1use std::env;
2use std::process::Command;
3use std::str::{self, FromStr};
4
5// The rustc-cfg strings below are *not* public API. Please let us know by
6// opening a GitHub issue if your build environment requires some way to enable
7// these cfgs other than by executing our build script.
8fn main() {
9 println!("cargo:rerun-if-changed=build.rs");
10
11 let minor = match rustc_minor_version() {
12 Some(minor) => minor,
13 None => return,
14 };
15
16 let target = env::var("TARGET").unwrap();
17 let emscripten = target == "asmjs-unknown-emscripten" || target == "wasm32-unknown-emscripten";
18
19 // TryFrom, Atomic types, non-zero signed integers, and SystemTime::checked_add
20 // stabilized in Rust 1.34:
21 // https://blog.rust-lang.org/2019/04/11/Rust-1.34.0.html#tryfrom-and-tryinto
22 // https://blog.rust-lang.org/2019/04/11/Rust-1.34.0.html#library-stabilizations
23 if minor < 34 {
24 println!("cargo:rustc-cfg=no_core_try_from");
25 println!("cargo:rustc-cfg=no_num_nonzero_signed");
26 println!("cargo:rustc-cfg=no_systemtime_checked_add");
27 println!("cargo:rustc-cfg=no_relaxed_trait_bounds");
28 }
29
30 // f32::copysign and f64::copysign stabilized in Rust 1.35.
31 // https://blog.rust-lang.org/2019/05/23/Rust-1.35.0.html#copy-the-sign-of-a-floating-point-number-onto-another
32 if minor < 35 {
33 println!("cargo:rustc-cfg=no_float_copysign");
34 }
35
36 // Current minimum supported version of serde_derive crate is Rust 1.56.
37 if minor < 56 {
38 println!("cargo:rustc-cfg=no_serde_derive");
39 }
40
41 // Support for #[cfg(target_has_atomic = "...")] stabilized in Rust 1.60.
42 if minor < 60 {
43 println!("cargo:rustc-cfg=no_target_has_atomic");
44 // Allowlist of archs that support std::sync::atomic module. This is
45 // based on rustc's compiler/rustc_target/src/spec/*.rs.
46 let has_atomic64 = target.starts_with("x86_64")
47 || target.starts_with("i686")
48 || target.starts_with("aarch64")
49 || target.starts_with("powerpc64")
50 || target.starts_with("sparc64")
51 || target.starts_with("mips64el")
52 || target.starts_with("riscv64");
53 let has_atomic32 = has_atomic64 || emscripten;
54 if minor < 34 || !has_atomic64 {
55 println!("cargo:rustc-cfg=no_std_atomic64");
56 }
57 if minor < 34 || !has_atomic32 {
58 println!("cargo:rustc-cfg=no_std_atomic");
59 }
60 }
61
62 // Support for core::ffi::CStr and alloc::ffi::CString stabilized in Rust 1.64.
63 // https://blog.rust-lang.org/2022/09/22/Rust-1.64.0.html#c-compatible-ffi-types-in-core-and-alloc
64 if minor < 64 {
65 println!("cargo:rustc-cfg=no_core_cstr");
66 }
67}
68
69fn rustc_minor_version() -> Option<u32> {
70 let rustc = match env::var_os("RUSTC") {
71 Some(rustc) => rustc,
72 None => return None,
73 };
74
75 let output = match Command::new(rustc).arg("--version").output() {
76 Ok(output) => output,
77 Err(_) => return None,
78 };
79
80 let version = match str::from_utf8(&output.stdout) {
81 Ok(version) => version,
82 Err(_) => return None,
83 };
84
85 let mut pieces = version.split('.');
86 if pieces.next() != Some("rustc 1") {
87 return None;
88 }
89
90 let next = match pieces.next() {
91 Some(next) => next,
92 None => return None,
93 };
94
95 u32::from_str(next).ok()
96}
97