use-after-free in `proc_macro` handle

[gobanos]

I'm the author of a proc_macro crate : https://github.com/gobanos/aoc-runner-derive, where I store syn::Ident & Box<syn::Type> in a thread_local HashMap.
When I retrieve data from another proc_macro handle, an use-after-free error occur.

I tried this code:

#[aoc_generator(...)] // <- store name & output type in a map
fn gen(input: &str) -> Vec<i32> {
    ...
}

#[aoc(...)] // <- retrieve them from the map
fn run(input: &[i32]) -> i32 {
    ...
}

Meta

rustc --version --verbose:
rustc 1.32.0-nightly (d09466c 2018-11-30)
binary: rustc
commit-hash: d09466c
commit-date: 2018-11-30
host: x86_64-unknown-linux-gnu
release: 1.32.0-nightly
LLVM version: 8.0

PS: was working find few days ago :
rustc 1.32.0-nightly (edaac35 2018-11-24)
binary: rustc
commit-hash: edaac35
commit-date: 2018-11-24
host: x86_64-unknown-linux-gnu
release: 1.32.0-nightly
LLVM version: 8.0

[kevinmehall]

Macros aren't allowed to maintain state between calls.

Given that you're not using unsafe, it probably shouldn't allow a use-after-free, though. #56058 is about preventing the use of thread local storage.

[gobanos]

Ok, so I should find a way to serialize data between calls.

I think it should be a compile time error, if possible.

Thanks for your time !