thread 'rustc' panicked at 'assertion failed: target_offset >= offset'

[weiznich]

Happens with rustc nightly from 21.6.19 in rust playground.

#![feature(async_await)]

use std::cell::RefCell;
use std::future::Future;

//use futures::future::FutureExt;


struct Connection {
    a: RefCell<()>
}


impl Connection {
    async fn execute<'a>(&'a mut self, _sql: &'a str) -> Result<(), ()> {
        Ok(())
    }
    
    async fn transaction<'a, 'b, T, R, FT>(&'a mut self, f: T) -> Result<R, ()> 
    where T: FnOnce(&mut Connection) -> FT + 'static, 
          FT: Future<Output = Result<R, ()>> + 'b,
          'b: 'a,
    {
        self.execute("BEGIN").await?;
        match f(self).await {
            Ok(res) => {
                self.execute("COMMIT").await?;
                Ok(res)
            }
            Err(err) => {
                self.execute("ROLLBACK ").await?;
                Err(err)
            }
        }
    }   
}


async fn foo(_conn: &mut Connection) -> Result<(), ()> {
    Ok(())
}

async fn bar(_conn: &mut Connection) -> Result<(),()> {
    Ok(())
} 

async fn do_something(conn: &mut Connection) -> Result<(), ()> {
    foo(conn).await?;
    bar(conn).await?;
    Ok(())
}


fn assert_send<F>(_f: F) where F: Future + Send {}

fn main() {
    let res = async {
        let mut conn = Connection {
            a: RefCell::new(())
        };
        conn.transaction(async move |conn| {
            //do_something(conn).await?;
            //foo(conn).await?;
            Ok(())
        }).await
    };
    
    assert_send(res);

    println!("Hello, world!");
}

(Playground)

Backtrace:

thread 'rustc' panicked at 'assertion failed: target_offset >= offset', src/librustc_codegen_llvm/type_of.rs:130:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.29/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:212
   6: rustc::util::common::panic_hook
   7: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:479
   8: std::panicking::begin_panic
   9: rustc_codegen_llvm::type_of::struct_llfields
  10: <rustc_target::abi::TyLayout<&rustc::ty::TyS> as rustc_codegen_llvm::type_of::LayoutLlvmExt>::llvm_type
  11: <rustc_target::abi::TyLayout<&rustc::ty::TyS> as rustc_codegen_llvm::type_of::LayoutLlvmExt>::llvm_type
  12: <rustc_target::abi::call::FnType<&rustc::ty::TyS> as rustc_codegen_llvm::abi::FnTypeLlvmExt>::llvm_type
  13: rustc_codegen_llvm::declare::<impl rustc_codegen_ssa::traits::declare::DeclareMethods for rustc_codegen_llvm::context::CodegenCx>::declare_fn
  14: rustc_codegen_llvm::mono_item::<impl rustc_codegen_ssa::traits::declare::PreDefineMethods for rustc_codegen_llvm::context::CodegenCx>::predefine_fn
  15: <rustc::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::predefine
  16: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  17: rustc::dep_graph::graph::DepGraph::with_task
  18: rustc_codegen_llvm::base::compile_codegen_unit
  19: rustc_codegen_ssa::base::codegen_crate
  20: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_utils::codegen_backend::CodegenBackend>::codegen_crate
  21: rustc::util::common::time
  22: rustc_interface::passes::start_codegen
  23: rustc::ty::context::tls::enter_global
  24: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  25: rustc_interface::passes::create_global_ctxt::{{closure}}
  26: rustc_interface::passes::BoxedGlobalCtxt::enter
  27: rustc_interface::queries::Query<T>::compute
  28: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::ongoing_codegen
  29: rustc_interface::interface::run_compiler_in_existing_thread_pool
  30: std::thread::local::LocalKey<T>::with
  31: scoped_tls::ScopedKey<T>::set
  32: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
query stack during panic:
end of query stack

[cramertj]

Dup of #61793