dialyzer: make -Wunknown a default; add -Wno_unknown flag

Dialyzer's warnings about unknown functions and types are enabled by
default.

Prior to this PR, Dialyzer used to have disabled (by default) warnings
about unknown types and functions.

This default value has been overwritten; Dialyzer now warns about
unknown types and functions (as requested by the community in erlangGH-5695).
Thus, the following two examples are equivalent, i.e., passing the
`-Wunknown` function is enabled by default:

```bash
dialyzer moduler.erl -Wunknown -Wmissing_return
dialyzer moduler.erl -Wmissing_return
```

Dialyzer has a new flag, `-Wno_unknown`. Its purpose is to supress
warnings about unknown functions and types (erlangGH-5995).

Users who wish to suppress these warnings can invoke Dialyzer using this
flag. Example:

```bash
dialyzer module.erl -Wno_unknown
```

lib/dialyzer/src/dialyzer.hrl

@@ -126,6 +126,7 @@
                        | 'no_return'
                        | 'no_undefined_callbacks'
                        | 'no_underspecs'
+                       | 'no_unknown'
                        | 'no_unused'
                        | 'underspecs'
                        | 'unknown'

lib/dialyzer/src/dialyzer_cl_parse.erl

@@ -594,6 +594,11 @@ warning_options_msg() ->
   -Wno_undefined_callbacks
      Suppress warnings about behaviours that have no -callback attributes for
      their callbacks.
+  -Wno_unknown
+     Suppress warnings about unknown functions and types. The default is to
+     warn about unknown functions and types when setting the exit
+     status. When using Dialyzer from Erlang, warnings about unknown functions
+     and types are returned.
   -Wunmatched_returns ***
      Include warnings for function calls which ignore a structured return
      value or do not match against one of many possible return value(s).
@@ -612,11 +617,10 @@ warning_options_msg() ->
      Warn about overloaded functions whose specification include types that overlap.
   -Wunknown ***
      Let warnings about unknown functions and types affect the
-     exit status of the command line version. The default is to ignore
-     warnings about unknown functions and types when setting the exit
+     exit status of the command line version. The default is to
+     warn about unknown functions and types when setting the exit
      status. When using the Dialyzer from Erlang, warnings about unknown
-     functions and types are returned; the default is not to return
-     such warnings.
+     functions and types are returned.
 
 The following options are also available but their use is not recommended:
 (they are mostly for Dialyzer developers and internal debugging)

lib/dialyzer/src/dialyzer_options.erl

@@ -32,20 +32,21 @@
 
 build(Opts) ->
   DefaultWarns = [?WARN_RETURN_NO_RETURN,
-		  ?WARN_NOT_CALLED,
-		  ?WARN_NON_PROPER_LIST,
-		  ?WARN_FUN_APP,
-		  ?WARN_MATCHING,
-		  ?WARN_OPAQUE,
-		  ?WARN_CALLGRAPH,
-		  ?WARN_FAILING_CALL,
-		  ?WARN_BIN_CONSTRUCTION,
-		  ?WARN_MAP_CONSTRUCTION,
-		  ?WARN_CONTRACT_RANGE,
-		  ?WARN_CONTRACT_TYPES,
-		  ?WARN_CONTRACT_SYNTAX,
-		  ?WARN_BEHAVIOUR,
-		  ?WARN_UNDEFINED_CALLBACK],
+                  ?WARN_NOT_CALLED,
+                  ?WARN_NON_PROPER_LIST,
+                  ?WARN_FUN_APP,
+                  ?WARN_MATCHING,
+                  ?WARN_OPAQUE,
+                  ?WARN_CALLGRAPH,
+                  ?WARN_FAILING_CALL,
+                  ?WARN_BIN_CONSTRUCTION,
+                  ?WARN_MAP_CONSTRUCTION,
+                  ?WARN_CONTRACT_RANGE,
+                  ?WARN_CONTRACT_TYPES,
+                  ?WARN_CONTRACT_SYNTAX,
+                  ?WARN_BEHAVIOUR,
+                  ?WARN_UNDEFINED_CALLBACK,
+                  ?WARN_UNKNOWN],
   DefaultWarns1 = ordsets:from_list(DefaultWarns),
   DefaultOpts = #options{},
   DefaultOpts1 = DefaultOpts#options{legal_warnings = DefaultWarns1},
@@ -429,6 +430,8 @@ build_warnings([Opt|Opts], Warnings) ->
 	ordsets:del_element(?WARN_RETURN_NO_RETURN, Warnings);
       no_unused ->
 	ordsets:del_element(?WARN_NOT_CALLED, Warnings);
+      no_unknown ->
+    ordsets:del_element(?WARN_UNKNOWN, Warnings);
       no_improper_lists ->
 	ordsets:del_element(?WARN_NON_PROPER_LIST, Warnings);
       no_fun_app ->

lib/dialyzer/test/cplt_SUITE.erl

@@ -108,7 +108,8 @@ build_xdg_plt(Config) ->
       fun() ->
         ?assertMatch([], dialyzer:run(
                            [{analysis_type, plt_build},
-                            {apps, [erts]}])),
+                            {apps, [erts]},
+                            {warnings, [no_unknown]}])),
         ?assertMatch(
            {ok,_}, file:read_file(
                      filename:join(
@@ -243,7 +244,8 @@ update_plt(Config) ->
     Opts = [{check_plt, true}, {from, byte_code}],
     [] = dialyzer:run([{analysis_type, plt_build},
                        {files, [Beam, ErlangBeam]},
-                       {output_plt, Plt}] ++ Opts),
+                       {output_plt, Plt},
+                       {warnings, [no_unknown]}] ++ Opts),
 
     Prog2 = <<"-module(plt_gc).
                -export([two/0]).
@@ -296,7 +298,8 @@ local_fun_same_as_callback(Config) when is_list(Config) ->
     Opts = [{check_plt, true}, {from, byte_code}],
     [] = dialyzer:run([{analysis_type, plt_build},
                        {files, [Beam, ErlangBeam]},
-                       {output_plt, Plt}] ++ Opts),
+                       {output_plt, Plt},
+                       {warnings, [no_unknown]}] ++ Opts),
 
     Prog2 =
         <<"-module(bad_child).
@@ -342,15 +345,18 @@ remove_plt(Config) ->
         dialyzer:run([{analysis_type, plt_build},
                       {files, [Beam1, Beam2]},
                       {get_warnings, true},
-                      {output_plt, Plt}] ++ Opts),
+                      {output_plt, Plt},
+                      {warnings, [no_unknown]}] ++ Opts),
 
     [] = dialyzer:run([{init_plt, Plt},
                        {files, [Beam2]},
-                       {analysis_type, plt_remove}]),
+                       {analysis_type, plt_remove},
+                       {warnings, [no_unknown]}]),
 
     [] =  dialyzer:run([{analysis_type, succ_typings},
                         {files, [Beam1]},
-                        {init_plt, Plt}] ++ Opts),
+                        {init_plt, Plt},
+                        {warnings, [no_unknown]}] ++ Opts),
     ok.
 
 %% ERL-283, OTP-13979. As of OTP-14323 this test no longer does what
@@ -567,7 +573,8 @@ create(Config, PltFile) ->
     _ = file:delete(PltFile),
     [] = dialyzer:run([{files,Files},
                        {output_plt, PltFile},
-                       {analysis_type, plt_build}]),
+                       {analysis_type, plt_build},
+                       {warnings, [no_unknown]}]),
     BeamFile.
 
 succ(PltFile, BeamFile2) ->
@@ -922,10 +929,10 @@ compile(Config, Prog, Module, CompileOpts) ->
 
 run_dialyzer(Analysis, Files, Opts) ->
     dialyzer:run([{analysis_type, Analysis},
-		  {files, Files},
-		  {from, byte_code} |
-		  Opts]).
-
+                  {files, Files},
+                  {from, byte_code},
+                  {warnings, [no_unknown]} |
+                  Opts]).
 
 m_src_without_warning() -> <<"
   -module(m).

lib/dialyzer/test/dialyzer_cl_SUITE.erl

@@ -56,7 +56,8 @@ call_to_missing_warning_includes_callsite(Config) when is_list(Config) ->
     {ok, BeamFileForPlt} = compile(Config, previously_defined, []),
     [] = dialyzer:run([{analysis_type, plt_build},
                       {files, [BeamFileForPlt]},
-                      {output_plt, Plt}]),
+                      {output_plt, Plt},
+                       {warnings, [no_unknown]}]),
 
     {ok, Beam} = compile(Config, call_to_missing_example, []),
     Opts =

lib/dialyzer/test/dialyzer_common.erl

@@ -107,9 +107,14 @@ obtain_plt(PltFilename) ->
 
 build_plt(PltFilename) ->
     io:format("Building plt from scratch:"),
+    %% note: suppress unknown type and fn errors. this is simply because
+    %% build_plt builds the plt using defaults, and one would need to add other
+    %% apps to silence missing unknown dependencies such as dependencies to
+    %% crypto and compiler amont others.
+    DefaultWarnings = {warnings, [no_unknown]},
     try dialyzer:run([{analysis_type, plt_build},
 		      {apps, ?required_modules},
-		      {output_plt, PltFilename}]) of
+		      {output_plt, PltFilename}, DefaultWarnings]) of
 	[] ->
 	    io:format("Successfully created plt!"),
 	    ok

lib/dialyzer/test/incremental_SUITE.erl

@@ -202,7 +202,7 @@ add_and_remove_test(Config) ->
     ToPath = fun(Modules) -> [PrivDir ++ atom_to_list(Module) ++ ".beam" || Module <- Modules] end,
     Plt = filename:join(PrivDir, "add_and_remove.iplt"),
     compile_all(DataDir, PrivDir),
-    Opts = [{init_plt, [Plt]}, {report_mode, verbose}],
+    Opts = [{init_plt, [Plt]}, {report_mode, verbose}, {warnings, [no_unknown]}],
     Run = fun(Mods) -> run_dialyzer_for_modules_analyzed(incremental, [erlang_module() | ToPath(Mods)], Opts) end,
     AllSubSets = [Mods || Mods <- all_subsets(all_mods())],
     %Pairs = [{I, N} || I <- AllSubSets, N <- AllSubSets], % All pairs takes ~ 10 mins to run
@@ -584,7 +584,7 @@ report_legal_warnings_added(Config) ->
     ToPath = fun(Modules) -> [PrivDir ++ atom_to_list(Module) ++ ".beam" || Module <- Modules] end,
     Plt = filename:join(PrivDir, atom_to_list(?FUNCTION_NAME) ++ ".iplt"),
     compile_all(DataDir, PrivDir),
-    Opts = [{init_plt, [Plt]}, {report_mode, verbose}],
+    Opts = [{init_plt, [Plt]}, {report_mode, verbose}, {warnings, [no_unknown]}],
     _WarningsBeforeTouchingFile = run_dialyzer(incremental, [erlang_module() | ToPath(all_mods())], Opts),
     Opts1 = [{init_plt, [Plt]}, {report_mode, verbose}, {warnings, [unknown]}, {metrics_file, MetricsFile}],
     {_WarningsAfterTouchingFile, Stdout} = run_dialyzer_capture(incremental, [erlang_module() | ToPath(all_mods())], Opts1),
@@ -615,7 +615,7 @@ report_legal_warnings_removed(Config) ->
     compile_all(DataDir, PrivDir),
     Opts = [{init_plt, [Plt]}, {report_mode, verbose}, {warnings, [unknown]}],
     _ = run_dialyzer(incremental, [erlang_module() | ToPath(all_mods())], Opts),
-    Opts1 = [{init_plt, [Plt]}, {report_mode, verbose}, {metrics_file, MetricsFile}],
+    Opts1 = [{init_plt, [Plt]}, {report_mode, verbose}, {metrics_file, MetricsFile}, {warnings, [no_unknown]}],
     {_, Stdout} = run_dialyzer_capture(incremental, [erlang_module() | ToPath(all_mods())], Opts1),
 
     ExpectedLine =
@@ -713,9 +713,10 @@ all_mods() -> [m1,m2,m3,m4,m5,m6].
 
 run_dialyzer(Analysis, Files, Opts) ->
     dialyzer:run([{analysis_type, Analysis},
-		  {files, Files},
-		  {from, byte_code}|
-		  Opts]).
+      {files, Files},
+      {from, byte_code},
+      {warnings, [no_unknown]}|
+      Opts]).
 
 run_dialyzer_for_modules_analyzed(Analysis, Files, Opts) ->
     dialyzer:run_report_modules_analyzed([{analysis_type, Analysis},

lib/dialyzer/test/indent2_SUITE_data/dialyzer_options

@@ -1 +1 @@
-{dialyzer_options, [{warnings, [no_unused, no_return, specdiffs]}]}.
+{dialyzer_options, [{warnings, [no_unused, no_return, no_unknown, specdiffs]}]}.

lib/dialyzer/test/indent_SUITE_data/dialyzer_options

@@ -1 +1 @@
-{dialyzer_options, [{warnings, [no_unused, no_return, overlapping_contract]}]}.
+{dialyzer_options, [{warnings, [no_unused, no_return, no_unknown, overlapping_contract]}]}.

lib/dialyzer/test/iplt_SUITE.erl

@@ -115,7 +115,8 @@ build_xdg_plt(Config) ->
       fun() ->
         ?assertMatch([], dialyzer:run(
                            [{analysis_type, incremental},
-                            {apps, [erts]}])),
+                            {apps, [erts]},
+                            {warnings, [no_unknown]}])),
         ?assertMatch(
            {ok,_}, file:read_file(
                      filename:join(
@@ -178,7 +179,7 @@ local_fun_same_as_callback(Config) when is_list(Config) ->
                          EBeam
                  end,
     Plt = filename:join(PrivDir, "plt_bad_behaviour.iplt"),
-    Opts = [{from, byte_code}],
+    Opts = [{from, byte_code}, {warnings, [no_unknown]}],
     [] = dialyzer:run([{analysis_type, incremental},
                        {files, [Beam, ErlangBeam]},
                        {output_plt, Plt}] ++ Opts),
@@ -587,7 +588,9 @@ check_plt_deps(Config, TestName, DependerSrc, ExpectedTypeDepsInPltUnsorted) ->
     PltFile = filename:join(PrivDir, atom_to_list(TestName) ++ ".iplt"),
     {ok, DepsBeamFile} = compile(Config, type_deps, []),
     {ok, DependerBeamFile} = compile(Config, DependerSrc, depender, []),
-    [] = run_dialyzer(incremental, [DependerBeamFile, DepsBeamFile], [{init_plt, PltFile}, {output_plt, PltFile}]),
+    [] = run_dialyzer(incremental,
+                      [DependerBeamFile, DepsBeamFile],
+                      [{init_plt, PltFile}, {output_plt, PltFile}, {warnings, [no_unknown]}]),
     {_ResPlt, #iplt_info{mod_deps = DepsByModule}} = dialyzer_iplt:plt_and_info_from_file(PltFile),
 
     ActualTypeDepsInPlt =
@@ -623,9 +626,10 @@ compile(Config, Prog, Module, CompileOpts) ->
 
 run_dialyzer(Analysis, Files, Opts) ->
     dialyzer:run([{analysis_type, Analysis},
-		  {files, Files},
-		  {from, byte_code} |
-		  Opts]).
+                  {files, Files},
+                  {from, byte_code},
+                  {warnings, [no_unknown]} |
+                  Opts]).
 
 
 m_src_without_warning() -> <<"
@@ -721,7 +725,8 @@ reading_from_one_plt_and_writing_to_another_does_not_mutate_the_input_plt(Config
     ?assertMatch([], dialyzer:run([{analysis_type, incremental},
                        {files, [Beam1]},
                        {init_plt, Plt1},
-                       {from, byte_code}])),
+                       {from, byte_code},
+                       {warnings, [no_unknown]}])),
 
     % Now PLT v1 should exist
     Plt1ContentsBefore = dialyzer_plt:get_all_contracts(dialyzer_iplt:from_file(Plt1)),
@@ -746,7 +751,8 @@ reading_from_one_plt_and_writing_to_another_does_not_mutate_the_input_plt(Config
                        {files, [Beam2]},
                        {init_plt, Plt1},
                        {output_plt, Plt2},
-                       {from, byte_code}])),
+                       {from, byte_code},
+                       {warnings, [no_unknown]}])),
 
     % Now PLT v1 should be the same, but PLT v2 should have the changes in it
     Plt1ContentsAfter = dialyzer_plt:get_all_contracts(dialyzer_iplt:from_file(Plt1)),
@@ -775,7 +781,8 @@ reading_from_and_writing_to_one_plt_mutates_it(Config) when is_list(Config) ->
     ?assertMatch([], dialyzer:run([{analysis_type, incremental},
                        {files, [Beam1]},
                        {init_plt, Plt},
-                       {from, byte_code}])),
+                       {from, byte_code},
+                       {warnings, [no_unknown]}])),
 
     % Now PLT should exist after running incremental mode
     PltContentsBefore = dialyzer_plt:get_all_contracts(dialyzer_iplt:from_file(Plt)),
@@ -799,7 +806,8 @@ reading_from_and_writing_to_one_plt_mutates_it(Config) when is_list(Config) ->
                        {files, [Beam2]},
                        {init_plt, Plt},
                        {output_plt, Plt},
-                       {from, byte_code}])),
+                       {from, byte_code},
+                       {warnings, [no_unknown]}])),
 
     % Now PLT should have been mutated to contain the new version of module 'foo'
     PltContentsAfter = dialyzer_plt:get_all_contracts(dialyzer_iplt:from_file(Plt)),

lib/dialyzer/test/line_SUITE_data/dialyzer_options

@@ -1 +1 @@
-{dialyzer_options, [{error_location, line}, {warnings, [no_return]}]}.
+{dialyzer_options, [{error_location, line}, {warnings, [no_return, no_unknown]}]}.

lib/dialyzer/test/map_SUITE_data/dialyzer_options

@@ -1,2 +1,2 @@
-{dialyzer_options, [{indent_opt, false}]}.
+{dialyzer_options, [{indent_opt, false}, {warnings, [no_unknown]}]}.
 {time_limit, 30}.

lib/dialyzer/test/opaque_SUITE_data/dialyzer_options

@@ -1,2 +1,2 @@
-{dialyzer_options, [{indent_opt, false}, {warnings, [no_unused, no_return]}]}.
+{dialyzer_options, [{indent_opt, false}, {warnings, [no_unused, no_return, no_unknown]}]}.
 {time_limit, 40}.

lib/dialyzer/test/options1_SUITE_data/dialyzer_options

@@ -1,2 +1,2 @@
-{dialyzer_options, [{indent_opt, false}, {include_dirs, ["my_include"]}, {defines, [{'COMPILER_VSN', 42}]}, {warnings, [no_improper_lists]}]}.
+{dialyzer_options, [{indent_opt, false}, {include_dirs, ["my_include"]}, {defines, [{'COMPILER_VSN', 42}]}, {warnings, [no_improper_lists, no_unknown]}]}.
 {time_limit, 30}.

lib/dialyzer/test/options2_SUITE_data/dialyzer_options

@@ -1 +1 @@
-{dialyzer_options, [{indent_opt, false}, {defines, [{'vsn', 4}]}, {warnings, [unknown, no_return]}]}.
+{dialyzer_options, [{indent_opt, false}, {defines, [{'vsn', 4}]}, {warnings, [no_return]}]}.

lib/dialyzer/test/r9c_SUITE_data/dialyzer_options

@@ -1,2 +1,2 @@
-{dialyzer_options, [{indent_opt, false}, {defines, [{vsn, 42}]}]}.
+{dialyzer_options, [{indent_opt, false}, {defines, [{vsn, 42}]}, {warnings, [no_unknown]}]}.
 {time_limit, 20}.

lib/dialyzer/test/small_SUITE_data/dialyzer_options

@@ -1 +1 @@
-{dialyzer_options, [{indent_opt, false}, {error_location, column}, {warnings, [overlapping_contract]}]}.
+{dialyzer_options, [{indent_opt, false}, {error_location, column}, {warnings, [no_unknown, overlapping_contract]}]}.

lib/dialyzer/test/underspecs_SUITE_data/dialyzer_options

@@ -1 +1 @@
-{dialyzer_options, [{indent_opt, false}, {warnings, [underspecs]}]}.
+{dialyzer_options, [{indent_opt, false}, {warnings, [no_unknown, underspecs]}]}.

lib/dialyzer/test/user_SUITE_data/dialyzer_options

@@ -1,2 +1,2 @@
-{dialyzer_options, [{indent_opt, false}]}.
-{time_limit, 3}.
+{dialyzer_options, [{indent_opt, false}, {warnings, [no_unknown]}]}.
+{time_limit, 3}.

lib/stdlib/src/erl_lint.erl

@@ -3414,7 +3414,7 @@ is_function_dialyzer_option(Option) ->
 is_module_dialyzer_option(Option) ->
     lists:member(Option,
                  [no_return,no_unused,no_improper_lists,no_fun_app,
-                  no_match,no_opaque,no_fail_call,no_contracts,
+                  no_match,no_opaque,no_fail_call,no_contracts,no_unknown,
                   no_behaviours,no_undefined_callbacks,unmatched_returns,
                   error_handling,race_conditions,no_missing_calls,
                   specdiffs,overspecs,underspecs,unknown,