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-rw-r--r--vendor/io-lifetimes/build.rs67
1 files changed, 67 insertions, 0 deletions
diff --git a/vendor/io-lifetimes/build.rs b/vendor/io-lifetimes/build.rs
new file mode 100644
index 000000000..81026863f
--- /dev/null
+++ b/vendor/io-lifetimes/build.rs
@@ -0,0 +1,67 @@
+use std::env::var;
+use std::io::Write;
+
+fn main() {
+ // Niche optimizations for `Borrowed*` and `Owned*` depend on `rustc_attrs`
+ // which, outside of `std`, are only available on nightly.
+ use_feature_or_nothing("rustc_attrs");
+
+ // Rust 1.56 and earlier don't support panic in const fn.
+ if has_panic_in_const_fn() {
+ use_feature("panic_in_const_fn")
+ }
+
+ // Don't rerun this on changes other than build.rs, as we only depend on
+ // the rustc version.
+ println!("cargo:rerun-if-changed=build.rs");
+}
+
+fn use_feature_or_nothing(feature: &str) {
+ if has_feature(feature) {
+ use_feature(feature);
+ }
+}
+
+fn use_feature(feature: &str) {
+ println!("cargo:rustc-cfg={}", feature);
+}
+
+/// Test whether the rustc at `var("RUSTC")` supports the given feature.
+fn has_feature(feature: &str) -> bool {
+ let out_dir = var("OUT_DIR").unwrap();
+ let rustc = var("RUSTC").unwrap();
+
+ let mut child = std::process::Command::new(rustc)
+ .arg("--crate-type=rlib") // Don't require `main`.
+ .arg("--emit=metadata") // Do as little as possible but still parse.
+ .arg("--out-dir")
+ .arg(out_dir) // Put the output somewhere inconsequential.
+ .arg("-") // Read from stdin.
+ .stdin(std::process::Stdio::piped()) // Stdin is a pipe.
+ .spawn()
+ .unwrap();
+
+ writeln!(child.stdin.take().unwrap(), "#![feature({})]", feature).unwrap();
+
+ child.wait().unwrap().success()
+}
+
+/// Test whether the rustc at `var("RUSTC")` supports panic in `const fn`.
+fn has_panic_in_const_fn() -> bool {
+ let out_dir = var("OUT_DIR").unwrap();
+ let rustc = var("RUSTC").unwrap();
+
+ let mut child = std::process::Command::new(rustc)
+ .arg("--crate-type=rlib") // Don't require `main`.
+ .arg("--emit=metadata") // Do as little as possible but still parse.
+ .arg("--out-dir")
+ .arg(out_dir) // Put the output somewhere inconsequential.
+ .arg("-") // Read from stdin.
+ .stdin(std::process::Stdio::piped()) // Stdin is a pipe.
+ .spawn()
+ .unwrap();
+
+ writeln!(child.stdin.take().unwrap(), "const fn foo() {{ panic!() }}").unwrap();
+
+ child.wait().unwrap().success()
+}