lists:flatten(S),
+    ok.