assertion_on_constants lint: false positive?

[sanmai-NL]

The following code:

if let Some(data_sub) = &data.get(range) {
    *data_sub
} else {
    debug_assert!(false, "Out-of-bounds read. ");
}

Triggers assertion_on_constants for me. https://rust-lang.github.io/rust-clippy/master/index.html#assertions_on_constants explains that this assertion would be optimized out by the compiler. That shouldn't be so. A statically false assertion should become a panic, not be optimized away. Since this assertion is only triggered in debug builds, using a plain unreachable! or panic! isn't an equivalent alternative. So as long as debug_unreachable! isn't part of the standard library, this lint should not fire in cases like the above. Furthermore, the lint explanation should be corrected to say that (only) statically true assertions may be optimized out.

clippy 0.0.212 (6ce78d12 2019-01-29)

[phansch]

This is probably fixed by #3740, however that's not included in a nightly yet.

It might be good to add this test case to the UI tests: https://github.com/rust-lang/rust-clippy/blob/master/tests/ui/assertions_on_constants.rs

[mcarton]

Confirmed: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=eba556d590a3e9f3c718e6061130e0f5
This doesn't trigger any warning anymore and is being tested by said PR.

[sanmai-NL]

@mcarton: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=213800165b6b1581281c97c4d040110e still triggers a warning when I run Clippy against this kind of code locally too, and I just just updated to the latest nightly and Clippy component. You've closed the issue, were you aware of @phansch's observation? Can you please explain how the issue can be solved downstream for the programmer using Clippy?

[bjorn-ove]

This lint still triggers in the clippy version that comes with rustup in nightly-2019-04-12-x86_64-unknown-linux-gnu

[bjorn@devbox debug_assert_test]$ cat src/lib.rs 
pub fn panic_when_debug_build() {
    debug_assert!(false, "This is a debug build");
}

[bjorn@devbox debug_assert_test]$ cargo +nightly-2019-04-14-x86_64-unknown-linux-gnu clippy
    Checking debug_assert_test v0.1.0 (/home/bjorn_andersen/tmp/debug_assert_test)
warning: assert!(false) should probably be replaced
 --> src/lib.rs:2:5
  |
2 |     debug_assert!(false, "This is a debug build");
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: #[warn(clippy::assertions_on_constants)] on by default
  = help: use panic!() or unreachable!()
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#assertions_on_constants
  = note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

    Finished dev [unoptimized + debuginfo] target(s) in 0.31s

[flip1995]

cc #3948

This lint should not be triggered at all for debug_assert!(false). I will fix this ASAP.