Bug running in debug mode in cargo

[fahdfady]

there's some weird error pops out when running metassr with cargo run in debug mode. something related to unsafe:

[metassr-dev]:~/metassr$ cargo run -- --root ./tests/web-app/ build
warning: /home/fahdashour/metassr/Cargo.toml: only one of `license` or `license-file` is necessary
`license` should be used if the package license can be expressed with a standard SPDX expression.
`license-file` should be used if the package uses a non-standard license.
See https://doc.rust-lang.org/cargo/reference/manifest.html#the-license-and-license-file-fields for more information.
   Compiling regex-automata v0.1.10
warning: unused variable: `params`
  --> crates/metassr-server/src/handler.rs:48:29
   |
48 |                 move |Query(params): Query<HashMap<String, String>>,
   |                             ^^^^^^ help: if this is intentional, prefix it with an underscore: `_params`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `path`
  --> crates/metassr-server/src/handler.rs:49:28
   |
49 |                       Path(path): Path<HashMap<String, String>>| async move {
   |                            ^^^^ help: if this is intentional, prefix it with an underscore: `_path`

warning: `metassr-server` (lib) generated 2 warnings
   Compiling matchers v0.1.0
   Compiling tracing-subscriber v0.3.18
   Compiling logger v0.0.1-alpha (/home/fahdashour/metassr/crates/logger)
   Compiling metassr v0.0.1-alpha (/home/fahdashour/metassr)
warning: unused variable: `instant`
  --> metassr-cli/src/cli/builder.rs:29:13
   |
29 |         let instant = Instant::now();
   |             ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_instant`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: `metassr` (bin "metassr") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 8.88s
     Running `target/debug/metassr --root ./tests/web-app/ build`

thread '<unnamed>' panicked at library/core/src/panicking.rs:225:5:
unsafe precondition(s) violated: NonNull::new_unchecked requires that the pointer is non-null

This indicates a bug in the program. This Undefined Behavior check is optional, and cannot be relied on for safety.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
thread caused non-unwinding panic. aborting.
Stack trace (most recent call last) in thread 58799:
#31   Object "/gnu/store/9ygpsbp5gfbrwrin5jdmkd3m84vdsai5-libuv-1.49.1/lib/libuv.so.1", at 0x7f2298049275, in uv_run
#30   Object "/gnu/store/9ygpsbp5gfbrwrin5jdmkd3m84vdsai5-libuv-1.49.1/lib/libuv.so.1", at 0x7f229805b7a2, in 
#29   Object "/gnu/store/9ygpsbp5gfbrwrin5jdmkd3m84vdsai5-libuv-1.49.1/lib/libuv.so.1", at 0x7f22980486c2, in 
#28   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f2240988424, in 
#27   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f22408cbd96, in node::CallbackScope::~CallbackScope()
#26   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f22408cbd30, in node::InternalCallbackScope::~InternalCallbackScope()
#25   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f22408cbaf8, in node::InternalCallbackScope::Close()
#24   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f224117cf8e, in v8::internal::MicrotaskQueue::PerformCheckpointInternal(v8::Isolate*)
#23   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f224117cc55, in v8::internal::MicrotaskQueue::RunMicrotasks(v8::internal::Isolate*)
#22   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f224114d2e9, in v8::internal::Execution::TryRunMicrotasks(v8::internal::Isolate*, v8::internal::MicrotaskQueue*)
#21   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f224114c185, in 
#20   Object "[0x7f21e0c8b402]", at 0x7f21e0c8b402, in 
#19   Object "[0x7f21e0cbc918]", at 0x7f21e0cbc918, in 
#18   Object "[0x7f21e0dab274]", at 0x7f21e0dab274, in 
#17   Object "[0x7f21e0c8d8dd]", at 0x7f21e0c8d8dd, in 
#16   Object "[0x7f21e0c8f5e1]", at 0x7f21e0c8f5e1, in 
#15   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f2240962334, in 
#14   Object "/gnu/store/lq4c37dxvbd8f4g5b7p0flf2w05s3h9r-metacall-0.9.14/lib/libnode_loader.so", at 0x7f2248d6bab9, in 
#13   Object "/gnu/store/lq4c37dxvbd8f4g5b7p0flf2w05s3h9r-metacall-0.9.14/lib/libnode_loader.so", at 0x7f2248d64288, in 
#12   Object "target/debug/metassr", at 0x564f2d6a8826, in 
#11   Object "target/debug/metassr", at 0x564f2d6980cf, in 
#10   Object "target/debug/metassr", at 0x564f2d6a6b8c, in 
#9    Object "target/debug/metassr", at 0x564f2d809791, in 
#8    Object "target/debug/metassr", at 0x564f2d8096fc, in 
#7    Object "target/debug/metassr", at 0x564f2d7e849c, in 
#6    Object "target/debug/metassr", at 0x564f2d7e71a8, in 
#5    Object "target/debug/metassr", at 0x564f2d7e87d5, in 
#4    Object "target/debug/metassr", at 0x564f2d7e8bf2, in 
#3    Object "target/debug/metassr", at 0x564f2d7eabc9, in 
#2    Object "/lib/x86_64-linux-gnu/libc.so.6", at 0x7f229ab968fe, in abort
#1    Object "/lib/x86_64-linux-gnu/libc.so.6", at 0x7f229abb327d, in gsignal
#0    Object "/lib/x86_64-linux-gnu/libc.so.6", at 0x7f229ac0cb2c, in pthread_kill
Aborted (Signal sent by tkill() 58302 1000)
Aborted (core dumped)

For some reason, this doesn't happen in release mode, even with the same exact command just with -r in it:

fahdashour:~/metassr$ cargo run -r -- --root ./tests/web-app/ build
warning: /home/fahdashour/metassr/Cargo.toml: only one of `license` or `license-file` is necessary
`license` should be used if the package license can be expressed with a standard SPDX expression.
`license-file` should be used if the package uses a non-standard license.
See https://doc.rust-lang.org/cargo/reference/manifest.html#the-license-and-license-file-fields for more information.
warning: unused variable: `params`
  --> crates/metassr-server/src/handler.rs:48:29
   |
48 |                 move |Query(params): Query<HashMap<String, String>>,
   |                             ^^^^^^ help: if this is intentional, prefix it with an underscore: `_params`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `path`
  --> crates/metassr-server/src/handler.rs:49:28
   |
49 |                       Path(path): Path<HashMap<String, String>>| async move {
   |                            ^^^^ help: if this is intentional, prefix it with an underscore: `_path`

warning: `metassr-server` (lib) generated 2 warnings
warning: unused variable: `instant`
  --> metassr-cli/src/cli/builder.rs:29:13
   |
29 |         let instant = Instant::now();
   |             ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_instant`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: `metassr` (bin "metassr") generated 1 warning
    Finished `release` profile [optimized] target(s) in 0.21s
     Running `target/release/metassr --root ./tests/web-app/ build`
2025-09-11T09:32:24.142867781+03:00  INFO [builder] Client building is completed time: 448ms 
2025-09-11T09:32:24.252963111+03:00  INFO [builder] Server building is completed time: 110ms 

[fahdfady]

the stack trace gives me a hint. it layers as:

• libuv, an event loop library used in Node js
• node js, with linking to libnode.so, maybe related to metacall?
• metacall
• Rust debug binary

maybe this will help

[fahdfady]

fahdashour:~/metassr$ RUST_BACKTRACE=full cargo run -- --root ./tests/web-app/ build
warning: /home/fahdashour/metassr/Cargo.toml: only one of `license` or `license-file` is necessary
`license` should be used if the package license can be expressed with a standard SPDX expression.
`license-file` should be used if the package uses a non-standard license.
See https://doc.rust-lang.org/cargo/reference/manifest.html#the-license-and-license-file-fields for more information.
warning: unused variable: `params`
  --> crates/metassr-server/src/handler.rs:48:29
   |
48 |                 move |Query(params): Query<HashMap<String, String>>,
   |                             ^^^^^^ help: if this is intentional, prefix it with an underscore: `_params`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `path`
  --> crates/metassr-server/src/handler.rs:49:28
   |
49 |                       Path(path): Path<HashMap<String, String>>| async move {
   |                            ^^^^ help: if this is intentional, prefix it with an underscore: `_path`

warning: `metassr-server` (lib) generated 2 warnings
   Compiling metassr v0.0.1-alpha (/home/fahdashour/metassr)
warning: unused variable: `instant`
  --> metassr-cli/src/cli/builder.rs:29:13
   |
29 |         let instant = Instant::now();
   |             ^^^^^^^ help: if this is intentional, prefix it with an underscore: `_instant`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: `metassr` (bin "metassr") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.40s
     Running `target/debug/metassr --root ./tests/web-app/ build`

thread '<unnamed>' panicked at library/core/src/panicking.rs:225:5:
unsafe precondition(s) violated: NonNull::new_unchecked requires that the pointer is non-null

This indicates a bug in the program. This Undefined Behavior check is optional, and cannot be relied on for safety.
stack backtrace:
   0:     0x55ce518aab52 - std::backtrace_rs::backtrace::libunwind::trace::h0a5fcb8b4db3bad3
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
   1:     0x55ce518aab52 - std::backtrace_rs::backtrace::trace_unsynchronized::he7a804d21c58af1d
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14
   2:     0x55ce518aab52 - std::sys::backtrace::_print_fmt::h1ef011aafedbe169
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/sys/backtrace.rs:66:9
   3:     0x55ce518aab52 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h8ce760ad42a959df
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/sys/backtrace.rs:39:26
   4:     0x55ce518d0663 - core::fmt::rt::Argument::fmt::head038d92b6711ae
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/core/src/fmt/rt.rs:173:76
   5:     0x55ce518d0663 - core::fmt::write::h17deacb9d093717d
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/core/src/fmt/mod.rs:1446:25
   6:     0x55ce518a7113 - std::io::default_write_fmt::h802cbaee6f18e63d
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/io/mod.rs:639:11
   7:     0x55ce518a7113 - std::io::Write::write_fmt::h8edc637e3ed34e58
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/io/mod.rs:1914:13
   8:     0x55ce518aa9a2 - std::sys::backtrace::BacktraceLock::print::hf4e931b5b8f47af6
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/sys/backtrace.rs:42:9
   9:     0x55ce518abf02 - std::panicking::default_hook::{{closure}}::h1aa602af6f79c655
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/panicking.rs:300:22
  10:     0x55ce518abd05 - std::panicking::default_hook::hb6d5039bf2b4cecd
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/panicking.rs:327:9
  11:     0x55ce518ac922 - std::panicking::rust_panic_with_hook::h1a38b2651d61b684
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/panicking.rs:833:13
  12:     0x55ce518ac676 - std::panicking::begin_panic_handler::{{closure}}::h68b9b893aa0276cd
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/panicking.rs:699:13
  13:     0x55ce518ab049 - std::sys::backtrace::__rust_end_short_backtrace::h1e1d1741d128b4db
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/sys/backtrace.rs:168:18
  14:     0x55ce518ac33d - __rustc[4c7992aec7d05df4]::rust_begin_unwind
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/std/src/panicking.rs:697:5
  15:     0x55ce518cd59d - core::panicking::panic_nounwind_fmt::runtime::ha3ed9b2a319027ad
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/core/src/panicking.rs:117:22
  16:     0x55ce518cd59d - core::panicking::panic_nounwind_fmt::he1541e8b480fcdcf
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/core/src/intrinsics/mod.rs:3175:9
  17:     0x55ce518cd632 - core::panicking::panic_nounwind::h2f15cd04cb9018c2
                               at /rustc/16d2276fa6fccb0cc239a542d4c3f0eb46f660ec/library/core/src/panicking.rs:225:5
  18:     0x55ce5176742d - core::ptr::non_null::NonNull<T>::new_unchecked::precondition_check::h5e2723c0a3f9a918
                               at /home/fahdashour/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ub_checks.rs:68:21
  19:     0x55ce5175feb0 - core::ptr::non_null::NonNull<T>::new_unchecked::h8ac3aa9007836eae
                               at /home/fahdashour/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ub_checks.rs:75:17
  20:     0x55ce5175feb0 - core::ptr::unique::Unique<T>::new_unchecked::h4140e45b1ae1e82f
                               at /home/fahdashour/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ptr/unique.rs:90:36
  21:     0x55ce5175feb0 - alloc::boxed::Box<T,A>::from_raw_in::h7bc9201b50135856
                               at /home/fahdashour/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/boxed.rs:1154:22
  22:     0x55ce5175feb0 - alloc::boxed::Box<T>::from_raw::h2751d0c405a38c64
                               at /home/fahdashour/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/boxed.rs:1045:18
  23:     0x55ce51769287 - metacall::types::metacall_future::resolver::h669dd936a9e01181
                               at /home/fahdashour/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/metacall-0.5.1/src/types/metacall_future.rs:121:21
  24:     0x7f22b0738289 - <unknown>
  25:     0x7f22b073faba - <unknown>
  26:     0x7f2268962335 - <unknown>
  27:     0x7f2208c8f5e2 - <unknown>
thread caused non-unwinding panic. aborting.
Stack trace (most recent call last) in thread 94893:
#31   Object "/gnu/store/9ygpsbp5gfbrwrin5jdmkd3m84vdsai5-libuv-1.49.1/lib/libuv.so.1", at 0x7f22c0028275, in uv_run
#30   Object "/gnu/store/9ygpsbp5gfbrwrin5jdmkd3m84vdsai5-libuv-1.49.1/lib/libuv.so.1", at 0x7f22c003a7a2, in 
#29   Object "/gnu/store/9ygpsbp5gfbrwrin5jdmkd3m84vdsai5-libuv-1.49.1/lib/libuv.so.1", at 0x7f22c00276c2, in 
#28   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f2268988424, in 
#27   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f22688cbd96, in node::CallbackScope::~CallbackScope()
#26   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f22688cbd30, in node::InternalCallbackScope::~InternalCallbackScope()
#25   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f22688cbaf8, in node::InternalCallbackScope::Close()
#24   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f226917cf8e, in v8::internal::MicrotaskQueue::PerformCheckpointInternal(v8::Isolate*)
#23   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f226917cc55, in v8::internal::MicrotaskQueue::RunMicrotasks(v8::internal::Isolate*)
#22   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f226914d2e9, in v8::internal::Execution::TryRunMicrotasks(v8::internal::Isolate*, v8::internal::MicrotaskQueue*)
#21   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f226914c185, in 
#20   Object "[0x7f2208c8b402]", at 0x7f2208c8b402, in 
#19   Object "[0x7f2208cbc918]", at 0x7f2208cbc918, in 
#18   Object "[0x7f2208dab274]", at 0x7f2208dab274, in 
#17   Object "[0x7f2208c8d8dd]", at 0x7f2208c8d8dd, in 
#16   Object "[0x7f2208c8f5e1]", at 0x7f2208c8f5e1, in 
#15   Object "/gnu/store/3611k5c6iki74mzrp2lj670kv7csp0wh-libnode-22.12.0/lib/libnode.so.127", at 0x7f2268962334, in 
#14   Object "/gnu/store/lq4c37dxvbd8f4g5b7p0flf2w05s3h9r-metacall-0.9.14/lib/libnode_loader.so", at 0x7f22b073fab9, in 
#13   Object "/gnu/store/lq4c37dxvbd8f4g5b7p0flf2w05s3h9r-metacall-0.9.14/lib/libnode_loader.so", at 0x7f22b0738288, in 
#12   Object "target/debug/metassr", at 0x55ce51769286, in 
#11   Object "target/debug/metassr", at 0x55ce5175feaf, in 
#10   Object "target/debug/metassr", at 0x55ce5176742c, in 
#9    Object "target/debug/metassr", at 0x55ce518cd631, in 
#8    Object "target/debug/metassr", at 0x55ce518cd59c, in 
#7    Object "target/debug/metassr", at 0x55ce518ac33c, in 
#6    Object "target/debug/metassr", at 0x55ce518ab048, in 
#5    Object "target/debug/metassr", at 0x55ce518ac675, in 
#4    Object "target/debug/metassr", at 0x55ce518aca92, in 
#3    Object "target/debug/metassr", at 0x55ce518aea69, in 
#2    Object "/lib/x86_64-linux-gnu/libc.so.6", at 0x7f22c25728fe, in abort
#1    Object "/lib/x86_64-linux-gnu/libc.so.6", at 0x7f22c258f27d, in gsignal
#0    Object "/lib/x86_64-linux-gnu/libc.so.6", at 0x7f22c25e8b2c, in pthread_kill
Aborted (Signal sent by tkill() 94534 1000)
Aborted (core dumped)```

[fahdfady]

maybe it's working on release mode because core::ptr::non_null::NonNull<T>::new_unchecked::precondition_check is only in debug?
this notes that it's still an unsafe rust problem. anyways i found some related links that supports why it's showing only on debug
https://doc.rust-lang.org/beta/core/ptr/struct.NonNull.html#method.new_unchecked
https://doc.rust-lang.org/beta/core/macro.assert_unsafe_precondition.html

[fahdfady]

@viferga @hulxv
the stack trace mentions /.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/metacall-0.5.1/src/types/metacall_future.rs:121:21 this indicates that the problem is within using MetaCallFuture in unsafe

unsafe extern "C" fn resolver(resolve_data: *mut c_void, upper_data: *mut c_void) -> *mut c_void {
    let (resolve, _, data) = *Box::from_raw(upper_data as *mut MetaCallFutureFFIData);
    let user_data = Box::from_raw(data);

    let result = (resolve.unwrap())(
        cast::raw_to_metacallobj_untyped_leak(resolve_data),
        user_data,
    );

    if let Some(ret) = metacallobj_untyped_to_raw(result) {
        return ret;
    }

    unsafe { metacall_value_create_null() }
}

the error is in:

let user_data = Box::from_raw(data);

I think the problem is (correct me if i'm wrong):

• MetaCallFuture purpose is to create raw pointers to deal with JavaScript async primitives and deal with it as futures.
• later retrieve those pointers into a Box.
• a null pointer is being passed where a valid future pointer was expected.

This is a runtime issue. so, even though it runs successfully in release mode, the debug mode tells us there is a serious memory issue that'll eventually face our users.
Review that please and tell me if we should open an issue on metacall/core for solving this MetaCallFuture thing.