Debugger crashes when frame no longer exists

[lukaszsamson]

Extracted from #451

Environment

• Elixir & Erlang versions (elixir --version): all
• Operating system: all
• Editor or IDE name (e.g. Emacs/VSCode): all
• Editor Plugin/LSP Client name: 0.6.2

Logs

If I now set a breakpoing to page_controller.ex at line 5 and I visit the page with a browser, the debugger stops at that line, but if I wait more or less one minute the debugger process crashes. This is the log:

(Debugger) Terminating because an exception was raised:
    ** (MatchError) no match of right hand side value: nil
        (elixir_ls_debugger 0.6.2) lib/debugger/server.ex:291: ElixirLS.Debugger.Server.handle_request/2
        (elixir_ls_debugger 0.6.2) lib/debugger/server.ex:90: ElixirLS.Debugger.Server.handle_cast/2
        (stdlib 3.12) gen_server.erl:637: :gen_server.try_dispatch/4
        (stdlib 3.12) gen_server.erl:711: :gen_server.handle_msg/6
        (stdlib 3.12) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
ElixirLS debugger has crashed
[error] GenServer ElixirLS.Debugger.Server terminating
** (MatchError) no match of right hand side value: nil
    (elixir_ls_debugger 0.6.2) lib/debugger/server.ex:291: ElixirLS.Debugger.Server.handle_request/2
    (elixir_ls_debugger 0.6.2) lib/debugger/server.ex:90: ElixirLS.Debugger.Server.handle_cast/2
    (stdlib 3.12) gen_server.erl:637: :gen_server.try_dispatch/4
    (stdlib 3.12) gen_server.erl:711: :gen_server.handle_msg/6
    (stdlib 3.12) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Last message: {:"$gen_cast", {:receive_packet, %{"arguments" => %{"frameId" => 2}, "command" => "scopes", "seq" => 11, "type" => "request"}}}
State: %ElixirLS.Debugger.Server{breakpoints: %{"/tmp/hello_world/lib/hello_world_web/controllers/page_controller.ex" => [{HelloWorldWeb.PageController, 5}]}, client_info: %{"adapterID" => "Elixir", "clientID" => "vscode", "clientName" => "Visual Studio Code", "columnsStartAt1" => true, "linesStartAt1" => true, "locale" => "en-us", "pathFormat" => "path", "supportsRunInTerminalRequest" => true, "supportsVariablePaging" => true, "supportsVariableType" => true}, config: %{"cwd" => "/tmp/hello_world", "name" => "Elixir::Phoenix<10>", "program" => nil, "projectDir" => "/tmp/hello_world", "request" => "launch", "task" => "phx.server", "taskArgs" => nil, "type" => "Elixir"}, next_id: 24, output: ElixirLS.Debugger.Output, paused_processes: %{#PID<0.1338.0> => %ElixirLS.Debugger.Server.PausedProcess{frames: %{16 => %ElixirLS.Debugger.Stacktrace.Frame{args: [%Plug.Conn{adapter: {Plug.Cowboy.Conn, :...}, assigns: %{}, before_send: [#Function<33.103228614/1 in :dbg_ieval.expr/3>, #Function<33.103228614/1 in :dbg_ieval.expr/3>], body_params: %{}, cookies: %{"_bolgia_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio", "_hello_world_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, halted: false, host: "localhost", method: "GET", owner: #PID<0.1338.0>, params: %{}, path_info: [], path_params: %{}, port: 4000, private: %{HelloWorldWeb.Router => {[], %{}}, :phoenix_endpoint => HelloWorldWeb.Endpoint, :phoenix_request_logger => {"request_logger", "request_logger"}, :phoenix_router => HelloWorldWeb.Router, :plug_session_fetch => #Function<33.103228614/1 in :dbg_ieval.expr/3>}, query_params: %{}, query_string: "", remote_ip: {127, 0, 0, 1}, req_cookies: %{"_bolgia_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio", "_hello_world_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, req_headers: [{"accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"}, {"accept-encoding", "gzip, deflate"}, {"accept-language", "it,en;q=0.7,en-US;q=0.3"}, {"cache-control", "max-age=0"}, {"connection", "keep-alive"}, {"cookie", "_bolgia_key=SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio; _hello_world_key=SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, {"dnt", "1"}, {"host", "localhost:4000"}, {"sec-gpc", "1"}, {"upgrade-insecure-requests", "1"}, {"user-agent", "Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Firefox/78.0"}], request_path: "/", resp_body: nil, resp_cookies: %{}, resp_headers: [{"cache-control", "max-age=0, private, must-revalidate"}, {"x-request-id", "Flf8OOCTPs9cm2cAAAFD"}], scheme: :http, script_name: [], secret_key_base: :..., state: :unset, status: nil}, {%{conn: nil, log: :debug, path_params: %{}, pipe_through: [:browser], plug: HelloWorldWeb.PageController, plug_opts: :index, route: "/"}, #Function<39.103228614/2 in :dbg_ieval.expr/3>, #Function<33.103228614/1 in :dbg_ieval.expr/3>, {HelloWorldWeb.PageController, :index}}], bindings: %{___STACKTRACE__@1: [], _conn@1: %Plug.Conn{adapter: {Plug.Cowboy.Conn, :...}, assigns: %{}, before_send: [#Function<33.103228614/1 in :dbg_ieval.expr/3>, #Function<33.103228614/1 in :dbg_ieval.expr/3>], body_params: %{}, cookies: %{"_bolgia_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio", "_hello_world_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, halted: false, host: "localhost", method: "GET", owner: #PID<0.1338.0>, params: %{}, path_info: [], path_params: %{}, port: 4000, private: %{HelloWorldWeb.Router => {[], %{}}, :phoenix_endpoint => HelloWorldWeb.Endpoint, :phoenix_request_logger => {"request_logger", "request_logger"}, :phoenix_router => HelloWorldWeb.Router, :plug_session_fetch => #Function<33.103228614/1 in :dbg_ieval.expr/3>}, query_params: %{}, query_string: "", remote_ip: {127, 0, 0, 1}, req_cookies: %{"_bolgia_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio", "_hello_world_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, req_headers: [{"accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"}, {"accept-encoding", "gzip, deflate"}, {"accept-language", "it,en;q=0.7,en-US;q=0.3"}, {"cache-control", "max-age=0"}, {"connection", "keep-alive"}, {"cookie", "_bolgia_key=SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio; _hello_world_key=SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, {"dnt", "1"}, {"host", "localhost:4000"}, {"sec-gpc", "1"}, {"upgrade-insecure-requests", "1"}, {"user-agent", "Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Firefox/78.0"}], request_path: "/", resp_body: nil, resp_cookies: %{}, resp_headers: [{"cache-control", "max-age=0, private, must-revalidate"}, {"x-request-id", "Flf8OOCTPs9cm2cAAAFD"}], scheme: :http, script_name: [], secret_key_base: :..., state: :unset, status: nil}, _conn@2: %Plug.Conn{adapter: {Plug.Cowboy.Conn, :...}, assigns: %{}, before_send: [#Function<33.103228614/1 in :dbg_ieval.expr/3>, #Function<33.103228614/1 in :dbg_ieval.expr/3>], body_params: %{}, cookies: %{"_bolgia_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio", "_hello_world_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, halted: false, host: "localhost", method: "GET", owner: #PID<0.1338.0>, params: %{}, path_info: [], path_params: %{}, port: 4000, private: %{HelloWorldWeb.Router => {[], %{}}, :phoenix_endpoint => HelloWorldWeb.Endpoint, :phoenix_request_logger => {"request_logger", "request_logger"}, :phoenix_router => HelloWorldWeb.Router, :plug_session_fetch => #Function<33.103228614/1 in :dbg_ieval.expr/3>}, query_params: %{}, query_string: "", remote_ip: {127, 0, 0, 1}, req_cookies: %{"_bolgia_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio", "_hello_world_key" => "SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, req_headers: [{"accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"}, {"accept-encoding", "gzip, deflate"}, {"accept-language", "it,en;q=0.7,en-US;q=0.3"}, {"cache-control", "max-age=0"}, {"connection", "keep-alive"}, {"cookie", "_bolgia_key=SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYbjUtVXZZY2YwZjFOUHBMdmk4YjVfeXNG.Q8tKVpXGZnIO-r8VPA9b6AhslXZv6QwGDsSeZFpBcio; _hello_world_key=SFMyNTY.g3QAAAABbQAAAAtfY3NyZl90b2tlbm0AAAAYVUMxTlVvRG9GY1V0QkZyanAzT01XcXF4.TK47nkYvBBd_jjdmBzfkIdBccPFau4K5FTHYHosPfzU"}, {"dnt", "1"}, {"h (truncated)

The crash happens in

elixir-ls/apps/elixir_ls_debugger/lib/debugger/server.ex

Line 291 in 3acc1fd

{pid, frame} = find_frame(state.paused_processes, frame_id)

Most likely a timeout in cowboy http request handler is killing the debugged process, which is not properly handled.