tests/lapi: add coroutine test

The patch adds a fuzzing tests for Lua coroutine library.

Author: ligurio

tests/lapi/coroutine_test.lua

@@ -0,0 +1,145 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+2.6 – Coroutines
+https://www.lua.org/manual/5.3/manual.html#2.6
+
+Computation of stack limit when entering a coroutine is wrong,
+https://github.com/lua/lua/commit/e1d8770f12542d34a3e32b825c95b93f8a341ee1
+
+C-stack overflow with deep nesting of coroutine.close,
+https://www.lua.org/bugs.html#5.4.4-9
+
+C stack overflow (again),
+https://github.com/lua/lua/commit/34affe7a63fc5d842580a9f23616d057e17dfe27
+
+When a coroutine tries to resume a non-suspended coroutine,
+it can do some mess (and break C assertions) before detecting the error,
+https://www.lua.org/bugs.html#5.3.3-4
+
+Suspended __le metamethod can give wrong result,
+https://www.lua.org/bugs.html#5.3.0-3
+
+Resuming the running coroutine makes it unyieldable,
+https://www.lua.org/bugs.html#5.2.2-8
+
+pcall may not restore previous error function when inside coroutines,
+https://www.lua.org/bugs.html#5.2.1-2
+
+Wrong handling of nCcalls in coroutines,
+https://www.lua.org/bugs.html#5.2.0-4
+
+coroutine.resume pushes element without ensuring stack size,
+https://www.lua.org/bugs.html#5.1.3-2
+
+Recursive coroutines may overflow C stack,
+https://www.lua.org/bugs.html#5.1.2-4
+
+Stand-alone interpreter shows incorrect error message when the
+"message" is a coroutine,
+https://www.lua.org/bugs.html#5.1.2-12
+
+Debug hooks may get wrong when mixed with coroutines,
+https://www.lua.org/bugs.html#5.1-7
+
+Values held in open upvalues of suspended threads may be
+incorrectly collected,
+https://www.lua.org/bugs.html#5.0.2-3
+
+Attempt to resume a running coroutine crashes Lua,
+https://www.lua.org/bugs.html#5.0-2
+
+Synopsis:
+
+coroutine.close(co)
+coroutine.create(f)
+coroutine.isyieldable([co])
+coroutine.resume(co [, val1, ...])
+coroutine.running()
+coroutine.status(co)
+coroutine.wrap(f)
+coroutine.yield(...)
+]]
+
+local luzer = require("luzer")
+
+local C = {}
+
+local STATUS_CREATE = "CREATE"
+local STATUS_CLOSE = "CLOSE"
+local STATUS_YIELD = "YIELD"
+local STATUS_RESUME = "RESUME"
+local STATUS_DEAD = "DEAD"
+
+local CORO_MAX_NUMBER = 10^53
+
+local CORO_STATE = {
+    STATUS_CLOSE,
+    STATUS_CREATE,
+    STATUS_RESUME,
+    STATUS_YIELD,
+}
+
+-- Forward declaration.
+local coro_loop
+
+local function random_coro(fdp)
+    local coro, coro_n = fdp:one_of(C)
+    local coro_status = coroutine.status(coro)
+    if coro_status == STATUS_DEAD then
+        table.remove(C, coro_n)
+        coro = coroutine.create(coro_loop)
+        table.insert(C, coro)
+        coroutine.resume(coro, 1)
+    end
+    return fdp:one_of(C)
+end
+
+local function coro_step(fdp)
+    local state = fdp:one_of(CORO_STATE)
+    if state == STATUS_CREATE then
+        local co = coroutine.create(coro_loop)
+        table.insert(C, co)
+        coroutine.resume(co, 1)
+        return
+    end
+
+    state = fdp:one_of(CORO_STATE)
+    local coro = random_coro(fdp)
+    local status = coroutine.status(coro)
+    if status == STATUS_DEAD then
+        return
+    end
+    io.write(("[%0.6s] STATE: %s -> %s\n"):format(#C, status, state))
+    if state == STATUS_CLOSE then
+        coroutine.close(coro)
+    elseif state == STATUS_YIELD and coroutine.isyieldable(coro) then
+        coroutine.yield(coro)
+    elseif state == STATUS_RESUME then
+        coroutine.resume(coro)
+    end
+
+    return
+end
+
+coro_loop = function(fdp, max_n)
+    local n = fdp:consume_integer(1, max_n)
+    for _ = 1, n do
+        coro_step(fdp)
+    end
+end
+
+local function TestOneInput(buf, _size)
+    local fdp = luzer.FuzzedDataProvider(buf)
+    local co = coroutine.create(coro_loop)
+    table.insert(C, co)
+    -- The function `coroutine.resume` starts the execution of
+    -- a coroutine, changing its state from suspended to running.
+    coroutine.resume(co, fdp, CORO_MAX_NUMBER)
+end
+
+local args = {
+    artifact_prefix = "coroutine_create_",
+}
+luzer.Fuzz(TestOneInput, nil, args)