dialyzer: Unfold cerl patterns containing maps

Dialyzer relies heavily on the assumption that the type of a literal
that is used as a pattern is the type of any value that can match that
pattern. For maps, that is not true, and it was causing bad analysis
results. A new help function dialyzer_utils:refold_pattern/1 identifies
maps in literal patterns, and unfolds and labels them, allowing them to
be properly analysed.

11 files changed, 114 insertions, 35 deletions

diff --git a/lib/compiler/src/cerl.erl b/lib/compiler/src/cerl.erl
index 37ec4e97c9..6dc162db40 100644
--- a/lib/compiler/src/cerl.erl
+++ b/lib/compiler/src/cerl.erl
@@ -135,7 +135,7 @@
 	 ann_c_map_pattern/2,
 	 map_pair_op/1,map_pair_key/1,map_pair_val/1,
 	 update_c_map_pair/4,
-	 c_map_pair/2,
+	 c_map_pair/2, c_map_pair_exact/2,
 	 ann_c_map_pair/4
      ]).
 
@@ -1694,6 +1694,11 @@ map_pair_op(#c_map_pair{op=Op}) -> Op.
 c_map_pair(Key,Val) ->
     #c_map_pair{op=#c_literal{val=assoc},key=Key,val=Val}.
 
+-spec c_map_pair_exact(cerl(), cerl()) -> c_map_pair().
+
+c_map_pair_exact(Key,Val) ->
+    #c_map_pair{op=#c_literal{val=exact},key=Key,val=Val}.
+
 -spec ann_c_map_pair([term()], cerl(), cerl(), cerl()) ->
         c_map_pair().
 
diff --git a/lib/dialyzer/src/dialyzer_dataflow.erl b/lib/dialyzer/src/dialyzer_dataflow.erl
index a3b3e3291c..9827fda6e3 100644
--- a/lib/dialyzer/src/dialyzer_dataflow.erl
+++ b/lib/dialyzer/src/dialyzer_dataflow.erl
@@ -1482,7 +1482,9 @@ bind_pat_vars([Pat|PatLeft], [Type|TypeLeft], Acc, Map, State, Rev) ->
   {NewMap, TypeOut} =
     case cerl:type(Pat) of
       alias ->
-	AliasPat = cerl:alias_pat(Pat),
+	%% Map patterns are more allowing than the type of their literal. We
+	%% must unfold AliasPat if it is a literal.
+	AliasPat = dialyzer_utils:refold_pattern(cerl:alias_pat(Pat)),
 	Var = cerl:alias_var(Pat),
 	Map1 = enter_subst(Var, AliasPat, Map),
 	{Map2, [PatType]} = bind_pat_vars([AliasPat], [Type], [],
@@ -1523,11 +1525,20 @@ bind_pat_vars([Pat|PatLeft], [Type|TypeLeft], Acc, Map, State, Rev) ->
 	    {Map1, t_cons(HdType, TlType)}
 	end;
       literal ->
-	Literal = literal_type(Pat),
-	case t_is_none(t_inf(Literal, Type, Opaques)) of
+	Pat0 = dialyzer_utils:refold_pattern(Pat),
+	case cerl:is_literal(Pat0) of
 	  true ->
-	    bind_opaque_pats(Literal, Type, Pat, State);
-	  false -> {Map, Literal}
+	    Literal = literal_type(Pat),
+	    case t_is_none(t_inf(Literal, Type, Opaques)) of
+	      true ->
+		bind_opaque_pats(Literal, Type, Pat, State);
+	      false -> {Map, Literal}
+	    end;
+	  false ->
+	    %% Retry with the unfolded pattern
+	    {Map1, [PatType]}
+	      = bind_pat_vars([Pat0], [Type], [], Map, State, Rev),
+	    {Map1, PatType}
 	end;
       map ->
 	MapT = t_inf(Type, t_map(), Opaques),
@@ -2742,8 +2753,9 @@ store_map(Key, Val, #map{dict = Dict, ref = undefined} = Map) ->
 store_map(Key, Val, #map{dict = Dict, modified = Mod} = Map) ->
   Map#map{dict = dict:store(Key, Val, Dict), modified = [Key | Mod]}.
 
-enter_subst(Key, Val, #map{subst = Subst} = MS) ->
+enter_subst(Key, Val0, #map{subst = Subst} = MS) ->
   KeyLabel = get_label(Key),
+  Val = dialyzer_utils:refold_pattern(Val0),
   case cerl:is_literal(Val) of
     true ->
       store_map(KeyLabel, literal_type(Val), MS);
diff --git a/lib/dialyzer/src/dialyzer_typesig.erl b/lib/dialyzer/src/dialyzer_typesig.erl
index 12d6673d28..810b7c55e9 100644
--- a/lib/dialyzer/src/dialyzer_typesig.erl
+++ b/lib/dialyzer/src/dialyzer_typesig.erl
@@ -393,8 +393,18 @@ traverse(Tree, DefinedVars, State) ->
       {State2, _} = traverse_list(Funs, DefinedVars1, State1),
       traverse(Body, DefinedVars1, State2);
     literal ->
-      Type = t_from_term(cerl:concrete(Tree)),
-      {State, Type};
+      %% Maps are special; a literal pattern matches more than just the value
+      %% constructed by the literal. For example #{} constructs the empty map,
+      %% but matches every map.
+      case state__is_in_match(State) of
+	true ->
+	  Tree1 = dialyzer_utils:refold_pattern(Tree),
+	  case cerl:is_literal(Tree1) of
+	    false -> traverse(Tree1, DefinedVars, State);
+	    true -> {State, t_from_term(cerl:concrete(Tree))}
+	  end;
+	_ -> {State, t_from_term(cerl:concrete(Tree))}
+      end;
     module ->
       Defs = cerl:module_defs(Tree),
       Funs = [Fun || {_Var, Fun} <- Defs],
@@ -1110,7 +1120,9 @@ bitstr_val_constr(SizeType, UnitVal, Flags) ->
       end
   end.
 
-get_safe_underapprox_1([Pat|Left], Acc, Map) ->
+get_safe_underapprox_1([Pat0|Left], Acc, Map) ->
+  %% Maps should be treated as patterns, not as literals
+  Pat = dialyzer_utils:refold_pattern(Pat0),
   case cerl:type(Pat) of
     alias ->
       APat = cerl:alias_pat(Pat),
diff --git a/lib/dialyzer/src/dialyzer_utils.erl b/lib/dialyzer/src/dialyzer_utils.erl
index 5fc1c0e691..b3505f5197 100644
--- a/lib/dialyzer/src/dialyzer_utils.erl
+++ b/lib/dialyzer/src/dialyzer_utils.erl
@@ -49,6 +49,7 @@
 	 process_record_remote_types/1,
          sets_filter/2,
 	 src_compiler_opts/0,
+	 refold_pattern/1,
 	 parallelism/0,
          family/1
 	]).
@@ -834,6 +835,56 @@ pp_atom(Atom) ->
 
 %%------------------------------------------------------------------------------
 
+-spec refold_pattern(cerl:cerl()) -> cerl:cerl().
+
+refold_pattern(Pat) ->
+  %% Avoid the churn of unfolding and refolding
+  case cerl:is_literal(Pat) andalso find_map(cerl:concrete(Pat)) of
+    true ->
+      Tree = refold_concrete_pat(cerl:concrete(Pat)),
+      [{label, Label}] = cerl:get_ann(Tree),
+      cerl:set_ann(Tree, [{label, Label}|cerl:get_ann(Pat)]);
+    false -> Pat
+  end.
+
+find_map(#{}) -> true;
+find_map(Tuple) when is_tuple(Tuple) -> find_map(tuple_to_list(Tuple));
+find_map([H|T]) -> find_map(H) orelse find_map(T);
+find_map(_) -> false.
+
+refold_concrete_pat(Val) ->
+  case Val of
+    _ when is_tuple(Val) ->
+      Els = lists:map(fun refold_concrete_pat/1, tuple_to_list(Val)),
+      case lists:all(fun cerl:is_literal/1, Els) of
+	true -> cerl:abstract(Val);
+	false -> label(cerl:c_tuple_skel(Els))
+      end;
+    [H|T] ->
+      case  cerl:is_literal(HP=refold_concrete_pat(H))
+	and cerl:is_literal(TP=refold_concrete_pat(T))
+      of
+	true -> cerl:abstract(Val);
+	false -> label(cerl:c_cons_skel(HP, TP))
+      end;
+    M when is_map(M) ->
+      %% Map patterns are not generated by the parser(!), but they have a
+      %% property we want, namely that they are never folded into literals.
+      %% N.B.: The key in a map pattern is an expression, *not* a pattern.
+      label(cerl:c_map_pattern([cerl:c_map_pair_exact(cerl:abstract(K),
+						      refold_concrete_pat(V))
+				|| {K, V} <- maps:to_list(M)]));
+    _ ->
+      cerl:abstract(Val)
+  end.
+
+label(Tree) ->
+      %% Sigh
+      Label = -erlang:unique_integer([positive]),
+      cerl:set_ann(Tree, [{label, Label}]).
+
+%%------------------------------------------------------------------------------
+
 -spec parallelism() -> integer().
 
 parallelism() ->
diff --git a/lib/dialyzer/test/map_SUITE_data/results/exact b/lib/dialyzer/test/map_SUITE_data/results/exact
index 03090e5803..374ada8869 100644
--- a/lib/dialyzer/test/map_SUITE_data/results/exact
+++ b/lib/dialyzer/test/map_SUITE_data/results/exact
@@ -1,6 +1,3 @@
 
 exact.erl:15: Function t2/1 has no local return
-exact.erl:16: The call exact:has_a(M::#{}) will never return since it differs in the 1st argument from the success typing arguments: (#{'a':=_, ...})
-exact.erl:22: Function has_a/1 has no local return
-exact.erl:23: A key of type 'a' cannot exist in a map of type #{}
-exact.erl:8: The pattern ~{'a':=_}~ can never match the type #{}
+exact.erl:19: The variable _ can never match since previous clauses completely covered the type #{'a':=_, ...}
diff --git a/lib/dialyzer/test/map_SUITE_data/results/initial_dataflow b/lib/dialyzer/test/map_SUITE_data/results/initial_dataflow
index e69de29bb2..69144f9208 100644
--- a/lib/dialyzer/test/map_SUITE_data/results/initial_dataflow
+++ b/lib/dialyzer/test/map_SUITE_data/results/initial_dataflow
@@ -0,0 +1,4 @@
+
+initial_dataflow.erl:11: The variable Q can never match since previous clauses completely covered the type #{}
+initial_dataflow.erl:5: Function test/0 has no local return
+initial_dataflow.erl:6: The pattern 'false' can never match the type 'true'
diff --git a/lib/dialyzer/test/map_SUITE_data/results/map_galore b/lib/dialyzer/test/map_SUITE_data/results/map_galore
index 08c99e0c9a..721b417bb3 100644
--- a/lib/dialyzer/test/map_SUITE_data/results/map_galore
+++ b/lib/dialyzer/test/map_SUITE_data/results/map_galore
@@ -2,9 +2,6 @@
 map_galore.erl:1000: A key of type 42 cannot exist in a map of type #{1:='a', 2:='b', 4:='d', 5:='e', float()=>'c' | 'v'}
 map_galore.erl:1080: A key of type 'nonexisting' cannot exist in a map of type #{#{'map':='key', 'one':='small'}:=[32 | 49 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'second':='small'}:=[32 | 50 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'third':='small'}:=[32 | 51 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], 10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 16:='a6', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 26:='b6', 27:='b7', 28:='b8', 29:='b9', 30:=[48 | 99,...], 31:=[49 | 99,...], 32:=[50 | 99,...], 33:=[51 | 99,...], 34:=[52 | 99,...], 35:=[53 | 99,...], 36:=[54 | 99,...], 37:=[55 | 99,...], 38:=[56 | 99,...], 39:=[57 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | float() | {[[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...],...]} | #{10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 27:='b7', 28:='b8', 29:='b9', 30:=[48 | 99,...], 31:=[49 | 99,...], 32:=[50 | 99,...], 33:=[51 | 99,...], 34:=[52 | 99,...], 35:=[53 | 99,...], 37:=[55 | 99,...], 38:=[56 | 99,...], 39:=[57 | 99,...], 'k16'=>'a6', 'k26'=>'b6', 'k36'=>[54 | 99,...], 16=>'a6', 26=>'b6', 36=>[54 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | {[[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...],...]}=>[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 100 | 101,...]}=>atom() | [1..255,...]}
 map_galore.erl:1082: A key of type 42 cannot exist in a map of type #{#{'map':='key', 'one':='small'}:=[32 | 49 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'second':='small'}:=[32 | 50 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'third':='small'}:=[32 | 51 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], 10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 16:='a6', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 26:='b6', 27:='b7', 28:='b8', 29:='b9', 30:=[48 | 99,...], 31:=[49 | 99,...], 32:=[50 | 99,...], 33:=[51 | 99,...], 34:=[52 | 99,...], 35:=[53 | 99,...], 36:=[54 | 99,...], 37:=[55 | 99,...], 38:=[56 | 99,...], 39:=[57 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | float() | {[[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...],...]} | #{10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 27:='b7', 28:='b8', 29:='b9', 30:=[48 | 99,...], 31:=[49 | 99,...], 32:=[50 | 99,...], 33:=[51 | 99,...], 34:=[52 | 99,...], 35:=[53 | 99,...], 37:=[55 | 99,...], 38:=[56 | 99,...], 39:=[57 | 99,...], 'k16'=>'a6', 'k26'=>'b6', 'k36'=>[54 | 99,...], 16=>'a6', 26=>'b6', 36=>[54 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | {[[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...],...]}=>[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 100 | 101,...]}=>atom() | [1..255,...]}
-map_galore.erl:1109: Function t_guard_bifs/1 has no local return
-map_galore.erl:1114: The pattern 'true' can never match the type 'false'
-map_galore.erl:1123: The pattern ~{}~ can never match the type #{'a':=1, <<_:16>>=>[104 | 105,...]}
 map_galore.erl:1140: The call map_galore:map_guard_sequence_1(#{'seq':=6, 'val':=[101,...]}) will never return since it differs in the 1st argument from the success typing arguments: (#{'seq':=1 | 2 | 3 | 4 | 5, 'val':=[97 | 98 | 99 | 100 | 101,...], #{'map':='key', 'one':='small'}=>[32 | 49 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'second':='small'}=>[32 | 50 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'third':='small'}=>[32 | 51 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], 10=>'a0', 11=>'a1', 12=>'a2', 13=>'a3', 14=>'a4', 15=>'a5', 16=>'a6', 17=>'a7', 18=>'a8', 19=>'a9', 20=>'b0', 21=>'b1', 22=>'b2', 23=>'b3', 24=>'b4', 25=>'b5', 26=>'b6', 27=>'b7', 28=>'b8', 29=>'b9', 30=>[48 | 99,...], 31=>[49 | 99,...], 32=>[50 | 99,...], 33=>[51 | 99,...], 34=>[52 | 99,...], 35=>[53 | 99,...], 36=>[54 | 99,...], 37=>[55 | 99,...], 38=>[56 | 99,...], 39=>[57 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | float() | {[any(),...]} | #{10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 27:='b7', 28:='b8', 29:='b9', 30:=[any(),...], 31:=[any(),...], 32:=[any(),...], 33:=[any(),...], 34:=[any(),...], 35:=[any(),...], 37:=[any(),...], 38:=[any(),...], 39:=[any(),...], 'k16'=>'a6', 'k26'=>'b6', 'k36'=>[any(),...], 16=>'a6', 26=>'b6', 36=>[any(),...], <<_:16>> | [any(),...] | {_}=>[any(),...]}=>atom() | [1..255,...]})
 map_galore.erl:1141: The call map_galore:map_guard_sequence_2(#{'b':=5}) will never return since it differs in the 1st argument from the success typing arguments: (#{'a':='gg' | 'kk' | 'sc' | 3 | 4, 'b'=>'other' | 3 | 4 | 5, 'c'=>'sc2', #{'map':='key', 'one':='small'}=>[32 | 49 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'second':='small'}=>[32 | 50 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'third':='small'}=>[32 | 51 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], 10=>'a0', 11=>'a1', 12=>'a2', 13=>'a3', 14=>'a4', 15=>'a5', 16=>'a6', 17=>'a7', 18=>'a8', 19=>'a9', 20=>'b0', 21=>'b1', 22=>'b2', 23=>'b3', 24=>'b4', 25=>'b5', 26=>'b6', 27=>'b7', 28=>'b8', 29=>'b9', 30=>[48 | 99,...], 31=>[49 | 99,...], 32=>[50 | 99,...], 33=>[51 | 99,...], 34=>[52 | 99,...], 35=>[53 | 99,...], 36=>[54 | 99,...], 37=>[55 | 99,...], 38=>[56 | 99,...], 39=>[57 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | float() | {[any(),...]} | #{10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 27:='b7', 28:='b8', 29:='b9', 30:=[any(),...], 31:=[any(),...], 32:=[any(),...], 33:=[any(),...], 34:=[any(),...], 35:=[any(),...], 37:=[any(),...], 38:=[any(),...], 39:=[any(),...], 'k16'=>'a6', 'k26'=>'b6', 'k36'=>[any(),...], 16=>'a6', 26=>'b6', 36=>[any(),...], <<_:16>> | [any(),...] | {_}=>[any(),...]}=>atom() | [1..255,...]})
 map_galore.erl:1209: The call map_galore:map_guard_sequence_1(#{'seq':=6, 'val':=[101,...], #{'map':='key', 'one':='small'}:=[32 | 49 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'second':='small'}:=[32 | 50 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'third':='small'}:=[32 | 51 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], 10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 16:='a6', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 26:='b6', 27:='b7', 28:='b8', 29:='b9', 30:=[48 | 99,...], 31:=[49 | 99,...], 32:=[50 | 99,...], 33:=[51 | 99,...], 34:=[52 | 99,...], 35:=[53 | 99,...], 36:=[54 | 99,...], 37:=[55 | 99,...], 38:=[56 | 99,...], 39:=[57 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | float() | {[[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | 3,...]} | #{10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 27:='b7', 28:='b8', 29:='b9', 30:=[48 | 99,...], 31:=[49 | 99,...], 32:=[50 | 99,...], 33:=[51 | 99,...], 34:=[52 | 99,...], 35:=[53 | 99,...], 37:=[55 | 99,...], 38:=[56 | 99,...], 39:=[57 | 99,...], 'k16'=>'a6', 'k26'=>'b6', 'k36'=>[54 | 99,...], 16=>'a6', 26=>'b6', 36=>[54 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | {[[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...],...]}=>[48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 100 | 101,...]}=>atom() | [1..255,...]}) will never return since it differs in the 1st argument from the success typing arguments: (#{'seq':=1 | 2 | 3 | 4 | 5, 'val':=[97 | 98 | 99 | 100 | 101,...], #{'map':='key', 'one':='small'}=>[32 | 49 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'second':='small'}=>[32 | 50 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], #{'map':='key', 'third':='small'}=>[32 | 51 | 97 | 101 | 107 | 108 | 109 | 112 | 115 | 121,...], 10=>'a0', 11=>'a1', 12=>'a2', 13=>'a3', 14=>'a4', 15=>'a5', 16=>'a6', 17=>'a7', 18=>'a8', 19=>'a9', 20=>'b0', 21=>'b1', 22=>'b2', 23=>'b3', 24=>'b4', 25=>'b5', 26=>'b6', 27=>'b7', 28=>'b8', 29=>'b9', 30=>[48 | 99,...], 31=>[49 | 99,...], 32=>[50 | 99,...], 33=>[51 | 99,...], 34=>[52 | 99,...], 35=>[53 | 99,...], 36=>[54 | 99,...], 37=>[55 | 99,...], 38=>[56 | 99,...], 39=>[57 | 99,...], <<_:16>> | [48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57,...] | float() | {[any(),...]} | #{10:='a0', 11:='a1', 12:='a2', 13:='a3', 14:='a4', 15:='a5', 17:='a7', 18:='a8', 19:='a9', 20:='b0', 21:='b1', 22:='b2', 23:='b3', 24:='b4', 25:='b5', 27:='b7', 28:='b8', 29:='b9', 30:=[any(),...], 31:=[any(),...], 32:=[any(),...], 33:=[any(),...], 34:=[any(),...], 35:=[any(),...], 37:=[any(),...], 38:=[any(),...], 39:=[any(),...], 'k16'=>'a6', 'k26'=>'b6', 'k36'=>[any(),...], 16=>'a6', 26=>'b6', 36=>[any(),...], <<_:16>> | [any(),...] | {_}=>[any(),...]}=>atom() | [1..255,...]})
@@ -27,10 +24,5 @@ map_galore.erl:2304: Cons will produce an improper list since its 2nd argument i
 map_galore.erl:2304: The call maps:from_list(nonempty_improper_list({'a','b'},{'b','a'})) will never return since it differs in the 1st argument from the success typing arguments: ([{_,_}])
 map_galore.erl:2305: The call maps:from_list('a') will never return since it differs in the 1st argument from the success typing arguments: ([{_,_}])
 map_galore.erl:2306: The call maps:from_list(42) will never return since it differs in the 1st argument from the success typing arguments: ([{_,_}])
-map_galore.erl:2735: Function t_has_map_fields/1 has no local return
-map_galore.erl:2743: The call map_galore:has_map_fields_2(#{'b':=2, 'c':=1}) will never return since it differs in the 1st argument from the success typing arguments: (#{'a':=3, 'b':=2, 'c':=1, 'x'=>42})
-map_galore.erl:2743: The pattern 'false' can never match the type 'true'
-map_galore.erl:2763: The pattern ~{}~ can never match the type #{'b':=2, 'c':=1, 'x'=>42}
-map_galore.erl:2765: Function has_map_fields_3/1 will never be called
 map_galore.erl:997: A key of type 'nonexisting' cannot exist in a map of type #{}
 map_galore.erl:998: A key of type 'nonexisting' cannot exist in a map of type #{1:='a', 2:='b', 4:='d', 5:='e', float()=>'c'}
diff --git a/lib/dialyzer/test/map_SUITE_data/results/typeflow b/lib/dialyzer/test/map_SUITE_data/results/typeflow
index c4339e91a0..e3378a24bb 100644
--- a/lib/dialyzer/test/map_SUITE_data/results/typeflow
+++ b/lib/dialyzer/test/map_SUITE_data/results/typeflow
@@ -1,9 +1,4 @@
 
-typeflow.erl:12: Function a_is_integer/1 has no local return
-typeflow.erl:12: The pattern ~{'a':=X}~ can never match the type #{}
 typeflow.erl:14: Function t2/1 has no local return
-typeflow.erl:15: The call typeflow:a_is_integer(M::#{}) will never return since it differs in the 1st argument from the success typing arguments: (#{'a':=integer(), ...})
-typeflow.erl:19: Function t3/1 has no local return
-typeflow.erl:20: The call maps:get('a',M::#{}) will never return since the success typing arguments are (any(),map())
-typeflow.erl:5: Function t1/1 has no local return
-typeflow.erl:6: The call typeflow:a_is_integer(M::#{}) will never return since it differs in the 1st argument from the success typing arguments: (#{'a':=integer(), ...})
+typeflow.erl:16: The call lists:sort(integer()) will never return since it differs in the 1st argument from the success typing arguments: ([any()])
+typeflow.erl:9: The variable _ can never match since previous clauses completely covered the type #{'a':=integer(), ...}
diff --git a/lib/dialyzer/test/map_SUITE_data/results/typeflow2 b/lib/dialyzer/test/map_SUITE_data/results/typeflow2
index aa47845fb1..3bce165275 100644
--- a/lib/dialyzer/test/map_SUITE_data/results/typeflow2
+++ b/lib/dialyzer/test/map_SUITE_data/results/typeflow2
@@ -5,11 +5,9 @@ typeflow2.erl:26: Function t2/1 has no local return
 typeflow2.erl:29: The call lists:sort(integer()) will never return since it differs in the 1st argument from the success typing arguments: ([any()])
 typeflow2.erl:42: The pattern ~{'a':=X}~ can never match since previous clauses completely covered the type #{'a':=integer()}
 typeflow2.erl:43: The variable _ can never match since previous clauses completely covered the type #{'a':=integer()}
-typeflow2.erl:48: The pattern ~{}~ can never match the type #{'a':=atom() | maybe_improper_list() | integer()}
+typeflow2.erl:48: The pattern ~{}~ can never match since previous clauses completely covered the type #{'a':=atom() | maybe_improper_list() | integer()}
 typeflow2.erl:58: The pattern ~{'a':=X}~ can never match the type #{'a'=>none(), _=>maybe_improper_list() | integer()}
 typeflow2.erl:59: The pattern ~{'a':=X}~ can never match the type #{'a'=>none(), _=>maybe_improper_list() | integer()}
 typeflow2.erl:60: The pattern ~{'a':=X}~ can never match the type #{'a'=>none(), _=>maybe_improper_list() | integer()}
-typeflow2.erl:80: The pattern ~{'a':=X}~ can never match the type #{}
-typeflow2.erl:81: The pattern ~{'a':=X}~ can never match the type #{}
 typeflow2.erl:82: The pattern ~{'a':=X}~ can never match the type #{}
 typeflow2.erl:83: The pattern ~{'a':=X}~ can never match the type #{}
diff --git a/lib/dialyzer/test/map_SUITE_data/src/bug.erl b/lib/dialyzer/test/map_SUITE_data/src/bug.erl
new file mode 100644
index 0000000000..9e152bf461
--- /dev/null
+++ b/lib/dialyzer/test/map_SUITE_data/src/bug.erl
@@ -0,0 +1,14 @@
+-module(bug).
+
+-export([t1/0, f1/1]).
+
+t1() ->
+    V = f1(#{a=>b}),
+    case V of
+	#{a := Q} -> Q; %% Must not warn here
+	_ -> ok
+    end,
+    ok.
+
+f1(M) -> %% Should get map() succ typing
+    #{} = M.
diff --git a/lib/dialyzer/test/small_SUITE_data/results/maps1 b/lib/dialyzer/test/small_SUITE_data/results/maps1
index 6cd1c662c4..ec8748b7b8 100644
--- a/lib/dialyzer/test/small_SUITE_data/results/maps1
+++ b/lib/dialyzer/test/small_SUITE_data/results/maps1
@@ -1,5 +1,4 @@
 
 maps1.erl:43: Function t3/0 has no local return
-maps1.erl:46: Function foo/2 has no local return
-maps1.erl:47: A key of type 'beta' cannot exist in a map of type #{'alfa':=42}
-maps1.erl:52: The call Mod:'function'(~{'literal'=>'map'}~,'another_arg') requires that Mod is of type atom() not #{}
+maps1.erl:44: The call maps1:foo(~{'greger'=>3, ~{'arne'=>'anka'}~=>45}~,1) will never return since it differs in the 1st and 2nd argument from the success typing arguments: (#{'beta':=_, ...},'b')
+maps1.erl:52: The variable Mod can never match since previous clauses completely covered the type #{}