Make promisify catch errors

Closes #12

CHANGELOG.md

@@ -5,6 +5,8 @@
 - Fix issue with Promise.race/all always cancelling instead of only cancelling if the Promise has no other consumers
 - Make error checking more robust across many methods.
 - Promise.Status members are now strings instead of symbols, and indexing a non-existent value will error.
+- Improve stack traces
+- Promise.promisify will now turn errors into rejections even if they occur after a yield.
 
 # 2.4.0
 

lib/README.md

@@ -129,6 +129,8 @@ docs:
       desc: |
         Wraps a function that yields into one that returns a Promise.
 
+        Any errors that occur while executing the function will be turned into rejections.
+
         ```lua
         local sleep = Promise.promisify(wait)
 

lib/init.lua

@@ -368,10 +368,16 @@ end
 ]]
 function Promise.promisify(callback)
 	return function(...)
+		local traceback = debug.traceback()
 		local length, values = pack(...)
-		return Promise.new(function(resolve)
+		return Promise.new(function(resolve, reject)
 			coroutine.wrap(function()
-				resolve(callback(unpack(values, 1, length)))
+				local ok, resultLength, resultValues = packResult(pcall(callback, unpack(values, 1, length)))
+				if ok then
+					resolve(unpack(resultValues, 1, resultLength))
+				else
+					reject((resultValues[1] or "error") .. "\n" .. traceback)
+				end
 			end)()
 		end)
 	end

lib/init.spec.lua

@@ -624,6 +624,21 @@ return function()
 			expect(status).to.equal(Promise.Status.Resolved)
 			expect(result).to.equal(2)
 		end)
+
+		it("should catch errors after a yield", function()
+			local bindable = Instance.new("BindableEvent")
+			local test = Promise.promisify(function ()
+				bindable.Event:Wait()
+				error('errortext')
+			end)
+
+			local promise = test()
+
+			expect(promise:getStatus()).to.equal(Promise.Status.Started)
+			bindable:Fire()
+			expect(promise:getStatus()).to.equal(Promise.Status.Rejected)
+			expect(promise._values[1]:find("errortext")).to.be.ok()
+		end)
 	end)
 
 	describe("Promise.tap", function()