tests/lapi: add coroutine test

The patch adds a fuzzing tests for Lua coroutine library.

Author: ligurio

tests/lapi/coroutine_test.lua

@@ -0,0 +1,168 @@
+--[[
+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
+
+debug.getlocal on a coroutine suspended in a hook can crash the interpreter,
+https://www.lua.org/bugs.html#5.3.0-2
+
+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
+
+debug.getlocal on a coroutine suspended in a hook can crash the interpreter,
+https://www.lua.org/bugs.html#5.3.0-2
+
+debug.sethook/gethook may overflow the thread's stack,
+https://www.lua.org/bugs.html#5.1.2-13
+
+Memory hoarding when creating Lua hooks for coroutines,
+https://www.lua.org/bugs.html#5.2.0-1
+
+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 test_lib = require("lib")
+
+local CORO_OBJECTS
+
+-- Possible coroutine statuses, described in Lua 5.1 Reference Manual,
+-- https://www.lua.org/manual/5.4/manual.html#6.2
+local CORO_STATUS = {
+    DEAD = "dead",
+    NORMAL = "normal",
+    RUNNING = "running",
+    SUSPENDED = "suspended",
+}
+
+local CORO_ACTION_NAME = {
+    "close",
+    "create",
+    "resume",
+    "yield",
+}
+
+-- Forward declaration.
+local coro_function
+
+local function hook_func(_event)
+    local level = 2
+    local i = 1
+    while true do
+        local name, v = debug.getlocal(level, i)
+        io.stderr:write(name .. "\n")
+        i = i + 1
+    end
+end
+
+local function sethook(co, fdp)
+    local set_hook = fdp:consume_boolean()
+    local hook_args = {}
+    if not set_hook then
+        return
+    end
+    table.insert(hook_args, hook_func)
+    table.insert(hook_args, fdp:oneof({"c", "r", "l"}))
+    debug.sethook(co, unpack(hook_args))
+end
+
+local function coro_random_action(fdp, coro_max_number)
+    local action = fdp:oneof(CORO_ACTION_NAME)
+    if action == "create" or #CORO_OBJECTS < coro_max_number then
+        local co = coroutine.create(coro_function)
+        table.insert(CORO_OBJECTS, co)
+    end
+
+    action = fdp:oneof(CORO_ACTION_NAME)
+    local co, co_idx = fdp:oneof(CORO_OBJECTS)
+    if coroutine.status(co) == CORO_STATUS["DEAD"] then
+        -- FIXME: Remove `coro` in `CORO_OBJECTS`,
+        -- https://github.com/ligurio/luzer/pull/57.
+        assert(co_idx)
+        table.remove(CORO_OBJECTS, co_idx)
+        return
+    elseif action == "close" then
+        coroutine.close(co)
+    elseif action == "yield" and coroutine.isyieldable(co) then
+        coroutine.yield(co)
+    elseif action == "resume" then
+        coroutine.resume(co)
+    end
+    sethook(co, fdp)
+end
+
+coro_function = function(fdp, coro_max_number)
+    local iter = fdp:consume_integer(1, test_lib.MAX_INT)
+    for _ = 1, iter do
+        coro_random_action(fdp, coro_max_number)
+    end
+end
+
+local function TestOneInput(buf, _size)
+    CORO_OBJECTS = {}
+    local fdp = luzer.FuzzedDataProvider(buf)
+    local coro_max_number = fdp:consume_integer(1, 1000)
+    local co = coroutine.create(coro_function)
+    table.insert(CORO_OBJECTS, 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_",
+}
+luzer.Fuzz(TestOneInput, nil, args)