1 use std::env;
2 use std::process::Command;
3 use std::str;
4 
main()5 fn main() {
6     let compiler = match rustc_minor_version() {
7         Some(compiler) => compiler,
8         None => return,
9     };
10 
11     if compiler < 32 {
12         // u64::from_ne_bytes.
13         // https://doc.rust-lang.org/std/primitive.u64.html#method.from_ne_bytes
14         println!("cargo:rustc-cfg=no_from_ne_bytes");
15     }
16 
17     if compiler < 33 {
18         // Exhaustive integer patterns. On older compilers, a final `_` arm is
19         // required even if every possible integer value is otherwise covered.
20         // https://github.com/rust-lang/rust/issues/50907
21         println!("cargo:rustc-cfg=no_exhaustive_int_match");
22     }
23 
24     if compiler < 36 {
25         // extern crate alloc.
26         // https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html#the-alloc-crate-is-stable
27         println!("cargo:rustc-cfg=no_alloc_crate");
28     }
29 
30     if compiler < 39 {
31         // const Vec::new.
32         // https://doc.rust-lang.org/std/vec/struct.Vec.html#method.new
33         println!("cargo:rustc-cfg=no_const_vec_new");
34     }
35 
36     if compiler < 40 {
37         // #[non_exhaustive].
38         // https://blog.rust-lang.org/2019/12/19/Rust-1.40.0.html#non_exhaustive-structs-enums-and-variants
39         println!("cargo:rustc-cfg=no_non_exhaustive");
40     }
41 
42     if compiler < 45 {
43         // String::strip_prefix.
44         // https://doc.rust-lang.org/std/primitive.str.html#method.repeat
45         println!("cargo:rustc-cfg=no_str_strip_prefix");
46     }
47 
48     if compiler < 46 {
49         // #[track_caller].
50         // https://blog.rust-lang.org/2020/08/27/Rust-1.46.0.html#track_caller
51         println!("cargo:rustc-cfg=no_track_caller");
52     }
53 
54     if compiler < 52 {
55         // #![deny(unsafe_op_in_unsafe_fn)].
56         // https://github.com/rust-lang/rust/issues/71668
57         println!("cargo:rustc-cfg=no_unsafe_op_in_unsafe_fn_lint");
58     }
59 
60     if compiler < 53 {
61         // Efficient intrinsics for count-leading-zeros and count-trailing-zeros
62         // on NonZero integers stabilized in 1.53.0. On many architectures these
63         // are more efficient than counting zeros on ordinary zeroable integers.
64         // https://doc.rust-lang.org/std/num/struct.NonZeroU64.html#method.leading_zeros
65         // https://doc.rust-lang.org/std/num/struct.NonZeroU64.html#method.trailing_zeros
66         println!("cargo:rustc-cfg=no_nonzero_bitscan");
67     }
68 }
69 
rustc_minor_version() -> Option<u32>70 fn rustc_minor_version() -> Option<u32> {
71     let rustc = env::var_os("RUSTC")?;
72     let output = Command::new(rustc).arg("--version").output().ok()?;
73     let version = str::from_utf8(&output.stdout).ok()?;
74     let mut pieces = version.split('.');
75     if pieces.next() != Some("rustc 1") {
76         return None;
77     }
78     pieces.next()?.parse().ok()
79 }
80