nested macro repetions can cause fatal OOM

[colin-kiegel]

oom in two lines

macro_rules! oom { ( $($( ),*)* ) => { } }
oom!( );

=> fatal out-of-memory (warning: DON'T try to compile this without sufficient precautions - my computer runs out of RAM in 2 seconds with 16GB RAM installed). It doesn't matter what inside or outside of the brackets .. $($( .. ),*)* ...

Tested on LINUX, reproducible with stable-1.5, beta-1.6 and nightly.

This modified version is caught by the compiler and safe

macro_rules! no_oom { ( $($( ),*);* ) => { } }
no_oom!( );

src/main.rs:5:1: 5:10 error: ambiguity: multiple successful parses
src/main.rs:5 no_oom!( );
              ^~~~~~~~~

It would be nice if the compiler could check for anything that might oom like this. I think the safe version gives a hint at what is going wrong with the first version.

[colin-kiegel]

PS: Playpen will just kill the process
https://play.rust-lang.org/?gist=76fc85245426a4532655&version=stable

[jonas-schievink]

Duplicate of #5067

[huonw]

Indeed, closing as a dupe. Thanks for filing!