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.

2 files changed, 32 insertions, 0 deletions

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}}).