Migrate build-rs to the Cargo repo (#14786)

### What does this PR try to resolve?

Fixes #12432

### How should we test and review this PR?

This pulls in https://github.com/cad97/build-rs at
eb389d1 with the following changes:
- `Cargo.toml` metadata
- Removal of `.github`, `.gitignore`, `Cargo.lock`

We'll need to integrate `test-lib` into our processes but that seemed
more invasive, so I wanted to leave that for a future PR.

### Additional information

Infra changes are being coordinated in
https://rust-lang.zulipchat.com/#narrow/channel/242791-t-infra/topic/Transfering.20.60build-rs.60.20crate.20to.20rust-lang/near/480779960

Context: per [Cargo's
charter](https://doc.crates.io/contrib/team.html#decision-process), we
approved this transfer in an
[FCP](#12432 (comment)).

Cargo.toml

@@ -24,6 +24,7 @@ anstyle = "1.0.8"
 anyhow = "1.0.86"
 base64 = "0.22.1"
 blake3 = "1.5.2"
+build-rs = { version = "0.2.0", path = "crates/build-rs" }
 bytesize = "1.3"
 cargo = { path = "" }
 cargo-credential = { version = "0.4.2", path = "credential/cargo-credential" }
@@ -107,6 +108,7 @@ tracing = { version = "0.1.40", default-features = false, features = ["std"] } #
 tracing-chrome = "0.7.2"
 tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
 unicase = "2.7.0"
+unicode-ident = "1.0.13"
 unicode-width = "0.2.0"
 unicode-xid = "0.2.4"
 url = "2.5.2"

crates/build-rs-test-lib/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "build-rs-test-lib"
+version = "0.0.0"
+edition.workspace = true
+publish = false
+
+[features]
+unstable = ["build-rs/unstable"]
+
+[build-dependencies]
+build-rs.workspace = true

crates/build-rs-test-lib/build.rs

@@ -0,0 +1,78 @@
+fn main() {
+    smoke_test_inputs();
+
+    build_rs::output::rerun_if_changed("build.rs");
+    build_rs::output::rustc_check_cfgs(&["did_run_build_script"]);
+    build_rs::output::rustc_cfg("did_run_build_script");
+}
+
+fn smoke_test_inputs() {
+    use build_rs::input::*;
+    dbg!(cargo());
+    dbg!(cargo_cfg("careful"));
+    dbg!(cargo_cfg_debug_assertions());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_fmt_debug());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_overflow_checks());
+    dbg!(cargo_cfg_panic());
+    dbg!(cargo_cfg_proc_macro());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_relocation_model());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_sanitize());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_sanitizer_cfi_generalize_pointers());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_sanitizer_cfi_normalize_integers());
+    dbg!(cargo_cfg_target_abi());
+    dbg!(cargo_cfg_target_arch());
+    dbg!(cargo_cfg_target_endian());
+    dbg!(cargo_cfg_target_env());
+    dbg!(cargo_cfg_target_feature());
+    dbg!(cargo_cfg_target_has_atomic());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_target_has_atomic_equal_alignment());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_target_has_atomic_load_store());
+    dbg!(cargo_cfg_target_os());
+    dbg!(cargo_cfg_target_pointer_width());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_target_thread_local());
+    dbg!(cargo_cfg_target_vendor());
+    #[cfg(feature = "unstable")]
+    dbg!(cargo_cfg_ub_checks());
+    dbg!(cargo_cfg_unix());
+    dbg!(cargo_cfg_windows());
+    dbg!(cargo_encoded_rustflags());
+    dbg!(cargo_feature("unstable"));
+    dbg!(cargo_manifest_dir());
+    dbg!(cargo_manifest_links());
+    dbg!(cargo_pkg_authors());
+    dbg!(cargo_pkg_description());
+    dbg!(cargo_pkg_homepage());
+    dbg!(cargo_pkg_license());
+    dbg!(cargo_pkg_license_file());
+    dbg!(cargo_pkg_name());
+    dbg!(cargo_pkg_readme());
+    dbg!(cargo_pkg_repository());
+    dbg!(cargo_pkg_rust_version());
+    dbg!(cargo_pkg_version());
+    dbg!(cargo_pkg_version_major());
+    dbg!(cargo_pkg_version_minor());
+    dbg!(cargo_pkg_version_patch());
+    dbg!(cargo_pkg_version_pre());
+    dbg!(debug());
+    dbg!(dep_metadata("z", "include"));
+    dbg!(host());
+    dbg!(num_jobs());
+    dbg!(opt_level());
+    dbg!(out_dir());
+    dbg!(profile());
+    dbg!(rustc());
+    dbg!(rustc_linker());
+    dbg!(rustc_workspace_wrapper());
+    dbg!(rustc_wrapper());
+    dbg!(rustdoc());
+    dbg!(target());
+}

crates/build-rs-test-lib/src/lib.rs

@@ -0,0 +1,4 @@
+#[test]
+fn test() {
+    assert!(cfg!(did_run_build_script));
+}

crates/build-rs/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "build-rs"
+version = "0.2.0"
+rust-version.workspace = true
+edition.workspace = true
+license.workspace = true
+homepage.workspace = true
+repository.workspace = true
+description = "API for writing Cargo `build.rs` files"
+
+[features]
+## Experimental API. This feature flag is **NOT** semver stable.
+unstable = []
+
+[dependencies]
+unicode-ident.workspace = true

crates/build-rs/README.md

@@ -0,0 +1,2 @@
+> This crate is maintained by the Cargo team for use by the wider
+> ecosystem. This crate follows semver compatibility for its APIs.

crates/build-rs/src/allow_use.rs

@@ -0,0 +1,46 @@
+use std::{process::Command, sync::OnceLock};
+
+fn rust_version_minor() -> u32 {
+    static VERSION_MINOR: OnceLock<u32> = OnceLock::new();
+    *VERSION_MINOR.get_or_init(|| {
+        crate::input::cargo_pkg_rust_version()
+            .split('.')
+            .nth(1)
+            // assume build-rs's MSRV if none specified for the current package
+            .unwrap_or(env!("CARGO_PKG_RUST_VERSION").split('.').nth(1).unwrap())
+            .parse()
+            .unwrap()
+    })
+}
+
+fn cargo_version_minor() -> u32 {
+    static VERSION_MINOR: OnceLock<u32> = OnceLock::new();
+    *VERSION_MINOR.get_or_init(|| {
+        let out = Command::new(crate::input::cargo())
+            .arg("-V")
+            .output()
+            .expect("running `cargo -V` should succeed");
+        assert!(out.status.success(), "running `cargo -V` should succeed");
+
+        // > cargo -V # example output
+        // cargo 1.82.0 (8f40fc59f 2024-08-21)
+
+        String::from_utf8(out.stdout).expect("`cargo -V` should output valid UTF-8")
+            ["cargo 1.".len()..]
+            .split('.')
+            .next()
+            .expect("`cargo -V` format should be stable")
+            .parse()
+            .unwrap()
+    })
+}
+
+pub(crate) fn double_colon_directives() -> bool {
+    // cargo errors on `cargo::` directives with insufficient package.rust-version
+    rust_version_minor() >= 77
+}
+
+pub(crate) fn check_cfg() -> bool {
+    // emit check-cfg if the toolchain being used supports it
+    cargo_version_minor() >= 80
+}

crates/build-rs/src/ident.rs

@@ -0,0 +1,27 @@
+use unicode_ident::{is_xid_continue, is_xid_start};
+
+pub(crate) fn is_feature_name(s: &str) -> bool {
+    s.chars()
+        .all(|ch| is_xid_continue(ch) || matches!(ch, '-' | '+' | '.'))
+}
+
+pub(crate) fn is_ident(s: &str) -> bool {
+    let mut cs = s.chars();
+    cs.next()
+        .is_some_and(|ch| is_xid_start(ch) || matches!(ch, '_'))
+        && cs.all(is_xid_continue)
+}
+
+pub(crate) fn is_ascii_ident(s: &str) -> bool {
+    let mut cs = s.chars();
+    cs.next()
+        .is_some_and(|ch| ch.is_ascii_alphabetic() || matches!(ch, '_'))
+        && cs.all(|ch| ch.is_ascii_alphanumeric() || matches!(ch, '_'))
+}
+
+pub(crate) fn is_crate_name(s: &str) -> bool {
+    let mut cs = s.chars();
+    cs.next()
+        .is_some_and(|ch| is_xid_start(ch) || matches!(ch, '-' | '_'))
+        && cs.all(|ch| is_xid_continue(ch) || matches!(ch, '-'))
+}