1 #![warn(rust_2018_idioms, single_use_lifetimes)]
2 
3 use autocfg::AutoCfg;
4 use std::env;
5 
6 include!("no_atomic_cas.rs");
7 
8 // The rustc-cfg listed below are considered public API, but it is *unstable*
9 // and outside of the normal semver guarantees:
10 //
11 // - `futures_no_atomic_cas`
12 //      Assume the target does *not* support atomic CAS operations.
13 //      This is usually detected automatically by the build script, but you may
14 //      need to enable it manually when building for custom targets or using
15 //      non-cargo build systems that don't run the build script.
16 //
17 // With the exceptions mentioned above, the rustc-cfg strings below are
18 // *not* public API. Please let us know by opening a GitHub issue if your build
19 // environment requires some way to enable these cfgs other than by executing
20 // our build script.
main()21 fn main() {
22     let target = match env::var("TARGET") {
23         Ok(target) => target,
24         Err(e) => {
25             println!(
26                 "cargo:warning={}: unable to get TARGET environment variable: {}",
27                 env!("CARGO_PKG_NAME"),
28                 e
29             );
30             return;
31         }
32     };
33 
34     // Note that this is `no_*`, not `has_*`. This allows treating
35     // `cfg(target_has_atomic = "ptr")` as true when the build script doesn't
36     // run. This is needed for compatibility with non-cargo build systems that
37     // don't run the build script.
38     if NO_ATOMIC_CAS_TARGETS.contains(&&*target) {
39         println!("cargo:rustc-cfg=futures_no_atomic_cas");
40     }
41 
42     let cfg = match AutoCfg::new() {
43         Ok(cfg) => cfg,
44         Err(e) => {
45             println!(
46                 "cargo:warning={}: unable to determine rustc version: {}",
47                 env!("CARGO_PKG_NAME"),
48                 e
49             );
50             return;
51         }
52     };
53 
54     // Function like procedural macros in expressions patterns statements stabilized in Rust 1.45:
55     // https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html#stabilizing-function-like-procedural-macros-in-expressions-patterns-and-statements
56     if cfg.probe_rustc_version(1, 45) {
57         println!("cargo:rustc-cfg=fn_like_proc_macro");
58     }
59 
60     println!("cargo:rerun-if-changed=no_atomic_cas.rs");
61 }
62