Exponential compile time with nested &dyn Fn type · Issue #104583 · rust-lang/rust (original) (raw)

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Description

Found with a modified fuzz-rustc

Code

fn id( f: &dyn Fn(u32) ) -> &dyn Fn( &dyn Fn( &dyn Fn( &dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(u32))))))))) ) ) ) { f }

fn main() {}

Time complexity

Seems exponential:

Where it's slow

• From -Z time-passes: item_bodies_checking (full output)
• From sampling: seems like recursion involving type inference (head of sample tree)

Not a recent regression

It's slow at least as far back as nightly-2018-01-01

Version

rustc 1.67.0-nightly (a00f8ba7f 2022-11-15)
binary: rustc
commit-hash: a00f8ba7fcac1b27341679c51bf5a3271fa82df3
commit-date: 2022-11-15
host: x86_64-apple-darwin
release: 1.67.0-nightly
LLVM version: 15.0.4

@rustbot label +I-compiletime