tests/lapi: add debug tests

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

TODO:

debug.getmetatable
debug.setmetatable
debug.setupvalue
debug.setlocal

Author: ligurio

tests/lapi/debug_getinfo_test.lua

@@ -0,0 +1,92 @@
+--[[
+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
+
+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.
+}
+
+local what_modes
+
+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 function debug_hook()
+    debug.getinfo(1, table.concat(what_modes))
+end
+
+local function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+
+    -- Generate a random 'what'.
+    what_modes = {}
+    local n_modes = fdp:consume_integer(0, #what)
+    for _ = 0, n_modes do
+        table.insert(what_modes, fdp:oneof(what))
+    end
+
+    -- 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))
+
+    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_getinfo_",
+}
+-- 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)

tests/lapi/debug_getlocal_test.lua

@@ -0,0 +1,67 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+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
+
+Synopsis: debug.getlocal([thread,] level, local)
+]]
+
+local luzer = require("luzer")
+local test_lib = require("lib")
+
+-- Extract locals.
+local function debug_hook()
+    local level = 2
+    local i = 1
+    while true do
+        local name, _ = debug.getlocal(level, i)
+        if name == nil then break end
+        i = i + 1
+    end
+end
+
+local loadstring = type(loadstring) == "function" and loadstring or load
+
+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 function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+
+    -- 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))
+
+    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_getlocal_",
+}
+-- 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)

tests/lapi/debug_getupvalue_test.lua

@@ -0,0 +1,65 @@
+--[[
+SPDX-License-Identifier: ISC
+Copyright (c) 2023-2025, Sergey Bronnikov.
+
+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)
+]]
+
+local luzer = require("luzer")
+local test_lib = require("lib")
+
+-- Extract upvalues.
+local function debug_hook()
+    local level = 2
+    local ar = debug.getinfo(level)
+    local func = ar.func
+    local nups = debug.getinfo(level, 'u').nups
+    for i = 1, nups do
+        local n, _ = debug.getupvalue(func, i)
+        if not n then break end
+    end
+end
+
+local loadstring = type(loadstring) == "function" and loadstring or load
+
+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 function TestOneInput(buf)
+    local fdp = luzer.FuzzedDataProvider(buf)
+
+    -- 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))
+
+    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_getupvalue_",
+}
+-- 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)