dialyzer: Fix crash when adding multiple PLTs to a PLT

The code previously assumed that multiple PLTs would only be used in
combination with an analysis, but adding multiple PLTs to another
without analysis was not considered.

The existing logic for merging PLTs was used in the context of an
analysis, with different data to hand, so here we just validate the
merge, then sequentially add each PLT.

2 files changed, 41 insertions, 6 deletions

diff --git a/lib/dialyzer/src/dialyzer_cl.erl b/lib/dialyzer/src/dialyzer_cl.erl
index dd235d9025..a46336617c 100644
--- a/lib/dialyzer/src/dialyzer_cl.erl
+++ b/lib/dialyzer/src/dialyzer_cl.erl
@@ -105,7 +105,16 @@ init_opts_for_build(Opts) ->
 add_to_plt(Opts) ->
   Opts1 = init_opts_for_add(Opts),
   AddFiles = get_files_from_opts(Opts1),
-  plt_common(Opts1, [], AddFiles).
+  case Opts1#options.init_plts of
+    [] -> plt_common(Opts1, [], AddFiles);
+    [_] -> plt_common(Opts1, [], AddFiles);
+    PltFiles ->
+      Plts = [dialyzer_cplt:from_file(F) || F <- PltFiles],
+      % Check merge safety
+      _ = dialyzer_cplt:merge_plts_or_report_conflicts(PltFiles, Plts),
+      _ = [plt_common(Opts#options{init_plts=[Plt]}, [], AddFiles) || Plt <- PltFiles],
+      {{?RET_NOTHING_SUSPICIOUS, []}, [], []}
+  end.
 
 init_opts_for_add(Opts) ->
   case Opts#options.output_plt =:= none of
@@ -229,19 +238,19 @@ plt_common(#options{init_plts = [InitPlt]} = Opts, RemoveFiles, AddFiles) ->
 	  enrich_with_modules_changed(do_analysis(AnalFiles, Opts, Plt, #plt_info{files=Md5, mod_deps=ModDeps1}), ChangedOrRemovedMods)
       end;
     {error, no_such_file} ->
-      Msg = io_lib:format("Could not find the PLT: ~ts\n~s",
+      Msg = io_lib:format("Could not find the PLT: ~ts~n~s",
 			  [InitPlt, default_plt_error_msg()]),
       cl_error(Msg);
     {error, not_valid} ->
-      Msg = io_lib:format("The file: ~ts is not a valid PLT file\n~s",
+      Msg = io_lib:format("The file: ~ts is not a valid PLT file~n~s",
 			  [InitPlt, default_plt_error_msg()]),
       cl_error(Msg);
     {error, read_error} ->
-      Msg = io_lib:format("Could not read the PLT: ~ts\n~s",
+      Msg = io_lib:format("Could not read the PLT: ~ts~n~s",
 			  [InitPlt, default_plt_error_msg()]),
       cl_error(Msg);
     {error, {no_file_to_remove, F}} ->
-      Msg = io_lib:format("Could not remove the file ~ts from the PLT: ~ts\n",
+      Msg = io_lib:format("Could not remove the file ~ts from the PLT: ~ts~n",
 			  [F, InitPlt]),
       cl_error(Msg)
   end.
diff --git a/lib/dialyzer/test/dialyzer_cl_SUITE.erl b/lib/dialyzer/test/dialyzer_cl_SUITE.erl
index ed84fc6068..a639b1cae4 100644
--- a/lib/dialyzer/test/dialyzer_cl_SUITE.erl
+++ b/lib/dialyzer/test/dialyzer_cl_SUITE.erl
@@ -9,14 +9,16 @@
 
 %% Test cases must be exported.
 -export([
+    can_add_multiple_plts_to_another_plt/1,
     unknown_function_warning_includes_callsite/1,
     call_to_missing_warning_includes_callsite/1
 ]).
 
-suite() -> [{timetrap, {minutes, 1}}].
+suite() -> [{timetrap, {minutes, 3}}].
 
 all() ->
     [
+        can_add_multiple_plts_to_another_plt,
         unknown_function_warning_includes_callsite,
         call_to_missing_warning_includes_callsite
     ].
@@ -119,6 +121,30 @@ unknown_function_warning_includes_callsite(Config) when is_list(Config) ->
 
     ok.
 
+% See GitHub issue erlang/OTP #6850
+can_add_multiple_plts_to_another_plt(Config) when is_list(Config) ->
+
+    PrivDir = proplists:get_value(priv_dir,Config),
+
+    StdlibPlt = filename:join(PrivDir, "stdlib.plt"),
+    ErtsPlt = filename:join(PrivDir, "erts.plt"),
+    OutputPlt = filename:join(PrivDir, "merged.plt"),
+
+    _ = dialyzer:run([{analysis_type, plt_build},
+                      {apps, [stdlib]},
+                      {output_plt, StdlibPlt}]),
+    _ = dialyzer:run([{analysis_type, plt_build},
+                      {apps, [erts]},
+                      {output_plt, ErtsPlt}]),
+    ?assertEqual(
+       [],
+       dialyzer:run([{analysis_type, plt_add},
+                     {apps, [erts, stdlib]},
+                     {plts, [ErtsPlt, StdlibPlt]},
+                     {output_plt, OutputPlt}])),
+
+    ok.
+
 compile(Config, Module, CompileOpts) ->
     Source = lists:concat([Module, ".erl"]),
     PrivDir = proplists:get_value(priv_dir,Config),