Running out of RAM during compilation

[optimalstrategy]

Hi

Incorrectly closing the parentheses around an if expression causes the compiler to be stuck in endless recursion (probably), causing the computer to run out of memory.

I encountered this bug while trying to return Some(if cond { ... } else { ... }) from a function by accidentally placing the left parenthesis right after the if condition: Some(if ...) { } else { }.

The code below is the minimal example I came up with that reproduces the bug. Please run it carefully since it rapidly consumes RAM (2 GB/s on my machine).

// t.rs
fn main() { 
   (if true)
}

Compiler output:

$ rustc t.rs
error: expected `{`, found `)`
 --> t.rs:2:13
  |
2 |     (if true)
  |      --     ^ expected `{`
  |      |
  |      this `if` statement has a condition, but no block

error: expected expression, found `<eof>`
 --> t.rs:3:1
  |
3 | }
  | ^ expected expression   # at this point the compiler is stuck
^C

Meta

The bug is present in both available for me compilers:

$ rustc --version --verbose
rustc 1.37.0-nightly (7840a0b75 2019-05-31)
binary: rustc
commit-hash: 7840a0b753a065a41999f1fb6028f67d33e3fdd5
commit-date: 2019-05-31
host: x86_64-unknown-linux-gnu
release: 1.37.0-nightly
LLVM version: 8.0

and

$ rustc --version --verbose
rustc 1.35.0 (3c235d560 2019-05-20)
binary: rustc
commit-hash: 3c235d5600393dfe6c36eeed34042efad8d4f26e
commit-date: 2019-05-20
host: x86_64-unknown-linux-gnu
release: 1.35.0
LLVM version: 8.0

My OS is Arch Linux 5.1.11-arch1-1-ARCH.

[estebank]

Thank you for filing the ticket! I'm closing this as duplicate of #61858. #62607 is already out to fix it. Don't know if we will have a stable point release due to this but it seems likely that we will.