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Compiler hangs during recursive monomorphisation #39684
Description
use std::iter;
fn silly<I: Iterator<Item=()>>(it: I) {
silly(it.chain(iter::empty()))
}
fn main() {
println!("Start");
silly(iter::empty());
println!("Done");
}This code causes compiler to be stuck wasting CPU cycles, instead of printing some kind of recursion limit error.
Activity
[-]Compiler hangs when computing infinite type[/-][+]Compiler hangs during recursive monomorphisation[/+]Aatch commentedon Feb 9, 2017
This is actually a monomorphisation issue, though I'm surprised it hangs since we do try to detect recursive monomorphisations too.
Aatch commentedon Feb 10, 2017
So this seems to be related to resolving the
Iterator::chainmethod, though I'm not sure exactly what is going on. It will eventually hit the recursion limit (probably) though.Mark-Simulacrum commentedon May 22, 2017
After waiting for a little bit, this is the log I get. So I think part of the problem here is that we slowly recurse; that is, each step appears to take quite a while, so our recursion depth isn't really growing fast.
gbip commentedon Oct 26, 2017
Hello,
I just wanted to say that I add the same problem with the following code :
Here is playground link.
This was on the latest stable (1.21).
ishitatsuyuki commentedon Feb 14, 2018
@Mark-Simulacrum could the slow part being caused by exponential blowup? We can only reproduce with infinite recursion currently, so we can't easily confirm what's going on here. However, it's possible something like breadth-first search was used and causing the blowup here.
Anyway, here's a log dump (from debug-assertions build) for examination:
silly.log.gz
ishitatsuyuki commentedon Feb 15, 2018
This is exponential. Have fun.
ishitatsuyuki commentedon Feb 15, 2018
This tracks down to the same cause as #38528 (comment).
Random suspension stack trace:
ishitatsuyuki commentedon Feb 17, 2018
With PoC in #48296 this resolves in finite time. The error is too silly though.
`-Z time-passes` with silly error message
Rollup merge of rust-lang#48296 - ishitatsuyuki:exp-unblow, r=nikomat…