Fix parallel.* hanging when called with no args (#863)

src/main/resources/data/computercraft/lua/rom/apis/parallel.lua

@@ -32,6 +32,7 @@ end
 
 local function runUntilLimit(_routines, _limit)
     local count = #_routines
+    if count < 1 then return 0 end
     local living = count
 
     local tFilters = {}

src/test/resources/test-rom/spec/apis/parallel_spec.lua

@@ -0,0 +1,124 @@
+describe("The parallel library", function()
+    describe("parallel.waitForAny", function()
+        it("validates arguments", function()
+            expect.error(parallel.waitForAny, ""):eq("bad argument #1 (expected function, got string)")
+            expect.error(parallel.waitForAny, function() end, 2):eq("bad argument #2 (expected function, got number)")
+        end)
+
+        it("returns immediately with no arguments", function()
+            expect(parallel.waitForAny()):eq(0)
+        end)
+
+        it("runs functions in parallel", function()
+            local entries = {}
+            local function a()
+                entries[#entries + 1] = "first"
+                local s = coroutine.yield()
+                entries[#entries + 1] = s
+            end
+            local function b()
+                entries[#entries + 1] = "second"
+                local s = coroutine.yield()
+                entries[#entries + 1] = s
+            end
+            os.queueEvent("yield")
+            parallel.waitForAny(a, b)
+            expect(entries):same({ "first", "second", "yield" })
+        end)
+
+        it("accepts an arbitrary number of functions", function()
+            local count = 0
+            local fns = {}
+            for i = 1, 50 do fns[i] = function()
+                count = count + 1
+                coroutine.yield()
+            end end
+            os.queueEvent("dummy")
+            parallel.waitForAny(table.unpack(fns))
+            expect(count):eq(50)
+        end)
+
+        it("passes errors to the caller", function()
+            expect.error(parallel.waitForAny, function() error("Test error") end):str_match("Test error$")
+        end)
+
+        it("returns the number of the function that exited first", function()
+            os.queueEvent("dummy")
+            os.queueEvent("dummy")
+            expect(parallel.waitForAny(function()
+                coroutine.yield()
+                coroutine.yield()
+            end, function()
+                coroutine.yield()
+                return
+            end, function()
+                coroutine.yield()
+                coroutine.yield()
+            end)):eq(2)
+        end)
+    end)
+
+    describe("parallel.waitForAll", function()
+        it("validates arguments", function()
+            expect.error(parallel.waitForAll, ""):eq("bad argument #1 (expected function, got string)")
+            expect.error(parallel.waitForAll, function() end, 2):eq("bad argument #2 (expected function, got number)")
+        end)
+
+        it("returns immediately with no arguments", function()
+            parallel.waitForAll()
+        end)
+
+        it("runs functions in parallel", function()
+            local entries = {}
+            local function a()
+                entries[#entries + 1] = "first"
+                local s = coroutine.yield()
+                entries[#entries + 1] = s
+            end
+            local function b()
+                entries[#entries + 1] = "second"
+                local s = coroutine.yield()
+                entries[#entries + 1] = s
+            end
+            os.queueEvent("yield")
+            parallel.waitForAll(a, b)
+            expect(entries):same({ "first", "second", "yield", "yield" })
+        end)
+
+        it("accepts an arbitrary number of functions", function()
+            local count = 0
+            local fns = {}
+            for i = 1, 50 do fns[i] = function()
+                count = count + 1
+                coroutine.yield()
+            end end
+            os.queueEvent("dummy")
+            parallel.waitForAll(table.unpack(fns))
+            expect(count):eq(50)
+        end)
+
+        it("passes errors to the caller", function()
+            expect.error(parallel.waitForAll, function() error("Test error") end):str_match("Test error$")
+        end)
+
+        it("completes all functions before exiting", function()
+            local exitCount = 0
+            os.queueEvent("dummy")
+            os.queueEvent("dummy")
+            parallel.waitForAll(function()
+                coroutine.yield()
+                coroutine.yield()
+                exitCount = exitCount + 1
+            end, function()
+                coroutine.yield()
+                exitCount = exitCount + 1
+                return
+            end, function()
+                coroutine.yield()
+                coroutine.yield()
+                exitCount = exitCount + 1
+            end)
+            expect(exitCount):eq(3)
+        end)
+    end)
+end)