Build hangs for some build scripts

[aldanor]

For larger projects, chances are there's always going to be some proc-macro dependencies involved, seems like cargo remark build just hangs; here's the simplest example (taken from paste docs):

use paste::paste; // add `paste = "1.0"` to deps

paste! { const [<Q R S T>]: &str = "success!"; }

fn main() {
    assert_eq!(paste! { [<Q R S T>].len() }, 8);
}

which results in hanging forever here:

❯ cargo +nightly remark build
[2023-10-11T15:19:31Z INFO  cargo_remark::cargo] Optimization remarks will be stored into target/remarks/yaml.
   Compiling paste v1.0.14
    Building [====>                        ] 1/5: paste(build.rs)

Edit: not sure if it's proc-macro-related, or if it's something to do with paste. Or dependencies that have a custom build.rs perhaps?

[aldanor]

Update, tracked it down to a single line in paste's build.rs; minimal example that seems to hang is this: add build.rs with

fn main() {
    _ = "".split('.'); // <-- ???
}

This causes it to hang forever:

❯ cargo +nightly remark build
   Compiling test-remark v0.1.0 (test-remark)
    Building [                             ] 0/3: test-remark(build.rs)

[aldanor]

Looking into it a bit further, just running

RUSTFLAGS="-Cremark=all -Cdebuginfo=1" cargo +nightly build --release

causes

note: /rustc/59edd67056919c83c59001a8b4f2d8749359377a/library/core/src/char/methods.rs:1767:0 asm-printer (analysis): 179 instructions in function

note: /rustc/59edd67056919c83c59001a8b4f2d8749359377a/library/core/src/str/pattern.rs:544:32 gisel-irtranslator-memsize (analysis): Call to memset. Memory operation size: 4 bytes.
       Written Variables: <unknown> (4 bytes).

note: /rustc/59edd67056919c83c59001a8b4f2d8749359377a/library/core/src/str/pattern.rs:543:0 size-info (analysis): IRTranslator: Function: _ZN52_$LT$char$u20$as$u20$core..str..pattern..Pattern$GT$13into_searcher17h80469adc07d8dc57E: MI Instruction count changed from 0 to 43; Delta: 43

note: /rustc/59edd67056919c83c59001a8b4f2d8749359377a/library/core/src/str/pattern.rs:543:0 size-info (analysis): AArch64O0PreLegalizerCombiner: Function: _ZN52_$LT$char$u20$as$u20$core..str..pattern..Pattern$GT$13into_searcher17h80469adc07d8dc57E: MI Instruction count changed from 43 to 40; Delta: -3

note: /rustc/59edd67056919c83c59001a8b4f2d8749359377a/library/core/src/str/pattern.rs:546:9 gisel-legalize (missed): unable to legalize instruction: G_STORE %26:_(<4 x s8>), %25:_(p0) :: (store (<4 x s8>) into %ir.18, align 8)

error: could not compile `test-remark` (build script)

So,

• Why does ^ happen?... Could/should -Cremark be disabled for build-scripts if possible?
• cargo-remark should probably crash loudly and not hang in cases like this?

Perhaps related: rust-lang/cargo#6375 (re: not passing RUSTFLAGS down to build scripts which can cause all sorts of problems like here)

[Kobzol]

Hi, thanks for investigating this! To be clear, you were able to reproduce this with an empty Cargo project containing the mentioned build script? I can't reproduce the build script error on such an empty project with a build script.

[aldanor]

Yes, the following hangs:

cargo new --bin foo
cd foo
echo 'fn main() { _ = "".split(\'.\'); }' > build.rs
cargo +nightly remark build

(to clarify, this is on M1 macOS, things may behave different on x64/linux I think)

rustc version: rustc 1.75.0-nightly (59edd6705 2023-10-09)

[Kobzol]

I see. This works for me on Linux, so it's hard for me to reproduce 😅 I think that the fact that it errors out for you (not the cargo remark hang, but the -Cremark=all error) should be reported to rust-lang/rust as a bug.