dialyzer_contracts: Consider #{} a violation

This is analogous to the case of nil. Since #{} is a base-case of almost
all map types, contract and success typing sharing #{} does not mean
much, and is often sign of a violation.

3 files changed, 61 insertions, 12 deletions

diff --git a/lib/dialyzer/src/dialyzer_contracts.erl b/lib/dialyzer/src/dialyzer_contracts.erl
index e03e4d5bb4..1895a98e96 100644
--- a/lib/dialyzer/src/dialyzer_contracts.erl
+++ b/lib/dialyzer/src/dialyzer_contracts.erl
@@ -277,28 +277,45 @@ check_extraneous_1(Contract, SuccType) ->
   case [CR || CR <- CRngs,
               erl_types:t_is_none(erl_types:t_inf(CR, STRng))] of
     [] ->
-      CRngList = list_part(CRng),
-      STRngList = list_part(STRng),
-      case is_not_nil_list(CRngList) andalso is_not_nil_list(STRngList) of
-        false -> ok;
-        true ->
-          CRngElements = erl_types:t_list_elements(CRngList),
-          STRngElements = erl_types:t_list_elements(STRngList),
-          Inf = erl_types:t_inf(CRngElements, STRngElements),
-          case erl_types:t_is_none(Inf) of
-            true -> {error, invalid_contract};
-            false -> ok
-          end
+      case bad_extraneous_list(CRng, STRng)
+	orelse bad_extraneous_map(CRng, STRng)
+      of
+	true -> {error, invalid_contract};
+	false -> ok
       end;
     CRs -> {error, {extra_range, erl_types:t_sup(CRs), STRng}}
   end.
 
+bad_extraneous_list(CRng, STRng) ->
+  CRngList = list_part(CRng),
+  STRngList = list_part(STRng),
+  case is_not_nil_list(CRngList) andalso is_not_nil_list(STRngList) of
+    false -> false;
+    true ->
+      CRngElements = erl_types:t_list_elements(CRngList),
+      STRngElements = erl_types:t_list_elements(STRngList),
+      Inf = erl_types:t_inf(CRngElements, STRngElements),
+      erl_types:t_is_none(Inf)
+  end.
+
 list_part(Type) ->
   erl_types:t_inf(erl_types:t_list(), Type).
 
 is_not_nil_list(Type) ->
   erl_types:t_is_list(Type) andalso not erl_types:t_is_nil(Type).
 
+bad_extraneous_map(CRng, STRng) ->
+  CRngMap = map_part(CRng),
+  STRngMap = map_part(STRng),
+  (not is_empty_map(CRngMap)) andalso (not is_empty_map(STRngMap))
+    andalso is_empty_map(erl_types:t_inf(CRngMap, STRngMap)).
+
+map_part(Type) ->
+  erl_types:t_inf(erl_types:t_map(), Type).
+
+is_empty_map(Type) ->
+  erl_types:t_is_equal(Type, erl_types:t_from_term(#{})).
+
 %% This is the heart of the "range function"
 -spec process_contracts([contract_pair()], [erl_types:erl_type()]) ->
                            erl_types:erl_type().
diff --git a/lib/dialyzer/test/map_SUITE_data/results/contract_violation b/lib/dialyzer/test/map_SUITE_data/results/contract_violation
new file mode 100644
index 0000000000..958321618f
--- /dev/null
+++ b/lib/dialyzer/test/map_SUITE_data/results/contract_violation
@@ -0,0 +1,3 @@
+
+contract_violation.erl:12: The pattern #{I:=Loc} can never match the type #{}
+contract_violation.erl:16: Invalid type specification for function contract_violation:beam_disasm_lines/2. The success typing is ('none' | <<_:32,_:_*8>>,_) -> #{pos_integer()=>{'location',_,_}}
diff --git a/lib/dialyzer/test/map_SUITE_data/src/contract_violation.erl b/lib/dialyzer/test/map_SUITE_data/src/contract_violation.erl
new file mode 100644
index 0000000000..850f2cad34
--- /dev/null
+++ b/lib/dialyzer/test/map_SUITE_data/src/contract_violation.erl
@@ -0,0 +1,29 @@
+-module(contract_violation).
+
+-export([entry/1, beam_disasm_lines/2]).
+
+%%-----------------------------------------------------------------------
+
+-type lines() :: #{non_neg_integer() => {string(), non_neg_integer()}}.
+
+entry(Bin) ->
+    I = 42,
+    case beam_disasm_lines(Bin, ':-)') of
+	#{I := Loc} -> {good, Loc};
+	_ -> bad
+    end.
+
+-spec beam_disasm_lines(binary() | none, module()) -> lines().
+
+beam_disasm_lines(none, _) -> #{};
+beam_disasm_lines(<<NumLines:32, LineBin:NumLines/binary, FileBin/binary>>,
+		  _Module) ->
+    Lines = binary_to_term(LineBin),
+    Files = binary_to_term(FileBin),
+    lines_collect_items(Lines, Files, #{}).
+
+lines_collect_items([], _, Acc) -> Acc;
+lines_collect_items([{FileNo, LineNo}|Rest], Files, Acc) ->
+    #{FileNo := File} = Files,
+    lines_collect_items(
+      Rest, Files, Acc#{map_size(Acc)+1 => {location, File, LineNo}}).