tests/lapi: add debug tests

The commit adds tests for the following functions in debug library:
`debug.getlocal()`, `debug.getupvalue()` and `debug.getinfo()`.

Author: ligurio

tests/lapi/debug_torture_test.lua

@@ -0,0 +1,198 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+Parameter 'what' of 'debug.getinfo' cannot start with '>',
+https://www.lua.org/bugs.html#5.4.2-2
+
+Access to debug information in line hook of stripped function,
+https://github.com/lua/lua/commit/ae5b5ba529753c7a653901ffc29b5ea24c3fdf3a
+
+Return hook may not see correct values for active local variables when function returns,
+https://www.lua.org/bugs.html#5.3.0-4
+
+The PC out-of-range in lj_debug_frameline(),
+https://github.com/LuaJIT/LuaJIT/issues/1369
+
+LuaJIT segfault in debug.getinfo(),
+https://github.com/LuaJIT/LuaJIT/issues/509
+
+Negation overflow in getlocal/setlocal,
+https://github.com/lua/lua/commit/a585eae6e7ada1ca9271607a4f48dfb17868ab7b
+
+debug.getlocal on a coroutine suspended in a hook can crash the interpreter,
+https://www.lua.org/bugs.html#5.3.0-2
+
+lua_getupvalue and lua_setupvalue do not check for index too small,
+https://www.lua.org/bugs.html#5.0.2-2
+
+Synopsis: debug.getupvalue (f, up)
+Synopsis: debug.getlocal([thread,] level, local)
+Synopsis: debug.getinfo([thread,] function [, what])
+]]
+
+local luzer = require("luzer")
+local test_lib = require("lib")
+
+local what = {
+    "n", -- Fills in the field `name` and `namewhat`.
+    "S", -- Fills in the fields `source`, `short_src`,
+         -- `linedefined`, `lastlinedefined`, and `what`.
+    "l", -- Fills in the field `currentline`.
+    "u", -- Fills in the field `nups`.
+    "f", -- Pushes onto the stack the function that is running at
+         -- the given level.
+    "L", -- Pushes onto the stack a table whose indices are the
+         -- numbers of the lines that are valid on the function.
+}
+-- Fills in the field `istailcall`.
+if test_lib.lua_current_version_ge_than(5, 2) then
+    table.insert(what, "t")
+end
+-- Fills in the fields `ftransfer` and `ntransfer`.
+if test_lib.lua_current_version_ge_than(5, 4) then
+    table.insert(what, "r")
+end
+
+local hook_mask = {
+    "c", -- The hook is called every time Lua calls a function.
+    "r", -- The hook is called every time Lua returns from a
+         -- function.
+    "l", -- The hook is called every time Lua enters a new line of
+         -- code.
+}
+
+local loadstring = type(loadstring) == "function" and loadstring or load
+
+local what_modes_str
+local what_modes_map
+
+local function check_getinfo(ar)
+    if what_modes_map.S then
+        assert(ar.source ~= nil and type(ar.source) == "string")
+        assert(ar.short_src ~= nil and type(ar.short_src) == "string")
+        assert(ar.linedefined ~= nil and type(ar.linedefined) == "number")
+        assert(ar.lastlinedefined ~= nil and
+               type(ar.lastlinedefined) == "number")
+        assert(ar.what ~= nil and (ar.what == "Lua" or
+                                   ar.what == "C" or
+                                   ar.what == "main"))
+        -- Beware, in PUC Rio Lua `srclen` can be omitted with
+        -- `S` mode, see <ldebug.c>.
+        assert(ar.srclen == nil or type(ar.srclen) == "number")
+    end
+
+    if what_modes_map.l then
+        assert(ar.currentline ~= nil and type(ar.currentline) == "number")
+    end
+
+    if what_modes_map.t then
+        assert(ar.name == nil or type(ar.name) == "string")
+        assert(ar.namewhat == "global" or
+               ar.namewhat == "local" or
+               ar.namewhat == "method" or
+               ar.namewhat == "field" or
+               ar.namewhat == "upvalue" or
+               ar.namewhat == "" or
+               -- Undocumented in PUC Rio Lua (5.4+?).
+               ar.namewhat == "hook" or
+               ar.namewhat == "metamethod" or
+               ar.namewhat == nil)
+    end
+
+    if what_modes_map.t then
+        assert(type(ar.istailcall) == "boolean")
+    end
+
+    if what_modes_map.u then
+        assert(ar.nups ~= nil and type(ar.nups) == "number")
+        assert(ar.nparams ~= nil and type(ar.nparams) == "number")
+        if ar.what == "C" then
+            assert(ar.nparams == 0)
+            assert(ar.isvararg == true)
+        end
+        assert(type(ar.isvararg) == "boolean")
+    end
+
+    if what_modes_map.r then
+        assert(ar.ftransfer ~= nil and type(ar.ftransfer) == "number")
+        assert(ar.ntransfer ~= nil and type(ar.ntransfer) == "number")
+    end
+end
+
+local function touch_upvalues(func, nups)
+    if not func then return end
+    for j = 1, nups do
+        local n, _ = debug.getupvalue(func, j)
+        if not n then break end
+    end
+end
+
+local function debug_hook()
+    local level = 0
+    local ar = debug.getinfo(level, what_modes_str)
+    while ar do
+        -- "Touch" fields.
+        check_getinfo(ar)
+
+        -- "Touch" locals.
+        local i = 1
+        while true do
+            local name, _ = debug.getlocal(level, i)
+            if name == nil then break end
+            i = i + 1
+        end
+
+        -- "Touch" upvalues.
+        local func = debug.getinfo(level, what_modes_str).func
+        local nups = debug.getinfo(level, "u").nups
+        touch_upvalues(func, nups)
+
+        level = level + 1
+        ar = debug.getinfo(level, what_modes_str)
+    end
+end
+
+local function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+
+    -- Generate a random 'what'.
+    what_modes_map = {}
+    local what_modes_array = {}
+    local count_modes = fdp:consume_integer(0, #what)
+    for _ = 0, count_modes do
+        local mode = fdp:oneof(what)
+        table.insert(what_modes_array, mode)
+        what_modes_map[mode] = true
+    end
+    what_modes_str = table.concat(what_modes_array)
+
+    -- Generate a random hook mask.
+    local n_hook_mask = fdp:consume_integer(0, #hook_mask)
+    local mask = {}
+    for _ = 0, n_hook_mask do
+        table.insert(mask, fdp:oneof(hook_mask))
+    end
+
+    -- Turn on the hook.
+    debug.sethook(debug_hook, table.concat(mask), 1)
+
+    local code = fdp:consume_string(test_lib.MAX_STR_LEN)
+    local chunk = loadstring(code)
+    if chunk == nil then
+        return -1
+    end
+    pcall(chunk)
+
+    -- Turn off the hook.
+    debug.sethook()
+end
+
+local args = {
+    artifact_prefix = "debug_torture_",
+}
+-- lj_bcread.c:123: bcread_byte: buffer read overflow
+if test_lib.lua_version() == "LuaJIT" then
+    args.only_ascii = 1
+end
+luzer.Fuzz(TestOneInput, nil, args)