stdlib: Improve error handling in module io_lib

2 files changed, 46 insertions, 15 deletions

diff --git a/lib/stdlib/src/io_lib.erl b/lib/stdlib/src/io_lib.erl
index 3a5aba60b4..8223a52873 100644
--- a/lib/stdlib/src/io_lib.erl
+++ b/lib/stdlib/src/io_lib.erl
@@ -178,11 +178,11 @@ fread(Cont, Chars, Format) ->
       Data :: [term()].
 
 format(Format, Args) ->
-    case catch io_lib_format:fwrite(Format, Args) of
-	{'EXIT',_} ->
-	    erlang:error(badarg, [Format, Args]);
-	Other ->
-	    Other
+    try io_lib_format:fwrite(Format, Args)
+    catch
+        C:R:S ->
+            test_modules_loaded(C, R, S),
+            erlang:error(badarg, [Format, Args])
     end.
 
 -spec format(Format, Data, Options) -> chars() when
@@ -193,11 +193,11 @@ format(Format, Args) ->
       CharsLimit :: chars_limit().
 
 format(Format, Args, Options) ->
-    case catch io_lib_format:fwrite(Format, Args, Options) of
-	{'EXIT',_} ->
-	    erlang:error(badarg, [Format, Args, Options]);
-	Other ->
-	    Other
+    try io_lib_format:fwrite(Format, Args, Options)
+    catch
+        C:R:S ->
+            test_modules_loaded(C, R, S),
+            erlang:error(badarg, [Format, Args])
     end.
 
 -spec scan_format(Format, Data) -> FormatList when
@@ -208,7 +208,9 @@ format(Format, Args, Options) ->
 scan_format(Format, Args) ->
     try io_lib_format:scan(Format, Args)
     catch
-        _:_ -> erlang:error(badarg, [Format, Args])
+        C:R:S ->
+            test_modules_loaded(C, R, S),
+            erlang:error(badarg, [Format, Args])
     end.
 
 -spec unscan_format(FormatList) -> {Format, Data} when
@@ -223,7 +225,12 @@ unscan_format(FormatList) ->
       FormatList :: [char() | format_spec()].
 
 build_text(FormatList) ->
-    io_lib_format:build(FormatList).
+    try io_lib_format:build(FormatList)
+    catch
+        C:R:S ->
+            test_modules_loaded(C, R, S),
+            erlang:error(badarg, [FormatList])
+    end.
 
 -spec build_text(FormatList, Options) -> chars() when
       FormatList :: [char() | format_spec()],
@@ -232,7 +239,23 @@ build_text(FormatList) ->
       CharsLimit :: chars_limit().
 
 build_text(FormatList, Options) ->
-    io_lib_format:build(FormatList, Options).
+    try io_lib_format:build(FormatList, Options)
+    catch
+        C:R:S ->
+            test_modules_loaded(C, R, S),
+            erlang:error(badarg, [FormatList, Options])
+    end.
+
+%% Failure to load a module must not be labeled as badarg.
+%% C, R, and S are included so that the original error, which could be
+%% a bug in io_lib_format, can be found by tracing on
+%% test_modules_loaded/3.
+test_modules_loaded(_C, _R, _S) ->
+    Modules = [io_lib_format, io_lib_pretty, string, unicode],
+    case code:ensure_modules_loaded(Modules) of
+        ok -> ok;
+        Error -> erlang:error(Error)
+    end.
 
 -spec print(Term) -> chars() when
       Term :: term().
diff --git a/lib/stdlib/test/io_SUITE.erl b/lib/stdlib/test/io_SUITE.erl
index 79cee54335..f097552e8c 100644
--- a/lib/stdlib/test/io_SUITE.erl
+++ b/lib/stdlib/test/io_SUITE.erl
@@ -31,7 +31,7 @@
          otp_10836/1, io_lib_width_too_small/1,
          io_with_huge_message_queue/1, format_string/1,
 	 maps/1, coverage/1, otp_14178_unicode_atoms/1, otp_14175/1,
-         otp_14285/1, limit_term/1, otp_14983/1, otp_15103/1,
+         otp_14285/1, limit_term/1, otp_14983/1, otp_15103/1, otp_15076/1,
          otp_15159/1]).
 
 -export([pretty/2, trf/3]).
@@ -64,7 +64,7 @@ all() ->
      io_lib_print_binary_depth_one, otp_10302, otp_10755, otp_10836,
      io_lib_width_too_small, io_with_huge_message_queue,
      format_string, maps, coverage, otp_14178_unicode_atoms, otp_14175,
-     otp_14285, limit_term, otp_14983, otp_15103, otp_15159].
+     otp_14285, limit_term, otp_14983, otp_15103, otp_15076, otp_15159].
 
 %% Error cases for output.
 error_1(Config) when is_list(Config) ->
@@ -2639,3 +2639,11 @@ otp_15159(_Config) ->
     "[atom]" =
         lists:flatten(io_lib:format("~p", [[atom]], [{chars_limit,5}])),
     ok.
+
+otp_15076(_Config) ->
+    {'EXIT', {badarg, _}} = (catch io_lib:format("~c", [a])),
+    L = io_lib:scan_format("~c", [a]),
+    {"~c", [a]} = io_lib:unscan_format(L),
+    {'EXIT', {badarg, _}} = (catch io_lib:build_text(L)),
+    {'EXIT', {badarg, _}} = (catch io_lib:build_text(L, [])),
+    ok.