Merge branch 'hasse/dialyzer/improve_contract_warnings/OTP-14982'

* hasse/dialyzer/improve_contract_warnings/OTP-14982:
  erts: Improve contracts of zlib
  kernel: Improve contracts
  erts: Improve a contract
  stdlib: Improve a contract
  compiler: Improve a contract
  dialyzer: Refine the test for overspecified functions

5 files changed, 87 insertions, 0 deletions

diff --git a/lib/dialyzer/test/overspecs_SUITE_data/dialyzer_options b/lib/dialyzer/test/overspecs_SUITE_data/dialyzer_options
new file mode 100644
index 0000000000..ff4517e59d
--- /dev/null
+++ b/lib/dialyzer/test/overspecs_SUITE_data/dialyzer_options
@@ -0,0 +1 @@
+{dialyzer_options, [{warnings, [overspecs]}]}.
diff --git a/lib/dialyzer/test/overspecs_SUITE_data/results/iodata b/lib/dialyzer/test/overspecs_SUITE_data/results/iodata
new file mode 100644
index 0000000000..d9c70330ec
--- /dev/null
+++ b/lib/dialyzer/test/overspecs_SUITE_data/results/iodata
@@ -0,0 +1,2 @@
+
+iodata.erl:7: The success typing for iodata:encode/2 implies that the function might also return integer() but the specification return is binary() | maybe_improper_list(binary() | maybe_improper_list(any(),binary() | []) | byte(),binary() | [])
diff --git a/lib/dialyzer/test/overspecs_SUITE_data/results/iolist b/lib/dialyzer/test/overspecs_SUITE_data/results/iolist
new file mode 100644
index 0000000000..ca556f017c
--- /dev/null
+++ b/lib/dialyzer/test/overspecs_SUITE_data/results/iolist
@@ -0,0 +1,2 @@
+
+iolist.erl:7: The success typing for iolist:encode/2 implies that the function might also return integer() but the specification return is maybe_improper_list(binary() | maybe_improper_list(any(),binary() | []) | byte(),binary() | [])
diff --git a/lib/dialyzer/test/overspecs_SUITE_data/src/iodata.erl b/lib/dialyzer/test/overspecs_SUITE_data/src/iodata.erl
new file mode 100644
index 0000000000..caa44f6c91
--- /dev/null
+++ b/lib/dialyzer/test/overspecs_SUITE_data/src/iodata.erl
@@ -0,0 +1,41 @@
+-module(iodata).
+
+%% A small part of beam_asm.
+
+-export([encode/2]).
+
+-spec encode(non_neg_integer(), integer()) -> iodata(). % extra range binary()
+
+encode(Tag, N) when Tag >= 0, N < 0 ->
+    encode1(Tag, negative_to_bytes(N));
+encode(Tag, N) when Tag >= 0, N < 16 ->
+    (N bsl 4) bor Tag; % not in the specification
+encode(Tag, N) when Tag >= 0, N < 16#800  ->
+    [((N bsr 3) band 2#11100000) bor Tag bor 2#00001000, N band 16#ff];
+encode(Tag, N) when Tag >= 0 ->
+    encode1(Tag, to_bytes(N)).
+
+encode1(Tag, Bytes) ->
+    case iolist_size(Bytes) of
+	Num when 2 =< Num, Num =< 8 ->
+	    [((Num-2) bsl 5) bor 2#00011000 bor Tag| Bytes];
+	Num when 8 < Num ->
+	    [2#11111000 bor Tag, encode(0, Num-9)| Bytes]
+    end.
+
+to_bytes(N) ->
+    Bin = binary:encode_unsigned(N),
+    case Bin of
+	<<0:1,_/bits>> -> Bin;
+	<<1:1,_/bits>> -> [0,Bin]
+    end.
+
+negative_to_bytes(N) when N >= -16#8000 ->
+    <<N:16>>;
+negative_to_bytes(N) ->
+    Bytes = byte_size(binary:encode_unsigned(-N)),
+    Bin = <<N:Bytes/unit:8>>,
+    case Bin of
+	<<0:1,_/bits>> -> [16#ff,Bin];
+	<<1:1,_/bits>> -> Bin
+    end.
diff --git a/lib/dialyzer/test/overspecs_SUITE_data/src/iolist.erl b/lib/dialyzer/test/overspecs_SUITE_data/src/iolist.erl
new file mode 100644
index 0000000000..7cceeda24e
--- /dev/null
+++ b/lib/dialyzer/test/overspecs_SUITE_data/src/iolist.erl
@@ -0,0 +1,41 @@
+-module(iolist).
+
+%% A small part of beam_asm.
+
+-export([encode/2]).
+
+-spec encode(non_neg_integer(), integer()) -> iolist().
+
+encode(Tag, N) when Tag >= 0, N < 0 ->
+    encode1(Tag, negative_to_bytes(N));
+encode(Tag, N) when Tag >= 0, N < 16 ->
+    (N bsl 4) bor Tag; % not in the specification
+encode(Tag, N) when Tag >= 0, N < 16#800  ->
+    [((N bsr 3) band 2#11100000) bor Tag bor 2#00001000, N band 16#ff];
+encode(Tag, N) when Tag >= 0 ->
+    encode1(Tag, to_bytes(N)).
+
+encode1(Tag, Bytes) ->
+    case iolist_size(Bytes) of
+	Num when 2 =< Num, Num =< 8 ->
+	    [((Num-2) bsl 5) bor 2#00011000 bor Tag| Bytes];
+	Num when 8 < Num ->
+	    [2#11111000 bor Tag, encode(0, Num-9)| Bytes]
+    end.
+
+to_bytes(N) ->
+    Bin = binary:encode_unsigned(N),
+    case Bin of
+	<<0:1,_/bits>> -> Bin;
+	<<1:1,_/bits>> -> [0,Bin]
+    end.
+
+negative_to_bytes(N) when N >= -16#8000 ->
+    <<N:16>>;
+negative_to_bytes(N) ->
+    Bytes = byte_size(binary:encode_unsigned(-N)),
+    Bin = <<N:Bytes/unit:8>>,
+    case Bin of
+	<<0:1,_/bits>> -> [16#ff,Bin];
+	<<1:1,_/bits>> -> Bin
+    end.