This produces a lifetime much longer than correct: it produces a reference to vec data that has a local lifetime but extends that to 'a.
Furthermore, since this is in an IntoIterator impl, most of the time this gets used it will be unsound: the vector is dropped immediately after IntoIterator, but these references could potentially be held on to for much longer.
If the Iterator API cannot express what is necessary here, we should not use the iterator API.
Is there a reason that second tuple field is needed anyway? It feels like we can do better exposing a .last() method or something.
use minifier::js;
fn main() {
let source = "function foo() {}";
let tokens = js::tokenize(source);
let token = tokens.into_iter().next().unwrap();
println!("{:?}", token);
}
fails on miri:
```
$ cargo +nightly miri run --example example
Preparing a sysroot for Miri (target: x86_64-unknown-linux-gnu)... done
Finished dev [unoptimized + debuginfo] target(s) in 0.00s
Running `/home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/cargo-miri runner target/miri/x86_64-unknown-linux-gnu/debug/examples/example`
error: Undefined Behavior: constructing invalid value: encountered a dangling reference (use-after-free)
--> /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:2278:1
|
2278 | fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered a dangling reference (use-after-free)
|
= help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
= help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
= note: BACKTRACE:
= note: inside `<&minifier::js::Token<'_> as std::fmt::Debug>::fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:2268:71: 2268:78
= note: inside `<&&minifier::js::Token<'_> as std::fmt::Debug>::fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:2268:62: 2268:82
= note: inside closure at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/builders.rs:322:17: 322:36
= note: inside `std::result::Result::<(), std::fmt::Error>::and_then::<(), [closure@std::fmt::DebugTuple<'_, '_>::field::{closure#0}]>` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/result.rs:1319:22: 1319:27
= note: inside `std::fmt::DebugTuple::<'_, '_>::field` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/builders.rs:309:23: 324:11
= note: inside `std::fmt::Formatter::<'_>::debug_tuple_field1_finish` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:2035:9: 2035:30
= note: inside `> as std::fmt::Debug>::fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:559:37: 559:42
= note: inside `<&std::option::Option<&minifier::js::Token<'_>> as std::fmt::Debug>::fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:2268:62: 2268:82
= note: inside closure at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/builders.rs:322:17: 322:36
= note: inside `std::result::Result::<(), std::fmt::Error>::and_then::<(), [closure@std::fmt::DebugTuple<'_, '_>::field::{closure#0}]>` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/result.rs:1319:22: 1319:27
= note: inside `std::fmt::DebugTuple::<'_, '_>::field` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/builders.rs:309:23: 324:11
= note: inside `<(minifier::js::Token<'_>, std::option::Option<&minifier::js::Token<'_>>) as std::fmt::Debug>::fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:2461:25: 2461:46
= note: inside `core::fmt::rt::Argument::<'_>::fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/rt.rs:138:9: 138:40
= note: inside `std::fmt::write` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/mod.rs:1094:17: 1094:40
= note: inside ` as std::io::Write>::write_fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/io/mod.rs:1714:15: 1714:43
= note: inside `<&std::io::Stdout as std::io::Write>::write_fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/io/stdio.rs:726:9: 726:36
= note: inside `::write_fmt` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/io/stdio.rs:700:9: 700:33
= note: inside `std::io::stdio::print_to::` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/io/stdio.rs:1018:21: 1018:47
= note: inside `std::io::_print` at /home/manishearth/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/io/stdio.rs:1095:5: 1095:37
note: inside `main`
--> examples/example.rs:11:5
|
11 | println!("{:?}", token);
| ^^^^^^^^^^^^^^^^^^^^^^^
= note: this error originates in the macro `fmt_refs` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
```
https://github.com/GuillaumeGomez/minifier-rs/blob/c8e8bee18b0ecca0603afdfd5f9c259f700deb72/src/js/token.rs#L1076-L1089
This produces a lifetime much longer than correct: it produces a reference to vec data that has a local lifetime but extends that to
'a.Furthermore, since this is in an IntoIterator impl, most of the time this gets used it will be unsound: the vector is dropped immediately after IntoIterator, but these references could potentially be held on to for much longer.
If the Iterator API cannot express what is necessary here, we should not use the iterator API.
Is there a reason that second tuple field is needed anyway? It feels like we can do better exposing a
.last()method or something.fails on miri: