Latest sync (0.651) causes segfault specifically on ubuntu-20.04

[JohnnyMorganz]

Attempting to sync to Luau 0.651 for luau-lsp causes a crash on ubuntu-20.04 when executing the binary: JohnnyMorganz/luau-lsp#813

Running in gdb gives:

Program received signal SIGSEGV, Segmentation fault.
0x00005555555df637 in std::_Optional_payload<Luau::FragmentParseResumeSettings, false, false, false>::_Optional_payload_base(bool, std::_Optional_payload_base<Luau::FragmentParseResumeSettings> const&) ()
(gdb) bt
#0  0x00005555555df637 in std::_Optional_payload<Luau::FragmentParseResumeSettings, false, false, false>::_Optional_payload_base(bool, std::_Optional_payload_base<Luau::FragmentParseResumeSettings> const&) ()
#1  0x00005555555df671 in std::_Optional_base<Luau::FragmentParseResumeSettings, false, false>::_Optional_base(std::_Optional_base<Luau::FragmentParseResumeSettings, false, false> const&) ()
#2  0x00005555555da9c7 in std::optional<Luau::FragmentParseResumeSettings>::optional(std::optional<Luau::FragmentParseResumeSettings> const&) ()
#3  0x00005555555daa15 in Luau::ParseOptions::ParseOptions(Luau::ParseOptions const&) ()
#4  0x0000555555d5beac in Luau::Config::Config(Luau::Config const&) ()
#5  0x0000555555d5f508 in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#6  0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#7  0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#8  0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#9  0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#10 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#11 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#12 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#13 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#14 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#15 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#16 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#17 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#18 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#19 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#20 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#21 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#22 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#23 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#24 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#25 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#26 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#27 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#28 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#29 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Confi
...
#27546 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#27547 0x0000555555d5f52c in std::enable_if<std::__and_<std::__not_<std::__is_tuple_like<Luau::Config> >, std::is_move_constructible<Luau::Config>, std::is_move_assignable<Luau::Config> >::value, void>::type std::swap<Luau::Config>(Luau::Config&, Luau::Config&) ()
#27548 0x0000555555d5c28a in Luau::Config::operator=(Luau::Config const&) ()
#27549 0x0000555555c6443e in WorkspaceFileResolver::readConfigRec(std::filesystem::__cxx11::path const&) const ()
#27550 0x0000555555c63d05 in WorkspaceFileResolver::getConfig(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) const ()
#27551 0x00005555557f2a41 in Luau::Frontend::getSourceNode(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) ()
#27552 0x00005555557ed837 in Luau::Frontend::parseGraph(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, std::function<bool (std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)>) ()
#27553 0x00005555557eb96d in Luau::Frontend::check(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::optional<Luau::FrontendOptions>) ()
#27554 0x0000555555c6b4cb in WorkspaceFolder::checkStrict(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool) ()
#27555 0x0000555555cf5910 in WorkspaceFolder::completion(lsp::CompletionParams const&) ()
#27556 0x00005555555fe414 in (anonymous namespace)::DOCTEST_ANON_CLASS_6::f() ()
#27557 0x00005555555fe210 in (anonymous namespace)::DOCTEST_ANON_FUNC_7() ()
#27558 0x00005555555bac3d in doctest::Context::run() ()
#27559 0x00005555555bb662 in main ()

which repeats for several stackframes (snipped), indicating a problem in the implementation for Luau::Config::operator=(Luau::Config const&) ()

https://github.com/luau-lang/luau/blob/e6bf71871a6b9f601545dba8a42ce89c6069675c/Config/src/Config.cpp#L43C1-L51C2

[JohnnyMorganz]

Can also reproduce this with luau-analyze on ubuntu-20.04, with a similar backtrace in gdb:

$ mkdir build && cd build
$ cmake ..
$ cmake --build . --target Luau.Analyze.CLI
$ touch test.lua
$ ./luau-analyze test.lua
Segmentation fault

[vrn-sn]

@JohnnyMorganz this is a sneaky bug — I believe I have a fix on my end, but I want to make sure there isn't something else going on.

Config's move constructor and assignment are both marked noexcept, but DenseHashMap's move constructor and assignment aren't. On your platform, I believe this is causing the std::swap to perform copy assignment instead of move assignment, which creates an infinite loop (Config's copy assignment calls std::swap, which calls Config's copy assignment, which calls std::swap, etc.)

Editing the previous solution I had posted before (not sure it was safe). Try going to Config.h and removing the noexcepts here:

luau/Config/include/Luau/Config.h

Lines 24 to 27 in 53e6e4b

	Config(const Config& other) noexcept;
	Config& operator=(const Config& other) noexcept;
	Config(Config&& other) noexcept = default;
	Config& operator=(Config&& other) noexcept = default;

Also, remove the noexcepts in Config.cpp for the explicitly defined copy constructor and assignment operator.

luau/Config/src/Config.cpp

Line 20 in 53e6e4b

Config::Config(const Config& other) noexcept

luau/Config/src/Config.cpp

Line 43 in 53e6e4b

Config& Config::operator=(const Config& other) noexcept

If that works for you, I'll put in a PR (let me know).

[JohnnyMorganz]

Thanks @vrn-sn, I've tested with removing the noexcept in Config on ubuntu-20.04 via WSL and it seems to be working for me!

diff --git a/Config/include/Luau/Config.h b/Config/include/Luau/Config.h
index d6016229..64b76f07 100644
--- a/Config/include/Luau/Config.h
+++ b/Config/include/Luau/Config.h
@@ -21,10 +21,10 @@ constexpr const char* kConfigName = ".luaurc";
 struct Config
 {
     Config();
-    Config(const Config& other) noexcept;
-    Config& operator=(const Config& other) noexcept;
-    Config(Config&& other) noexcept = default;
-    Config& operator=(Config&& other) noexcept = default;
+    Config(const Config& other);
+    Config& operator=(const Config& other);
+    Config(Config&& other) = default;
+    Config& operator=(Config&& other) = default;

     Mode mode = Mode::Nonstrict;

diff --git a/Config/src/Config.cpp b/Config/src/Config.cpp
index 3760fd9e..345e039c 100644
--- a/Config/src/Config.cpp
+++ b/Config/src/Config.cpp
@@ -17,7 +17,7 @@ Config::Config()
     enabledLint.setDefaults();
 }

-Config::Config(const Config& other) noexcept
+Config::Config(const Config& other)
     : mode(other.mode)
     , parseOptions(other.parseOptions)
     , enabledLint(other.enabledLint)
@@ -40,7 +40,7 @@ Config::Config(const Config& other) noexcept
     }
 }

-Config& Config::operator=(const Config& other) noexcept
+Config& Config::operator=(const Config& other)
 {
     if (this != &other)
     {

[vrn-sn]

Fix is merged. Let me know if you have any other issues!