util.promise: Add all_settled, which follows semantics of allSettled from ES2020

2 files changed, 76 insertions, 0 deletions

diff --git a/spec/util_promise_spec.lua b/spec/util_promise_spec.lua
index 0008c6a2..6fb5d6bd 100644
--- a/spec/util_promise_spec.lua
+++ b/spec/util_promise_spec.lua
@@ -353,6 +353,60 @@ describe("util.promise", function ()
 			assert.equal("fail", result);
 		end);
 	end);
+	describe("all_settled()", function ()
+		it("works with fulfilled promises", function ()
+			local p1, p2 = promise.resolve("yep"), promise.resolve("nope");
+			local p = promise.all_settled({ p1, p2 });
+			local result;
+			p:next(function (v)
+				result = v;
+			end);
+			assert.same({
+				{ status = "fulfilled", value = "yep" };
+				{ status = "fulfilled", value = "nope" };
+			}, result);
+		end);
+		it("works with pending promises", function ()
+			local r1, r2;
+			local p1, p2 = promise.new(function (resolve) r1 = resolve end), promise.new(function (resolve) r2 = resolve end);
+			local p = promise.all_settled({ p1, p2 });
+
+			local result;
+			local cb = spy.new(function (v)
+				result = v;
+			end);
+			p:next(cb);
+			assert.spy(cb).was_called(0);
+			r2("yep");
+			assert.spy(cb).was_called(0);
+			r1("nope");
+			assert.spy(cb).was_called(1);
+			assert.same({
+				{ status = "fulfilled", value = "nope" };
+				{ status = "fulfilled", value = "yep" };
+			}, result);
+		end);
+		it("works when some promises reject", function ()
+			local r1, r2;
+			local p1, p2 = promise.new(function (resolve) r1 = resolve end), promise.new(function (_, reject) r2 = reject end);
+			local p = promise.all_settled({ p1, p2 });
+
+			local result;
+			local cb = spy.new(function (v)
+				result = v;
+			end);
+			p:next(cb);
+			assert.spy(cb).was_called(0);
+			r2("this fails");
+			assert.spy(cb).was_called(0);
+			r1("this succeeds");
+			assert.spy(cb).was_called(1);
+			assert.same({
+				{ status = "fulfilled", value = "this succeeds" };
+				{ status = "rejected", reason = "this fails" };
+			}, result);
+		end);
+	end);
 	describe("catch()", function ()
 		it("works", function ()
 			local result;
diff --git a/util/promise.lua b/util/promise.lua
index 0b182b54..6ebb0dd6 100644
--- a/util/promise.lua
+++ b/util/promise.lua
@@ -104,6 +104,27 @@ local function all(promises)
 	end);
 end
 
+local function all_settled(promises)
+	return new(function (resolve)
+		local count, total, results = 0, #promises, {};
+		for i = 1, total do
+			promises[i]:next(function (v)
+				results[i] = { status = "fulfilled", value = v };
+				count = count + 1;
+				if count == total then
+					resolve(results);
+				end
+			end, function (e)
+				results[i] = { status = "rejected", reason = e };
+				count = count + 1;
+				if count == total then
+					resolve(results);
+				end
+			end);
+		end
+	end);
+end
+
 local function race(promises)
 	return new(function (resolve, reject)
 		for i = 1, #promises do
@@ -149,6 +170,7 @@ return {
 	resolve = resolve;
 	reject = reject;
 	all = all;
+	all_settled = all_settled;
 	race = race;
 	try = try;
 	is_promise = is_promise;