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Better error reporter interface (#61)
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We were a bit hasty with the changes that were made to v2.0.0! It seems prudent to circle back and make a few improvements:

Reverts the default behavior to throwing the error instead of printing it (this aligns better with expectations from Rodux 1.x)
Don't inherit the deferred and immediate abstraction from external codebases. Instead, categorize errors into ones that occur when processing actions with reportReducerError (running reducers on dispatched actions) and ones that occur when updating listeners with reportUpdateError (flushing new state)
For the error reporter interface, provide a set of data relevant to each situation. This includes recent actions, store state, and the thrown error
Removes error reporting from signal, to try to keep it simple and generic; most usage of rodux is through helper libraries that manage the signal connections, anyway.
Updates tests to account for new expected behavior
Carves out some overzealous printing logic; users of the error reporter API can opt into it isntead
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@ZoteTheMighty
ZoteTheMighty authored Mar 25, 2021
1 parent c9b9807 commit d0c21a7
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Showing 9 changed files with 331 additions and 391 deletions.
48 changes: 10 additions & 38 deletions src/Signal.lua
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,6 @@
Handlers are fired in order, and (dis)connections are properly handled when
executing an event.
]]
local inspect = require(script.Parent.inspect).inspect

local function immutableAppend(list, ...)
local new = {}
local len = #list
Expand Down Expand Up @@ -56,8 +54,8 @@ function Signal:connect(callback)
if self._store and self._store._isDispatching then
error(
'You may not call store.changed:connect() while the reducer is executing. ' ..
'If you would like to be notified after the store has been updated, subscribe from a ' ..
'component and invoke store:getState() in the callback to access the latest state. '
'If you would like to be notified after the store has been updated, subscribe from a ' ..
'component and invoke store:getState() in the callback to access the latest state. '
)
end

Expand All @@ -72,14 +70,13 @@ function Signal:connect(callback)

local function disconnect()
if listener.disconnected then
local errorMessage = ("Listener connected at: \n%s\n" ..
"was already disconnected at: \n%s\n"):format(
tostring(listener.connectTraceback),
tostring(listener.disconnectTraceback)
)
self._store._errorReporter:reportErrorDeferred(errorMessage, debug.traceback())

return
error((
"Listener connected at: \n%s\n" ..
"was already disconnected at: \n%s\n"
):format(
tostring(listener.connectTraceback),
tostring(listener.disconnectTraceback)
))
end

if self._store and self._store._isDispatching then
Expand All @@ -96,35 +93,10 @@ function Signal:connect(callback)
}
end

function Signal:reportListenerError(listener, callbackArgs, error_)
local message = ("Caught error when calling event listener (%s), " ..
"originally subscribed from: \n%s\n" ..
"with arguments: \n%s\n"):format(
tostring(listener.callback),
tostring(listener.connectTraceback),
inspect(callbackArgs)
)

if self._store then
self._store._errorReporter:reportErrorImmediately(message, error_)
else
print(message .. tostring(error_))
end
end

function Signal:fire(...)
for _, listener in ipairs(self._listeners) do
if not listener.disconnected then
local ok, result = pcall(function(...)
listener.callback(...)
end, ...)
if not ok then
self:reportListenerError(
listener,
{...},
result
)
end
listener.callback(...)
end
end
end
Expand Down
107 changes: 39 additions & 68 deletions src/Signal.spec.lua
View file
Original file line number Diff line number Diff line change
Expand Up @@ -112,84 +112,55 @@ return function()
expect(countB).to.equal(0)
end)

describe("when event handlers error", function()
local reportedErrorError, reportedErrorMessage
local mockStore = {
_errorReporter = {
reportErrorImmediately = function(_self, message, error_)
reportedErrorMessage = message
reportedErrorError = error_
end,
reportErrorDeferred = function(_self, message, error_)
reportedErrorMessage = message
reportedErrorError = error_
end
}
}

beforeEach(function()
reportedErrorError = ""
reportedErrorMessage = ""
end)
it("should throw an error if the argument to `connect` is not a function", function()
local signal = Signal.new()
expect(function()
signal:connect("not a function")
end).to.throw()
end)

it("first listener succeeds when second listener errors", function()
local signal = Signal.new(mockStore)
local countA = 0
it("should throw an error when disconnecting more than once", function()
local signal = Signal.new()

signal:connect(function()
countA = countA + 1
end)
local connection = signal:connect(function() end)
-- Okay to disconnect once
expect(connection.disconnect).never.to.throw()

signal:connect(function()
error("connectionB")
end)
-- Throw an error if we disconnect twice
expect(connection.disconnect).to.throw()
end)

signal:fire()
it("should throw an error when subscribing during dispatch", function()
local mockStore = {
_isDispatching = false
}
local signal = Signal.new(mockStore)

expect(countA).to.equal(1)
local caughtErrorMessage = "Caught error when calling event listener"
expect(string.find(reportedErrorMessage, caughtErrorMessage)).to.be.ok()
local caughtErrorError = "connectionB"
expect(string.find(reportedErrorError, caughtErrorError)).to.be.ok()
signal:connect(function()
-- Subscribe while listeners are being fired
signal:connect(function() end)
end)

it("second listener succeeds when first listener errors", function()
local signal = Signal.new(mockStore)
local countB = 0

signal:connect(function()
error("connectionA")
end)

signal:connect(function()
countB = countB + 1
end)

mockStore._isDispatching = true
expect(function()
signal:fire()
end).to.throw()
end)

expect(countB).to.equal(1)
local caughtErrorMessage = "Caught error when calling event listener"
expect(string.find(reportedErrorMessage, caughtErrorMessage)).to.be.ok()
local caughtErrorError = "connectionA"
expect(string.find(reportedErrorError, caughtErrorError)).to.be.ok()
end)

it("serializes table arguments when reporting errors", function()
local signal = Signal.new(mockStore)

signal:connect(function()
error("connectionA")
end)

local actionCommand = "SENTINEL"
signal:fire({actionCommand = actionCommand})
it("should throw an error when unsubscribing during dispatch", function()
local mockStore = {
_isDispatching = false
}
local signal = Signal.new(mockStore)

local caughtErrorMessage = "Caught error when calling event listener"
local caughtErrorArg = "actionCommand: \"" .. actionCommand .. "\""
expect(string.find(reportedErrorMessage, caughtErrorMessage)).to.be.ok()
expect(string.find(reportedErrorMessage, caughtErrorArg)).to.be.ok()
local caughtErrorError = "connectionA"
expect(string.find(reportedErrorError, caughtErrorError)).to.be.ok()
local connection
connection = signal:connect(function()
connection.disconnect()
end)

mockStore._isDispatching = true
expect(function()
signal:fire()
end).to.throw()
end)
end
90 changes: 51 additions & 39 deletions src/Store.lua
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,19 +2,22 @@ local RunService = game:GetService("RunService")

local Signal = require(script.Parent.Signal)
local NoYield = require(script.Parent.NoYield)
local inspect = require(script.Parent.inspect).inspect

local defaultErrorReporter = {
reportErrorDeferred = function(self, message, stacktrace)
print(message)
print(stacktrace)
local ACTION_LOG_LENGTH = 3

local rethrowErrorReporter = {
reportReducerError = function(prevState, action, errorResult)
error(string.format("Received error: %s\n\n%s", errorResult.message, errorResult.thrownValue))
end,
reportUpdateError = function(prevState, currentState, lastActions, errorResult)
error(string.format("Received error: %s\n\n%s", errorResult.message, errorResult.thrownValue))
end,
reportErrorImmediately = function(self, message, stacktrace)
print(message)
print(stacktrace)
end
}

local function tracebackReporter(message)
return debug.traceback(tostring(message))
end

local Store = {}

-- This value is exposed as a private value so that the test code can stay in
Expand Down Expand Up @@ -49,19 +52,21 @@ function Store.new(reducer, initialState, middlewares, errorReporter)

local self = {}

self._errorReporter = errorReporter or defaultErrorReporter
self._errorReporter = errorReporter or rethrowErrorReporter
self._isDispatching = false
self._reducer = reducer
local initAction = {
type = "@@INIT",
}
self._lastAction = initAction
local ok, result = pcall(function()
self._actionLog = { initAction }
local ok, result = xpcall(function()
self._state = reducer(initialState, initAction)
end)
end, tracebackReporter)
if not ok then
local message = ("Caught error with init action of reducer (%s): %s"):format(tostring(reducer), tostring(result))
errorReporter:reportErrorImmediately(message, debug.traceback())
self._errorReporter.reportReducerError(initialState, initAction, {
message = "Caught error in reducer with init",
thrownValue = result,
})
self._state = initialState
end
self._lastState = self._state
Expand Down Expand Up @@ -110,20 +115,6 @@ function Store:getState()
return self._state
end

function Store:_reportReducerError(failedAction, error_, traceback)
local message = ("Caught error when running action (%s) " ..
"through reducer (%s): \n%s \n" ..
"previous action type was: %s"
):format(
tostring(failedAction),
tostring(self._reducer),
tostring(error_),
inspect(self._lastAction)
)

self._errorReporter:reportErrorImmediately(message, traceback)
end

--[[
Dispatch an action to the store. This allows the store's reducer to mutate
the state of the application by creating a new copy of the state.
Expand All @@ -142,7 +133,7 @@ function Store:dispatch(action)
if action.type == nil then
error("Actions may not have an undefined 'type' property. " ..
"Have you misspelled a constant? \n" ..
inspect(action), 2)
tostring(action), 2)
end

if self._isDispatching then
Expand All @@ -158,13 +149,20 @@ function Store:dispatch(action)
self._isDispatching = false

if not ok then
self:_reportReducerError(
self._errorReporter.reportReducerError(
self._state,
action,
result,
debug.traceback()
{
message = "Caught error in reducer",
thrownValue = result,
}
)
end
self._lastAction = action

if #self._actionLog == ACTION_LOG_LENGTH then
table.remove(self._actionLog, 1)
end
table.insert(self._actionLog, action)
end

--[[
Expand Down Expand Up @@ -193,11 +191,25 @@ function Store:flush()
-- unless we cache this value first
local state = self._state

-- If a changed listener yields, *very* surprising bugs can ensue.
-- Because of that, changed listeners cannot yield.
NoYield(function()
self.changed:fire(state, self._lastState)
end)
local ok, errorResult = xpcall(function()
-- If a changed listener yields, *very* surprising bugs can ensue.
-- Because of that, changed listeners cannot yield.
NoYield(function()
self.changed:fire(state, self._lastState)
end)
end, tracebackReporter)

if not ok then
self._errorReporter.reportUpdateError(
self._lastState,
state,
self._actionLog,
{
message = "Caught error flushing store updates",
thrownValue = errorResult,
}
)
end

self._lastState = state
end
Expand Down
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