non_std support issue in toml v0.92

[bodzhang]

I tried toml v0.92 in non_std environment for x86_64-unknown-none target, with features = ["parse", "serde"].

The build complains about f64::copysign() method in value.rs is not available. By patching the code to use libm::copysign, I was able to get the build and test pass.

Can the toml-rs team confirm whether this is a bug?

[epage]

Can you provide full reproduction steps and the actual error?

The docs for core say its available: https://doc.rust-lang.org/core/primitive.f64.html#method.copysign

[bodzhang]

test app repo show the following error:

$ cargo build --target x86_64-unknown-none
Compiling toml v0.9.2
error[E0599]: no method named copysign found for type f64 in the current scope
--> /home/bodzhang/.cargo/registry/src/index.crates.io-6f17d22bba15001f/toml-0.9.2/src/value.rs:899:27
|
899 | value = value.copysign(1.0);
| ^^^^^^^^ method not found in f64

[epage]

I'm not seeing that error but

• display feature is missing (since to_string is called)
• toml doesn't disable std in toml_writer

Fixing those in #1019 and then will check again to see if there is any problems.

[epage]

With 0.9.3, I'm getting the following error with the reproduction case:

error: no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait

[bodzhang]

Found out the different test result with the reproduction case might be due to Rust tool version. When using stable Rust 1.83.0, I still see copysign issue with toml v0.95. The issue is only resolved in newer Rust nightly versions. Updated the reproduction case to lock to Rust 1.83.0 for reproduction.

[bodzhang]

According to rust-lang/rust#131304, copysign moved to libcore in Rust 1.84.0. My version of Rust tool is too old.