From 6ee18b6104ec2ea8d21ed8545331383842fba5ac Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Mon, 27 Dec 2021 23:03:15 +0100
Subject: [PATCH 01/10] refactor(broker): Don't use a macro

---
 apps/emqx/rebar.config     |  2 +-
 apps/emqx/src/emqx_rpc.erl | 14 ++++++--------
 mix.exs                    |  2 +-
 rebar.config               |  2 +-
 4 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/apps/emqx/rebar.config b/apps/emqx/rebar.config
index f573ddc87..4ec68d585 100644
--- a/apps/emqx/rebar.config
+++ b/apps/emqx/rebar.config
@@ -16,7 +16,7 @@
     , {cowboy, {git, "https://github.com/emqx/cowboy", {tag, "2.9.0"}}}
     , {esockd, {git, "https://github.com/emqx/esockd", {tag, "5.9.0"}}}
     , {ekka, {git, "https://github.com/emqx/ekka", {tag, "0.11.2"}}}
-    , {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.5.1"}}}
+    , {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.8.0"}}}
     , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.22.2"}}}
     , {pbkdf2, {git, "https://github.com/emqx/erlang-pbkdf2.git", {tag, "2.0.4"}}}
     , {recon, {git, "https://github.com/ferd/recon", {tag, "2.5.1"}}}
diff --git a/apps/emqx/src/emqx_rpc.erl b/apps/emqx/src/emqx_rpc.erl
index 527123745..0ea2814b0 100644
--- a/apps/emqx/src/emqx_rpc.erl
+++ b/apps/emqx/src/emqx_rpc.erl
@@ -30,27 +30,25 @@
           , rpc_nodes/1
           ]}).
 
--define(RPC, gen_rpc).
-
 -define(DefaultClientNum, 1).
 
 call(Node, Mod, Fun, Args) ->
-    filter_result(?RPC:call(rpc_node(Node), Mod, Fun, Args)).
+    filter_result(gen_rpc:call(rpc_node(Node), Mod, Fun, Args)).
 
 call(Key, Node, Mod, Fun, Args) ->
-    filter_result(?RPC:call(rpc_node({Key, Node}), Mod, Fun, Args)).
+    filter_result(gen_rpc:call(rpc_node({Key, Node}), Mod, Fun, Args)).
 
 multicall(Nodes, Mod, Fun, Args) ->
-    filter_result(?RPC:multicall(rpc_nodes(Nodes), Mod, Fun, Args)).
+    filter_result(gen_rpc:multicall(rpc_nodes(Nodes), Mod, Fun, Args)).
 
 multicall(Key, Nodes, Mod, Fun, Args) ->
-    filter_result(?RPC:multicall(rpc_nodes([{Key, Node} || Node <- Nodes]), Mod, Fun, Args)).
+    filter_result(gen_rpc:multicall(rpc_nodes([{Key, Node} || Node <- Nodes]), Mod, Fun, Args)).
 
 cast(Node, Mod, Fun, Args) ->
-    filter_result(?RPC:cast(rpc_node(Node), Mod, Fun, Args)).
+    filter_result(gen_rpc:cast(rpc_node(Node), Mod, Fun, Args)).
 
 cast(Key, Node, Mod, Fun, Args) ->
-    filter_result(?RPC:cast(rpc_node({Key, Node}), Mod, Fun, Args)).
+    filter_result(gen_rpc:cast(rpc_node({Key, Node}), Mod, Fun, Args)).
 
 rpc_node(Node) when is_atom(Node) ->
     {Node, rand:uniform(max_client_num())};
diff --git a/mix.exs b/mix.exs
index b4b9ef701..ca66f0c6d 100644
--- a/mix.exs
+++ b/mix.exs
@@ -54,7 +54,7 @@ defmodule EMQXUmbrella.MixProject do
       {:esockd, github: "emqx/esockd", tag: "5.9.0", override: true},
       {:mria, github: "emqx/mria", tag: "0.1.5", override: true},
       {:ekka, github: "emqx/ekka", tag: "0.11.2", override: true},
-      {:gen_rpc, github: "emqx/gen_rpc", tag: "2.5.1", override: true},
+      {:gen_rpc, github: "emqx/gen_rpc", tag: "2.8.0", override: true},
       {:minirest, github: "emqx/minirest", tag: "1.2.9", override: true},
       {:ecpool, github: "emqx/ecpool", tag: "0.5.2"},
       {:replayq, "0.3.3", override: true},
diff --git a/rebar.config b/rebar.config
index 17d4a0ce3..49e37e4af 100644
--- a/rebar.config
+++ b/rebar.config
@@ -55,7 +55,7 @@
     , {esockd, {git, "https://github.com/emqx/esockd", {tag, "5.9.0"}}}
     , {mria, {git, "https://github.com/emqx/mria", {tag, "0.1.5"}}}
     , {ekka, {git, "https://github.com/emqx/ekka", {tag, "0.11.2"}}}
-    , {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.5.1"}}}
+    , {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.8.0"}}}
     , {minirest, {git, "https://github.com/emqx/minirest", {tag, "1.2.9"}}}
     , {ecpool, {git, "https://github.com/emqx/ecpool", {tag, "0.5.2"}}}
     , {replayq, "0.3.3"}

From 5c2a559991c38071ef8428434ca7bbd54c675b95 Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Tue, 4 Jan 2022 10:55:16 +0100
Subject: [PATCH 02/10] feat(bpapi): Initial commit

---
 apps/emqx/src/emqx_broker.erl                 |   2 +-
 apps/emqx/src/emqx_rpc.erl                    |   4 +-
 apps/emqx/src/proto/emqx_broker_proto_v1.erl  |  34 +++
 apps/emqx_bpapi/README.md                     |   5 +
 apps/emqx_bpapi/include/bpapi.hrl             |   6 +
 apps/emqx_bpapi/priv/.gitkeep                 |   0
 apps/emqx_bpapi/src/emqx_bpapi.app.src        |  15 ++
 apps/emqx_bpapi/src/emqx_bpapi.erl            |  54 +++++
 .../src/emqx_bpapi_static_checks.erl          | 147 +++++++++++++
 apps/emqx_bpapi/src/emqx_bpapi_trans.erl      | 200 ++++++++++++++++++
 10 files changed, 465 insertions(+), 2 deletions(-)
 create mode 100644 apps/emqx/src/proto/emqx_broker_proto_v1.erl
 create mode 100644 apps/emqx_bpapi/README.md
 create mode 100644 apps/emqx_bpapi/include/bpapi.hrl
 create mode 100644 apps/emqx_bpapi/priv/.gitkeep
 create mode 100644 apps/emqx_bpapi/src/emqx_bpapi.app.src
 create mode 100644 apps/emqx_bpapi/src/emqx_bpapi.erl
 create mode 100644 apps/emqx_bpapi/src/emqx_bpapi_static_checks.erl
 create mode 100644 apps/emqx_bpapi/src/emqx_bpapi_trans.erl

diff --git a/apps/emqx/src/emqx_broker.erl b/apps/emqx/src/emqx_broker.erl
index 9dbfb0b43..bdb6acd4f 100644
--- a/apps/emqx/src/emqx_broker.erl
+++ b/apps/emqx/src/emqx_broker.erl
@@ -300,7 +300,7 @@ forward(Node, To, Delivery, sync) ->
     end.
 
 -spec(dispatch(emqx_types:topic(), emqx_types:delivery()) -> emqx_types:deliver_result()).
-dispatch(Topic, Delivery) ->
+dispatch(Topic, Delivery = #delivery{}) when is_binary(Topic) ->
     case emqx:is_running() of
         true  ->
             do_dispatch(Topic, Delivery);
diff --git a/apps/emqx/src/emqx_rpc.erl b/apps/emqx/src/emqx_rpc.erl
index 0ea2814b0..ad7e9891f 100644
--- a/apps/emqx/src/emqx_rpc.erl
+++ b/apps/emqx/src/emqx_rpc.erl
@@ -14,9 +14,11 @@
 %% limitations under the License.
 %%--------------------------------------------------------------------
 
-%% @doc wrap gen_rpc?
 -module(emqx_rpc).
 
+%% Note: please don't forget to add new API functions to
+%% `emqx_bpapi_trans:extract_mfa'
+
 -export([ call/4
         , call/5
         , cast/4
diff --git a/apps/emqx/src/proto/emqx_broker_proto_v1.erl b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
new file mode 100644
index 000000000..a40884c38
--- /dev/null
+++ b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
@@ -0,0 +1,34 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+-module(emqx_broker_proto_v1).
+
+-introduced_in("5.0.0").
+
+-export([ forward/3
+        , forward_async/3
+        ]).
+
+-include_lib("emqx_bpapi/include/bpapi.hrl").
+-include("emqx.hrl").
+
+-spec forward(node(), emqx_types:topic(), emqx_types:delivery()) -> emqx_types:deliver_result().
+forward(Node, Topic, Delivery = #delivery{}) when is_binary(Topic) ->
+    emqx_rpc:call(Topic, Node, emqx_broker, dispatch, [Topic, Delivery]).
+
+-spec forward_async(node(), emqx_types:topic(), emqx_types:delivery()) -> ok.
+forward_async(Node, Topic, Delivery = #delivery{}) when is_binary(Topic) ->
+    emqx_rpc:cast(Topic, Node, emqx_broker, dispatch, [Topic, Delivery]).
diff --git a/apps/emqx_bpapi/README.md b/apps/emqx_bpapi/README.md
new file mode 100644
index 000000000..78f529a4c
--- /dev/null
+++ b/apps/emqx_bpapi/README.md
@@ -0,0 +1,5 @@
+emqx_bpapi
+=====
+
+A library that helps maintaining EMQX's backplane API backward and
+forward compatibility.
diff --git a/apps/emqx_bpapi/include/bpapi.hrl b/apps/emqx_bpapi/include/bpapi.hrl
new file mode 100644
index 000000000..b4e52d50f
--- /dev/null
+++ b/apps/emqx_bpapi/include/bpapi.hrl
@@ -0,0 +1,6 @@
+-ifndef(EMQX_BPAPI_HRL).
+-define(EMQX_BPAPI_HRL, true).
+
+-compile({parse_transform, emqx_bpapi_trans}).
+
+-endif.
diff --git a/apps/emqx_bpapi/priv/.gitkeep b/apps/emqx_bpapi/priv/.gitkeep
new file mode 100644
index 000000000..e69de29bb
diff --git a/apps/emqx_bpapi/src/emqx_bpapi.app.src b/apps/emqx_bpapi/src/emqx_bpapi.app.src
new file mode 100644
index 000000000..45a3efc10
--- /dev/null
+++ b/apps/emqx_bpapi/src/emqx_bpapi.app.src
@@ -0,0 +1,15 @@
+{application, emqx_bpapi,
+ [{description, "A library for verifying safety of RPC calls"},
+  {vsn, "0.1.0"},
+  {registered, []},
+  {applications,
+   [kernel,
+    stdlib,
+    typerefl %% Just for some metaprogramming utils
+   ]},
+  {env,[]},
+  {modules, []},
+
+  {licenses, ["Apache 2.0"]},
+  {links, []}
+ ]}.
diff --git a/apps/emqx_bpapi/src/emqx_bpapi.erl b/apps/emqx_bpapi/src/emqx_bpapi.erl
new file mode 100644
index 000000000..284de4dfc
--- /dev/null
+++ b/apps/emqx_bpapi/src/emqx_bpapi.erl
@@ -0,0 +1,54 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+-module(emqx_bpapi).
+
+-export([parse_semver/1, api_and_version/1]).
+
+-export_type([var_name/0, call/0, rpc/0, bpapi_meta/0]).
+
+-type semver() :: {non_neg_integer(), non_neg_integer(), non_neg_integer()}.
+
+-type api() :: atom().
+-type api_version() :: non_neg_integer().
+-type var_name() :: atom().
+-type call() :: {module(), atom(), [var_name()]}.
+-type rpc() :: {_From :: call(), _To :: call()}.
+
+-type bpapi_meta() ::
+        #{ api     := api()
+         , version := api_version()
+         , calls   := [rpc()]
+         , casts   := [rpc()]
+         }.
+
+-spec parse_semver(string()) -> {ok, semver()}
+                              | false.
+parse_semver(Str) ->
+    Opts = [{capture, all_but_first, list}],
+    case re:run(Str, "^([0-9]+)\\.([0-9]+)\\.([0-9]+)$", Opts) of
+        {match, [A, B, C]} -> {ok, {list_to_integer(A), list_to_integer(B), list_to_integer(C)}};
+        nomatch            -> error
+    end.
+
+-spec api_and_version(module()) -> {atom(), non_neg_integer()}.
+api_and_version(Module) ->
+  Opts = [{capture, all_but_first, list}],
+  case re:run(atom_to_list(Module), "(.*)_proto_v([0-9]+)$", Opts) of
+    {match, [API, VsnStr]} ->
+      {ok, list_to_atom(API), list_to_integer(VsnStr)};
+    nomatch ->
+      error(Module)
+  end.
diff --git a/apps/emqx_bpapi/src/emqx_bpapi_static_checks.erl b/apps/emqx_bpapi/src/emqx_bpapi_static_checks.erl
new file mode 100644
index 000000000..de252b2b2
--- /dev/null
+++ b/apps/emqx_bpapi/src/emqx_bpapi_static_checks.erl
@@ -0,0 +1,147 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+-module(emqx_bpapi_static_checks).
+
+-export([run/1, run/0]).
+
+-include_lib("emqx/include/logger.hrl").
+
+%% `emqx_bpapi:call' enriched with dialyzer spec
+-type typed_call() :: {emqx_bpapi:call(), _DialyzerSpec}.
+-type typed_rpc() :: {typed_call(), typed_call()}.
+
+-type fulldump() :: #{emqx_bpapi:api() =>
+                          #{emqx_bpapi:api_version() =>
+                                #{ calls := [typed_rpc()]
+                                 , casts := [typed_rpc()]
+                                 }
+                           }}.
+
+%% Applications we wish to ignore in the analysis:
+-define(IGNORED_APPS, "gen_rpc, recon, observer_cli, snabbkaffe, ekka, mria").
+%% List of known RPC backend modules:
+-define(RPC_MODULES, "gen_rpc, erpc, rpc, emqx_rpc").
+%% List of functions in the RPC backend modules that we can ignore:
+-define(IGNORED_RPC_CALLS, "gen_rpc:nodes/0").
+
+-define(XREF, myxref).
+
+run() ->
+    case {filelib:wildcard("*_plt"), filelib:wildcard("_build/emqx*/lib")} of
+        {[PLT|_], [RelDir|_]} ->
+            run(#{plt => PLT, reldir => RelDir});
+        _ ->
+            error("failed to guess run options")
+    end.
+
+-spec run(map()) -> boolean().
+run(Opts) ->
+    put(bpapi_ok, true),
+    PLT = prepare(Opts),
+    %% First we run XREF to find all callers of any known RPC backend:
+    Callers = find_remote_calls(Opts),
+    {BPAPICalls, NonBPAPICalls} = lists:partition(fun is_bpapi_call/1, Callers),
+    warn_nonbpapi_rpcs(NonBPAPICalls),
+    CombinedAPI = collect_bpapis(BPAPICalls, PLT),
+    dump_api(CombinedAPI),
+    erase(bpapi_ok).
+
+prepare(#{reldir := RelDir, plt := PLT}) ->
+    ?INFO("Starting xref...", []),
+    xref:start(?XREF),
+    filelib:wildcard(RelDir ++ "/*/ebin/") =:= [] andalso
+        error("No applications found in the release directory. Wrong directory?"),
+    xref:set_default(?XREF, [{warnings, false}]),
+    xref:add_release(?XREF, RelDir),
+    %% Now to the dialyzer stuff:
+    ?INFO("Loading PLT...", []),
+    dialyzer_plt:from_file(PLT).
+
+find_remote_calls(_Opts) ->
+    Query = "XC | (A - [" ?IGNORED_APPS "]:App)
+               || ([" ?RPC_MODULES "] : Mod - " ?IGNORED_RPC_CALLS ")",
+    {ok, Calls} = xref:q(?XREF, Query),
+    ?INFO("Calls to RPC modules ~p", [Calls]),
+    {Callers, _Callees} = lists:unzip(Calls),
+    Callers.
+
+-spec warn_nonbpapi_rpcs([mfa()]) -> ok.
+warn_nonbpapi_rpcs([]) ->
+    ok;
+warn_nonbpapi_rpcs(L) ->
+    setnok(),
+    lists:foreach(fun({M, F, A}) ->
+                          ?ERROR("~p:~p/~p does a remote call outside of a dedicated "
+                                 "backplane API module. "
+                                 "It may break during rolling cluster upgrade",
+                                 [M, F, A])
+                  end,
+                  L).
+
+-spec is_bpapi_call(mfa()) -> boolean().
+is_bpapi_call({Module, _Function, _Arity}) ->
+    case catch Module:bpapi_meta() of
+        #{api := _} -> true;
+        _           -> false
+    end.
+
+-spec dump_api(fulldump()) -> ok.
+dump_api(Term) ->
+    Filename = filename:join(code:priv_dir(emqx_bpapi), emqx_app:get_release() ++ ".bpapi"),
+    file:write_file(Filename, io_lib:format("~0p.", [Term])).
+
+-spec collect_bpapis([mfa()], _PLT) -> fulldump().
+collect_bpapis(L, PLT) ->
+    Modules = lists:usort([M || {M, _F, _A} <- L]),
+    lists:foldl(fun(Mod, Acc) ->
+                        #{ api     := API
+                         , version := Vsn
+                         , calls   := Calls0
+                         , casts   := Casts0
+                         } = Mod:bpapi_meta(),
+                        Calls = enrich(PLT, Calls0),
+                        Casts = enrich(PLT, Casts0),
+                        Acc#{API => #{Vsn => #{ calls => Calls
+                                              , casts => Casts
+                                              }}}
+                end,
+                #{},
+                Modules
+               ).
+
+%% Add information about types from the PLT
+-spec enrich(_PLT, [emqx_bpapi:rpc()]) -> [typed_rpc()].
+enrich(PLT, Calls) ->
+    [case {lookup_type(PLT, From), lookup_type(PLT, To)} of
+         {{value, TFrom}, {value, TTo}} ->
+             {{From, TFrom}, {To, TTo}};
+         {_, none} ->
+             setnok(),
+             ?CRITICAL("Backplane API function ~s calls a missing remote function ~s",
+                       [format_call(From), format_call(To)]),
+             error(missing_target)
+     end
+     || {From, To} <- Calls].
+
+lookup_type(PLT, {M, F, A}) ->
+    dialyzer_plt:lookup(PLT, {M, F, length(A)}).
+
+format_call({M, F, A}) ->
+    io_lib:format("~p:~p/~p", [M, F, length(A)]).
+
+setnok() ->
+    put(bpapi_ok, false).
diff --git a/apps/emqx_bpapi/src/emqx_bpapi_trans.erl b/apps/emqx_bpapi/src/emqx_bpapi_trans.erl
new file mode 100644
index 000000000..bdcab83af
--- /dev/null
+++ b/apps/emqx_bpapi/src/emqx_bpapi_trans.erl
@@ -0,0 +1,200 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2020-2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+%% @hidden This parse transform generates BPAPI metadata function for
+%% a module, and helps dialyzer typechecking RPC calls
+-module(emqx_bpapi_trans).
+
+-export([parse_transform/2, format_error/1]).
+
+%%-define(debug, true).
+
+-define(META_FUN, bpapi_meta).
+
+-type semantics() :: call | cast.
+
+-record(s,
+        { api              :: atom()
+        , module           :: atom()
+        , version          :: non_neg_integer() | undefined
+        , introduced_in    :: emqx_bpapi:semver() | undefined
+        , deprecated_since :: emqx_bpapi:semver() | undefined
+        , targets = []     :: [{semantics(), emqx_bpapi:call(), emqx_bpapi:call()}]
+        , errors = []      :: [string()]
+        , file
+        }).
+
+format_error(invalid_name) ->
+  "BPAPI module name should follow <API>_proto_v<number> pattern";
+format_error(invalid_introduced_in) ->
+  "-introduced_in attribute should be present and its value should be a semver string";
+format_error(invalid_deprecated_since) ->
+  "value of -deprecated_since attribute should be a semver string";
+format_error({invalid_fun, Name, Arity}) ->
+  io_lib:format("malformed function ~p/~p. "
+                "BPAPI functions should have exactly one clause "
+                "and call (emqx_|e)rpc at the top level",
+                [Name, Arity]).
+
+parse_transform(Forms, _Options) ->
+  log("Original:~n~p", [Forms]),
+  State = #s{file = File} = lists:foldl(fun go/2, #s{}, Forms),
+  log("parse_trans state: ~p", [State]),
+  case check(State) of
+    [] ->
+      finalize(Forms, State);
+    Errors ->
+      {error, [{File, [{Line, ?MODULE, Msg} || {Line, Msg} <- Errors]}], []}
+  end.
+
+%% Scan erl_forms:
+go({attribute, _, file, {File, _}}, S) ->
+  S#s{file = File};
+go({attribute, Line, module, Mod}, S) ->
+  case emqx_bpapi:api_and_version(Mod) of
+    {ok, API, Vsn} -> S#s{api = API, version = Vsn, module = Mod};
+    error          -> push_err(Line, invalid_name, S)
+  end;
+go({attribute, _Line, introduced_in, Str}, S) ->
+  case is_list(Str) andalso emqx_bpapi:parse_semver(Str) of
+    {ok, Vsn} -> S#s{introduced_in = Vsn};
+    false     -> S %% Don't report error here, it's done in check/1
+  end;
+go({attribute, Line, deprecated_since, Str}, S) ->
+  case is_list(Str) andalso emqx_bpapi:parse_semver(Str) of
+    {ok, Vsn} -> S#s{deprecated_since = Vsn};
+    false     -> push_err(Line, invalid_deprecated_since, S)
+  end;
+go({function, Line, Name, Arity, Clauses}, S) ->
+  analyze_fun(Line, Name, Arity, Clauses, S);
+go(_, S) ->
+  S.
+
+check(#s{errors = Err0, introduced_in = II}) ->
+  [{none, invalid_introduced_in} || II =:= undefined] ++
+    Err0.
+
+finalize(Forms, S) ->
+  {Attrs, Funcs} = lists:splitwith(fun is_attribute/1, Forms),
+  AST = mk_meta_fun(S),
+  log("Meta fun:~n~p", [AST]),
+  Attrs ++ [mk_export()] ++ [AST|Funcs].
+
+mk_meta_fun(#s{api = API, version = Vsn, targets = Targets}) ->
+  Line = 0,
+  Calls = [{From, To} || {call, From, To} <- Targets],
+  Casts = [{From, To} || {cast, From, To} <- Targets],
+  Ret = typerefl_quote:const(Line, #{ api => API
+                                    , version => Vsn
+                                    , calls => Calls
+                                    , casts => Casts
+                                    }),
+  {function, Line, ?META_FUN, _Arity = 0,
+   [{clause, Line, _Args = [], _Guards = [],
+     [Ret]}]}.
+
+mk_export() ->
+  {attribute, 0, export, [{?META_FUN, 0}]}.
+
+is_attribute({attribute, _Line, _Attr, _Val}) -> true;
+is_attribute(_)                               -> false.
+
+%% Extract the target function of the RPC call
+analyze_fun(Line, Name, Arity, [{clause, Line, Head, _Guards, Exprs}], S) ->
+  analyze_exprs(Line, Name, Arity, Head, Exprs, S);
+analyze_fun(Line, Name, Arity, _Clauses, S) ->
+  invalid_fun(Line, Name, Arity, S).
+
+analyze_exprs(Line, Name, Arity, Head, Exprs, S) ->
+  log("~p/~p (~p):~n~p", [Name, Arity, Head, Exprs]),
+  try
+    [{call, _, CallToBackend, CallArgs}] = Exprs,
+    OuterArgs = extract_outer_args(Head),
+    Key = {S#s.module, Name, OuterArgs},
+    {Semantics, Target} = extract_target_call(CallToBackend, CallArgs),
+    push_target({Semantics, Key, Target}, S)
+  catch
+    _:Err:Stack ->
+      log("Failed to process function call:~n~s~nStack: ~p", [Err, Stack]),
+      invalid_fun(Line, Name, Arity, S)
+  end.
+
+-spec extract_outer_args(erl_parse:abstract_form()) -> [atom()].
+extract_outer_args(Abs) ->
+  lists:map(fun({var, _, Var}) ->
+                Var;
+               ({match, _, {var, _, Var}, _}) ->
+                Var;
+               ({match, _, _, {var, _, Var}}) ->
+                Var
+            end,
+            Abs).
+
+-spec extract_target_call(Abs, [Abs]) -> {semantics(), emqx_bpapi:call()}
+          when Abs :: erl_parse:abstract_form().
+extract_target_call(RPCBackend, OuterArgs) ->
+  {Semantics, {atom, _, M}, {atom, _, F}, A} = extract_mfa(RPCBackend, OuterArgs),
+  {Semantics, {M, F, list_to_args(A)}}.
+
+-define(BACKEND(MOD, FUN), {remote, _, {atom, _, MOD}, {atom, _, FUN}}).
+-define(IS_RPC(MOD), (MOD =:= erpc orelse MOD =:= rpc)).
+
+-spec extract_mfa(Abs, #s{}) -> {call | cast, Abs, Abs, Abs}
+          when Abs :: erl_parse:abstract_form().
+%% gen_rpc:
+extract_mfa(?BACKEND(gen_rpc, _), _) ->
+  %% gen_rpc has an extremely messy API, thankfully it's fully wrapped
+  %% by emqx_rpc, so we simply forbid direct calls to it:
+  error("direct call to gen_rpc");
+%% emqx_rpc:
+extract_mfa(?BACKEND(emqx_rpc, CallOrCast), [_Node, M, F, A]) ->
+  {call_or_cast(CallOrCast), M, F, A};
+extract_mfa(?BACKEND(emqx_rpc, CallOrCast), [_Tag, _Node, M, F, A]) ->
+  {call_or_cast(CallOrCast), M, F, A};
+%% (e)rpc:
+extract_mfa(?BACKEND(RPC, CallOrCast), [_Node, M, F, A]) when ?IS_RPC(RPC) ->
+  {call_or_cast(CallOrCast), M, F, A};
+extract_mfa(?BACKEND(RPC, CallOrCast), [_Node, M, F, A, _Timeout]) when ?IS_RPC(RPC) ->
+  {call_or_cast(CallOrCast), M, F, A};
+extract_mfa(_, _) ->
+  error("unrecognized RPC call").
+
+call_or_cast(cast)      -> cast;
+call_or_cast(multicast) -> cast;
+call_or_cast(multicall) -> call;
+call_or_cast(call)      -> call.
+
+list_to_args({cons, _, {var, _, A}, T}) ->
+  [A|list_to_args(T)];
+list_to_args({nil, _}) ->
+  [].
+
+invalid_fun(Line, Name, Arity, S) ->
+  push_err(Line, {invalid_fun, Name, Arity}, S).
+
+push_err(Line, Err, S = #s{errors = Errs}) ->
+  S#s{errors = [{Line, Err}|Errs]}.
+
+push_target(Target, S = #s{targets = Targets}) ->
+  S#s{targets = [Target|Targets]}.
+
+-ifdef(debug).
+log(Fmt, Args) ->
+  io:format(user, "!! " ++ Fmt ++ "~n", Args).
+-else.
+log(_, _) ->
+  ok.
+-endif.

From 96fdd0c31f3dbae17cb93e16b62c24833124e34c Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Tue, 4 Jan 2022 12:07:40 +0100
Subject: [PATCH 03/10] fix(bpapi): Fix build order

---
 apps/emqx/src/emqx.app.src | 1 +
 1 file changed, 1 insertion(+)

diff --git a/apps/emqx/src/emqx.app.src b/apps/emqx/src/emqx.app.src
index 0989cd7f1..597e1596f 100644
--- a/apps/emqx/src/emqx.app.src
+++ b/apps/emqx/src/emqx.app.src
@@ -17,6 +17,7 @@
                  , jiffy
                  , lc
                  , hocon
+                 , emqx_bpapi
                  ]},
   {mod, {emqx_app,[]}},
   {env, []},

From 2c3af8d9fe9fe6eab885409502ea1ec10e82f59c Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Tue, 4 Jan 2022 15:39:09 +0100
Subject: [PATCH 04/10] feat(bpapi): Move to emqx

Fix standalone build
---
 apps/{emqx_bpapi => emqx}/include/bpapi.hrl       |  0
 apps/{emqx_bpapi => emqx}/priv/.gitkeep           |  0
 apps/emqx/rebar.config                            |  2 ++
 .../src => emqx/src/bpapi}/emqx_bpapi.erl         |  0
 .../src/bpapi}/emqx_bpapi_static_checks.erl       |  0
 .../src => emqx/src/bpapi}/emqx_bpapi_trans.erl   |  0
 apps/emqx/src/emqx.app.src                        |  1 -
 apps/emqx/src/proto/emqx_broker_proto_v1.erl      |  2 +-
 apps/emqx_bpapi/README.md                         |  5 -----
 apps/emqx_bpapi/src/emqx_bpapi.app.src            | 15 ---------------
 rebar.config                                      |  2 ++
 11 files changed, 5 insertions(+), 22 deletions(-)
 rename apps/{emqx_bpapi => emqx}/include/bpapi.hrl (100%)
 rename apps/{emqx_bpapi => emqx}/priv/.gitkeep (100%)
 rename apps/{emqx_bpapi/src => emqx/src/bpapi}/emqx_bpapi.erl (100%)
 rename apps/{emqx_bpapi/src => emqx/src/bpapi}/emqx_bpapi_static_checks.erl (100%)
 rename apps/{emqx_bpapi/src => emqx/src/bpapi}/emqx_bpapi_trans.erl (100%)
 delete mode 100644 apps/emqx_bpapi/README.md
 delete mode 100644 apps/emqx_bpapi/src/emqx_bpapi.app.src

diff --git a/apps/emqx_bpapi/include/bpapi.hrl b/apps/emqx/include/bpapi.hrl
similarity index 100%
rename from apps/emqx_bpapi/include/bpapi.hrl
rename to apps/emqx/include/bpapi.hrl
diff --git a/apps/emqx_bpapi/priv/.gitkeep b/apps/emqx/priv/.gitkeep
similarity index 100%
rename from apps/emqx_bpapi/priv/.gitkeep
rename to apps/emqx/priv/.gitkeep
diff --git a/apps/emqx/rebar.config b/apps/emqx/rebar.config
index 4ec68d585..be8989dcd 100644
--- a/apps/emqx/rebar.config
+++ b/apps/emqx/rebar.config
@@ -4,6 +4,8 @@
 {xref_checks,[undefined_function_calls,undefined_functions,locals_not_used,
               deprecated_function_calls,warnings_as_errors,deprecated_functions]}.
 
+{erl_first_files, ["apps/emqx/src/bpapi/emqx_bpapi.erl"]}.
+
 %% Deps here may duplicate with emqx.git root level rebar.config
 %% but there not be any descrpancy.
 %% This rebar.config is necessary because the app may be used as a
diff --git a/apps/emqx_bpapi/src/emqx_bpapi.erl b/apps/emqx/src/bpapi/emqx_bpapi.erl
similarity index 100%
rename from apps/emqx_bpapi/src/emqx_bpapi.erl
rename to apps/emqx/src/bpapi/emqx_bpapi.erl
diff --git a/apps/emqx_bpapi/src/emqx_bpapi_static_checks.erl b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
similarity index 100%
rename from apps/emqx_bpapi/src/emqx_bpapi_static_checks.erl
rename to apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
diff --git a/apps/emqx_bpapi/src/emqx_bpapi_trans.erl b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
similarity index 100%
rename from apps/emqx_bpapi/src/emqx_bpapi_trans.erl
rename to apps/emqx/src/bpapi/emqx_bpapi_trans.erl
diff --git a/apps/emqx/src/emqx.app.src b/apps/emqx/src/emqx.app.src
index 597e1596f..0989cd7f1 100644
--- a/apps/emqx/src/emqx.app.src
+++ b/apps/emqx/src/emqx.app.src
@@ -17,7 +17,6 @@
                  , jiffy
                  , lc
                  , hocon
-                 , emqx_bpapi
                  ]},
   {mod, {emqx_app,[]}},
   {env, []},
diff --git a/apps/emqx/src/proto/emqx_broker_proto_v1.erl b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
index a40884c38..178fa2f08 100644
--- a/apps/emqx/src/proto/emqx_broker_proto_v1.erl
+++ b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
@@ -22,7 +22,7 @@
         , forward_async/3
         ]).
 
--include_lib("emqx_bpapi/include/bpapi.hrl").
+-include("bpapi.hrl").
 -include("emqx.hrl").
 
 -spec forward(node(), emqx_types:topic(), emqx_types:delivery()) -> emqx_types:deliver_result().
diff --git a/apps/emqx_bpapi/README.md b/apps/emqx_bpapi/README.md
deleted file mode 100644
index 78f529a4c..000000000
--- a/apps/emqx_bpapi/README.md
+++ /dev/null
@@ -1,5 +0,0 @@
-emqx_bpapi
-=====
-
-A library that helps maintaining EMQX's backplane API backward and
-forward compatibility.
diff --git a/apps/emqx_bpapi/src/emqx_bpapi.app.src b/apps/emqx_bpapi/src/emqx_bpapi.app.src
deleted file mode 100644
index 45a3efc10..000000000
--- a/apps/emqx_bpapi/src/emqx_bpapi.app.src
+++ /dev/null
@@ -1,15 +0,0 @@
-{application, emqx_bpapi,
- [{description, "A library for verifying safety of RPC calls"},
-  {vsn, "0.1.0"},
-  {registered, []},
-  {applications,
-   [kernel,
-    stdlib,
-    typerefl %% Just for some metaprogramming utils
-   ]},
-  {env,[]},
-  {modules, []},
-
-  {licenses, ["Apache 2.0"]},
-  {links, []}
- ]}.
diff --git a/rebar.config b/rebar.config
index 49e37e4af..f333d3e51 100644
--- a/rebar.config
+++ b/rebar.config
@@ -13,6 +13,8 @@
             {d, snk_kind, msg}
            ]}.
 
+{erl_first_files, ["apps/emqx/src/bpapi/emqx_bpapi.erl"]}.
+
 {xref_checks,[undefined_function_calls,undefined_functions,locals_not_used,
               deprecated_function_calls,warnings_as_errors,deprecated_functions]}.
 

From 64378be9a09af5e37456d430083bda821583bcd9 Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Tue, 4 Jan 2022 17:45:42 +0100
Subject: [PATCH 05/10] fix(bpapi): Optimize BPAPI dump size

---
 .../src/bpapi/emqx_bpapi_static_checks.erl    | 101 ++++++++++--------
 1 file changed, 59 insertions(+), 42 deletions(-)

diff --git a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
index de252b2b2..2065a70cf 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
@@ -16,21 +16,23 @@
 
 -module(emqx_bpapi_static_checks).
 
--export([run/1, run/0]).
+-export([dump/1, dump/0]).
 
 -include_lib("emqx/include/logger.hrl").
 
-%% `emqx_bpapi:call' enriched with dialyzer spec
--type typed_call() :: {emqx_bpapi:call(), _DialyzerSpec}.
--type typed_rpc() :: {typed_call(), typed_call()}.
-
--type fulldump() :: #{emqx_bpapi:api() =>
-                          #{emqx_bpapi:api_version() =>
-                                #{ calls := [typed_rpc()]
-                                 , casts := [typed_rpc()]
-                                 }
+-type api_dump() :: #{{emqx_bpapi:api(), emqx_bpapi:api_version()} =>
+                          #{ calls := [emqx_bpapi:rpc()]
+                           , casts := [emqx_bpapi:rpc()]
                            }}.
 
+-type dialyzer_spec() :: {_Type, [_Type]}.
+
+-type dialyzer_dump() :: #{mfa() => dialyzer_spec()}.
+
+-type fulldump() :: #{ api        => api_dump()
+                     , signatures => dialyzer_dump()
+                     }.
+
 %% Applications we wish to ignore in the analysis:
 -define(IGNORED_APPS, "gen_rpc, recon, observer_cli, snabbkaffe, ekka, mria").
 %% List of known RPC backend modules:
@@ -40,24 +42,26 @@
 
 -define(XREF, myxref).
 
-run() ->
+dump() ->
     case {filelib:wildcard("*_plt"), filelib:wildcard("_build/emqx*/lib")} of
         {[PLT|_], [RelDir|_]} ->
-            run(#{plt => PLT, reldir => RelDir});
+            dump(#{plt => PLT, reldir => RelDir});
         _ ->
             error("failed to guess run options")
     end.
 
--spec run(map()) -> boolean().
-run(Opts) ->
+%% Collect the local BPAPI modules to a dump file:
+-spec dump(map()) -> boolean().
+dump(Opts) ->
     put(bpapi_ok, true),
     PLT = prepare(Opts),
     %% First we run XREF to find all callers of any known RPC backend:
     Callers = find_remote_calls(Opts),
     {BPAPICalls, NonBPAPICalls} = lists:partition(fun is_bpapi_call/1, Callers),
     warn_nonbpapi_rpcs(NonBPAPICalls),
-    CombinedAPI = collect_bpapis(BPAPICalls, PLT),
-    dump_api(CombinedAPI),
+    APIDump = collect_bpapis(BPAPICalls),
+    DialyzerDump = collect_signatures(PLT, APIDump),
+    dump_api(#{api => APIDump, signatures => DialyzerDump}),
     erase(bpapi_ok).
 
 prepare(#{reldir := RelDir, plt := PLT}) ->
@@ -100,45 +104,58 @@ is_bpapi_call({Module, _Function, _Arity}) ->
     end.
 
 -spec dump_api(fulldump()) -> ok.
-dump_api(Term) ->
-    Filename = filename:join(code:priv_dir(emqx_bpapi), emqx_app:get_release() ++ ".bpapi"),
+dump_api(Term = #{api := _, signatures := _}) ->
+    Filename = filename:join(code:priv_dir(emqx), emqx_app:get_release() ++ ".bpapi"),
     file:write_file(Filename, io_lib:format("~0p.", [Term])).
 
--spec collect_bpapis([mfa()], _PLT) -> fulldump().
-collect_bpapis(L, PLT) ->
+-spec collect_bpapis([mfa()]) -> api_dump().
+collect_bpapis(L) ->
     Modules = lists:usort([M || {M, _F, _A} <- L]),
     lists:foldl(fun(Mod, Acc) ->
                         #{ api     := API
                          , version := Vsn
-                         , calls   := Calls0
-                         , casts   := Casts0
+                         , calls   := Calls
+                         , casts   := Casts
                          } = Mod:bpapi_meta(),
-                        Calls = enrich(PLT, Calls0),
-                        Casts = enrich(PLT, Casts0),
-                        Acc#{API => #{Vsn => #{ calls => Calls
-                                              , casts => Casts
-                                              }}}
+                        Acc#{{API, Vsn} => #{ calls => Calls
+                                            , casts => Casts
+                                            }}
                 end,
                 #{},
                 Modules
                ).
 
-%% Add information about types from the PLT
--spec enrich(_PLT, [emqx_bpapi:rpc()]) -> [typed_rpc()].
-enrich(PLT, Calls) ->
-    [case {lookup_type(PLT, From), lookup_type(PLT, To)} of
-         {{value, TFrom}, {value, TTo}} ->
-             {{From, TFrom}, {To, TTo}};
-         {_, none} ->
-             setnok(),
-             ?CRITICAL("Backplane API function ~s calls a missing remote function ~s",
-                       [format_call(From), format_call(To)]),
-             error(missing_target)
-     end
-     || {From, To} <- Calls].
+-spec collect_signatures(_PLT, api_dump()) -> dialyzer_dump().
+collect_signatures(PLT, APIs) ->
+    maps:fold(fun(_APIAndVersion, #{calls := Calls, casts := Casts}, Acc0) ->
+                      Acc1 = lists:foldl(fun enrich/2, {Acc0, PLT}, Calls),
+                      {Acc, PLT} = lists:foldl(fun enrich/2, Acc1, Casts),
+                      Acc
+              end,
+              #{},
+              APIs).
 
-lookup_type(PLT, {M, F, A}) ->
-    dialyzer_plt:lookup(PLT, {M, F, length(A)}).
+%% Add information about the call types from the PLT
+-spec enrich(emqx_bpapi:rpc(), {dialyzer_dump(), _PLT}) -> {dialyzer_dump(), _PLT}.
+enrich({From0, To0}, {Acc0, PLT}) ->
+    From = call_to_mfa(From0),
+    To   = call_to_mfa(To0),
+    case {dialyzer_plt:lookup(PLT, From), dialyzer_plt:lookup(PLT, To)} of
+        {{value, TFrom}, {value, TTo}} ->
+            Acc = Acc0#{ From => TFrom
+                       , To   => TTo
+                       },
+            {Acc, PLT};
+        {_, none} ->
+            setnok(),
+            ?CRITICAL("Backplane API function ~s calls a missing remote function ~s",
+                      [format_call(From0), format_call(To0)]),
+            error(missing_target)
+     end.
+
+-spec call_to_mfa(emqx_bpapi:call()) -> mfa().
+call_to_mfa({M, F, A}) ->
+    {M, F, length(A)}.
 
 format_call({M, F, A}) ->
     io_lib:format("~p:~p/~p", [M, F, length(A)]).

From eaa71438b276d7acb429171123dfb34e06b876cd Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Tue, 4 Jan 2022 20:01:23 +0100
Subject: [PATCH 06/10] feat(bpapi): Typecheck function parameters

---
 .../src/bpapi/emqx_bpapi_static_checks.erl    | 114 ++++++++++++++++--
 1 file changed, 106 insertions(+), 8 deletions(-)

diff --git a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
index 2065a70cf..c77ede7a3 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
@@ -16,7 +16,7 @@
 
 -module(emqx_bpapi_static_checks).
 
--export([dump/1, dump/0]).
+-export([dump/1, dump/0, check_compat/1]).
 
 -include_lib("emqx/include/logger.hrl").
 
@@ -31,8 +31,11 @@
 
 -type fulldump() :: #{ api        => api_dump()
                      , signatures => dialyzer_dump()
+                     , release    => string()
                      }.
 
+-type param_types() :: #{emqx_bpapi:var_name() => _Type}.
+
 %% Applications we wish to ignore in the analysis:
 -define(IGNORED_APPS, "gen_rpc, recon, observer_cli, snabbkaffe, ekka, mria").
 %% List of known RPC backend modules:
@@ -42,6 +45,101 @@
 
 -define(XREF, myxref).
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Functions related to BPAPI compatibility checking
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+-spec check_compat([file:filename()]) -> boolean().
+check_compat(DumpFilenames) ->
+    put(bpapi_ok, true),
+    Dumps = lists:map(fun(FN) ->
+                              {ok, [Dump]} = file:consult(FN),
+                              Dump
+                      end,
+                      DumpFilenames),
+    [check_compat(I, J) || I <- Dumps, J <- Dumps],
+    erase(bpapi_ok).
+
+%% Note: sets nok flag
+-spec check_compat(fulldump(), fulldump()) -> ok.
+check_compat(Dump1, Dump2) ->
+    check_api_immutability(Dump1, Dump2),
+    typecheck_apis(Dump1, Dump2).
+
+%% It's not allowed to change BPAPI modules. Check that no changes
+%% have been made. (sets nok flag)
+-spec check_api_immutability(fulldump(), fulldump()) -> ok.
+check_api_immutability(#{release := Rel1, api := APIs1}, #{release := Rel2, api := APIs2})
+  when Rel2 >= Rel1 ->
+    %% TODO: Handle API deprecation
+    maps:map(fun(Key = {API, Version}, Val) ->
+                         case maps:get(Key, APIs2, undefined) of
+                             Val ->
+                                 ok;
+                             undefined ->
+                                 setnok(),
+                                 ?ERROR("API ~p v~p was removed in release ~p without being deprecated.",
+                                        [API, Version, Rel2]);
+                             _Val ->
+                                 setnok(),
+                                 ?ERROR("API ~p v~p was changed between ~p and ~p. Backplane API should be immutable.",
+                                        [API, Version, Rel1, Rel2])
+                         end
+                 end,
+                 APIs1),
+    ok;
+check_api_immutability(_, _) ->
+    ok.
+
+%% Note: sets nok flag
+-spec typecheck_apis(fulldump(), fulldump()) -> ok.
+typecheck_apis( #{release := CallerRelease, api := CallerAPIs, signatures := CallerSigs}
+              , #{release := CalleeRelease, signatures := CalleeSigs}
+              ) ->
+    AllCalls = lists:flatten([[Calls, Casts]
+                              || #{calls := Calls, casts := Casts} <- maps:values(CallerAPIs)]),
+    lists:foreach(fun({From, To}) ->
+                          Caller = get_param_types(CallerSigs, From),
+                          Callee = get_param_types(CalleeSigs, To),
+                          %% TODO: check return types
+                          case typecheck_rpc(Caller, Callee) of
+                              [] ->
+                                  ok;
+                              TypeErrors ->
+                                  setnok(),
+                                  [?ERROR("Incompatible RPC call: "
+                                          "type of the parameter ~p of RPC call ~s on release ~p "
+                                          "is not a subtype of the target function ~s on release ~p",
+                                          [Var, format_call(From), CallerRelease,
+                                           format_call(To), CalleeRelease])
+                                   || Var <- TypeErrors]
+                          end
+                  end,
+                  AllCalls).
+
+-spec typecheck_rpc(param_types(), param_types()) -> [emqx_bpapi:var_name()].
+typecheck_rpc(Caller, Callee) ->
+    maps:fold(fun(Var, CalleeType, Acc) ->
+                      #{Var := CallerType} = Caller,
+                      case erl_types:t_is_subtype(CallerType, CalleeType) of
+                          true  -> Acc;
+                          false -> [Var|Acc]
+                      end
+              end,
+              [],
+              Callee).
+
+-spec get_param_types(dialyzer_dump(), emqx_bpapi:call()) -> param_types().
+get_param_types(Signatures, {M, F, A}) ->
+    Arity = length(A),
+    #{{M, F, Arity} := {_RetType, AttrTypes}} = Signatures,
+    Arity = length(AttrTypes), % assert
+    maps:from_list(lists:zip(A, AttrTypes)).
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%% Functions related to BPAPI dumping
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
 dump() ->
     case {filelib:wildcard("*_plt"), filelib:wildcard("_build/emqx*/lib")} of
         {[PLT|_], [RelDir|_]} ->
@@ -50,7 +148,7 @@ dump() ->
             error("failed to guess run options")
     end.
 
-%% Collect the local BPAPI modules to a dump file:
+%% Collect the local BPAPI modules to a dump file
 -spec dump(map()) -> boolean().
 dump(Opts) ->
     put(bpapi_ok, true),
@@ -61,7 +159,8 @@ dump(Opts) ->
     warn_nonbpapi_rpcs(NonBPAPICalls),
     APIDump = collect_bpapis(BPAPICalls),
     DialyzerDump = collect_signatures(PLT, APIDump),
-    dump_api(#{api => APIDump, signatures => DialyzerDump}),
+    Release = emqx_app:get_release(),
+    dump_api(#{api => APIDump, signatures => DialyzerDump, release => Release}),
     erase(bpapi_ok).
 
 prepare(#{reldir := RelDir, plt := PLT}) ->
@@ -104,8 +203,8 @@ is_bpapi_call({Module, _Function, _Arity}) ->
     end.
 
 -spec dump_api(fulldump()) -> ok.
-dump_api(Term = #{api := _, signatures := _}) ->
-    Filename = filename:join(code:priv_dir(emqx), emqx_app:get_release() ++ ".bpapi"),
+dump_api(Term = #{api := _, signatures := _, release := Release}) ->
+    Filename = filename:join(code:priv_dir(emqx), Release ++ ".bpapi"),
     file:write_file(Filename, io_lib:format("~0p.", [Term])).
 
 -spec collect_bpapis([mfa()]) -> api_dump().
@@ -122,8 +221,7 @@ collect_bpapis(L) ->
                                             }}
                 end,
                 #{},
-                Modules
-               ).
+                Modules).
 
 -spec collect_signatures(_PLT, api_dump()) -> dialyzer_dump().
 collect_signatures(PLT, APIs) ->
@@ -146,7 +244,7 @@ enrich({From0, To0}, {Acc0, PLT}) ->
                        , To   => TTo
                        },
             {Acc, PLT};
-        {_, none} ->
+        {{value, _}, none} ->
             setnok(),
             ?CRITICAL("Backplane API function ~s calls a missing remote function ~s",
                       [format_call(From0), format_call(To0)]),

From 0f6ec9d646998ffdccae2639cdd074c911214a7f Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Tue, 4 Jan 2022 20:28:31 +0100
Subject: [PATCH 07/10] fix(bpapi): Fix build

---
 apps/emqx/rebar.config                   |   2 -
 apps/emqx/src/bpapi/emqx_bpapi.erl       |  23 +--
 apps/emqx/src/bpapi/emqx_bpapi_trans.erl | 200 +++++++++++++----------
 rebar.config                             |   2 -
 4 files changed, 111 insertions(+), 116 deletions(-)

diff --git a/apps/emqx/rebar.config b/apps/emqx/rebar.config
index be8989dcd..4ec68d585 100644
--- a/apps/emqx/rebar.config
+++ b/apps/emqx/rebar.config
@@ -4,8 +4,6 @@
 {xref_checks,[undefined_function_calls,undefined_functions,locals_not_used,
               deprecated_function_calls,warnings_as_errors,deprecated_functions]}.
 
-{erl_first_files, ["apps/emqx/src/bpapi/emqx_bpapi.erl"]}.
-
 %% Deps here may duplicate with emqx.git root level rebar.config
 %% but there not be any descrpancy.
 %% This rebar.config is necessary because the app may be used as a
diff --git a/apps/emqx/src/bpapi/emqx_bpapi.erl b/apps/emqx/src/bpapi/emqx_bpapi.erl
index 284de4dfc..c3da7c067 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi.erl
@@ -15,9 +15,7 @@
 %%--------------------------------------------------------------------
 -module(emqx_bpapi).
 
--export([parse_semver/1, api_and_version/1]).
-
--export_type([var_name/0, call/0, rpc/0, bpapi_meta/0]).
+-export_type([var_name/0, call/0, rpc/0, bpapi_meta/0, semver/0]).
 
 -type semver() :: {non_neg_integer(), non_neg_integer(), non_neg_integer()}.
 
@@ -33,22 +31,3 @@
          , calls   := [rpc()]
          , casts   := [rpc()]
          }.
-
--spec parse_semver(string()) -> {ok, semver()}
-                              | false.
-parse_semver(Str) ->
-    Opts = [{capture, all_but_first, list}],
-    case re:run(Str, "^([0-9]+)\\.([0-9]+)\\.([0-9]+)$", Opts) of
-        {match, [A, B, C]} -> {ok, {list_to_integer(A), list_to_integer(B), list_to_integer(C)}};
-        nomatch            -> error
-    end.
-
--spec api_and_version(module()) -> {atom(), non_neg_integer()}.
-api_and_version(Module) ->
-  Opts = [{capture, all_but_first, list}],
-  case re:run(atom_to_list(Module), "(.*)_proto_v([0-9]+)$", Opts) of
-    {match, [API, VsnStr]} ->
-      {ok, list_to_atom(API), list_to_integer(VsnStr)};
-    nomatch ->
-      error(Module)
-  end.
diff --git a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
index bdcab83af..04366deba 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
@@ -38,139 +38,139 @@
         }).
 
 format_error(invalid_name) ->
-  "BPAPI module name should follow <API>_proto_v<number> pattern";
+    "BPAPI module name should follow <API>_proto_v<number> pattern";
 format_error(invalid_introduced_in) ->
-  "-introduced_in attribute should be present and its value should be a semver string";
+    "-introduced_in attribute should be present and its value should be a semver string";
 format_error(invalid_deprecated_since) ->
-  "value of -deprecated_since attribute should be a semver string";
+    "value of -deprecated_since attribute should be a semver string";
 format_error({invalid_fun, Name, Arity}) ->
-  io_lib:format("malformed function ~p/~p. "
-                "BPAPI functions should have exactly one clause "
-                "and call (emqx_|e)rpc at the top level",
-                [Name, Arity]).
+    io_lib:format("malformed function ~p/~p. "
+                  "BPAPI functions should have exactly one clause "
+                  "and call (emqx_|e)rpc at the top level",
+                  [Name, Arity]).
 
 parse_transform(Forms, _Options) ->
-  log("Original:~n~p", [Forms]),
-  State = #s{file = File} = lists:foldl(fun go/2, #s{}, Forms),
-  log("parse_trans state: ~p", [State]),
-  case check(State) of
-    [] ->
-      finalize(Forms, State);
-    Errors ->
-      {error, [{File, [{Line, ?MODULE, Msg} || {Line, Msg} <- Errors]}], []}
-  end.
+    log("Original:~n~p", [Forms]),
+    State = #s{file = File} = lists:foldl(fun go/2, #s{}, Forms),
+    log("parse_trans state: ~p", [State]),
+    case check(State) of
+        [] ->
+            finalize(Forms, State);
+        Errors ->
+            {error, [{File, [{Line, ?MODULE, Msg} || {Line, Msg} <- Errors]}], []}
+    end.
 
 %% Scan erl_forms:
 go({attribute, _, file, {File, _}}, S) ->
-  S#s{file = File};
+    S#s{file = File};
 go({attribute, Line, module, Mod}, S) ->
-  case emqx_bpapi:api_and_version(Mod) of
-    {ok, API, Vsn} -> S#s{api = API, version = Vsn, module = Mod};
-    error          -> push_err(Line, invalid_name, S)
-  end;
+    case api_and_version(Mod) of
+        {ok, API, Vsn} -> S#s{api = API, version = Vsn, module = Mod};
+        error          -> push_err(Line, invalid_name, S)
+    end;
 go({attribute, _Line, introduced_in, Str}, S) ->
-  case is_list(Str) andalso emqx_bpapi:parse_semver(Str) of
-    {ok, Vsn} -> S#s{introduced_in = Vsn};
-    false     -> S %% Don't report error here, it's done in check/1
-  end;
+    case is_list(Str) andalso parse_semver(Str) of
+        {ok, Vsn} -> S#s{introduced_in = Vsn};
+        error     -> S %% Don't report error here, it's done in check/1
+    end;
 go({attribute, Line, deprecated_since, Str}, S) ->
-  case is_list(Str) andalso emqx_bpapi:parse_semver(Str) of
-    {ok, Vsn} -> S#s{deprecated_since = Vsn};
-    false     -> push_err(Line, invalid_deprecated_since, S)
-  end;
+    case is_list(Str) andalso parse_semver(Str) of
+        {ok, Vsn} -> S#s{deprecated_since = Vsn};
+        error     -> push_err(Line, invalid_deprecated_since, S)
+    end;
 go({function, Line, Name, Arity, Clauses}, S) ->
-  analyze_fun(Line, Name, Arity, Clauses, S);
+    analyze_fun(Line, Name, Arity, Clauses, S);
 go(_, S) ->
-  S.
+    S.
 
 check(#s{errors = Err0, introduced_in = II}) ->
-  [{none, invalid_introduced_in} || II =:= undefined] ++
-    Err0.
+    [{none, invalid_introduced_in} || II =:= undefined] ++
+        Err0.
 
 finalize(Forms, S) ->
-  {Attrs, Funcs} = lists:splitwith(fun is_attribute/1, Forms),
-  AST = mk_meta_fun(S),
-  log("Meta fun:~n~p", [AST]),
-  Attrs ++ [mk_export()] ++ [AST|Funcs].
+    {Attrs, Funcs} = lists:splitwith(fun is_attribute/1, Forms),
+    AST = mk_meta_fun(S),
+    log("Meta fun:~n~p", [AST]),
+    Attrs ++ [mk_export()] ++ [AST|Funcs].
 
 mk_meta_fun(#s{api = API, version = Vsn, targets = Targets}) ->
-  Line = 0,
-  Calls = [{From, To} || {call, From, To} <- Targets],
-  Casts = [{From, To} || {cast, From, To} <- Targets],
-  Ret = typerefl_quote:const(Line, #{ api => API
-                                    , version => Vsn
-                                    , calls => Calls
-                                    , casts => Casts
-                                    }),
-  {function, Line, ?META_FUN, _Arity = 0,
-   [{clause, Line, _Args = [], _Guards = [],
-     [Ret]}]}.
+    Line = 0,
+    Calls = [{From, To} || {call, From, To} <- Targets],
+    Casts = [{From, To} || {cast, From, To} <- Targets],
+    Ret = typerefl_quote:const(Line, #{ api => API
+                                      , version => Vsn
+                                      , calls => Calls
+                                      , casts => Casts
+                                      }),
+    {function, Line, ?META_FUN, _Arity = 0,
+     [{clause, Line, _Args = [], _Guards = [],
+       [Ret]}]}.
 
 mk_export() ->
-  {attribute, 0, export, [{?META_FUN, 0}]}.
+    {attribute, 0, export, [{?META_FUN, 0}]}.
 
 is_attribute({attribute, _Line, _Attr, _Val}) -> true;
 is_attribute(_)                               -> false.
 
 %% Extract the target function of the RPC call
 analyze_fun(Line, Name, Arity, [{clause, Line, Head, _Guards, Exprs}], S) ->
-  analyze_exprs(Line, Name, Arity, Head, Exprs, S);
+    analyze_exprs(Line, Name, Arity, Head, Exprs, S);
 analyze_fun(Line, Name, Arity, _Clauses, S) ->
-  invalid_fun(Line, Name, Arity, S).
+    invalid_fun(Line, Name, Arity, S).
 
 analyze_exprs(Line, Name, Arity, Head, Exprs, S) ->
-  log("~p/~p (~p):~n~p", [Name, Arity, Head, Exprs]),
-  try
-    [{call, _, CallToBackend, CallArgs}] = Exprs,
-    OuterArgs = extract_outer_args(Head),
-    Key = {S#s.module, Name, OuterArgs},
-    {Semantics, Target} = extract_target_call(CallToBackend, CallArgs),
-    push_target({Semantics, Key, Target}, S)
-  catch
-    _:Err:Stack ->
-      log("Failed to process function call:~n~s~nStack: ~p", [Err, Stack]),
-      invalid_fun(Line, Name, Arity, S)
-  end.
+    log("~p/~p (~p):~n~p", [Name, Arity, Head, Exprs]),
+    try
+        [{call, _, CallToBackend, CallArgs}] = Exprs,
+        OuterArgs = extract_outer_args(Head),
+        Key = {S#s.module, Name, OuterArgs},
+        {Semantics, Target} = extract_target_call(CallToBackend, CallArgs),
+        push_target({Semantics, Key, Target}, S)
+    catch
+        _:Err:Stack ->
+            log("Failed to process function call:~n~s~nStack: ~p", [Err, Stack]),
+            invalid_fun(Line, Name, Arity, S)
+    end.
 
 -spec extract_outer_args(erl_parse:abstract_form()) -> [atom()].
 extract_outer_args(Abs) ->
-  lists:map(fun({var, _, Var}) ->
-                Var;
-               ({match, _, {var, _, Var}, _}) ->
-                Var;
-               ({match, _, _, {var, _, Var}}) ->
-                Var
-            end,
-            Abs).
+    lists:map(fun({var, _, Var}) ->
+                      Var;
+                 ({match, _, {var, _, Var}, _}) ->
+                      Var;
+                 ({match, _, _, {var, _, Var}}) ->
+                      Var
+              end,
+              Abs).
 
 -spec extract_target_call(Abs, [Abs]) -> {semantics(), emqx_bpapi:call()}
-          when Abs :: erl_parse:abstract_form().
+              when Abs :: erl_parse:abstract_form().
 extract_target_call(RPCBackend, OuterArgs) ->
-  {Semantics, {atom, _, M}, {atom, _, F}, A} = extract_mfa(RPCBackend, OuterArgs),
-  {Semantics, {M, F, list_to_args(A)}}.
+    {Semantics, {atom, _, M}, {atom, _, F}, A} = extract_mfa(RPCBackend, OuterArgs),
+    {Semantics, {M, F, list_to_args(A)}}.
 
 -define(BACKEND(MOD, FUN), {remote, _, {atom, _, MOD}, {atom, _, FUN}}).
 -define(IS_RPC(MOD), (MOD =:= erpc orelse MOD =:= rpc)).
 
 -spec extract_mfa(Abs, #s{}) -> {call | cast, Abs, Abs, Abs}
-          when Abs :: erl_parse:abstract_form().
+              when Abs :: erl_parse:abstract_form().
 %% gen_rpc:
 extract_mfa(?BACKEND(gen_rpc, _), _) ->
-  %% gen_rpc has an extremely messy API, thankfully it's fully wrapped
-  %% by emqx_rpc, so we simply forbid direct calls to it:
-  error("direct call to gen_rpc");
+    %% gen_rpc has an extremely messy API, thankfully it's fully wrapped
+    %% by emqx_rpc, so we simply forbid direct calls to it:
+    error("direct call to gen_rpc");
 %% emqx_rpc:
 extract_mfa(?BACKEND(emqx_rpc, CallOrCast), [_Node, M, F, A]) ->
-  {call_or_cast(CallOrCast), M, F, A};
+    {call_or_cast(CallOrCast), M, F, A};
 extract_mfa(?BACKEND(emqx_rpc, CallOrCast), [_Tag, _Node, M, F, A]) ->
-  {call_or_cast(CallOrCast), M, F, A};
+    {call_or_cast(CallOrCast), M, F, A};
 %% (e)rpc:
 extract_mfa(?BACKEND(RPC, CallOrCast), [_Node, M, F, A]) when ?IS_RPC(RPC) ->
-  {call_or_cast(CallOrCast), M, F, A};
+    {call_or_cast(CallOrCast), M, F, A};
 extract_mfa(?BACKEND(RPC, CallOrCast), [_Node, M, F, A, _Timeout]) when ?IS_RPC(RPC) ->
-  {call_or_cast(CallOrCast), M, F, A};
+    {call_or_cast(CallOrCast), M, F, A};
 extract_mfa(_, _) ->
-  error("unrecognized RPC call").
+    error("unrecognized RPC call").
 
 call_or_cast(cast)      -> cast;
 call_or_cast(multicast) -> cast;
@@ -178,23 +178,43 @@ call_or_cast(multicall) -> call;
 call_or_cast(call)      -> call.
 
 list_to_args({cons, _, {var, _, A}, T}) ->
-  [A|list_to_args(T)];
+    [A|list_to_args(T)];
 list_to_args({nil, _}) ->
-  [].
+    [].
 
 invalid_fun(Line, Name, Arity, S) ->
-  push_err(Line, {invalid_fun, Name, Arity}, S).
+    push_err(Line, {invalid_fun, Name, Arity}, S).
 
 push_err(Line, Err, S = #s{errors = Errs}) ->
-  S#s{errors = [{Line, Err}|Errs]}.
+    S#s{errors = [{Line, Err}|Errs]}.
 
 push_target(Target, S = #s{targets = Targets}) ->
-  S#s{targets = [Target|Targets]}.
+    S#s{targets = [Target|Targets]}.
+
+
+-spec parse_semver(string()) -> {ok, emqx_bpapi:semver()}
+                              | error.
+parse_semver(Str) ->
+    Opts = [{capture, all_but_first, list}],
+    case re:run(Str, "^([0-9]+)\\.([0-9]+)\\.([0-9]+)$", Opts) of
+        {match, [A, B, C]} -> {ok, {list_to_integer(A), list_to_integer(B), list_to_integer(C)}};
+        nomatch            -> error
+    end.
+
+-spec api_and_version(module()) -> {ok, emqx_bpapi:api(), emqx_bpapi:version()} | error.
+api_and_version(Module) ->
+    Opts = [{capture, all_but_first, list}],
+    case re:run(atom_to_list(Module), "(.*)_proto_v([0-9]+)$", Opts) of
+        {match, [API, VsnStr]} ->
+            {ok, list_to_atom(API), list_to_integer(VsnStr)};
+        nomatch ->
+            error
+    end.
 
 -ifdef(debug).
 log(Fmt, Args) ->
-  io:format(user, "!! " ++ Fmt ++ "~n", Args).
+    io:format(user, "!! " ++ Fmt ++ "~n", Args).
 -else.
 log(_, _) ->
-  ok.
+    ok.
 -endif.
diff --git a/rebar.config b/rebar.config
index f333d3e51..49e37e4af 100644
--- a/rebar.config
+++ b/rebar.config
@@ -13,8 +13,6 @@
             {d, snk_kind, msg}
            ]}.
 
-{erl_first_files, ["apps/emqx/src/bpapi/emqx_bpapi.erl"]}.
-
 {xref_checks,[undefined_function_calls,undefined_functions,locals_not_used,
               deprecated_function_calls,warnings_as_errors,deprecated_functions]}.
 

From 4f3f938d716e65e3ea4561f4382924f16b30ebe0 Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Wed, 5 Jan 2022 01:42:46 +0100
Subject: [PATCH 08/10] feat(bpapi): Introduce bpapi behavior

---
 apps/emqx/src/bpapi/emqx_bpapi.erl           | 12 +++++--
 apps/emqx/src/bpapi/emqx_bpapi_trans.erl     | 36 ++++----------------
 apps/emqx/src/proto/emqx_broker_proto_v1.erl |  8 +++--
 3 files changed, 22 insertions(+), 34 deletions(-)

diff --git a/apps/emqx/src/bpapi/emqx_bpapi.erl b/apps/emqx/src/bpapi/emqx_bpapi.erl
index c3da7c067..d76cb0085 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi.erl
@@ -15,9 +15,7 @@
 %%--------------------------------------------------------------------
 -module(emqx_bpapi).
 
--export_type([var_name/0, call/0, rpc/0, bpapi_meta/0, semver/0]).
-
--type semver() :: {non_neg_integer(), non_neg_integer(), non_neg_integer()}.
+-export_type([var_name/0, call/0, rpc/0, bpapi_meta/0]).
 
 -type api() :: atom().
 -type api_version() :: non_neg_integer().
@@ -31,3 +29,11 @@
          , calls   := [rpc()]
          , casts   := [rpc()]
          }.
+
+-callback introduced_in() -> string().
+
+-callback deprecated_since() -> string().
+
+-callback bpapi_meta() -> bpapi_meta().
+
+-optional_callbacks([deprecated_since/0]).
diff --git a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
index 04366deba..311edf399 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
@@ -30,8 +30,6 @@
         { api              :: atom()
         , module           :: atom()
         , version          :: non_neg_integer() | undefined
-        , introduced_in    :: emqx_bpapi:semver() | undefined
-        , deprecated_since :: emqx_bpapi:semver() | undefined
         , targets = []     :: [{semantics(), emqx_bpapi:call(), emqx_bpapi:call()}]
         , errors = []      :: [string()]
         , file
@@ -39,10 +37,6 @@
 
 format_error(invalid_name) ->
     "BPAPI module name should follow <API>_proto_v<number> pattern";
-format_error(invalid_introduced_in) ->
-    "-introduced_in attribute should be present and its value should be a semver string";
-format_error(invalid_deprecated_since) ->
-    "value of -deprecated_since attribute should be a semver string";
 format_error({invalid_fun, Name, Arity}) ->
     io_lib:format("malformed function ~p/~p. "
                   "BPAPI functions should have exactly one clause "
@@ -68,24 +62,18 @@ go({attribute, Line, module, Mod}, S) ->
         {ok, API, Vsn} -> S#s{api = API, version = Vsn, module = Mod};
         error          -> push_err(Line, invalid_name, S)
     end;
-go({attribute, _Line, introduced_in, Str}, S) ->
-    case is_list(Str) andalso parse_semver(Str) of
-        {ok, Vsn} -> S#s{introduced_in = Vsn};
-        error     -> S %% Don't report error here, it's done in check/1
-    end;
-go({attribute, Line, deprecated_since, Str}, S) ->
-    case is_list(Str) andalso parse_semver(Str) of
-        {ok, Vsn} -> S#s{deprecated_since = Vsn};
-        error     -> push_err(Line, invalid_deprecated_since, S)
-    end;
+go({function, _Line, introduced_in, 0, _}, S)  ->
+    S;
+go({function, _Line, deprecated_since, 0, _}, S)  ->
+    S;
 go({function, Line, Name, Arity, Clauses}, S) ->
     analyze_fun(Line, Name, Arity, Clauses, S);
 go(_, S) ->
     S.
 
-check(#s{errors = Err0, introduced_in = II}) ->
-    [{none, invalid_introduced_in} || II =:= undefined] ++
-        Err0.
+check(#s{errors = Err}) ->
+    %% Post-processing checks can be placed here
+    Err.
 
 finalize(Forms, S) ->
     {Attrs, Funcs} = lists:splitwith(fun is_attribute/1, Forms),
@@ -191,16 +179,6 @@ push_err(Line, Err, S = #s{errors = Errs}) ->
 push_target(Target, S = #s{targets = Targets}) ->
     S#s{targets = [Target|Targets]}.
 
-
--spec parse_semver(string()) -> {ok, emqx_bpapi:semver()}
-                              | error.
-parse_semver(Str) ->
-    Opts = [{capture, all_but_first, list}],
-    case re:run(Str, "^([0-9]+)\\.([0-9]+)\\.([0-9]+)$", Opts) of
-        {match, [A, B, C]} -> {ok, {list_to_integer(A), list_to_integer(B), list_to_integer(C)}};
-        nomatch            -> error
-    end.
-
 -spec api_and_version(module()) -> {ok, emqx_bpapi:api(), emqx_bpapi:version()} | error.
 api_and_version(Module) ->
     Opts = [{capture, all_but_first, list}],
diff --git a/apps/emqx/src/proto/emqx_broker_proto_v1.erl b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
index 178fa2f08..3efbcd3b0 100644
--- a/apps/emqx/src/proto/emqx_broker_proto_v1.erl
+++ b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
@@ -16,15 +16,19 @@
 
 -module(emqx_broker_proto_v1).
 
--introduced_in("5.0.0").
+-behaviour(emqx_bpapi).
 
--export([ forward/3
+-export([ introduced_in/0
+        , forward/3
         , forward_async/3
         ]).
 
 -include("bpapi.hrl").
 -include("emqx.hrl").
 
+introduced_in() ->
+    "5.0.0".
+
 -spec forward(node(), emqx_types:topic(), emqx_types:delivery()) -> emqx_types:deliver_result().
 forward(Node, Topic, Delivery = #delivery{}) when is_binary(Topic) ->
     emqx_rpc:call(Topic, Node, emqx_broker, dispatch, [Topic, Delivery]).

From 9c675194f502d0d92f0fa99d3d0f36a9eb7dc479 Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Wed, 5 Jan 2022 11:27:56 +0100
Subject: [PATCH 09/10] fix(bpapi): Fix dialyzer warnings

---
 .../src/bpapi/emqx_bpapi_static_checks.erl    | 31 ++++++++++---------
 apps/emqx/src/bpapi/emqx_bpapi_trans.erl      |  9 ++----
 2 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
index c77ede7a3..f26143219 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
@@ -72,21 +72,22 @@ check_compat(Dump1, Dump2) ->
 check_api_immutability(#{release := Rel1, api := APIs1}, #{release := Rel2, api := APIs2})
   when Rel2 >= Rel1 ->
     %% TODO: Handle API deprecation
-    maps:map(fun(Key = {API, Version}, Val) ->
-                         case maps:get(Key, APIs2, undefined) of
-                             Val ->
-                                 ok;
-                             undefined ->
-                                 setnok(),
-                                 ?ERROR("API ~p v~p was removed in release ~p without being deprecated.",
-                                        [API, Version, Rel2]);
-                             _Val ->
-                                 setnok(),
-                                 ?ERROR("API ~p v~p was changed between ~p and ~p. Backplane API should be immutable.",
-                                        [API, Version, Rel1, Rel2])
-                         end
-                 end,
-                 APIs1),
+    _ = maps:map(
+          fun(Key = {API, Version}, Val) ->
+                  case maps:get(Key, APIs2, undefined) of
+                      Val ->
+                          ok;
+                      undefined ->
+                          setnok(),
+                          ?ERROR("API ~p v~p was removed in release ~p without being deprecated.",
+                                 [API, Version, Rel2]);
+                      _Val ->
+                          setnok(),
+                          ?ERROR("API ~p v~p was changed between ~p and ~p. Backplane API should be immutable.",
+                                 [API, Version, Rel1, Rel2])
+                  end
+          end,
+          APIs1),
     ok;
 check_api_immutability(_, _) ->
     ok.
diff --git a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
index 311edf399..a2ef547c0 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
@@ -31,7 +31,7 @@
         , module           :: atom()
         , version          :: non_neg_integer() | undefined
         , targets = []     :: [{semantics(), emqx_bpapi:call(), emqx_bpapi:call()}]
-        , errors = []      :: [string()]
+        , errors = []      :: list()
         , file
         }).
 
@@ -120,7 +120,7 @@ analyze_exprs(Line, Name, Arity, Head, Exprs, S) ->
             invalid_fun(Line, Name, Arity, S)
     end.
 
--spec extract_outer_args(erl_parse:abstract_form()) -> [atom()].
+-spec extract_outer_args([erl_parse:abstract_form()]) -> [atom()].
 extract_outer_args(Abs) ->
     lists:map(fun({var, _, Var}) ->
                       Var;
@@ -131,8 +131,7 @@ extract_outer_args(Abs) ->
               end,
               Abs).
 
--spec extract_target_call(Abs, [Abs]) -> {semantics(), emqx_bpapi:call()}
-              when Abs :: erl_parse:abstract_form().
+-spec extract_target_call(_AST, [_AST]) -> {semantics(), emqx_bpapi:call()}.
 extract_target_call(RPCBackend, OuterArgs) ->
     {Semantics, {atom, _, M}, {atom, _, F}, A} = extract_mfa(RPCBackend, OuterArgs),
     {Semantics, {M, F, list_to_args(A)}}.
@@ -140,8 +139,6 @@ extract_target_call(RPCBackend, OuterArgs) ->
 -define(BACKEND(MOD, FUN), {remote, _, {atom, _, MOD}, {atom, _, FUN}}).
 -define(IS_RPC(MOD), (MOD =:= erpc orelse MOD =:= rpc)).
 
--spec extract_mfa(Abs, #s{}) -> {call | cast, Abs, Abs, Abs}
-              when Abs :: erl_parse:abstract_form().
 %% gen_rpc:
 extract_mfa(?BACKEND(gen_rpc, _), _) ->
     %% gen_rpc has an extremely messy API, thankfully it's fully wrapped

From 22bdcfa4b5772948d3f14b5bc208627d6b0ef86e Mon Sep 17 00:00:00 2001
From: k32 <10274441+k32@users.noreply.github.com>
Date: Wed, 5 Jan 2022 14:37:26 +0100
Subject: [PATCH 10/10] fix(bpapi): Apply remarks

---
 apps/emqx/src/bpapi/emqx_bpapi.erl               | 4 ++--
 apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl | 2 +-
 apps/emqx/src/bpapi/emqx_bpapi_trans.erl         | 8 ++++----
 apps/emqx/src/proto/emqx_broker_proto_v1.erl     | 2 +-
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/apps/emqx/src/bpapi/emqx_bpapi.erl b/apps/emqx/src/bpapi/emqx_bpapi.erl
index d76cb0085..d99f0e53b 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi.erl
@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -15,7 +15,7 @@
 %%--------------------------------------------------------------------
 -module(emqx_bpapi).
 
--export_type([var_name/0, call/0, rpc/0, bpapi_meta/0]).
+-export_type([api/0, api_version/0, var_name/0, call/0, rpc/0, bpapi_meta/0]).
 
 -type api() :: atom().
 -type api_version() :: non_neg_integer().
diff --git a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
index f26143219..5023e9b9f 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_static_checks.erl
@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
diff --git a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
index a2ef547c0..f39215069 100644
--- a/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
+++ b/apps/emqx/src/bpapi/emqx_bpapi_trans.erl
@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2020-2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -27,9 +27,9 @@
 -type semantics() :: call | cast.
 
 -record(s,
-        { api              :: atom()
-        , module           :: atom()
-        , version          :: non_neg_integer() | undefined
+        { api              :: emqx_bpapi:api()
+        , module           :: module()
+        , version          :: emqx_bpapi:api_version() | undefined
         , targets = []     :: [{semantics(), emqx_bpapi:call(), emqx_bpapi:call()}]
         , errors = []      :: list()
         , file
diff --git a/apps/emqx/src/proto/emqx_broker_proto_v1.erl b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
index 3efbcd3b0..d5725b8ac 100644
--- a/apps/emqx/src/proto/emqx_broker_proto_v1.erl
+++ b/apps/emqx/src/proto/emqx_broker_proto_v1.erl
@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2021 EMQ Technologies Co., Ltd. All Rights Reserved.
+%% Copyright (c) 2022 EMQ Technologies Co., Ltd. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.