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File 3461-erl_lint-fix-unbound-singleton-types-in-unions.patch of Package erlang (Revision 54461a2357af3de1f765489d2fd0ee14)

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From 5cc02660d239ee38dee00592bee0e2d575e237f5 Mon Sep 17 00:00:00 2001
From: Kiko Fernandez-Reyes <kiko@erlang.org>
Date: Fri, 17 Feb 2023 11:29:32 +0100
Subject: [PATCH 1/5] erl_lint: fix unbound singleton types in unions

Dialyzer (erl_lint) was accepting code of the following form:

```erlang
-spec run_test(Opts) -> term()
      when Opts :: {join_specs, Bool} | {test, Bool}.
run_test(Opts) ->    {error, fail}.
```

But this cannot be ever checked by Dialyzer as the type variable `Bool`
is in an union, which means that `Bool` happened only once and thus, `Bool`
is an unbound type variable. Essentially, the example above should be
rejected by Dialyzer in the same manner as this other one below:

```erlang
-spec run_test_error(Opts) -> term()
      when Opts :: {join_specs, Bool}.
run_test_error(Opts) ->
    {error, fail}.
```

This commit fixes GH-6508 and adds a bunch of tests to `erl_lint.erl`
so that we can keep track of which singleton type variables should throw
an error and which ones are ok.
---
 lib/stdlib/src/erl_lint.erl        |  19 +++--
 lib/stdlib/test/erl_lint_SUITE.erl | 110 ++++++++++++++++++++++++++++-
 2 files changed, 122 insertions(+), 7 deletions(-)

diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index d6e7d768f3..e0d0117b79 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -3033,12 +3033,21 @@ check_type_2({type, A, record, [Name|Fields]}, SeenVars, St) ->
 	    check_record_types(A, Atom, Fields, SeenVars, St1);
 	_ -> {SeenVars, add_error(A, {type_syntax, record}, St)}
     end;
-check_type_2({type, _A, Tag, Args}, SeenVars, St) when Tag =:= product;
-                                                     Tag =:= union;
-                                                     Tag =:= tuple ->
+check_type_2({type, _A, Tag, Args}=_F, SeenVars, St) when Tag =:= product;
+                                                          Tag =:= tuple ->
     lists:foldl(fun(T, {AccSeenVars, AccSt}) ->
-			check_type_1(T, AccSeenVars, AccSt)
-		end, {SeenVars, St}, Args);
+                        check_type_1(T, AccSeenVars, AccSt)
+                end, {SeenVars, St}, Args);
+check_type_2({type, _A, union, Args}=_F, SeenVars, St) ->
+    lists:foldl(fun(T, {AccSeenVars, AccSt}) ->
+                        {SeenVars0, St0} = check_type_1(T, SeenVars, AccSt),
+                        UpdatedSeenVars = maps:merge_with(fun (_K, {seen_once, _}, {seen_once, _}=R) -> R;
+                                                              (_K, {seen_once, _}, Else) -> Else;
+                                                              (_K, Else, {seen_once, _}) -> Else;
+                                                              (_K, Else1, _Else2)        -> Else1
+                                                          end, SeenVars0, AccSeenVars),
+                        {UpdatedSeenVars, St0}
+                end, {SeenVars, St}, Args);
 check_type_2({type, Anno, TypeName, Args}, SeenVars, St) ->
     #lint{module = Module, types=Types} = St,
     Arity = length(Args),
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index 2331e4f395..93595459d4 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -35,7 +35,8 @@
 
 -export([all/0, suite/0, groups/0]).
 
--export([unused_vars_warn_basic/1,
+-export([singleton_type_var_errors/1,
+         unused_vars_warn_basic/1,
          unused_vars_warn_lc/1,
          unused_vars_warn_rec/1,
          unused_vars_warn_fun/1,
@@ -111,7 +112,8 @@ all() ->
      inline_nifs, warn_missing_spec, otp_16824,
      underscore_match, unused_record, unused_type2,
      eep49,
-     redefined_builtin_type].
+     redefined_builtin_type,
+     singleton_type_var_errors].
 
 groups() -> 
     [{unused_vars_warn, [],
@@ -903,6 +905,110 @@ unused_import(Config) when is_list(Config) ->
     [] = run(Config, Ts),
     ok.
 
+%% Test singleton type variables
+singleton_type_var_errors(Config) when is_list(Config) ->
+    Ts = [ {singleton_error1
+           , <<"-spec test_singleton_typevars_in_union(Opts) -> term() when
+                      Opts :: {ok, Unknown} | {error, Unknown}.
+                test_singleton_typevars_in_union(_) ->
+                  error.
+             ">>
+           , []
+           , {  errors
+             , [{{2,36},erl_lint,{singleton_typevar,'Unknown'}}]
+             , []
+             }
+           }
+         , { singleton_error2
+           , <<"-spec test_singleton_list_typevars_in_union([Opts]) -> term() when
+                      Opts :: {ok, Unknown} | {error, Unknown}.
+                test_singleton_list_typevars_in_union(_) ->
+                    error.">>
+           , []
+           , {  errors
+             , [{{2,36},erl_lint,{singleton_typevar,'Unknown'}}]
+             , []
+             }
+           }
+         , { singleton_error3
+           , <<"-spec test_singleton_list_typevars_in_list([Opts]) -> term() when
+                      Opts :: {ok, Unknown}.
+                test_singleton_list_typevars_in_list(_) ->
+                    error.">>
+           , []
+           , {  errors
+             , [{{2,36},erl_lint,{singleton_typevar,'Unknown'}}]
+             , []
+             }
+           }
+         , { singleton_error4
+           , <<"-spec test_singleton_list_typevars_in_list_with_type_subst([{ok, Unknown}]) -> term().
+                test_singleton_list_typevars_in_list_with_type_subst(_) ->
+                    error.">>
+           , []
+           , {  errors
+             , [{{1,86},erl_lint,{singleton_typevar,'Unknown'}}]
+             , []
+             }
+           }
+         , { singleton_error5
+           , <<"-spec test_singleton_buried_typevars_in_union(Opts) -> term() when
+                      Opts :: {ok, Foo} | {error, Foo},
+                      Foo  :: {true, X} | {false, X}.
+                test_singleton_buried_typevars_in_union(_) ->
+                    error.">>
+           , []
+           , {  errors
+             , [{{3,38},erl_lint,{singleton_typevar,'X'}}]
+             , []
+             }
+           }
+         , { singleton_error6
+           , <<"-spec test_multiple_subtypes_to_same_typevar(Opts) -> term() when
+                      Opts :: {Foo, Bar} | Y,
+                      Foo  :: X,
+                      Bar  :: X,
+                      Y    :: Z.
+                test_multiple_subtypes_to_same_typevar(_) ->
+                    error.">>
+           , []
+           , {  errors
+             , [{{5,31},erl_lint,{singleton_typevar,'Z'}}]
+             , []
+             }
+           }
+         , { singleton_error7
+           , <<"-spec test_duplicate_non_terminal_var_in_union(Opts) -> term() when
+                      Opts :: {ok, U, U} | {error, U, U},
+                      U    :: Foo.
+                test_duplicate_non_terminal_var_in_union(_) ->
+                    error.">>
+           , []
+           , {  errors
+             , [{{3,31},erl_lint,{singleton_typevar,'Foo'}}]
+             , []
+             }
+           }
+         , { singleton_ok1
+           , <<"-spec test_multiple_occurrences_singleton(Opts) -> term() when
+                      Opts :: {Foo, Foo}.
+                test_multiple_occurrences_singleton(_) ->
+                    ok.">>
+           , []
+           , []
+           }
+         , { singleton_ok2
+           , <<"-spec id(X) -> X.
+                id(X) ->
+                    X.">>
+           , []
+           , []
+           }
+
+         ],
+    [] = run(Config, Ts),
+    ok.
+
 %% Test warnings for unused functions.
 unused_function(Config) when is_list(Config) ->
     Ts = [{func1,
-- 
2.35.3

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File 3461-erl_lint-fix-unbound-singleton-types-in-unions.patch of Package erlang (Revision 54461a2357af3de1f765489d2fd0ee14)

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