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File 4272-stdlib-Let-the-linter-check-unused-types-properly.patch of Package erlang (Revision b4f72044e1af8cfe32130ab849a401a1)

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From 59cc16df4cb0b171e09e38e7924b7d719af1f834 Mon Sep 17 00:00:00 2001
From: Hans Bolinder <hasse@erlang.org>
Date: Fri, 4 Jun 2021 09:22:59 +0200
Subject: [PATCH 2/2] stdlib: Let the linter check unused types properly

See also https://github.com/erlang/otp/issues/4784.

A type like `t() :: [t()]' can now be reported as unused.

Types occurring in specs of unused functions or in unused records are
considered used. This is consistent with how the warning for unused
records is implemented.
---
 lib/stdlib/src/erl_lint.erl        | 67 +++++++++++++++++++++---------
 lib/stdlib/test/erl_lint_SUITE.erl | 62 ++++++++++++++++++++++++++-
 2 files changed, 108 insertions(+), 21 deletions(-)

diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index 7803273c5e..599f8443ff 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -93,6 +93,14 @@ value_option(Flag, Default, On, OnVal, Off, OffVal, Opts) ->
 
 -record(typeinfo, {attr, line}).
 
+-type type_id() :: {'export', []}
+                 | {'record', atom()}
+                 | {'spec', mfa()}
+                 | {'type', ta()}.
+
+-record(used_type, {anno :: erl_anno:anno(),
+                    at = {export, []} :: type_id()}).
+
 %% Usage of records, functions, and imports. The variable table, which
 %% is passed on as an argument, holds the usage of variables.
 -record(usage, {
@@ -130,6 +140,7 @@ value_option(Flag, Default, On, OnVal, Off, OffVal, Opts) ->
                not_removed=gb_sets:empty()      %Not considered removed
                    :: gb_sets:set(module_or_mfa()),
                func=[],                         %Current function
+               type_id=[],                      %Current type id
                warn_format=0,                   %Warn format calls
 	       enabled_warnings=[],		%All enabled warnings (ordset).
                nowarn_bif_clash=[],             %All no warn bif clashes (ordset).
@@ -1288,10 +1299,10 @@ check_undefined_types(#lint{usage=Usage,types=Def}=St0) ->
 		TA <- UTAs,
 		not is_map_key(TA, Def),
 		not is_default_type(TA)],
-    foldl(fun ({TA,L}, St) ->
-                  foldl( fun(Anno, St1) ->
+    foldl(fun ({TA,UsedTypeList}, St) ->
+                  foldl( fun(#used_type{anno = Anno}, St1) ->
                                  add_error(Anno, {undefined_type,TA}, St1)
-                         end, St, L)
+                         end, St, UsedTypeList)
 	  end, St0, Undef).
 
 %% check_bif_clashes(Forms, State0) -> State
@@ -1432,7 +1443,8 @@ export_type(Line, ETs, #lint{exp_types = ETs0} = St0) ->
 				   Warn = {duplicated_export_type,TA},
 				   add_warning(Line, Warn, St2);
 			       false ->
-                                   used_type(TA, Line, St2)
+                                   St3 = St2#lint{type_id = {export, []}},
+                                   used_type(TA, Line, St3)
 			   end,
 		      {gb_sets:add_element(TA, E), St}
 	      end,
@@ -2674,7 +2686,8 @@ record_def(Line, Name, Fs0, St0) ->
             St2 = St1#lint{records=maps:put(Name, {Line,Fs1},
                                               St1#lint.records)},
             Types = [T || {typed_record_field, _, T} <- Fs0],
-            check_type({type, nowarn(), product, Types}, St2)
+            St3 = St2#lint{type_id = {record, Name}},
+            check_type({type, nowarn(), product, Types}, St3)
     end.
 
 %% def_fields([RecDef], RecordName, State) -> {[DefField],State}.
@@ -2894,7 +2907,8 @@ type_def(Attr, Anno, TypeName, ProtoType, Args, St0) ->
         fun(St) ->
                 NewDefs = maps:put(TypePair, Info, TypeDefs),
                 CheckType = {type, nowarn(), product, [ProtoType|Args]},
-                check_type(CheckType, St#lint{types=NewDefs})
+                St1 = St#lint{types=NewDefs, type_id={type, TypePair}},
+                check_type(CheckType, St1)
         end,
     case is_default_type(TypePair) of
         true ->
@@ -3089,7 +3103,9 @@ check_record_types([], _Name, _DefFields, SeenVars, St, _SeenFields) ->
 
 used_type(TypePair, L, #lint{usage = Usage, file = File} = St) ->
     Used = Usage#usage.used_types,
-    NewUsed = maps_prepend(TypePair, erl_anno:set_file(File, L), Used),
+    UsedType = #used_type{anno = erl_anno:set_file(File, L),
+                          at = St#lint.type_id},
+    NewUsed = maps_prepend(TypePair, UsedType, Used),
     St#lint{usage=Usage#usage{used_types=NewUsed}}.
 
 is_default_type({Name, NumberOfTypeVariables}) ->
@@ -3120,12 +3136,12 @@ spec_decl(Line, MFA0, TypeSpecs, St00 = #lint{specs = Specs, module = Mod}) ->
     case is_map_key(MFA, Specs) of
 	true -> add_error(Line, {redefine_spec, MFA0}, St1);
 	false ->
-            case MFA of
-                {Mod, _, _} ->
-                    check_specs(TypeSpecs, spec_wrong_arity, Arity, St1);
-                _ ->
-                    add_error(Line, {bad_module, MFA}, St1)
-            end
+            St2 = case MFA of
+                      {Mod, _, _} -> St1;
+                      _ -> add_error(Line, {bad_module, MFA}, St1)
+                  end,
+            St3 = St2#lint{type_id = {spec, MFA}},
+            check_specs(TypeSpecs, spec_wrong_arity, Arity, St3)
     end.
 
 %% callback_decl(Line, Fun, Types, State) -> State.
@@ -3141,8 +3157,9 @@ callback_decl(Line, MFA0, TypeSpecs,
             St1 = St0#lint{callbacks = maps:put(MFA, Line, Callbacks)},
             case is_map_key(MFA, Callbacks) of
                 true -> add_error(Line, {redefine_callback, MFA0}, St1);
-                false -> check_specs(TypeSpecs, callback_wrong_arity,
-                                     Arity, St1)
+                false ->
+                    St2 = St1#lint{type_id = {spec, MFA}},
+                    check_specs(TypeSpecs, callback_wrong_arity, Arity, St2)
             end
     end.
 
@@ -3263,11 +3280,10 @@ check_unused_types(Forms, St) ->
         false -> St
     end.
 
-check_unused_types_1(Forms, #lint{usage=Usage, types=Ts, exp_types=ExpTs}=St) ->
+check_unused_types_1(Forms, #lint{types=Ts}=St) ->
     case [File || {attribute,_L,file,{File,_Line}} <- Forms] of
 	[FirstFile|_] ->
-	    D = Usage#usage.used_types,
-	    L = gb_sets:to_list(ExpTs) ++ maps:keys(D),
+            L = reached_types(St),
 	    UsedTypes = gb_sets:from_list(L),
 	    FoldFun =
                 fun({{record, _}=_Type, 0}, _, AccSt) ->
@@ -3291,6 +3307,19 @@ check_unused_types_1(Forms, #lint{usage=Usage, types=Ts, exp_types=ExpTs}=St) ->
 	    St
     end.
 
+reached_types(#lint{usage = Usage}) ->
+    Es = [{From, {type, To}} ||
+             {To, UsedTs} <- maps:to_list(Usage#usage.used_types),
+             #used_type{at = From} <- UsedTs],
+    Initial = initially_reached_types(Es),
+    G = sofs:family_to_digraph(sofs:rel2fam(sofs:relation(Es))),
+    R = digraph_utils:reachable(Initial, G),
+    true = digraph:delete(G),
+    [T || {type, T} <- R].
+
+initially_reached_types(Es) ->
+    [FromTypeId || {{T, _}=FromTypeId, _} <- Es, T =/= type].
+
 check_local_opaque_types(St) ->
     #lint{types=Ts, exp_types=ExpTs} = St,
     FoldFun =
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index f6888721db..77337a7e05 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -74,7 +74,8 @@
          unused_type/1,binary_types/1,removed/1, otp_16516/1,
          inline_nifs/1,
          warn_missing_spec/1,
-         unused_record/1]).
+         unused_record/1,
+         unused_type2/1]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
@@ -98,7 +99,7 @@ all() ->
      stacktrace_syntax, otp_14285, otp_14378, external_funs,
      otp_15456, otp_15563, unused_type, binary_types, removed, otp_16516,
      inline_nifs, warn_missing_spec,
-     unused_record].
+     unused_record, unused_type2].
 
 groups() -> 
     [{unused_vars_warn, [],
@@ -4634,6 +4635,63 @@ unused_record(Config) when is_list(Config) ->
 
     ok.
 
+unused_type2(Config) when is_list(Config) ->
+    Ts = [{unused_type2_1,
+           <<"-type t() :: [t()].
+              t() ->
+                  a.
+            ">>,
+           {[]},
+           {warnings,[{{1,22},erl_lint,{unused_type,{t,0}}},
+                      {{2,15},erl_lint,{unused_function,{t,0}}}]}},
+          {unused_type2_2,
+           <<"-type t1() :: t2().
+              -type t2() :: t1().
+               t() ->
+                   a.
+            ">>,
+           {[]},
+           {warnings,[{{1,22},erl_lint,{unused_type,{t1,0}}},
+                      {{2,16},erl_lint,{unused_type,{t2,0}}},
+                      {{3,16},erl_lint,{unused_function,{t,0}}}]}},
+          {unused_type2_3,
+           <<"-callback cb() -> t().
+              -type t() :: atom().
+               t() ->
+                   a.
+            ">>,
+           {[]},
+           {warnings,[{{3,16},erl_lint,{unused_function,{t,0}}}]}},
+          {unused_type2_4,
+           <<"-spec t() -> t().
+              -type t() :: atom().
+               t() ->
+                   a.
+            ">>,
+           {[]},
+           {warnings,[{{3,16},erl_lint,{unused_function,{t,0}}}]}},
+          {unused_type2_5,
+           <<"-export_type([t/0]).
+              -type t() :: atom().
+               t() ->
+                   a.
+            ">>,
+           {[]},
+           {warnings,[{{3,16},erl_lint,{unused_function,{t,0}}}]}},
+          {unused_type2_6,
+           <<"-record(r, {f :: t()}).
+              -type t() :: atom().
+               t() ->
+                   a.
+            ">>,
+           {[]},
+           {warnings,[{{1,22},erl_lint,{unused_record,r}},
+                      {{3,16},erl_lint,{unused_function,{t,0}}}]}}
+         ],
+    [] = run(Config, Ts),
+
+    ok.
+
 format_error(E) ->
     lists:flatten(erl_lint:format_error(E)).
 
-- 
2.26.2

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